Objective
We sought to study neonatal outcomes in early preterm births by delivery route.
Study Design
Delivery precursors were analyzed in 4352 singleton deliveries, 24 0/7 to 31 6/7 weeks’ gestation. In a subset (n = 2906) eligible for a trial of labor, neonatal mortality in attempted vaginal delivery (VD) was compared to planned cesarean delivery stratified by presentation.
Results
Delivery precursors were classified as maternal or fetal conditions (45.7%), preterm premature rupture of membranes (37.7%), and preterm labor (16.6%). For vertex presentation, 79% attempted VD and 84% were successful. There was no difference in neonatal mortality. For breech presentation, at 24 0/7 to 27 6/7 weeks’ gestation, 31.7% attempted VD and 27.6% were successful; neonatal mortality was increased (25.2% vs 13.2%, P = .003). At 28 0/7 to 31 6/7 weeks’ gestation, 30.5% attempted VD and 17.2% were successful; neonatal mortality was increased (6.0% vs 1.5%, P = .016).
Conclusion
Attempted VD for vertex presentation has a high success rate with no difference in neonatal mortality unlike breech presentation.
Fifty-four percent of all infant deaths in the United States occur among the 2% of infants born at <32 weeks’ gestation. The optimal route of delivery for the early preterm fetus remains controversial. Some observational studies have shown a lower neonatal mortality for planned cesarean delivery (CD) as compared with vaginal delivery (VD) for vertex and breech early preterm pregnancies whereas other studies do not show a difference by route of delivery for vertex or breech presentation.
For Editors’ Commentary, see Contents
The vertical uterine incision often required for CD at this gestational age increases the risks of hemorrhage, bladder injury, and other complications. There is also an increased risk of uterine rupture, placenta previa, and placenta accreta in subsequent pregnancies.
Six trials have attempted to randomize the route of delivery for women in preterm labor (PTL) at high risk for delivery. Recruitment difficulties limited combined enrollment in all of these trials to only 122 women. A metaanalysis of these trials found no statistically significant differences in neonatal outcomes by route of delivery, except for lower cord pH values among infants delivered by CD.
Because randomized trials to answer this question have not proven feasible, a study using recent cohort data to determine the effect of fetal presentation, gestational age, and the intended route of delivery on outcome would be valuable. Therefore, the purpose of this study was to use a contemporary cohort that reflects current obstetric and neonatal clinical practice to identify the precursors of early preterm delivery ≤32 weeks of gestation and to assess the effect of intended route of delivery on neonatal mortality for viable singleton early preterm births, stratified by presentation.
Materials and Methods
The Consortium on Safe Labor (CSL) was a study conducted by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, and has been described in detail elsewhere. Briefly, CSL was a retrospective cohort study involving 228,668 deliveries from 2002 through 2008 from 12 clinical centers and 19 hospitals representing 9 American Congress of Obstetricians and Gynecologists districts. All deliveries at ≥23 weeks’ gestation were included in the CSL cohort. Women could have >1 pregnancy in the cohort; so to avoid intraperson correlation only the first pregnancy enrolled was included for a total of 208,695 women.
Demographic data; medical history; prenatal, labor, and delivery information; as well as postpartum and neonatal outcomes were extracted from electronic medical records from each institution. Data from the neonatal intensive care unit (NICU) were collected and linked to the newborn record. Maternal and newborn discharge International Classification of Diseases, Ninth Revision ( ICD-9 ) codes were also collected for each delivery. Data were transferred in electronic format from each site and were mapped to common categories for each predefined variable at the data coordinating center. Data inquiries, cleaning, and logic checking were performed. Validation studies for 4 key outcome diagnoses (cesarean for nonreassuring fetal heart rate tracing, asphyxia, NICU admission for respiratory conditions, and shoulder dystocia) confirmed high level of accuracy. There was >95% concordance with the medical chart for 16/20 variables examined with the lowest concordance of 91.1% for clinical diagnosis of shoulder dystocia. Institutional review board approval was obtained by all participating institutions.
All singleton deliveries occurring between 24 0/7 to 31 6/7 weeks of gestation comprised the cohort for this analysis (n = 5055). The Figure summarizes the study population for analysis. Due to a high percentage of missing data for some neonatal and pregnancy variables, 2 sites were eliminated from further analyses (n = 703), resulting in 4352 pregnancies. We first categorized the possible precursors for preterm delivery. The indications for admission, delivery, and pregnancy complications in the electronic medical record fields were used to classify the precursors to delivery into 3 overall categories: PTL, preterm premature rupture of membranes (PPROM), and indicated delivery. These 3 categories were mutually exclusive, prioritizing PTL then PPROM and then indicated for classification. The conditions leading to an indicated preterm birth included preeclampsia, placental abruption, nonreassuring fetal status, fetal growth restriction, severe maternal medical disease, antepartum stillbirth, and major anomalies; these conditions were not mutually exclusive so multiple indications could be coded for a single pregnancy. For example, a pregnancy complicated by a major anomaly, fetal growth restriction, and nonreassuring fetal status would be counted in each of these 3 categories of indicated early PTB. Major anomalies were defined by ≥1 ICD-9 codes ( Table 1 ).
| ICD-9 code | Description |
|---|---|
| 740 | Anencephalus and similar anomalies |
| 741 | Spina bifida |
| 742 | Other congenital anomalies of nervous system |
| 745 | Bulbus cordis anomalies and anomalies of cardiac septal closure |
| 746 | Other congenital anomalies of heart |
| 747 | Other congenital anomalies of circulatory system |
| 748 | Congenital anomalies of respiratory system |
| 750 | Other congenital anomaly of upper alimentary tract |
| 751 | Other congenital anomalies of digestive system |
| 753 | Congenital anomalies of urinary system |
| 756 | Other congenital musculoskeletal anomalies |
| 757.1 | Ichthyosis congenita |
| 758 | Chromosomal anomalies |
| 759.3-759.8 | Other specified anomalies |
Next we investigated neonatal outcomes in pregnancies eligible for attempted VD vs planned CD. Pregnancies with conditions requiring immediate CD, such as fetal distress, placenta previa, and placental abruption, or that were associated with such poor neonatal outcome that route of delivery was unlikely to affect outcome, including antepartum stillbirth and fetal anomalies, were eliminated from further analyses (n = 1446), resulting in 2906 singleton pregnancies. These 2906 singleton nonanomalous pregnancies were then stratified by gestational age blocks: 24 0/7 to 27 6/7 weeks of gestation (n = 1102) and 28 0/7 to 31 6/7 weeks of gestation (n = 1804). These gestational age categories were based on the fact that the highest rates of neonatal mortality and morbidity occur between 24 0/7 and 27 6/7 weeks of gestation. Within each gestational age block, pregnancies were then stratified by vertex or breech presentation ( Figure ).
The following maternal characteristics were analyzed: race (white/Asian, black, Hispanic/other); maternal age (continuous variable); marital status (married, not married/unknown); insurance (private, public/self-pay/other/unknown); parity (nulliparas, multiparas); preexisting diabetes; preeclampsia; PTL; PPROM; smoking prior to/during pregnancy; alcohol use prior to/during pregnancy; illicit drug use prior to/during pregnancy; prepregnancy body mass index (BMI) (continuous variable); gestational age week (continuous variable); and birth weight (continuous variable). Antenatal corticosteroid (ACS) use (yes/no) was analyzed in a subset of pregnancies where this information was reported (n = 1094).
Attempted VD was then compared to planned CD for the following neonatal outcome variables: death (intrapartum death + neonatal death), asphyxia, respiratory distress syndrome, pneumonia, intraventricular hemorrhage (IVH), necrotizing enterocolitis, sepsis, and need for ventilation. The local NICU definitions as recorded in the neonatal medical chart were used. Diagnoses were also supplemented with ICD-9 codes.
Univariable analysis for all baseline and outcome variables was performed using χ 2 test comparing women undergoing attempted VD and planned CD. Multivariable analysis was then performed calculating adjusted relative risks (RRs) and 95% confidence intervals (CIs) to assess the strength of the relationship between attempted route of delivery stratified by presentation and the occurrence of neonatal mortality or morbidity. Missing values for maternal age (0.2% of cohort) and prepregnancy BMI (27.7% of cohort) were replaced with mean values. For birthweight, 4% of births were missing values and were replaced by the mean value within each gestational age week. To estimate RRs instead of odds ratios and also avoid the convergence pitfall associated with log binomial models, we used Poisson regression with a robust variance estimator as described by Zou and dealt with clustering by site using fixed effects covariates in the model. Statistical analyses were performed using software (SAS, version 9.2; SAS Institute Inc, Cary, NC).
Results
To address the precursors of early preterm birth, the entire cohort of 4352 singleton pregnancies at 24 0/7 to 31 6/7 weeks’ gestation with complete information on baseline and outcome variables was analyzed. The precursors leading to delivery by gestational age groupings (24-27 and 28-31 weeks’ gestation) are presented in Table 2 . The distribution of precursors was as follows: maternal or fetal indications (45.7%), PPROM (37.7%), and PTL (16.6%). Preeclampsia and major congenital anomalies were the leading contributors to indicated early preterm births. The distribution of the precursors leading to delivery was relatively similar across the 2 gestational age groupings.
| Variable | 24-31 wk (n = 4352), n (%) | 24-27 wk (n = 1701), n (%) | 28-31 wk (n = 2651), n (%) |
|---|---|---|---|
| Preterm labor a | 721 (16.6) | 320 (18.8) | 401 (15.1) |
| PPROM a | 1641 (37.7) | 665 (39.1) | 976 (36.8) |
| Indicated a | 1990 (45.7) | 716 (42.1) | 1274 (48.1) |
| Preeclampsia b | 627 (14.4) | 189 (11.1) | 438 (16.5) |
| Abruption b | 142 (3.3) | 60 (3.5) | 82 (3.1) |
| Nonreassuring fetal status b | 495 (11.4) | 161 (9.5) | 334 (12.6) |
| Fetal growth restriction b | 157 (3.6) | 59 (3.5) | 98 (3.7) |
| Severe maternal medical disease b | 29 (0.7) | 6 (0.4) | 23 (0.9) |
| Fetal death b | 153 (3.5) | 70 (4.1) | 83 (3.1) |
| Major anomalies b | 648 (14.9) | 278 (16.3) | 370 (14.0) |
a Mutually exclusive categories;
b “Indicated” subcategories are not mutually exclusive, pregnancy may be included in >1 “indicated” subcategory.
Univariable analyses comparing attempted VD to planned CD for gestational age subgroups stratified by presentation are presented in Tables 3 and 4 . At 24 0/7 to 27 6/7 weeks of gestation with a vertex presentation (n = 714), 22.8% underwent planned CD and 77.2% attempted VD. Of those attempting VD, 84.8% had a successful VD. The planned CD pregnancies were more likely to be multiparous, have diabetes, or have preeclampsia and less likely to have PPROM and PTL when compared to the attempted VD group ( P < .05) ( Table 3 ). Overall neonatal mortality in the group was 14.8% (106/714). When attempted VD was compared to planned CD, there were no differences in neonatal mortality or other neonatal outcomes ( Table 4 ).
| Variable | Gestational age: 24-27 wk, n = 1102 | Gestational age: 28-31 wk, n = 1804 | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Vertex, n = 714 | Breech, n = 388 | Vertex, n = 1424 | Breech, n = 380 | |||||||||
| Attempted VD, n = 551 (77.2%) | Planned CD, n = 163 (22.8%) | P value | Attempted VD, n = 123 (31.7%) | Planned CD, n = 265 (68.3%) | P value | Attempted VD, n = 1138 (79.9%) | Planned CD, n = 286 (20.1%) | P value | Attempted VD, n = 116 (30.5%) | Planned CD, n = 264 (69.5%) | P value | |
| n (%) | n (%) | n (%) | n (%) | n (%) | n (%) | n (%) | n (%) | |||||
| Mode of delivery | ||||||||||||
| CD | 84 (15.2) | 163 (100) | < .0001 | 89 (72.4) | 265 (100) | < .0001 | 179 (15.7) | 286 (100) | < .0001 | 96 (82.8) | 264 (100) | < .0001 |
| VD | 467 (84.8) | 0 (0.0) | – | 34 (27.6) | 0 (0.0) | – | 959 (84.3) | 0 (0.0) | – | 20 (17.2) | 0 (0.0) | – |
| Insurance | ||||||||||||
| Private | 215 (39.0) | 65 (39.9) | .8439 | 57 (46.3) | 115 (43.4) | .5869 | 470 (41.3) | 146 (51.0) | .0029 | 50 (43.1) | 123 (46.6) | .5296 |
| Public/self-pay/other/unknown | 336 (61.0) | 98 (60.1) | – | 66 (53.7) | 150 (56.6) | – | 668 (58.7) | 140 (49.0) | – | 66 (56.9) | 141 (53.4) | – |
| Maternal race | ||||||||||||
| White/Asian | 140 (25.4) | 29 (17.8) | .0705 | 34 (27.6) | 77 (29.1) | .9048 | 339 (29.8) | 68 (23.8) | .0891 | 51 (44.0) | 88 (33.3) | .0710 |
| Black | 255 (46.3) | 76 (46.6) | – | 54 (43.9) | 110 (41.5) | – | 454 (39.9) | 131 (45.8) | – | 29 (25.0) | 94 (35.6) | – |
| Hispanic/other | 156 (28.3) | 58 (35.6) | – | 35 (28.5) | 78 (29.4) | – | 345 (30.3) | 87 (30.4) | – | 36 (31.0) | 82 (31.1) | – |
| Parity | ||||||||||||
| 0 | 297 (53.9) | 54 (33.1) | < .0001 | 55 (44.7) | 119 (44.9) | .9882 | 546 (48.0) | 100 (35.0) | .0004 | 40 (34.5) | 100 (37.9) | .6004 |
| 1/2 | 188 (34.1) | 75 (46.0) | – | 52 (42.3) | 113 (42.6) | – | 432 (38.0) | 135 (47.2) | – | 57 (49.1) | 115 (43.6) | – |
| ≥3 | 66 (12.0) | 34 (20.9) | – | 16 (13.0) | 33 (12.5) | – | 160 (14.1) | 51 (17.8) | – | 19 (16.4) | 49 (18.6) | – |
| Alcohol/drug use and smoking | 90 (16.3) | 23 (14.1) | .4944 | 25 (20.3) | 54 (20.4) | .9905 | 162 (14.2) | 34 (11.9) | .3030 | 14 (12.1) | 45 (17.0) | .2174 |
| Diabetes | 26 (4.7) | 16 (9.8) | .0151 | 8 (6.5) | 15 (5.7) | .7433 | 83 (7.3) | 44 (15.4) | < .0001 | 10 (8.6) | 29 (11.0) | .4843 |
| Preeclampsia | 21 (3.8) | 42 (25.8) | < .0001 | 4 (3.3) | 42 (15.8) | .0004 | 106 (9.3) | 92 (32.2) | < .0001 | 5 (4.3) | 55 (20.8) | < .0001 |
| PPROM | 256 (46.5) | 57 (35.0) | .0094 | 52 (42.3) | 127 (47.9) | .2991 | 569 (50.0) | 96 (33.6) | < .0001 | 40 (34.5) | 107 (40.5) | .2650 |
| Preterm labor | 157 (28.5) | 33 (20.2) | .0363 | 32 (26.0) | 33 (12.5) | .0009 | 231 (20.3) | 30 (10.5) | .0001 | 34 (29.3) | 35 (13.3) | .0002 |
| Neonatal outcomes | Gestational age: 24-27 wk, n = 1102 | Gestational age: 28-31 wk, n = 1804 | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Vertex, n = 714 | Breech, n = 388 | Vertex, n = 1424 | Breech, n = 380 | |||||||||
| Attempted VD, n = 551 | Planned CD, n = 163 | P value | Attempted VD, n = 123 | Planned CD, n = 265 | P value | Attempted VD, n = 1138 | Planned CD, n = 286 | P value | Attempted VD, n = 116 | Planned CD, n = 264 | P value | |
| n (%) | n (%) | n (%) | n (%) | n (%) | n (%) | n (%) | n (%) | |||||
| Death | 84 (15.2) | 22 (13.5) | .5814 | 31 (25.2) | 35 (13.2) | .0034 | 25 (2.2) | 9 (3.1) | .3468 | 7 (6.0) | 4 (1.5) | .0155 |
| Asphyxia | 18 (3.3) | 7 (4.3) | .5306 | 3 (2.4) | 13 (4.9) | .2555 | 5 (0.4) | 6 (2.1) | .0042 | 3 (2.6) | 7 (2.7) | .9708 |
| IVH | 133 (24.1) | 40 (24.5) | .9162 | 29 (23.6) | 63 (23.8) | .9662 | 168 (14.8) | 22 (7.7) | .0017 | 7 (6.0) | 27 (10.2) | .1873 |
| NEC | 55 (10.0) | 15 (9.2) | .7688 | 14 (11.4) | 34 (12.8) | .6869 | 41 (3.6) | 13 (4.5) | .4556 | 8 (6.9) | 14 (5.3) | .5402 |
| Pneumonia | 85 (15.4) | 18 (11.0) | .1617 | 21 (17.1) | 39 (14.7) | .5503 | 59 (5.2) | 16 (5.6) | .7815 | 11 (9.5) | 18 (6.8) | .3676 |
| RDS | 430 (78.0) | 134 (82.2) | .2511 | 95 (77.2) | 224 (84.5) | .0805 | 528 (46.4) | 161 (56.3) | .0028 | 78 (67.2) | 165 (62.5) | .3754 |
| Sepsis | 293 (53.2) | 89 (54.6) | .7486 | 61 (49.6) | 168 (63.4) | .0101 | 354 (31.1) | 80 (28.0) | .3032 | 35 (30.2) | 101 (38.3) | .1300 |
| Ventilation | 341 (61.9) | 108 (66.3) | .3103 | 74 (60.2) | 190 (71.7) | .0234 | 349 (30.7) | 113 (39.5) | .0043 | 58 (50.0) | 123 (46.6) | .5400 |
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