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Keywords:

  • Register-based study;
  • postpartum hemorrhage;
  • blood transfusion;
  • cesarean delivery;
  • mode of delivery

Abstract

  1. Top of page
  2. Abstract
  3. Key Message
  4. Introduction
  5. Material and methods
  6. Results
  7. Discussion
  8. Funding
  9. References

Objective. To examine the prevalence and risk factors for blood transfusion during delivery. Design. Register-based retrospective cohort study from Finland. Setting. National Medical Birth Register data during 2006–2008. Sample. A total of 171 731 women having singleton deliveries, of whom 3394 (1.98%) received blood transfusion. Methods. We calculated odds ratios (ORs) with 95% confidence intervals (CIs) by multivariate logistic regression to adjust for confounders related to maternal background and mode of delivery. Main outcome measures. Blood transfusion rates by risk factors. Results. Blood transfusion rate during labor increased slightly, from 1.83% in 2006 to 2.27% in 2008 (p < 0.001), during the study period. The highest rate, almost 4%, was reported in central hospitals. Advanced maternal age and primiparity predisposed to blood transfusion. A previous cesarean section increased these rates also in subsequent vaginal delivery (2.64%) compared with women who had vaginal deliveries only (0.86%, OR 3.14, 95% CI 2.65–3.72). Induction of labor almost doubled the risk for blood transfusion (adjusted OR 1.74, 95% CI 1.60–1.89). All instrumental vaginal deliveries (adjusted OR 2.46, 95% CI 2.25–2.69) and any cesarean sections (adjusted OR 1.80, 95% CI 1.66–1.96) increased this risk. Delivery of a large-for-gestational age newborn increased the blood transfusion risk over twofold. Conclusions. As previous cesarean section includes an increased risk for blood transfusion, even in subsequent deliveries, it is essential to consider the mode of labor carefully. The blood transfusion rate was the highest in central hospitals, suggesting differences in blood transfusion practice.


Abbreviations: 
CI

confidence interval

MBR

Medical Birth Register

NA

not available

OR

odds ratio

PPH

postpartum hemorrhage

Key Message

  1. Top of page
  2. Abstract
  3. Key Message
  4. Introduction
  5. Material and methods
  6. Results
  7. Discussion
  8. Funding
  9. References

Blood transfusion practices vary considerably. In this study, the main risk factors for blood transfusion were induction of labor, non-elective cesarean delivery, operative vaginal delivery and especially previous cesarean delivery.

Introduction

  1. Top of page
  2. Abstract
  3. Key Message
  4. Introduction
  5. Material and methods
  6. Results
  7. Discussion
  8. Funding
  9. References

Severe postpartum hemorrhage (PPH) is major cause of maternal death worldwide. Increasing trends for PPH have been observed in many countries, with higher blood transfusion rates at childbirth observed in the USA, Australia and Denmark, but not in Canada or Belgium (1,2). At the same time, an increasing rate of severe adverse outcomes, such as hysterectomy for atonic PPH, Sheehan syndrome and hemorrhage-related maternal mortality, has been reported in many countries (1). In France, descriptive analysis of maternal deaths from PPH suggests that there may be room for improvement in transfusion procedures, especially regarding administration delays (3).

Transfusion practice varies between countries. In a recent Danish study, this rate was about 2%, which is quite high when compared with Australia, Canada, France or Norway (2–5). In countries where the blood transfusion rate is high, the sensitivity to detect severe PPH by using this parameter is good.

Estimation of blood loss at childbirth is inaccurate (6,7). Typically, overestimation of blood loss occurs in cesarean delivery (3). In clinical practice, underestimation of blood loss is a major problem. In moderate PPH, blood transfusion is not needed. Usually, there is no need to transfuse one unit of packed red blood cells only. Therefore, the blood transfusion rate offers an opportunity to use it as surrogate marker for PPH.

As there are several ongoing prospective studies on severe obstetric outcomes, such as NOSS (http://www.noss.nu) and INOSS (http://www.npeu.ox.ac.uk/inoss), we wanted to study risk factors for severe PPH retrospectively, by using blood transfusion at childbirth as a surrogate marker. We also wanted to evaluate differences in blood transfusion practices between hospital levels by using the high-quality Finnish Medical Birth Register (MBR) data.

Material and methods

  1. Top of page
  2. Abstract
  3. Key Message
  4. Introduction
  5. Material and methods
  6. Results
  7. Discussion
  8. Funding
  9. References

We received permission for this study from the National Institute for Health and Welfare (THL), as required by national data protection legislation. We used MBR data for the years 2006–2008. Since 2004, the MBR contains a check-box to indicate whether women received blood transfusion (i.e. one or more units of packed red blood cells) during delivery, in the intensive care unit or in the postpartum ward. The study population consisted of 171 731 women having a singleton birth.

The information in the MBR is collected on care and interventions for the mother during pregnancy and delivery and regarding the newborn during the first seven days. The MBR data are compiled by midwives at childbirth from all 31 delivery units in Finland. Of them, five are large tertiary university hospitals and 16 are central hospitals, while all others are smaller local hospitals. The number of home births is negligible. There are no midwife-led units. The mean annual delivery rate has been increasing, and was 1716 deliveries per unit (range 104–5692, median 1145) during the study period.

Less than 0.1% of all newborns are missing from the MBR (8), and information on those cases is routinely obtained by linking them to the Central Population Register and the Cause-of-Death Register. Following these linkages, the data in MBR are complete. Data are checked at the National Institute for Health and Welfare (THL), and confirmation of the data or revision may be asked from the hospitals. In general, the data correspond well with the information in hospital records (9).

The main outcome of the study was the blood transfusion rate among parturients. We compared parturients who received blood transfusion at childbirth with those women who did not. We evaluated the association of blood transfusion with predisposing maternal factors (age, parity, body mass index calculated as weight [in kilograms]/height [in meters]2, urbanism and maternal smoking) birth-related factors (such as pain relief during delivery, operative deliveries and mode of delivery) and birthweight of the newborn. In addition, we analysed the results for hospital level (university hospital, central hospital or local hospital).

Statistical analysis

We calculated crude odd ratios (ORs) and 95% confidence intervals (CIs) for the predisposing factors. Logistic regression analyses were used to control for the confounding factors. In the first model, we adjusted for maternal age, previous deliveries, body mass index and birthweight (adjusted 1). In the second model, we adjusted additionally for mode of delivery, classified as vaginal delivery, instrumental delivery and cesarean section (adjusted 2). The analyses were done separately for primiparous and multiparous women.

Results

  1. Top of page
  2. Abstract
  3. Key Message
  4. Introduction
  5. Material and methods
  6. Results
  7. Discussion
  8. Funding
  9. References

In this material, 3394 women (1.98%) received blood transfusion during delivery. We observed an increasing trend for blood transfusions from 2006 (1.83%) to 2008 (2.27%; for trend, p < 0.001). Women who delivered in central hospitals had a higher blood transfusion rate (3.87%) than women who delivered either in university hospitals (1.63%) or in smaller, district hospitals (1.62%). The sociodemographic factors of these women are presented in Table 1. The highest risk for blood transfusion was observed among women aged ≥40 years (2.48%) and primiparous women (2.76%). Very lean women (body mass index <18.5 kg/m2) also had an increased blood transfusion rate (2.08%), while overweight and obese women did not. Women who lived in urban areas more often received blood transfusions than those living in rural areas.

Table 1. Study population.
Characteristic n Blood transfusion
n %
  1. Abbreviation: NA, not available.

  2. *Calculated as weight (in kilograms)/height (in meters)2.

  3. †Including foreign countries.

Age (years)
 ≤19435266(1.52)
 20–2427 869464(1.66)
 25–2954 8271015(1.85)
 30–3453 1841110(2.09)
 35–3925 242584(2.31)
 ≥406254155(2.48)
 NA30(0.0) 
Previous deliveries
 Primiparous72 4311996(2.76)
 157 319894(1.56)
 2–333 730422(1.25)
 ≥4802382(1.02)
 NA2280(0.0) 
Body mass index*
 ≤18.424 295505(2.08)
 18.5–24.988 5381687(1.91)
 25–29.935 304653(1.85)
 30–34.912 713243(1.91)
 ≥355873105(1.79)
 NA5008201(4.01)
Hospital
 University60 260980(1.63)
 Central26 9381043(3.87)
 District hospital84 5331371(1.62)
Urban/rural
 Urban municipalities11 3942378(2.09)
 Semi-urban municipalities29 076556(1.91)
 Rural municipalities28 391454(1.60)
 Other†/NA3246(1.85)
Smoking
 No146 4762961(2.02)
 Yes25 255433(1.71)
Total171 7313394(1.98)

Smokers had fewer blood transfusions (1.71%) than non-smokers (2.02%; Table 2), but this difference disappeared after adjusting for age and parity (adjusted OR 1.08, 95% CI 0.98–1.20). Parturients with infertility treatment had increased risk for blood transfusion, even after adjusting for age and parity (adjusted OR 1.97, 95% CI 1.71–2.26). These risks were similar for all treatment modalities (intrauterine insemination, ovulation induction and in vitro fertilization; data not shown).

Table 2. Maternal background and risk factors for blood transfusion during delivery.
ParameterCrude OR (95% CI)Adjusted* OR (95% CI)Adjusted† OR (95% CI)
  1. Abbreviations: CI, confidence interval; and OR, odds ratio.

  2. *Adjusted for maternal age, previous deliveries, body mass index and birthweight.

  3. †Adjusted for maternal age, previous deliveries, body mass index, birthweight, instrumental delivery and caesarean delivery.

Smoking during pregnancy0.85 (0.76–0.94)1.04 (0.93–1.16)1.06 (0.95–1.18)
Any infertility treatment2.80 (2.46–3.19)2.02 (1.75–2.31)2.00 (1.75–2.30)
Hypertension, essential1.41 (1.07–1.87)1.38 (1.03–1.84)1.30 (0.97–1.74)
Pregnancy-induced hypertension1.53 (1.30–1.80)1.49 (1.26–1.76)1.39 (1.17–1.64)
Pre-eclampsia1.61 (1.20–2.17)1.25 (0.90–1.73)1.01 (0.73–1.41)
Eclampsia4.96 (1.78–13.9)3.52 (1.08–11.5)2.37 (0.73–7.75)
Hospitalized for hypertension1.76 (1.48–2.09)1.66 (1.39–1.99)1.52 (1.27–1.82)
Gestational diabetes0.91 (0.79–1.04)0.91 (0.79–1.05)0.86 (0.74–0.99)
 Pathological 2 h oral glucose tolerance test0.98 (0.87–1.11)1.04 (0.91–1.18)1.05 (0.92–1.20)
 Insulin treatment0.65 (0.48–0.86)1.02 (0.82–1.28)1.11 (0.89–1.39)
Previous caesarean section1.57 (1.41–1.74)1.74 (1.56–1.94)1.28 (1.14–1.44)
Anemia3.08 (2.65–3.58)3.38 (2.91–3.93)3.30 (2.83–3.84)
Hospitalized for hemorrage1.82 (1.38–2.40)1.85 (1.40–2.44)1.73 (1.31–2.29)
Hospitalized for preterm birth thread0.83 (0.64–1.07)1.94 (1.76–2.14)1.76 (1.59–1.94)
Hospitalized for other reason0.91 (0.80–1.03)1.12 (0.98–1.27)1.20 (1.05–1.37)

Women with any of the maternal hypertensive diseases, such as hypertension, pregnancy-induced hypertension, hospitalization for hypertension, pre-eclampsia and eclampsia, had an increased risk for blood transfusion during delivery. In most cases, these risks disappeared after adjusting for mode of delivery (Table 2). Those women who had had anemia during pregnancy had over threefold risk for blood transfusion during delivery (adjusted 1 OR 3.38, 95% CI 2.91–3.93). Among women hospitalized for bleeding, this risk was almost twofold. Women with gestational diabetes and women treated with insulin had no increased risk for blood transfusion after adjusting for background variables. When adjusted also by the mode of delivery, the risk for blood transfusion was slightly decreased among women with gestational diabetes (adjusted OR 0.86, 95% CI 0.74–0.99).

Induction of labor increased the risk for blood transfusion almost twofold (adjusted 1 OR 1.74, 95% CI 1.60–1.89; Table 3). Women who received epidural analgesia (adjusted 1 OR 1.16, 95% CI 1.08–1.25) or combined spinal and epidural analgesia or non-medical pain relief had an increased risk for blood transfusion. Spinal analgesia, nitrous oxide or pudendal analgesia did not affect the blood transfusion risk. Paracervical blockade or other medical pain relief decreased the risk for transfusion (data not shown).

Table 3. Obstetric history, interventions and risk for blood transfusion.
ParameterCrude OR (95% CI)Adjusted OR* (95% CI)Adjusted OR† (95% CI)
  1. *Adjusted for maternal age, previous deliveries, body mass index and birthweight.

  2. †Adjusted for maternal age, previous deliveries, body mass index, birthweight, instrumental delivery and cesarean delivery.

  3. ‡Not adjusted for birthweight.

Induction of labor1.67 (1.54–1.81)1.74 (1.60–1.89)1.68 (1.55–1.83)
Episiotomy2.63 (2.45–2.81)2.12 (1.96–2.30)2.70 (2.43–2.99)
Shoulder dystocia1.40 (0.79–2.50)0.96 (0.54–1.73)0.73 (0.40–1.31)
Breech presentation0.94 (0.74–1.18)1.16 (0.91–1.47)1.68 (1.32–2.14)
Other abnormal presentation0.99 (0.82–1.18)1.04 (0.86–1.24)1.55 (1.29–1.86)
Instrumental delivery4.12 (3.78–4.50)2.46 (2.25–2.69)
Any cesarean section2.50 (2.30–2.71)1.80 (1.66–1.96)
 Elective1.00 (0.88–1.15)0.96 (0.83–1.10)
 Urgent2.84 (2.57–3.13)1.81 (1.64–1.99)
 Emergency5.84 (4.91–6.94)3.92 (3.29–4.66)
Repair of third or fourth degree perineal laceration6.05 (5.06–7.22)4.40 (3.67–5.28)3.68 (3.05–4.45)
Small for gestational age‡1.16 (0.93–1.45)1.02 (0.81–1.29)0.91 (0.72–1.15)
Large for gestational age‡1.96 (1.67–2.30)2.22 (1.89–2.61)1.99 (1.69–2.35)

Shoulder dystocia, breech presentation or other abnormal presentation at birth did not increase the risk for blood transfusion after adjusting for maternal background only (adjusted 1; Table 3). Increased risk for blood transfusion was observed for breech presentation and other abnormal presentation when including the mode of delivery in the model (adjusted 2). Instrumental vaginal delivery was associated with increased risk for blood transfusion (adjusted 1 OR 2.46, 95% CI 2.25–2.69). The number of forceps deliveries was low (n= 81), but increased rate for blood transfusion (9.88%) was observed. Episiotomy increased the risk for blood transfusion, as expected (adjusted 1 OR 2.12, 95% CI 1.96–2.30). Likewise, third or fourth degree lacerations increased the risk for blood transfusion fourfold (adjusted 1 OR 4.40, 95% CI 3.67–5.38).

Elective cesarean section did not influence the risk for blood transfusion (adjusted 1 OR 0.96, 95% CI 0.83–1.10). However, in urgent cesarean sections an increased risk for blood transfusion was observed (adjusted 1 OR 1.81, 95% CI 1.64–1.99). In emergency cesarean sections, this risk was even higher. In general, previous cesarean section predisposed to blood transfusion (adjusted 1 OR 1.74, 95% CI 1.56–1.94). In subsequent vaginal deliveries, the blood transfusion rate was 2.64% among women with previous cesarean and 0.86% among those with vaginal deliveries only (OR 3.14, 95% CI 2.65–3.72; Table 4). For operative vaginal deliveries, these rates were 8.29 and 2.61%, respectively (OR 3.37, 95% CI 2.40–4.74). A very significantly increased risk for blood transfusion was observed for women with previous cesarean and subsequent operative vaginal delivery when compared with women who had vaginal deliveries only (OR 10.49, 95% CI 8.30–13.25). For cesarean sections, the blood transfusion rate was lower (2.38%) among women with previous cesarean compared with women without (4.24%, OR 0.55, 95% CI 0.45–0.67).

Table 4. Mode of delivery and the risk for blood transfusion in subsequent delivery.
Previous deliveryCurrent deliveryPostpartum hemorrage (%)Adjusted 1 OR (95% CI)Adjusted 2 OR (95% CI)
  1. Adjusted 1 OR: reference population, previous and current delivery vaginal.

  2. Adjusted 2 OR: reference population, previous vaginal delivery in each mode of current delivery category.

VaginalVaginal0.861.001.00
Cesarean sectionVaginal2.643.14 (2.65–3.72)3.14 (2.65–3.72)
VaginalOperative vaginal2.613.11 (2.37–4.07)1.00
Cesarean sectionOperative vaginal8.2910.49 (8.30–13.25)3.37 (2.40–4.74)
VaginalCesarean section4.245.14 (4.45–5.94)1.00
Cesarean sectionCesarean section2.381.81 (1.49–2.21)0.55 (0.45–0.67)

Large-for-gestational age newborns had high blood transfusion risk (adjusted 1 OR 2.22, 95% CI 1.89–2.61), while small-for-gestational age newborns did not have excess blood transfusion risk.

We repeated these analyses for primiparous and multiparous women separately. In general, primiparous women had higher blood transfusion rates. Among multiparous women, both epidural analgesia and spinal analgesia decreased the blood transfusion rate (data not shown).

Discussion

  1. Top of page
  2. Abstract
  3. Key Message
  4. Introduction
  5. Material and methods
  6. Results
  7. Discussion
  8. Funding
  9. References

The frequency of blood transfusion during labor has increased slightly in Finland, as in the USA and Australia (1). The blood transfusion rates are the highest among older parturients and primiparous women. The most important delivery-related risk factors are induction of labor and operative deliveries. Cesarean section includes an increased risk for blood transfusion also in subsequent deliveries. In Finland, the proportion of cesarean sections has remained stable, but the frequency of vacuum deliveries has almost doubled to 8.6% in the last 20 years (10).

The definition of PPH varies. In many countries, hemorrhage of 500 mL or more following vaginal delivery or 1000 mL following cesarean delivery are reported abnormal according codes for PPH in the 10th version of the International Classification of Diseases (ICD-10). Severe PPH is often defined as hemorrhage of more than 1500 mL (6). An Australian study assessed accuracy of hospital discharge data regarding obstetric hemorrhage diagnoses and procedures. In general, severe bleeding was more likely to be reported than less severe cases. Postpartum hemorrhage was reported with sensitivity of 73.8%, but when limited to women requiring blood transfusion, sensitivity increased further to 92.5% (11). Estimation of the blood loss at childbirth is inaccurate (6,11). Typically, overestimation of blood loss at low volumes and underestimation at large volumes occurs. Also, a significant variability has been reported among doctors estimating the amount of blood loss during obstetric hemorrhage (6,12). Therefore, the rate of blood transfusions can be used as surrogate marker for severe PPH.

In the present study, we used information from the Finnish MBR, which contains reliable, population-based data on blood transfusions at childbirth. The MBR includes all births in Finland, and the notification form includes a check-box for blood transfusion. This variable was introduced in 2004, and we started our analysis in 2006 after allowing a two year learning process. Reported blood transfusion rates after delivery vary between <1 and 7% (2,13). In our study, this rate was 2%, which is relatively high rate compared with other international studies.

Heterogeneity in patient populations and different blood transfusion practices generate variability in blood transfusion rates. In our material, blood transfusion rates were the highest in central hospitals. It could have been assumed that this rate was highest in university hospitals, with high-risk pregnancies. Surprisingly, the rates in small district hospitals were similar to those in university hospitals. Variable criteria for blood transfusion are likely to exist in hospitals. One retrospective study assessed that up to one-third of all blood transfusions were inappropriate to parturients (7). Therefore, it is essential to evaluate obstetric blood transfusion policy and agree on blood transfusion criteria in clinical practice. These findings also highlight the fact that unexpected PPH can occur in any delivery hospital. In France, the highest risk for severe PPH was observed in public non-university hospitals. Presence of an obstetrician 24 h a day resulted in a tendency for decreased risk for severe PPH (14).

Most of the maternal risk factors, primiparity and advanced maternal age, are the same as those observed in other studies (5). In many populations, including Finland, maternal age at childbirth is increasing, which is known to be a risk factor for PPH and even peripartum hysterectomy (1,15,16). Among older multiparous mothers, however, the decision to perform hysterectomy may be easier than among younger mothers. Smokers had fewer blood transfusions than non-smokers, but this difference disappeared after adjustments. In Finland, nearly half of women in their twenties smoke regularly, while the corresponding figure is 10% among women older than 35 years.

Increased birthweight increases the risk for birth canal injuries, operative deliveries, non-elective cesarean sections and hemorrhage (5). Surprisingly, gestational diabetes and insulin-treated diabetes did not increase the blood transfusion risk. When adjusted by the mode of delivery, this risk was even decreased. Better antenatal care may result in a decreased rate of macrosomia. Most of the maternal hypertensive disorders increased the risk for transfusion. This was partly explained by operative deliveries, because in most cases the risk disappeared after adjusting for the background variables. Antepartum anemia or hospitalization for hemorrhage during pregnancy increased the risk for blood transfusions, as could be assumed.

Induction of labor has become more common. According to the MBR, approximately 17% of all births were induced in Finland during 2008–2009 (10). In our study, as in many previous studies, induction is an important reason for PPH (5,16,17). One possible explanation is that by lengthening labor induction may lead to atonic hemorrhage (1). Even though induction criteria vary in different hospitals, it should be emphasized that induction of labor should always be considered carefully.

In our study, epidural analgesia and combined epidural and spinal analgesia increased the risk for blood transfusion among all women. The underlying mechanism is probably by lengthening labor or negatively affecting the endogenous oxytocin level. Furthermore, we found a decreased risk for blood transfusion among multiparous women with epidural or combined epidural and spinal analgesia or spinal analgesia. This can be explained by the shorter labor of multiparous women. In another study, epidural was associated with reduced risk for severe PPH (14). The authors suspected that the presence of the epidural catheter facilitated immediate management of PPH. In the present study, paracervical analgesia was associated with decreased risk for blood transfusion. This is probably due to patient selection, because it is usually offered to parturients with expectation of a fast and uncomplicated delivery.

According to our results, increasing cesarean section rates predict high blood transfusion rates in ongoing and subsequent deliveries. In Finland, the cesarean section rate has remained quite stable in the last 10 years (from 15 to 16%), but globally these rates are rising (18). Previous studies suggest that blood transfusion rates are higher (3.3%) in cesarean deliveries than in vaginal deliveries (0.6%). In non-elective cesarean deliveries, the risk is even more increased (13), which is in accordance with our results. In our study, the blood transfusion risk was not increased in elective cesarean delivery, but in a Danish study it was associated with a reduced risk for blood transfusion when compared with women who had intended vaginal delivery (2). In repeated cesarean sections, the tissues are scarred and they may bleed less than in the first operation. We did not have information on intended mode of delivery. In contrast, a Norwegian study found a twofold risk for severe hemorrhage among women with elective cesarean section when compared with women who had spontaneous vaginal delivery (17).

Previous cesarean section is associated with an increased risk of abnormal placentation, hemorrhage and peripartum hysterectomy (1,14). In a Norwegian register study, the highest risk for severe hemorrhage was found among women with previous cesarean and induced labor leading into emergency cesarean (17). We observed the highest risk for blood transfusion, over 10-fold, among women with previous cesarean and subsequent operative vaginal delivery. In contrast, some other studies have reported that the rate of blood transfusion was lower among women with previous cesarean section and subsequent elective cesarean section than trial of vaginal delivery (2,19).

Blood transfusions in delivery have become more common in Finland. Increased frequency and severity of PPH has also been reported in other countries. The rate was highest in central hospitals, suggesting that practices for blood transfusion vary considerably between hospitals and hospital levels. In the present study, the main risk factors were induction of labor and operative delivery. Inductions should be carefully considered, as well as the first cesarean section, because it includes an increased risk for blood transfusion, even in subsequent deliveries.

Funding

  1. Top of page
  2. Abstract
  3. Key Message
  4. Introduction
  5. Material and methods
  6. Results
  7. Discussion
  8. Funding
  9. References

This study was financially supported by a grant from the Finnish Medical Society Duodecim.

References

  1. Top of page
  2. Abstract
  3. Key Message
  4. Introduction
  5. Material and methods
  6. Results
  7. Discussion
  8. Funding
  9. References