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Keywords:

  • birth certificate;
  • breech presentation;
  • case-control;
  • ethnicity;
  • logistic regression;
  • Medicaid;
  • race;
  • risk factors;
  • socioeconomic status

ABSTRACT

  1. Top of page
  2. ABSTRACT
  3. Methods and Materials
  4. Results
  5. Discussion
  6. Strengths and Limitations of the Study
  7. Future Directions
  8. Implications for Practice
  9. Acknowledgments
  10. REFERENCES

Objective: To investigate race and ethnicity as risk factors for breech presentation.

Design: Case-control study using a population-based birth certificate registry that included linkage to Medicaid/Women, Infants, & Children (WIC) eligibility data for a socioeconomic proxy variable.

Setting: Florida, USA.

Participants: 912,107 mothers of singletons born in Florida 1999 to 2003.

Methods: Maternal race and ethnicity were evaluated as risk factors for breech presentation using logistic regression. The dependent variable was birth presentation. Covariates were variable measures that have been repeatedly identified as risk factors for breech presentation in the literature and are known to be highly accurate birth certificate variable measures.

Results: White women were 69% more likely to have a breech baby (adjusted odds ratio [OR]=1.69, 95% confidence interval [CI] 1.63, 1.76) than Black women. Higher socioeconomic status was a risk factor in the bivariate analyses, but not in the adjusted analysis. Prematurity, nulliparity, female infant, and advancing maternal age were risk factors in the final model. The final model accounted for <5% of the total variance (Max Rescaled R2=4.18%), and thus was poorly fit (Hosmer and Lemeshow goodness of fit <0.0001).

Conclusions: White women were at increased risk of having a breech baby. However, important variables appear to be missing from the model.

Breech presentation is the most common birth malpresentation (3%–4%) (Rayl, Gibson, & Kickok, 1996) and is associated with increased perinatal morbidity and mortality (Albrechtsen, Rasmussen, Dalaker, & Irgens, 1998a). Surprisingly, although breech presentation is associated with a higher incidence of preterm and low-birth-weight babies, it occurs disproportionately in White women (Martin et al., 2005) and in middle- and upper-class women (Pop et al., 2004; Roberts, Algert, Peat, & Henderson-Smart, 1999), populations that are generally protected from other adverse pregnancy outcomes. This phenomenon is the breech paradox. Why is breech presentation an exception to the tendency for adverse pregnancy outcomes to occur disproportionately in disadvantaged populations?

Fewer than 50 studies were identified that evaluated risk factors for breech presentation. Retrospective birth registry studies have consistently identified younger gestational age, lower birth weight, older maternal age, a female fetus, and nulliparity as risk factors for breech presentation babies when compared with cephalic presentation babies (Amoa, Sapuri, & Klufio, 2001; Jonas & Roder, 1993; Rayl et al., 1996; Roberts et al., 1999; Vendittelli et al., 2008). Birth registry studies have also found that breech presentation is more common in parents who were born breech (Nordtveit, Melve, Albrechtsen, & Skjaerven, 2008), in a mother who has already had a breech baby (Albrechtsen, Rasmussen, Dalaker, & Irgens, 1998c), or in a mother who had a previous Cesarean section (Vendittelli et al.). Other variables of potential interest such as amniotic fluid volume (Luterkort, Persson, & Weldner, 1984; Rayl et al.), placental implantation site (Rayl et al.; Roberts et al.; Westgren, 1985), maternal smoking and drinking (Pop et al., 2004; Rayl et al.; Roberts et al.), and maternal disease (Pop et al.; Rayl et al.; Roberts et al.) are inconclusive risk factors and at times are inappropriately evaluated in databases, such as U.S. birth certificates, where these variables are known to be inaccurately documented (DiGiuseppe, Aron, Ranbom, Harper, & Rosenthal, 2002; Roohan et al., 2003; Yasmeen, Romano, Schembri, Keyzer, & Gilbert, 2006).

Inadequate prenatal care was evaluated as a risk factor for breech presentation in only two identified studies. A Papua New Guinea labor ward register study (N=1,004) (Amoa et al., 2001) and a Washington State birth certificate study (N=11,771) (Rayl et al., 1996) indicated mothers of breech babies received less prenatal care than did mothers of cephalic presentation babies. The Washington State findings must be accepted cautiously, however, because birth certificate data generally does not accurately document prenatal care (Northam & Knapp, 2005). Other important considerations for pregnancy outcomes such as genetics, the environment, stress, stress-related hormones, diet, and rest have not been evaluated as risk factors for breech presentation.

Neonatal orthopedic and neurologic evaluations and maternal anthropometric studies have been conducted less frequently and use smaller sample sizes than do birth registry studies; they also arrive at less conclusive results. The largest and best designed case-control study done to date of neonatal orthopedic and neurologic characteristics shows there is virtually no difference between breech presentation babies and cephalic presentation babies (Bartlett, Okun, Byrne, Watt, & Piper, 2000; Bartlett, Piper, Okun, Byrne, & Watt, 1997). Maternal pelvic size and shape were evaluated in only one identified study of risk factors for breech presentation. The pelvic inlet and pelvic outlet were not significantly different in Swedish mothers of breech babies and mothers of cephalic presentation babies (Luterkort et al., 1984). Recent magnetic resonance imaging (MRI) studies indicate there is no significant difference between White women and African American women in important pelvimetry measurements such as the interspinous diameter and the anteroposterior conjugate; the pelvic inlet and the pelvic outlet are statistically significantly wider in White women than in African American women (Handa et al., 2008). The authors did not indicate if the difference was clinically significant.

The cause of turning to cephalic presentation remains unknown (Sekulic, 2000). The purpose of this study was to determine if maternal race and ethnicity add further explanatory value to a model of accepted risk factors for breech presentation. The study hypothesis is that risk for breech presentation varies by maternal race and ethnicity after controlling for socioeconomic confounders in the logistic regression model.

Race and ethnicity are important variable measures to consider as possible risk factors for breech presentation for four reasons: (a) breech presentation unexpectedly occurs more commonly in White women than in Black or Hispanic women and thus offers a unique opportunity to explore adverse outcomes in a typically protected population; (b) differential health outcomes are now understood to be influenced, in part, by socio-political-economic processes for which race and ethnicity act as proxy variable measures; (c) the breech presentation baby is typically delivered by Cesarean section, a higher cost birth option, thus all potential risk factors should be investigated in an attempt to prevent or reverse breech presentation and decrease the rate of Cesarean sections (Agency for Health Care Administration: State Center for Health Statistics, 2006; Martin et al., 2009); and (d) race and ethnicity have not been published as risk factors in midwifery and obstetric texts, although this is common practice for other conditions (Cunningham et al., 2005).

Racial categorization is based mostly on skin color; genetics has only a small (15%) influence on apparent racial differences (Sarich & Miele, 2004). As such, group membership to any particular race assigns certain opportunities or disadvantages that far outweigh any shared genetic traits (Molnar, 2002). Ethnicity, in contrast, is a self-identified association with a group by phenotypic, cultural, linguistic, or behavioral characteristics (Molnar). A growing body of evidence suggests that social constraints differentially experienced by race and ethnic groups might contribute to adverse pregnancy outcomes such as low-birth-weight and preterm births (David & Collins, 2007; Dominguez, 2008; Williams & Mohammed, 2008). The rate of preterm and low-birth-weight births varies by state, but Blacks consistently have poorer pregnancy outcomes than do Whites or Hispanics in the United States (Martin et al., 2009). Although Black and low socioeconomic status women typically bear the brunt of adverse pregnancy outcomes, women who work in professional or executive occupations might have reproductive outcomes similar to those experienced by working-class women; white-collar workers appear to be protected (Boivin, Sanders, & Schmidt, 2006). The reasons for these shared pregnancy outcomes are not well understood, and pregnancy outcomes for professionals and executives have not been extensively studied.

We conducted a large population-based case-control study to evaluate the role of race, ethnicity, and socioeconomic factors in influencing breech presentation. Here we present our findings and suggest future directions for research.

Methods and Materials

  1. Top of page
  2. ABSTRACT
  3. Methods and Materials
  4. Results
  5. Discussion
  6. Strengths and Limitations of the Study
  7. Future Directions
  8. Implications for Practice
  9. Acknowledgments
  10. REFERENCES

Materials

The University of South Florida Institutional Review Board approved this study. The 1999 to 2003 deidentified linked Florida birth certificate registry was obtained with permission of the Florida Department of Health (DOH) and the Medicaid/WIC eligibility data set was obtained from the Agency for Health Care Administration (ACHA). All study linkages between the data sets were conducted by the University of Florida, which also removed duplicate observations and prepared the data set for analysis. The final analytic file consisted of one million observations. Birth certificate registry data were selected because they are comprehensive in that nearly all live births in all locations in the state are included, providing large numbers, reducing selection bias, and allowing for stratified analysis.

The Medicaid/WIC study population consisted of mothers who applied for, and were eligible to receive, Medicaid or WIC during pregnancy. To be eligible for Medicaid during the time period evaluated, households earned up to 185% of the federal poverty guidelines. By this standard, an eligible family of four could earn up to $32,200 in 2003 (Anonymous, 2003; Health Resources and Services Administration, 2003). To be eligible for WIC a household could earn up to 185% of the federal poverty guidelines and must have children younger than age 5 years, or women who are pregnant, breastfeeding, or up to 6 months postpartum (Florida Department of Health, 2009).

Inclusion/Exclusion Criteria

Inclusion criteria for the study sample included mothers of singletons born in Florida. No multiples were accepted because the natural progression of fetal positions differs between singletons and multiples. Only mothers who were of White or Black race or of Hispanic ethnicity were included because the other race and ethnic groups were much smaller. Race and ethnicity designations were combined for each individual, so each mother in the study was identified as White (White non-Hispanic), Black (Black non-Hispanic), or Hispanic. This strategy ensured that each individual in the study was counted only once. Black was the reference category. Exclusion criteria included babies born before 20 weeks or after 42 weeks and those weighing less than 500 g or more than 5,000 g. These babies were excluded because there were very few in those categories. Furthermore, births prior to 20 weeks and conceptus weighing less than 500 g are not considered to be viable. Women older than age 49 and younger than 12 years were also excluded due to their small numbers. The sample was selected after deletion of observations that did not meet the inclusion criteria, met the exclusion criteria, or had any missing salient information, such as education, age, or birth weight (100% capture of data was required for inclusion) (Figure 1). Preliminary analyses that included observations with missing data points had similar findings to the attenuated sample, so the decision was made to include only observations with 100% capture.

image

Figure 1.  Study sample (N=912,107) drawn from a data set of linked birth registry and Medicaid/WIC eligibility 1999 to 2003 (N=1,000,000) after eliminating observations with missing data and observations that met exclusion criteria.

Download figure to PowerPoint

Variable measures that were entered into the logistic regression model were those that have repeatedly been identified as risk factors for breech presentation (gestational age, birth weight, maternal age, female fetus, nulliparity; Amoa et al., 2001; Jonas & Roder, 1993; Rayl et al., 1996; Roberts et al., 1999; Vendittelli et al., 2008) or those that are confounders of race and ethnicity (education, and Medicaid/WIC eligibility). Only variable measures that are consistently recorded accurately in the birth certificate were included in the model (Baumeister, Marchi, Pearl, Williams, & Braveman, 2000; DiGiuseppe et al., 2002; Dobie et al., 1998; Frost, Starzyk, George, & McLaughlin, 1984; Roohan et al., 2003; Yasmeen et al., 2006; Zollinger, Przybylski, & Gamache, 2006). Prenatal care is generally overreported in birth certificate data, although initiation of prenatal care might be accurate (Northam & Knapp, 2005). Because of the inaccuracy of documenting prenatal care in birth certificate data, it was not included in the logistic regression model.

Statistical Methods

Univariate and bivariate analyses were conducted first to determine frequencies, percentages, means, standard deviations, and unadjusted odds ratios (ORs). After univariate and bivariate analyses, the data were subjected to multivariate unconditional logistic regression, which produced adjusted ORs. Adjusted ORs reflect associations between variable measures while taking into account covariates that influence the behavior of other variables in the model. The assumptions of logistic regression were first tested. Confounders and effect modifiers were evaluated with Mantel-Haenszel and Breslow-Day, respectively. Potential effect modifiers were tested in the final model. Max rescaled R2 was used to measure the predictive power of the model. The Hosmer and Lemeshow goodness-of-fit statistic was used to determine the model quality of fit (p=1 is a perfect fit). Diagnostic statistics were calculated after the final model was selected to check for the influence of outliers. SAS 9.1.3 (SAS Institute, Cary, NC) was used to analyze the data.

Results

  1. Top of page
  2. ABSTRACT
  3. Methods and Materials
  4. Results
  5. Discussion
  6. Strengths and Limitations of the Study
  7. Future Directions
  8. Implications for Practice
  9. Acknowledgments
  10. REFERENCES

Univariate and Bivariate Results

The final sample size for the 1999 to 2003 linked Florida birth registry and Medicaid/WIC eligibility data set was 912,107. Nearly 3% (2.76%) of the total sample had a breech baby. The sample was predominantly White (55%), followed by Hispanic (25%), and Black (20%). White women had the highest likelihood of having a breech baby (3.15%, unadjusted OR=1.39, 95% CI 1.35, 1.43) when compared to Hispanic women (2.69%, unadjusted OR=0.97, 95% CI 0.94, 1.00) and Black women (1.79%, OR=1.0) (Table 1). Almost all breech babies (93.89%) were delivered by Cesarean sections compared to 24.35% of cephalic presentation babies.

Table 1. Crude Odds Ratios Comparing Breech and Cephalic Presentation Births by Ethnicity
VariableBlack Non-HispanicWhite Non-HispanicHispanic
Crude OR95% CICrude OR95% CICrude OR95% CI
Medicaid or WIC eligible
 Yes0.690.64, 0.740.850.82, 0.880.820.78, 0.87
 No1.00 ref. 1.00 ref. 1.00 ref. 
Education (years)
 0–110.860.79, 0.930.860.82, 0.900.860.81, 0.91
 121.00 ref. 1.00 ref. 1.00 ref. 
 13–151.161.07, 1.261.030.99, 1.071.071.01, 1.14
 16+1.351.21, 1.491.141.10, 1.181.361.28, 1.44
Age (years)
 12–190.700.63, 0.760.790.45, 0.840.750.68, 0.81
 20–240.690.64, 0.740.740.71, 0.770.710.67, 0.76
 25–291.00 ref. 1.00 ref. 1.00 ref. 
 30–341.511.38, 1.651.151.11, 1.191.281.21, 1.36
 35–392.121.92, 2.351.311.25, 1.361.451.35, 1.55
 40–491.881.53, 2.301.461.34, 1.581.691.48, 1.94
Gestational age (weeks)
 20–329.618.81, 10.485.114.74, 5.502.924.40, 5.50
 33–361.541.39, 1.712.142.04, 2.251.991.83, 2.16
 37–421.00 ref. 1.00 ref. 1.0 ref. 
Female infant
 Yes1.071.00, 1.151.231.19, 1.271.131.07, 1.19
 No1.00 ref. 1.00 ref. 1.00 ref. 
First infant born
 Yes1.020.95, 1.101.571.52, 1.631.461.39, 1.54
 No1.00 ref. 1.00 ref. 1.00 ref. 

Nearly one half of the sample was Medicaid/WIC eligible (47.42%). Medicaid/WIC eligibility was protective against having a breech baby in the bivariate analyses. However, White mothers were least protected (unadjusted OR=0.85, 95% CI 0.82, 0.88). Mothers of breech babies of all ethnicities were more likely to have a college degree or graduate education (26.66%, unadjusted OR=1.29, 95% CI 1.26, 1.33) than were mothers of cephalic presentation babies (21.92%). Hispanic mothers with at least a college education were most at risk of having a breech baby (unadjusted OR=1.36, 95% CI 1.28, 1.44). Women older than 29 years of all ethnic groups were more highly represented by mothers of breech babies (45.77%) than by mothers of cephalic presentation babies (35.47%). Black mothers were younger in general than White or Hispanic mothers.

Mothers of breech babies were more likely to be nulliparous (51.82%) than were mothers of cephalic presentation babies (41.99%). White women who had a breech baby were most likely to have no previous births (unadjusted OR=1.57, 95% CI 1.52, 1.63) followed by Hispanic mothers (unadjusted OR=1.46, 95% CI 1.39, 1.54). Nulliparity was not a risk factor for Black women (unadjusted OR=1.02, 95% CI 0.95, 1.10).

Although the majority of all babies were born at term (92.68% cephalic, 79.87% breech) and weighed 2,500 to 4,000 g (85.33% cephalic, 77.63% breech), more breech babies were born earlier and weighed less than cephalic presentation babies (Table 2). This finding was particularly relevant for Black women where 35% of all breech births were prior to 37 weeks whereas only 18% of White and 17% of Hispanic breech babies were born preterm. Similarly, 33% of all Black breech babies were low birth weight (<2,500 g) whereas 14% of White and Hispanic breech babies were born with low birth weight. The babies of lowest gestational age (20–32 weeks) and lowest birth weight (500-1,499 g) were at the greatest risk of being born breech (unadjusted OR=5.49, 95% CI 5.23, 5.77 and unadjusted OR=6.69, 95% CI 6.33, 7.08, respectively). Again, the risk was highest for babies of Black mothers (unadjusted OR=9.61, 95% CI 8.81, 10.48 for 20–32 weeks and unadjusted OR=11.37, 95% CI 10.35, 12.49 for 500-1,499 g). In a preliminary analysis of this data set adequacy of prenatal care was assessed with the Kotelchuck Index (Kotelchuck, 1997). Interestingly, mothers of breech babies began prenatal care earlier and received more prenatal care than did mothers of cephalic presentation babies.

Table 2. Frequencies and Percentages for Newborn Characteristics Comparing Breech and Cephalic Presentation Births by Maternal Race and Ethnicity and for the Total Sample
 Black Non-Hispanic n=186,494 (20.45%)White Non-Hispanic n=496,938 (54.48%)Hispanic n=228,675 (25.07%)Total N=912,107
Cephalic n=183,149Breech n=3,345 (1.79%)Cephalic n=481,279Breech n=15,659 (3.15%)Cephalic n=222,521Breech n=6,154 (2.69%)Cephalic n=886,949Breech n=25,158 (2.76%)
N%n%n%n%n%n%n%n%
Gestational age (weeks)
 20–325,1262.8072521.675,3261.118475.412,8711.293726.0413,3291.501,9447.73
 33–3616,7349.1444913.4230,5106.341,98312.6613,2425.9568811.1860,4866.823,12012.40
 37–42161,28988.062,17164.90445,44392.5512,82981.93206,40892.765,09482.78813,14091.6820,09479.87
Birth weight (g)
 500–1,4993,5171.9260918.213,1290.656143.921,6880.762794.538,3360.941,5025.97
 1,500–2,49915,7978.6349214.7120,7724.321,5269.759,5774.305949.6546,1465.202,61210.38
 2,500–4,000155,41384.332,10162.81407,85384.7412,52679.99193,60787.014,90479.69756,87385.3319,53177.63
 4,001–5,0008,4224.601434.2849,52510.299936.3417,6497.933776.1375,5968.521,5136.01
Female infant
 Yes89,98749.131,70350.91232,97948.418,39753.62108,88448.933,19851.97431,85048.6913,29852.86

Logistic Regression Analysis

Birth weight and gestational age were collinear so each was tested in the model separately. Gestational age produced greater explanatory value so was kept in the model. Potential effect modifiers were tested in the model but did not add explanatory value, so were excluded from the final model. The confounders of gestational age and female infant were included in the model. After adjusting for all the variables in the logistic regression model (Table 3), mothers who were White were at greater risk for breech presentation (adjusted OR=1.69, 95% CI 1.63, 1.76) than in the bivariate analyses. Medicaid/WIC eligibility, however, no longer protected against breech presentation (adjusted OR=1.03, 95% CI 1.00, 1.06). Likewise, advanced education was no longer a risk factor for breech presentation (adjusted OR=0.97, 95% CI 0.93, 1.00). All other risk factors in the final model followed a pattern similar to that seen in the bivariate analyses.

Table 3. Logistic Regression Model, Breech Frequencies, and Crude Odds Ratios Comparing Breech and Cephalic Presentation Births
VariablesBreech n (%)Individual VariablesLogistic Regression Model
Crude OR95% CIAdjusted OR95% CI
Maternal ethnicity
 White non-Hispanic15,659 (54.26)1.391.35, 1.431.691.63, 1.76
 Hispanic6,154 (25.07)0.970.94, 1.001.461.40, 1.53
 Black non-Hispanic3,345 (20.45)1.00 ref. 1.00 ref. 
Medicaid/WIC eligibility
 Yes11,929 (47.42)0.740.72, 0.761.031.00, 1.06
 No 1.00 ref. 1.00 ref. 
Maternal education (years)
 0–114,425 (17.59)0.710.79, 0.841.091.05, 1.14
 127,920 (31.48)1.00 ref. 1.00 ref. 
 13–156,106 (24.27)1.081.05, 1.111.010.97, 1.04
 16–17+6,707 (26.66)1.291.26, 1.330.970.93, 1.00
Maternal age (years)
 12–192,302 (9.15)0.700.67, 0.730.580.55, 0.61
 20–244,945 (19.66)0.690.67, 0.710.730.70, 0.76
 25–296,397 (25.43)1.00 ref. 1.00 ref. 
 30–346,641 (26.40)1.281.24, 1.311.251.21, 1.30
 35–393,903 (15.51)1.471.42, 1.521.481.42, 1.54
 40–49970 (3.86)1.611.50, 1.711.651.54, 1.77
Gestational age (weeks)
 20–321,944 (7.73)5.495.23, 5.776.426.10, 6.76
 33–363,120 (12.40)1.931.86, 2.012.156.07, 2.23
 37–4220,094 (79.87)1.00 ref. 1.00 ref. 
Female infant
 Yes13,298 (52.86)1.181.15, 1.211.201.17, 1.23
 No 1.00 ref. 1.00 ref. 
First infant born
 Yes13,036 (51.82)1.491.45, 1.521.711.67, 1.76
 No 1.00 ref. 1.00 ref. 

The logistic regression model produced a max rescaled R2 of only 4.18%. This finding indicates that the variables in the model account for about 4% of the total variance observed in risk factors for breech presentation. Furthermore, the Hosmer and Lemeshow goodness-of-fit statistic was <0.0001 which indicates poor fit.

Discussion

  1. Top of page
  2. ABSTRACT
  3. Methods and Materials
  4. Results
  5. Discussion
  6. Strengths and Limitations of the Study
  7. Future Directions
  8. Implications for Practice
  9. Acknowledgments
  10. REFERENCES

This investigation employed the second largest database to date to evaluate risk factors for breech presentation and was the first study to include race and ethnicity as risk factors for breech presentation while controlling for other confounding and contextual variables. We found that White women were 69% more likely than Black women to have a breech baby. In the bivariate analyses Hispanic ethnicity was not a risk factor for breech presentation. However, after controlling for the other variables in the logistic regression model, Hispanic women were 46% more likely to have a breech baby than Black women. This finding is supported in existing literature that indicates Hispanic birth outcomes are more similar to those of White than to Black women (Alexander et al., 2003). The findings from the current study must be cautiously interpreted because the overall fit of the model was poor and explained less than 5% of total variance. Race, ethnicity, and the other variable measures in the model do not appear to be substantial risk factors for breech presentation. However, interpretation of the results might suggest future directions for research.

Risk factors for breech presentation appear to vary by race and ethnicity for all variable measures. Advanced education produced the greatest risk of having a breech baby for Hispanic women followed by Black women in the bivariate analyses. In the United States educational attainment is differentially distributed between races and ethnicities where Whites acquire more education than Blacks, and Blacks complete more years of education than Hispanics (U.S. Census Bureau, 2005). Although advanced education was not a risk factor in the final model, it is interesting to note the risk associated with education for each race and ethnic group was the inverse of the pattern of educational achievement viewed in the population. This association suggests that a sociocultural component might be influencing breech presentation. Whether this finding is related to socioeconomic status or role incongruency is unclear because the education variable and the Medicaid/WIC eligibility variable measures might not be adequately capturing these domains.

Role incongruency represents a lack of cultural consonance where individuals behave or think differently than their ascribed sociocultural role (Dressler, 1991). This incongruency has been associated with an increased risk of impaired physical (Dressler, Oths, Ribeiro, Balieiro, & Dos Santos, 2008) and mental health (Dressler, Balieiro, Ribeiro, & Dos Santos, 2007). Educational attainment and use of Medicaid/WIC eligibility as a socioeconomic variable are likely not sensitive enough to capture these finer sociocultural domains. However, this points to the need for more research in this area.

Women who achieve high levels of education often delay childbearing (Lampic, Svanberg, Karlstrom, & Tyden, 2006). Although advanced education and ineligibility for Medicaid/WIC were not risk factors in the final model, advancing maternal age remained a risk factor. The unadjusted and adjusted ORs for maternal age, however, were in the same direction and of similar magnitude. This lack of change in magnitude and direction suggests maternal age acts independently of education, and all other variables in the model including race and ethnicity, as a risk factor. Black women of advanced maternal age were at more risk of having a breech baby (age 35–39, unadjusted OR=2.12, 95% CI 1.92, 2.35) than were Hispanic women (unadjusted OR=1.45, 95% CI 1.35, 1.55) or White women (unadjusted OR=1.31, 95% CI 1.25, 1.36). However, Black women are less likely to have a baby at that time in their life (20%) than Hispanic women (26%) or White women (29%). This difference in reproductive patterns might, in part, explain why Blacks are less likely to have a breech baby. The weathering hypothesis suggests the increased risk of adverse pregnancy outcomes experienced by Black women beyond their teens and early twenties is related to consistent sociocultural barriers experienced by these women (Geronimus, 2001). Although the weathering hypothesis was not tested in this study, future investigations might benefit from use of this conceptual framework.

Women who have their first child after they are age 35 are often met with the dual challenges of anxiety produced by the culture of fear surrounding reproduction after age 35, and a social network that is at a different point in their reproductive life and thus not able to offer as much support (Suplee, Dawley, & Bloch, 2007). Although pregnancy after age 35 is widely believed to be more risky (Friese, Becker, & Nachtigall, 2006; Nassar & Usta, 2009), the impact of age alone as a risk factor for adverse pregnancy outcomes has not been rigorously tested by controlling for confounding factors such as lifestyle (Carolan, 2003). However, the culture of fear prevails and women older than age 35 are often subjected to extensive fetal diagnostic tests. These tests, meant to determine the health of the fetus, often provoke a sense of uncertainty about the viability of the pregnancy which in turn results in anxiety, fear, distancing, and decreased attachment to the baby (Carolan & Nelson, 2007; Hjelmstedt, Widstrom, & Collins, 2006; Lawson & Turriff-Jonasson, 2006). Additional research should be conducted that evaluates advanced maternal age as a risk factor while controlling for lifestyle variables. Maternal emotions and intrauterine attachment in breech pregnancies should also be investigated.

Similar to advancing maternal age, nulliparity appeared to affect Black women differently than White or Hispanic women. In the bivariate analyses nulliparity was not a risk factor for Black women but was a moderate risk factor for White women and for Hispanic women. Unlike advancing maternal age, nulliparity was a larger risk factor in the final model (adjusted OR=1.71, 95% CI 1.67, 1.76) than in the bivariate analyses (unadjusted OR=1.49, 95% CI 1.45, 1.52). This discrepancy in the response of maternal age and nulliparity to introduction into the model suggests nulliparity and advancing maternal age are measuring different phenomena and that they are acting independently of race and ethnicity. Although nulliparity is presented as a mechanical risk factor for breech presentation in the breech literature, nulliparity is also associated with psycho-social-cultural factors such as increased fear of childbirth (Nieminen, Stephansson, & Ryding, 2009) provoked in part by lack of social support and coping mechanisms (Laursen, Hedegaard, & Johansen, 2008). This fear of childbirth might lead to an increased desire for a Cesarean section (Rouhe, Salmela-Aro, Halmesmaki, & Saisto, 2009); an increased risk of having an emergency Cesarean section has also been noted in women who fear childbirth (Laursen, Johansen, & Hedegaard, 2009). The possible association between fear and mode of childbirth suggests that emotions and coping mechanisms should be included in future studies of risk factors for breech presentation.

The risk of having a preterm breech baby was far greater in Black women (35%) than in White women (18%) in this study. Yet White women were nearly twice as likely to have a breech baby (3.2%) than were Black women (1.7%). A great proportion of the risk for Black women having a breech baby might simply be due to their propensity to have preterm babies, thus not giving the baby sufficient time to turn. Low-birth-weight and preterm births are, in part, accounted for by insufficient prenatal care (Heaman, Newburn-Cook, Green, Elliott, & Helewa, 2008), but it is unclear what role prenatal care plays in breech presentation because a sound variable measure for this parameter was not available in the database.

Culture influences birth outcomes. This has been demonstrated repeatedly by the birth outcomes of new immigrants to the West exceeding those of their race or ethnic group already in residence (Ray et al., 2007). The comparison is particularly stark between Black immigrates and African Americans, where immigrants are about one third less likely to experience preterm and low-birth-weight births than African Americans (Urquia et al., 2009). This finding suggests that sociocultural, environmental, or lifestyle factors, rather than genetics, might be primarily influencing these birth outcomes. Unfortunately, immigrant health benefits begin to diminish within months of arrival and are generally completely erased in one generation (Gravlee, 2009; Ray et al.). Although a healthy immigrant effect appears to contribute to the positive health and birth outcomes of immigrants (Callister & Birkhead, 2002; McDonald & Kennedy, 2004), social factors also play a role as demonstrated by well-educated Canadian immigrants having poorer birth outcomes than all other immigrants and native-born Canadians (Auger, Luo, & Daniel, 2008). These findings suggest role incongruency might influence birth outcomes. Similarly, the East Indian immigrant paradox, characterized by adverse pregnancy outcomes in an otherwise protected U.S. population that receives adequate prenatal care and is highly educated, points to the possibility that sociocultural factors might play a role in determining health and birth outcomes (Gould, Madan, Qin, & Chavez, 2003).

In contrast to the East Indian immigrant paradox, the Hispanic paradox illustrates the impact that positive cultural practices such as a strong social network, high valuation of children, and deeply held religious values have on birth outcomes (Gallo, Penedo, de los Monteros, & Arguelles, 2009). Although Hispanics are a disadvantaged population in terms of income, access to health care, and discrimination, they have birth and health outcomes nearly as positive as Whites in the United States (Page, 2004). The role of culture in influencing birth outcomes was also evidenced following September 11, 2001. Michigan women with Arab surnames or maiden names were protected from experiencing an increased risk of having a preterm or low-birth-weight baby 6 months after 9/11 (El-Sayed, Hadley, & Galea, 2008), whereas Californian women with Arab surnames or maiden names experienced an increased risk in these adverse pregnancy outcomes during the same time period (Lauderdale, 2006). In Michigan the Arab population concentration is nearly twice as dense as that in California suggesting a sociocultural support system might cushion the probability of experiencing adverse pregnancy outcomes.

The breech paradox represents an adverse pregnancy outcome experienced disproportionately by White women and by women in middle or upper socioeconomic strata, groups typically protected from adverse pregnancy outcomes. Although race and ethnicity themselves are probably not important risk factors for breech presentation, the breech paradox provides an opportunity to explore possible reasons why Black women and women of lower socioeconomic strata are protected from this adverse pregnancy outcome whereas White women and women who are not of lower socioeconomic strata might be at increased risk. Typically, low social status produces physiologic stress (Sabbah, Watt, Sheilham, & Tsakos, 2008). However, in industrialized countries professional or executive occupations confer general health and reproductive health benefits to men, but not to women (Frankenhaeuser et al., 1989; Hopcroft, 2006; Light et al., 1995; Steptoe et al., 2003; Weeden, Abrams, Gree, & Sabini, 2006). Little is understood about why this might occur, but further exploration might be appropriate to discover additional risk factors for breech presentation.

The apparent association between race and ethnicity and breech presentation might represent the increased likelihood for White women to acquire advanced education and work in occupations with higher status (Bureau of Labor Statistics, 2008; U.S. Census Bureau, 2005). Thus, they are more exposed to what is termed the “stress of higher status” whereas minority women are less likely to experience this type of stress. The “stress of higher status” hypothesis asserts that the benefits of higher status employment, such as autonomy and nonroutine work, are offset, in part, by increased interpersonal conflict on the job and increased work–home conflict (Schieman & Reid, 2009). It is possible that mothers of breech babies are bearing the dual burden of occupational and family accomplishments and might be experiencing work–home conflict (Frone, 2003). High expectations and multiple roles have been found to produce more stress in women than in men (Stewart, Ahmad, Cheung, Bergman, & Dell, 2000). Women who have an advanced education and elite careers are particularly at risk (Hammig & Bauer, 2009). This might be due in part to the resistance women face when attempting to ascend in the occupational ranks (Carnes, Morrissey, & Geller, 2008; Eagly & Carli, 2007). Because Black and Hispanic women in the United States are less likely to have professional or executive occupations (Bureau of Labor Statistics) they are less likely than White women to experience a glass ceiling effect and thus are in part protected from the adverse stressors of professional or executive occupations.

Although no studies were identified that evaluated the possibility that stress might influence breech presentation, some researchers have hypothesized that sympathetic dominance might promote breech presentation secondary to constriction of the lower uterine segment thus impeding the baby from turning to cephalic presentation (Peterson, 1981). Physical, emotional, and mental stress are mediated via separate neuroendocrine pathways (Papousek, Schulter, & Premsberger, 2002; Walker, Anand, & Plotsky, 2001). Although the physiologic response to physical and emotional stress is highly evolved and well organized, the response to mental stress is less well coordinated. In fact, the sympathetic response to mental stress, such as that experienced by professional and executive women, produces primarily epinephrine rather than norepinephrine, which is produced by physical and emotional stress (Panter-Brick & Pollard, 1999). The lower uterine segment is under autonomic control. Unlike norepinephrine, epinephrine stimulates uterine α-adrenergic receptors (promoting contractions) and β-adrenergic receptors (promoting relaxation). Therefore the uterus is simultaneously given contradictory instructions that lead to a tonic state (Gibbs, Karlan, Haney, & Nygaard, 2008) and could influence the baby's position.

Only two studies on risk factors for breech presentation have included the race and ethnicity of the study participants. Black race was found to be protective against breech presentation when compared to White race in one Washington State study (unadjusted OR=0.4, 95% CI 0.3, 0.5) (Rayl et al., 1996) and in a South African study (unadjusted OR=0.2,; 95% CI not indicated) (Hofmeyr, Sadan, Myer, Galal, & Simko, 1986). The findings of the current study support this surprising result. The two previous studies are limited, however, because they did not account for confounders, such as socioeconomic status, or other factors that might influence risk like preterm birth and maternal age.

Unlike other studies, this study indicates the quality of fit of the model and the variance accounted for by the model. Although White race was a risk factor for breech presentation in the logistic regression model, the model was poorly fit in that it accounted for less than 5% of the total variance, which is an important limitation. It is unclear how this compares to other studies on the topic, because their goodness of fit was not indicated; however, this does mean that interpretation of individual variables should be cautiously undertaken. A poorly fit model might reflect improper specification of variables in the model, poor data quality, or important variables missing from the model. Variables in this model were respecified numerous times, and the quality of the data was insured by using only highly valid variables. However, the goodness of fit remained low. Previously published findings of risk factors for breech presentation ought to be interpreted with caution. Seven studies were identified that used logistic regression to evaluate risk factors for breech presentation (Albrechtsen, Rasmussen, Dalaker, & Irgens, 1998b; Albrechtsen et al., 1998c; Faber-Nijholt, Huisjes, Touwen, & Fidler, 1983; Nordtveit et al., 2008; Pop et al., 2004; Rayl et al., 1996; Roberts et al., 1999; Vendittelli et al., 2008). Of these, only Roberts et al. indicated goodness of fit (p=.02), thus indicating poor fit.

Strengths and Limitations of the Study

  1. Top of page
  2. ABSTRACT
  3. Methods and Materials
  4. Results
  5. Discussion
  6. Strengths and Limitations of the Study
  7. Future Directions
  8. Implications for Practice
  9. Acknowledgments
  10. REFERENCES

The strengths of this study were its large sample size, population-based capture, inclusion of only the most valid variable measures, and indication of the goodness of fit and of the variance accounted for by the model. Large data sets, such as birth registries, are essential for studying rare conditions such as breech presentation (Szklo & Nieto, 2000). The large sample size limits random errors, as reflected in the narrow confidence limits, and use of only the most valid variable measures enhances validity of the findings.

The study was limited because many variable measures of potential interest were not available in the birth certificate registry data. Other variable measures of potential interest that are recorded in the birth certificate are recorded inaccurately therefore they were not included in this study. Of additional concern was that no direct measure of income or occupation was used. Medicaid/WIC eligibility and education may not have been adequate means to measure the influence of socioeconomic factors, although this study included a representative sample of disadvantaged women in Florida. Our findings may have been different if the study was conducted in a different state where eligibility for Medicaid/WIC services was more restrictive than it is in Florida. Also of importance is the probability that the poor goodness of fit suggests important risk factors for breech presentation were simply not captured in the study.

Future Directions

  1. Top of page
  2. ABSTRACT
  3. Methods and Materials
  4. Results
  5. Discussion
  6. Strengths and Limitations of the Study
  7. Future Directions
  8. Implications for Practice
  9. Acknowledgments
  10. REFERENCES

Risk factors for breech presentation have been insufficiently researched. This lack of investigation appears to have occurred because breech presentation is accepted as a normal variant whose incidence is fairly consistent across time and across cultures (Bartlett & Okun, 1994). Of additional interest is that when risk factors are researched, it is often those associated with mechanical risk factors; psychological, sociocultural, and environmental variables have not been fully evaluated. Chiropractic medicine and Eastern medicine offer alternative models of explanation for breech presentation. Chiropractic asserts breech presentation is due to slight alterations (i.e., subluxations) of the joints of the mother's pelvis and the position of the uterus as influenced by the round ligaments. These biomechanical changes are treated with spinal manipulation using the Webster technique (Tiran, 2004). This technique has not been rigorously evaluated but is shown to be helpful (Pistolese, 2002). A future study evaluating the efficacy of this technique is needed.

Chinese and Ayurvedic medicine suggest a life out of balance is a risk factor for breech presentation. In this model turning to cephalic presentation is considered to be an important developmental stage for the baby that is influenced jointly by the fetus's readiness to individuate and the mother's ability to parent in a loving, consistent manner (Banks, 1998; Maciocia, 1998; McGilvray, 1994). In this model maternal stress, negative emotions such as fear, and a poor diet prevent a baby from turning to cephalic presentation. Although moxibustion, the Chinese medicine means of turning breech presentation, might be as effective as external cephalic version (Coyle, Smith, & Peat, 2009; Hutton & Hofmeyr, 2009), little research has been conducted on the risk factors for breech presentation identified in the Eastern psycho-social-cultural model.

Future studies should include more precise measures of income, job strain, coping mechanisms, role congruency, and biological responses to stress (such as cortisol or heart rate variability) as a means of measuring psycho-socio-cultural contributions to breech presentation. The chiropractic and Chinese medicine models of risk factors for breech presentation should also be further investigated.

Implications for Practice

  1. Top of page
  2. ABSTRACT
  3. Methods and Materials
  4. Results
  5. Discussion
  6. Strengths and Limitations of the Study
  7. Future Directions
  8. Implications for Practice
  9. Acknowledgments
  10. REFERENCES

White women are at greater risk of having a breech baby than are Black or Hispanic women. Although the reasons for this are unclear, it is possible that ethnicity is not a true risk factor. One possibility is that race and ethnicity are proxy variables. If they are proxy variables they might be referencing differential exposure to stressors and differential reproductive patterns by ethnicity related to age and biological tendencies for length of gestation. The primary clinical implication is that we might know less about risk factors for breech presentation than we thought.

In clinical practice consider the possibility that risk factors for breech presentation might be different for Black women, White women, and Hispanic women. For Black women who present with breech presentation consider the importance of preventing preterm labor. For White women consider the influence of advancing maternal age on pregnancy outcomes and encourage fitness, a healthy diet, and ways to reduce worry and anxiety (Lampinen, Vehvilainen-Julkunen, & Kankkunen, 2009). Hispanic women and Black women with at least a college education experience a higher risk of having a breech baby than similar White women. This finding suggests the importance of supporting Hispanic and Black women who might be experiencing cultural dissonance related to childbearing timing and educational achievement beyond that of their peers. Finally, because so little is understood about the cause of breech presentation take note of physiologic, behavioral, or psycho-social-cultural patterns you see in your patients with breech babies and address then directly. The breech paradox challenges us to continue exploring psychological, behavioral, cultural, and physiological contributions to health together.

Acknowledgments

  1. Top of page
  2. ABSTRACT
  3. Methods and Materials
  4. Results
  5. Discussion
  6. Strengths and Limitations of the Study
  7. Future Directions
  8. Implications for Practice
  9. Acknowledgments
  10. REFERENCES

Thanks to OHSU Dr. Patty Carney and Dr. Tom Gregory for paper revision mentoring, and to USF College of Public Health for partial funding.

REFERENCES

  1. Top of page
  2. ABSTRACT
  3. Methods and Materials
  4. Results
  5. Discussion
  6. Strengths and Limitations of the Study
  7. Future Directions
  8. Implications for Practice
  9. Acknowledgments
  10. REFERENCES
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