Objective
We sought to determine the proportion of evidence-based (EB), vs non-EB (NEB) iatrogenic late preterm birth, and to compare corresponding rates of neonatal intensive care unit (NICU) admission.
Study Design
We performed a retrospective cohort study. Cases were categorized as EB or NEB. NICU admission was compared between groups in both univariate and multivariate analysis.
Results
Of 2693 late preterm deliveries, 32.3% (872/2693) were iatrogenic; 56.7% were delivered for NEB indications. Women with NEB deliveries were older (30.0 vs 28.6 years, P = .001), and more likely to be pregnant with twins (18.8% vs 7.9%, P < .001), have private insurance (80.3% vs 59.0%, P < .001), or have a second complicating factor (27.5% vs 10.1%, P < .001). A total of 56% of EB deliveries resulted in NICU admissions. After controlling for confounders, early gestational age (34 vs 36 weeks: odds ratio, 19.34; 95% confidence interval, 4.28–87.5) and mode of delivery (cesarean: odds ratio, 1.88; 95% confidence interval, 1.15–3.05) were most strongly associated with NICU admission.
Conclusion
Over half of nonspontaneous late preterm births were NEB. EB guidelines are needed.
The morbidity associated with late preterm birth, defined as birth from 34 0/7-36 6/7 weeks, has recently become the topic of much debate and literature. We now understand that late preterm birth is associated with significantly higher rates of respiratory morbidity, but also results in other morbidities such as intraventricular hemorrhage, necrotizing enterocolitis, neonatal intensive care unit (NICU) admission, and sepsis, when compared to infants born at term. McIntire and Leveno compared the different types of morbidities associated with late preterm birth to birth at 39 weeks, the gestational age with the lowest morbidity in their cohort of 21,771 deliveries over an 18-year period. They found that ventilator use, transient tachypnea of the newborn, sepsis, phototherapy for hyperbilirubinemia, and intraventricular hemorrhage were all significantly higher in late preterm infants compared to term. Similarly, Yoder et al reviewed the epidemiology of respiratory disease in late preterm infants. They found that respiratory morbidity from all causes was higher at 34 weeks (22%), 35 weeks (8.5%), and 36 weeks (3.9%) when compared to 39 and 40 weeks (0.7% and 0.8%, respectively, P < .001). These findings were corroborated recently by the Safe Labor Consortium. Currently, the standard of care is not to administer antenatal corticosteroids to women at risk for late preterm delivery due to a lack of data showing benefit at these later gestational ages.
For Editors’ Commentary, see Table of Contents
See related editorial, page 395
Mortality is known to be higher as well. Tomashek et al and McIntire and Leveno both showed that infant mortality was up to 3 times higher after late preterm birth compared to birth at term. Reddy et al found that neonatal mortality and infant mortality were 9.5- and 5.4-fold higher following birth at 34 weeks compared to 39 weeks. The increased morbidity and mortality associated with late preterm birth when compared to term is concerning and raises the question as to whether the indications for these births are justified.
Additionally, long-term outcomes have been found to be poorer in late preterm infants compared to term. Tagle et al found that IQ scores were lower at 6 years of age in children of women with a late preterm birth compared with similar term children. Another study of preschool and kindergarten children born late preterm compared with term children showed that the late preterm children were more likely to have developmental delay and suspension and retention in kindergarten. Finally, Moster et al found that adults born late preterm in Norway were 2.7 times more likely to have cerebral palsy and 1.6 times more likely to have mental retardation. These data further question the need to deliver these infants in the late preterm period.
In an effort to understand the etiology of late preterm births at our respective institutions, we sought to define a cohort of these deliveries to review indications and neonatal outcomes. Our specific objectives were 3-fold: first, to evaluate the proportion of late preterm deliveries that were nonspontaneous (iatrogenic); second, to evaluate the proportion of nonspontaneous deliveries that were based on evidence as opposed to common local practice; and third, to identify the indications for late preterm birth that require further research.
Materials and Methods
Using 2 contemporaneously maintained obstetrical databases, all women from Columbia University Medical Center and Christiana Care Health System who delivered between 34 0/7-36 6/7 weeks from January 2003 through July 2007 were identified. Both datasets are entered by individuals who solely perform data abstraction from medical charts. Prior to data collection the institutional review boards from both institutions were consulted and this study was approved by both via expedited review. Data regarding indication for delivery were abstracted from direct chart review.
The primary outcome of this study was the rate of nonspontaneous, late preterm delivery with an indication that was supported by current evidence as endorsed by the American College of Obstetricians and Gynecologists (ACOG) or published expert opinion (level III evidence). Spontaneous causes of preterm delivery were considered to have occurred for women with preterm birth preceded by either preterm premature rupture of membranes (PPROM) or preterm labor with intact membranes. Women with PPROM were considered to have spontaneous preterm labor whether or not labor induction was performed. Women with triplet or higher-order multiple gestations were excluded from all analysis as the optimal period of delivery for these women remains controversial. Also excluded were women for whom the indication for delivery was indeterminate. Cases were designated as indeterminate under the following circumstances: (1) the indication was not identified in the medical record; (2) the indication was an appropriate indication but the clinical documentation failed to support the given reason (eg, severe preeclampsia with no record of blood pressure or other support of the diagnosis); or (3) the 2 reviewers were unable to reach consensus as to the appropriateness of the indication. We did not exclude fetuses with documented fetal lung maturity because this has not been shown to improve neonatal outcomes.
Indications for nonspontaneous deliveries were assessed through review of the medical records, and 2 authors (M.K.H. and C.G-B.) independently reviewed each indication for consensus. Outpatient records were not reviewed. Those indications supported by ACOG guidelines and/or expert opinion (level C evidence and consensus from obstetric texts) were defined as evidence based (EB), while indications not supported by either of these were labeled non-EB (NEB). Where multiple indications were listed, if at least one of the indications was EB, the patient would be classified as such. For example, patients with severe preeclampsia and a prior myomectomy would be classified as EB for severe preeclampsia diagnosis even though a history of myomectomy was considered NEB.
A list of diagnoses and their classifications are found in Table 1 . Diagnoses considered EB for the late preterm period included severe preeclampsia/eclampsia, growth restriction with abnormal fetal testing (abnormal testing included a biophysical profile of 6/10 or worse, abnormal umbilical artery or ductus venosus Doppler, or coexisting oligohydramnios), frank abruption, and a nonreassuring fetal heart tracing (a category II or III fetal heart tracing requiring immediate delivery). Deliveries defined as NEB included stable patients with the following diagnoses: chronic hypertension, mild preeclampsia, gestational hypertension, oligohydramnios (amniotic fluid index <5), intrauterine growth restriction with normal testing, and prior myomectomy/classic cesarean, not in labor.
| Indications for delivery | |
|---|---|
| Evidence based | Nonevidence based |
| Severe preeclampsia/eclampsia | Chronic hypertension/gestational hypertension/mild preeclampsia |
| IUGR with abnormal testing or poor interval growth | IUGR with normal testing and adequate interval growth |
| Acute abruption | Prior myomectomy/classic cesarean |
| Nonreassuring fetal heart rate tracing | Oligohydramnios |
| Cholestasis, bile acids >40 micromol/L | Cholestasis, bile acids <40 micromol/L |
| Uterine rupture | Elective |
We compared the rate of NICU admission for the 2 groups. At both institutions, infants are admitted to the NICU based primarily on morbidity. However, infants weighing <1800 g (Columbia) and <2200 g (Christiana) are automatically admitted to the NICU. There are no other protocol-based admission criteria. To detect the variable most likely associated with nonweight-based NICU admission, we excluded infants who weighed <1800 and <2200 g, respectively, at either institution. We also controlled for site (Columbia vs Christiana), mode of delivery, and gestational age in the multivariable logistic regression model that was created.
Statistical analysis was performed using Stata, Version 10.0 (Stata Corp, College Station, TX). Univariate analysis was performed using Student t test with unequal variance, Wilcoxon rank sum, χ 2 , and Fisher exact test when appropriate. A P value of < .05 was considered statistically significant.
Results
We identified 2756 late preterm pregnancies over the study period. We excluded 9 women with triplets and 54 women who had indeterminate causes of delivery ( Figure ). Of the remaining 2693 women, 1429 delivered due to spontaneous labor with intact membranes and 392 delivered for PPROM. Thus, the rate of nonspontaneous, iatrogenic deliveries in this late preterm cohort was 32.3% (n = 872/2693). We then categorized these deliveries by indication and found that the majority of iatrogenic deliveries, 56.7% (n = 494/872), were deemed NEB ( Table 2 ) for a total of 18.3% (494/2693) NEB deliveries in the entire late preterm cohort.
| Indication for delivery | n | Total | Nonevidence based |
|---|---|---|---|
| Mild preeclampsia | 149 | 17.1% | 31.4% |
| Oligohydramnios | 79 | 9.1% | 16.7% |
| Gestational hypertension | 71 | 8.1% | 15.0% |
| Elective | 61 | 7.0% | 12.9% |
| Other | 55 | 6.3% | 9.6% |
| Cholestasis | 22 | 2.5% | 4.6% |
| Previa | 48 | 5.5% | 4.4% |
| Myomectomy/prior classic | 12 | 1.4% | 2.5% |
| Chronic hypertension | 11 | 1.3% | 2.3% |
| Prior event a | 10 | 1.1% | 2.1% |
| Eclampsia | 6 | 0.7% | 1.3% |
| Cholelithiasis | 4 | 0.5% | 0.8% |
| Abnormal testing | 30 | 3.4% | 0.2% b |
| Abruption | 26 | 3.0% | 0.0% |
| IUGR | 30 | 3.4% | 0.0% |
| NRFHR | 31 | 3.6% | 0.0% |
| Severe preeclampsia | 219 | 25.1% | 0.0% |
| Uterine rupture | 8 | 0.9% | 0.0% |
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