Congenital anomalies in breech presentation: A nationwide record linkage study

Our study aimed to determine if congenital anomalies are associated with breech presentation at delivery. We conducted a nationwide, retrospective population‐based record linkage study and analyzed all singleton births in Finland from 1996 to 2016 using the mandatory health register data collected by the Finnish Institute for Health and Welfare. We compared all major congenital anomalies detected during pregnancy, birth, or the first year of life according to the fetus's presentation at the time of delivery using X2‐square statistic and Student's t test. We adjusted the results for known risk factors for congenital anomalies to estimate adjusted odds ratios and 95% confidence intervals. Fetuses in breech presentation at delivery had an increased risk for congenital anomalies (6.5%) compared with fetuses in cephalic presentation (3.6%), P < .001. Breech presentation was associated with nearly all types of examined congenital anomalies. The strongest associations were observed with congenital deformities of the hip, the central nervous system, the respiratory system, and the musculoskeletal system. Our study supports the theory that breech presentation is, in many cases, a symptom of a fundamental problem in fetal morphogenesis or function. Neonates born in the breech presentation have a higher risk of congenital anomalies and should undergo a postnatal screening.

interruption of an organ's normal development, caused by outer influences like teratogenic agents or a trauma. In the international classification of diseases system (ICD), congenital anomalies are classified according to organ systems or genetic defects. Preventive public health measures work to decrease the frequency of specific congenital anomalies by removing environmental risk factors or reinforcing protective factors such as preconceptionally folic acid use. Congenital anomalies can be detected through prenatal and neonatal screening. 1 Breech presentation of the fetus appears in around 2% to 4% of all births. 7 At delivery, breech presentation is a known marker for adverse neonatal outcomes. Previous studies have shown an association between breech presentation at delivery and congenital anomalies. [7][8][9][10][11] However, these studies are limited by study size and the lack of adjustments for common risk factors of congenital anomalies. First, we hypothesize that congenital anomalies are associated with breech presentation at delivery. Second, we aimed to investigate the types of anomalies associated with breech presentation and increase awareness of the need for prenatal and neonatal screening among the children born in the breech to improve these children's treatment and care.

| Study design and data sources
We conducted a population-based record linkage study using anonymized data of mothers and infants recorded on the National Medical Birth Register (MBR) and the Register on Congenital Malformations (RCM). The registers are maintained by the Finnish Institute for Health and Welfare. All maternity hospitals are obliged to report to the MBR and the RCM. In Finland, all live-born infants receive unique personal identification numbers; these numbers can be used to trace all healthcare data and diagnoses in the case of hospitalization or death. Stillbirths can be identified by using the mother's identification number.
A pediatrician routinely examines all newborns.
The MBR collects baseline data on pregnancies, deliveries, and newborn outcomes during the first days of life. These data include all live births and stillbirths with a birth weight of at least 500 g or a gesta- We analyzed all singleton live births in Finland from 1996 to 2016 using the Finnish Institute for Health and Welfare data. We compared all congenital anomalies detected at birth or during the first year of life according to the fetus's presentation at the time of delivery. Our study population included women with a singleton fetus either in breech or cephalic presentation at the delivery time. All other birth presentations were excluded. The classification for congenital anomalies was selected according to the ICD-10 classification (Table 1). ICD-9 codes (Atlanta modification for congenital anomalies) were matched to the ICD-10 codes. The selection of maternal variables and risk factors for congenital anomalies was based on the previous literature ( Table 2).
The congenital anomalies were adjusted for all significant variables and risk factors. The calculations were performed using SAS 9.4.
Statistical differences in categorical variables were evaluated with the Chi-squared test or Fisher's exact test when appropriate. We calculated odds ratios (ORs) with corresponding 95% confidence intervals using binary logistic regression. Differences were considered statistically significant, with a P-value of ≤.05.

| RESULTS
We analyzed the data on 1 184 499 women with a singleton delivery from 1996 to 2016. Women with a breech delivery numbered 34 030 (2.9%).
Among the neonates born in breech presentation, there were 2209 (6.5%) neonates presenting with at least one congenital anomaly, ( Table 3).
The incidence of nearly all congenital malformation types evaluated in this study was higher among children born breech than among children born in cephalic presentation ( Table 4).  (Table 4). Furthermore, malformations of the eye, ear, face, and neck, such as cleft lip and cleft palate, were more frequent among breech-born neonates than among cephalic-born neonates (Table 4).
There were some differences in the maternal characteristics and the exposures to other possible risk factors for congenital anomalies between the study groups. The study groups differed in the following variables: maternal age, smoking, maternal BMI, maternal hypothyroidism, maternal hyperthyroidism, gestational diabetes, maternal care for fetal injury by alcohol, maternal care for fetal injury by radiation, previous congenital anomaly, neonatal sex, and gestational age.

| DISCUSSION
Our study demonstrates a significant correlation between breech presentation at delivery and congenital anomalies. Breech presentation at delivery is associated with most of the congenital anomalies examined. Our study supports the theory that breech presentation is, in many cases, a symptom of a fundamental problem in fetal morphogenesis or function. 7,8,13 We confirmed and built on existing evidence from earlier smaller studies in which breech presentation at delivery has been demonstrated as a marker for congenital anomalies. 8,10,11,14 However, our results were based on a large sample size.
Moreover, we were able to adjust our results for common confounders for congenital anomalies. Our study results provide a new insight into the relationship between congenital anomalies and breech presentation at delivery. We were also able to estimate the increase in risk for the various congenital anomalies in breech presentation.
The analysis indicates the importance of prenatal and neonatal anomaly screening of children born in breech presentation, as such presentation may be a sign of congenital anomalies.
The prevalence of congenital anomalies in breech (6.5%) was twofold compared with the cephalic presentation (3.7%). Our rates are lower than the rates found by Mostello,8  Breech presentation is a known risk factor for dysplasia of the hip. 16 We also expected in our data this association. The children born in breech presentation had a significantly increased risk of having a congenital hip deformity. This is most likely one of the rare congenital anomalies caused by breech presentation. Breech presentation is one of the well-known causes for the hip's developmental dysplasia, as the fetal breech position can limit the fetal movements in the womb, particularly when the fetus's knees are extended (frank breech). 16,17 In this case, breech presentation is most likely the cause of a congenital anomaly and not a symptom. Fortunately, this association is recognized, and children born in breech presentations are in many countries routinely screened during the neonatal period for developmental dysplasia of the hip, and therefore early detected and treated.
Our data show that breech presentation at delivery increased the risk of the nervous system's congenital malformations and a higher risk for congenital malformations and deformations of the musculoskeletal system. These results are in line with the hypothesis that some fetuses in breech presentation lack movements or have the reduced ability to turn them into cephalic presentation. This reduced ability might be caused by neurological and musculoskeletal malformations. 18,19 We found that breech presentation at delivery was associated with various congenital malformations of different organ systems.
After adjusting, the only congenital malformation that was not associated with breech presentation was the digestive system's malformations. Our results confirm the previous findings from Mostello's work. 8 Some congenital anomalies are most likely associated with breech presentation as they impeach a fetal rotation into a cephalic presentation as the fetal head might not fit in the maternal pelvis through malformations of the fetal eye, ear, face, or neck. Many congenital malformations such as malformations of the respiratory system, the circulatory system, and cleft lip or cleft palate, are associated with polyhydramnios, 20,21 which is associated with abnormal fetal presentation. 21 Malformations of the genital organs and the urinary system might be associated with polyhydramnios 20,21 and oligohydramnios, both known risk factors for breech presentation. 9,21 Chromosomal abnormalities are often linked to intrauterine growth restriction, which is significantly associated with breech presentation. 9 This study is an extensive population-based record-linkage study on breech presentation and the risk of congenital malformations. Our research presents valuable information for evaluating newborns in the nursery. The study population includes 1 184 499 deliveries from Finland. We could link the neonatal outcome to maternal data and adjust our outcomes accordingly for known cofounders. A further strength relates to the critical information on the mother's characteristics and risk factors for congenital anomalies. There are, however, some limitations in our study. The study's retrospective character constrained the methodological choices. Another limitation is the design as a recordlinkage study, which restricted the variables to data availability. As an example, we could not see which women have participated in the nuchal translucency and anatomy scan during pregnancy. An additional limitation is that we do not know which pregnancies underwent an external cephalic version, and the question remains whether the children who have been turned into cephalic presentation have a higher risk of congenital anomalies. In addition, the connection of congenital anomalies with preterm breech deliveries remains unclear and would need further research and investigations in the future.
According to our study, breech presentation at birth may be a marker of congenital anomalies. Thus, we recommend careful postnatal screening for all children born in breech presentation.