Effect of labor on infant morbidity and mortality with preterm premature rupture of membranes: United States population- based study

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Abstract

Objective: To evaluate whether labor, in the setting of premature rupture of membranes (PROM), affects infant morbidity and mortality rates.

Methods: We derived data for this population-based cohort study from the United States national linked birth infant death data sets, comprised of singleton live births delivered between 1995 and 1997. We included women (n = 34,594) who had preterm PROM more than 12 hours and delivered between 23 and 32 weeks’ gestation. Birth records were used to determine whether delivery occurred with or without labor. Infants with birth weights below the tenth percentile for gestational age were classified as small for gestational age (SGA) on the basis of a nomogram of all singleton births in the United States between 1995 and 1997. Primary outcomes were early neonatal (0–6 days), late neonatal (7–27 days), postneonatal (28–365 days), and infant death (0–365 days). Secondary outcomes included respiratory distress syndrome (RDS), assisted ventilation, and neonatal seizures. Risks of infant mortality and morbidity from labor were examined separately for SGA and non-SGA infants.

Results: Overall rates were infant death 11.6%, RDS 15.1%, assisted ventilation 25.9%, and neonatal seizure 0.2%. Labor was associated with higher incidence of early neonatal death in SGA infants (adjusted relative risk [RR] 1.24, 95% confidence interval [CI] 1.11, 1.38) but had no effect on other outcomes. Among non-SGA infants, labor had no effect on infant death but was associated with higher rates of RDS (RR 1.15, 95% CI 1.08, 1.22) and assisted ventilation (RR 1.16, 95% CI 1.08, 1.24).

Conclusion: Although labor was associated with a slightly higher mortality rate in SGA infants and slightly more respiratory morbidity in non-SGA infants, recommendations regarding clinical treatment should await future clinical trials.

Section snippets

Materials and methods

Data were derived from the national linked Perinatal Mortality data files assembled by the National Center for Health Statistics. Between 1995 and 1997, there were 11,436,020 singleton live births in the United States. Among 242,392 singleton live births delivered between 23 and 32 completed weeks’ gestation, 39,251 (16.2%) had PROM, defined as rupture of membranes at least 12 hours before onset of labor. Labor was considered present if the birth record contained the indications tocolysis;

Results

Among 34,594 women who met study criteria, 73.4% (n = 25,382) were in labor before delivery, and 79.8% (n = 27,591) delivered infants in cephalic presentation. The demographic, obstetric, and infant characteristics of women who did and did not labor are presented in Table 1. The rates of infant death, RDS, assisted ventilation, and seizures were 11.6%, 15.1%, 25.9%, and 0.2%, respectively.

Risks and RR for infant death, RDS, assisted ventilation, and seizures for labored compared with nonlabored

Discussion

This study suggests that labor has an adverse effect on outcomes in preterm infants delivered by women with PROM. Infants with low or borderline reserve, (SGA) appear particularly vulnerable to effects of labor, manifested as greater risk of death particularly in the early neonatal period. The higher mortality rate in those infants might explain their lower risk of pulmonary complications, because fewer survive the early neonatal period. However, additional studies are needed to clarify the

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