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ORIGINAL RESEARCH |
From the Division of Maternal-Fetal Medicine, Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco, California.
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ABSTRACT |
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 ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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METHODS: This is a retrospective cohort study of 31,392 term, cephalic, singleton births. Women with neonates born in persistent occiput posterior position at delivery were compared to those with occiput anterior position. Women with occiput transverse position were excluded. The association between occiput posterior position and neonatal outcomes, including 5-minute Apgar scores, umbilical cord gases, meconium-stained amniotic fluid, meconium aspiration syndrome, birth trauma, admission to the intensive care nursery, and length of stay were examined using 
2 and Student t tests. Potential confounders (maternal age, ethnicity, parity, gestational age, epidural anesthesia, labor induction, length of labor, meconium, chorioamnionitis, birth weight, and year of delivery) were controlled for by using multivariable logistic regression and linear regression analyses.
RESULTS: There were 2,591 (8.2%) neonates delivered in occiput posterior position of the total cohort of 31,392 deliveries. Compared with occiput anterior, neonates delivered in occiput posterior position had higher risks for adverse outcomes, including 5-minute Apgar score less than 7 (odds ratio [OR] 1.50, 95% confidence interval [CI] 1.17–1.91), acidemic umbilical cord gases (OR 2.05, 95% CI 1.52–2.77), meconium-stained amniotic fluid (OR 1.29, 95% CI 1.17–1.42), birth trauma (OR 1.77, 95% CI 1.22–2.57), admission to the intensive care nursery (OR 1.57, 95% CI 1.28–1.92), and longer neonatal stay in the hospital (OR 2.69, 95% CI 2.22–3.25).
CONCLUSION: Persistent occiput posterior position at delivery is associated with higher risks of adverse neonatal outcomes compared with neonates delivered in the occiput anterior position. This information may be important in counseling women who experience persistent occiput posterior position in labor.
Level of Evidence: II-2
It has been reported that newborns delivered in occiput posterior position had lower 1-minute Apgar scores but not 5-minute Apgar scores when compared with those born in the occiput anterior position.6,10 Another study also reported no differences in 5-minute Apgar scores in newborns who delivered in the occiput posterior position (n = 776, 4.6%) as compared with occiput anterior (n = 16,005), but this analysis was not adequately powered to detect such a difference.3 More recently, secondary analysis of data derived from a randomized controlled trial examining delayed versus early pushing during second stage (n = 1,862) also investigated the association between fetal malposition and labor outcomes.7 The authors reported a difference in incidence of 5-minute Apgar score less than 8 between the comparison groups stratified by fetal head position, but there were no differences in abnormal fetal pH, intensive care nursery admissions, or neonatal trauma.7 However, the authors' focus in this study was to examine determinants of prolonged second stage of labor, and these neonatal outcomes were not evaluated further with multivariable techniques. Thus, it remains unclear whether an association between occiput posterior position and lower 5-minute Apgar scores exists.
Birth trauma, particularly Erb's and facial nerve palsies after forceps delivery, has also been associated with occiput posterior position.11 Yet, Senécal et al7 reported conflicting findings that there were no differences in the incidence of neonatal birth trauma according to fetal head position (occiput anterior versus occiput transverse versus occiput posterior) except in the subgroup whose fetal head position was not documented at the end of first stage of labor. Although these inconsistent findings could be due to differences in study focus or design, the association between fetal position at delivery and neonatal outcomes remains unclear.
Thus, the objective of this study was to elucidate whether an association exists between persistent occiput posterior position and adverse neonatal outcomes. We hypothesized that occiput posterior position contributes to prolonged labor and higher rates of operative deliveries, but with close fetal surveillance, occiput posterior position would not be associated with higher rates of neonatal complications.
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MATERIALS AND METHODS |
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Fetal position at delivery was determined and reported by the delivering physician or midwife. Fetal positions of right occiput posterior, direct occiput posterior, and left occiput posterior were designated as occiput posterior, and positions of right occiput-anterior, direct occiput anterior, and left occiput anterior were designated as occiput anterior. Outcomes of persistent occiput posterior position at delivery were compared with that of occiput anterior position. Neonatal outcomes evaluated included 5-minute Apgar score less than 7, acidemic umbilical cord gases as a composite variable of umbilical artery pH less than 7.0 or umbilical artery base excess less than –12, presence of meconium-stained amniotic fluid, diagnosis of meconium aspiration syndrome, and admission to the intensive care nursery. We created a composite variable, "birth trauma," to examine incidences of skull fracture, head laceration, cephalohematoma, clavicular fracture, facial nerve palsy, and Erb's palsy as diagnosed by the attending pediatrician or neonatologist caring for the neonates. Neonatal outcome was also examined using a composite variable, "neonatal morbidity," which included Apgar score less than 7, umbilical artery pH less than 7.0, base excess less than –12, meconium aspiration syndrome, birth trauma, and intensive care nursery admission. Maternal information, such as parity, age, weight, ethnicity, gestational age at delivery, year of delivery, labor induction, oxytocin augmentation of labor, epidural anesthesia, lengths of both first and second stages of labor, and birth weight, was examined as associated covariates of persistent occiput posterior position.
Statistical analysis was performed with STATA 7.0 (StataCorp, College Station, TX). Neonatal outcomes were compared with the 2 test and Student t test, and P < .05 and 95% confidence intervals were used to indicate statistical significance. Stratified analyses by parity and delivery modalities (spontaneous vaginal delivery versus operative vaginal delivery versus cesarean delivery) were also performed. Potential confounding variables, including maternal age, parity, ethnicity, gestational age at delivery, use of epidural anesthesia, meconium-stained amniotic fluid, chorioamnionitis, length of second stage of labor of 3 hours or more, birth weight, operative vaginal delivery, and year of delivery, were controlled for by using multivariable logistic regression analysis for categorical outcomes and linear regression analysis for continuous outcomes. To examine the primary outcomes of umbilical artery pH less than 7.0 and base excess less than –12, we estimated that, with a baseline rate of 1%, an overall sample size of approximately 30,000 women, of whom 8% had occiput posterior position, we would have 97% power to find a 1% difference between occiput anterior and occiput posterior position with an alpha of 0.05.
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RESULTS |
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Short-term neonatal outcomes of infants delivered in the occiput posterior position were compared with those in the occiput anterior position (Table 2). Neonates born in occiput posterior position had higher rates of 5-minute Apgar scores less than 7 (3.8% for occiput posterior versus 1.9% for occiput anterior position), umbilical artery pH less than 7 (1.8% for occiput posterior versus 0.5% for occiput anterior), and base excess less than –12 (2.2% for occiput posterior versus 0.9% for occiput anterior), which were also examined as a composite variable "umbilical cord gas acidemia" (Table 2). The risk for other undesirable outcomes, including meconium-stained amniotic fluid, meconium aspiration syndrome, birth trauma, and admission to the intensive care nursery, were also higher in neonates delivered in occiput posterior position than in those delivered in occiput anterior position (Table 2). The mean duration of stay in hospital was also higher for neonates delivered in occiput posterior position (3.68 days) compared with occiput anterior (2.60 days, P < .001). When a composite variable, "neonatal morbidity," was created to examine the association between fetal position and neonatal outcome, we observed higher rates of neonatal morbidity in occiput posterior delivery compared with occiput anterior (10.7% versus 6.0%, Table 2).
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The association between occiput posterior position and neonatal outcomes was examined using multivariable analysis to control for potential confounding bias. The covariates included in the multivariable regression model were maternal age, race/ethnicity, parity, gestational age at delivery, use of epidural anesthesia, meconium-stained amniotic fluid, chorioamnionitis, birth weight, operative vaginal delivery, and year of delivery. The adjusted odds ratio for these outcomes remained statistically significant, with the exception of meconium aspiration syndrome (Table 2). Compared with neonates born in occiput anterior position, those delivered in occiput posterior position had nearly 1.5 times the odds of having a 5-minute Apgar score less than 7 and 2 times the odds of having acidemic umbilical cord gases (Table 2). They were also more likely to have birth trauma (odds ratio [OR] 1.77, 95% confidence interval [CI] 1.22–2.57), be admitted to the intensive care nursery (OR 1.57, 95% CI 1.28–1.92), and have longer hospital stay (OR 2.69, 95% CI 2.22–3.25). When these neonatal outcomes were examined as the composite variable "neonatal morbidity," the association persisted (OR 1.45, 95% CI 1.24–1.65).
Because the study period spanned 26 years, delivery years were divided into 2 time intervals (1976–1988 and 1989–2001) to examine whether study duration was a confounder for neonatal outcomes. The adjusted odds ratio for neonatal outcomes comparing occiput posterior with occiput anterior delivery remained relatively similar by subgroup analysis for each of the neonatal outcome categories examined (Table 3). The stratified odds ratios were similar to those of the pooled estimates, suggesting that year of delivery was neither a confounder nor an effect modifier in our model.
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To examine the association between occiput posterior position and neonatal outcomes independent of parity, the study cohort was stratified into nulliparas and multiparas. In both subgroups, we observed that neonates delivered in occiput posterior position had higher rates of undesirable outcomes. For outcomes such as 5-minute Apgar score less than 7, umbilical cord gas acidemia, and intensive care nursery admission, the frequencies were nearly 1.5 to 2 times higher for occiput posterior position than for occiput anterior position for both nulliparas and multiparas (Table 4). Meconium-stained amniotic fluid was also more commonly seen in occiput posterior position than in occiput anterior position, independent of parity (P < .001, Table 4).
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To determine whether the association between occiput posterior position and adverse neonatal outcomes varied by mode of delivery, we stratified the study cohort into 3 delivery subgroups: spontaneous vaginal delivery, operative (forceps- and vacuum-assisted) vaginal delivery, and cesarean delivery. For neonates born by spontaneous vaginal delivery, higher rates of umbilical cord gas acidemia and meconium-stained amniotic fluid were observed for neonates delivered in occiput posterior position than for those in occiput anterior position (Table 5). For neonates born by operative vaginal delivery, those delivered in occiput posterior position had higher rates of 5-minute Apgar scores less than 7, birth trauma, and admission to the intensive care nursery. This association remained statistically significant when examined as a composite variable, "neonatal morbidity" (Table 5). For neonates delivered by cesarean, no differences between the occiput anterior and the occiput posterior subgroups were seen except for intensive care nursery admission (8.7% for occiput anterior and 6.6 % for occiput posterior).
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In addition to the subgroup analyses, we also controlled for potential confounding factors with multivariable regression analysis. Again, there were higher rates of short-term neonatal morbidity in those delivered in the occiput posterior position (Table 6). Neonates delivered by operative vaginal delivery in the occiput posterior position had nearly 2 times the odds of having a 5-minute Apgar score less than 7 (OR 1.99, 95% CI 1.31–3.04) and birth trauma (OR 2.57, 95% CI 1.54–4.28), and 1.5 times the odds of being admitted to intensive care nursery compared with those who were delivered in occiput anterior position (OR 1.53, 95% CI 1.03–2.27). However, there were no differences in neonatal length of hospital stay between neonates delivered in the occiput posterior and those in occiput anterior position via operative vaginal delivery (OR 0.98, 95% CI 0.63–1.53). Those neonates in the occiput posterior position who were delivered via cesarean did not exhibit differences from those delivered in the occiput anterior position for the adverse neonatal outcomes examined (Table 6).
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DISCUSSION |
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The finding of a positive association between persistent occiput posterior position and adverse neonatal outcomes differs from prior studies that reported no differences.3,6,7 This discrepancy may be due to variations in study focus or design, the outcomes we examined, or sample size. The advantage of our large cohort of nearly 2,600 women who delivered in occiput posterior position may be that we had adequate statistical power to detect a difference in adverse neonatal outcomes between the 2 groups (occiput anterior versus occiput posterior), in contrast to prior studies with sample sizes ranging from 2107 to 7703 women who delivered in occiput posterior position. Thus, negative findings in these prior studies may be due to a lack of statistical power, rather than the absence of an association.
In our study population, neonates delivered by operative vaginal delivery in the occiput posterior position, compared with those delivered in the occiput anterior position, were more likely to have a 5-minute Apgar score of 7 or less, to experience birth trauma, and to be admitted to the intensive care nursery. Because these women were not randomized to operative vaginal or cesarean delivery, we cannot assume a causal association for operative vaginal delivery. We do not suggest, based upon our findings, that for those neonates in persistent occiput posterior position, an operative vaginal delivery should be avoided in favor of cesarean delivery. Rather, it may be that a heightened degree of surveillance is required to ensure fetal well-being in such a scenario. For example, although we observed an adjusted odds ratio of 2.6 for birth trauma in the operative vaginal delivery subgroup, this is not likely due to operative vaginal delivery itself because both occiput anterior and occiput posterior groups had the same delivery modality. Perhaps neonates in this subgroup were more likely to experience birth trauma as a result of the interaction between abnormal labor and malposition. Further, this information may be important when counseling and consenting women with a persistent occiput posterior position regarding operative vaginal delivery and the potential morbidities for the mother and her neonate.
Rather than simply offering cesarean delivery to all women with a persistent occiput posterior position unlikely to achieve spontaneous vaginal delivery, it is still crucial to weigh the risks of surgery against the potential benefits. Considering that occiput posterior position is associated with increased maternal morbidities and neonatal complications, perhaps interventions such as manual rotation of the fetal occiput to "correct" malposition may offer an opportunity to reduce the attributable risk associated with malposition. For example, given an overall rate of 6% for neonatal morbidity and an odds ratio of 1.45, the number of successful rotations needed to avert an adverse neonatal outcome was 37. Although the notion of manual rotation of the fetal head is not new, few studies of this intervention exist that compare the potential benefits with the risks.12,13 If manual rotation of the fetal occiput can potentially lead to fewer operative deliveries and improved perinatal outcomes, such an intervention can, and should, be studied.
With this large retrospective cohort study, we were able to detect a difference in perinatal outcomes for neonates delivered in the occiput posterior position compared with those in the occiput anterior position. Yet, there are limitations. Measurement of effect and association can be biased by confounding due to the inherent differences in risk between comparison groups.14 This is particularly true of observational studies. We attempted to control for potential confounding by stratification and multivariable regression analysis. However, there may be residual confounding that may not be easily measured or accounted for by statistical techniques. For example, our cohort may have evolved during the study period, and practice style may differ with time or among clinicians. Although we attempted to adjust for this by accounting for year of delivery in our model, management of labor and delivery often differs depending on patient/physician preferences and may not always follow standard protocols. In addition, the association between short-term neonatal outcomes and long-term functionality requires longitudinal follow-up, which was not within the scope of this study. Another form of bias that can be seen in such retrospective studies is missing-data bias. However, the data used for this study was actually collected prospectively and is maintained with daily chart abstraction. Thus, for the majority of predictors and outcomes, we had 97–99.9% completeness of data. Further, despite the fact that our cohort was one of the largest in the literature, we were still underpowered to examine some of the outcomes when the study cohort was stratified into 3 subgroups by mode of delivery. For example, for the spontaneous vaginal delivery subgroup, we had a power of only 0.39 to find a 50% difference between the rates of 5-minute Apgar scores between occiput posterior and occiput anterior position and a power of 0.15 to detect a 50% difference in the rate of umbilical artery pH less than 7.0 in the study cohort.
To conclude, we report an association between occiput posterior position at delivery and several neonatal complications. We believe that our findings offer two primary clinical tools. First, the information we provide can be used to counsel women with fetuses in the occiput posterior position regarding neonatal outcomes and for all modes of delivery. Second, although these women do commonly deliver vaginally, the clinical findings should raise concern so that we can provide improved management of the fetus in the occiput posterior position.
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Footnotes |
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Corresponding author: Yvonne W. Cheng, MD, Division of Maternal-Fetal Medicine, Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco, 505 Parnassus Avenue, Box 0132, San Francisco, CA 94143; e-mail: yvecheng{at}hotmail.com.
doi:10.1097/01.AOG.0000206217.07883.a2
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REFERENCES |
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2. Lieberman E, Davidson K, Lee-Parritz A, Shearer E. Changes in fetal position during labor and their association with epidural anesthesia Obstet Gynecol 2005;105:974–82.
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