One in 15 neonates in a large, retrospective, observational study was delivered at 34-36 weeks’ gestation for potentially avoidable or elective precursors for late preterm delivery, and those deliveries were associated with greater risk of neonatal morbidity and mortality than were deliveries at or after 37 weeks for the same indications.
The findings suggest that nearly 7% of late preterm births – and possibly their associated morbidity and mortality – could be avoided, according to Dr. S. Katherine Laughon of the Eunice Kennedy Shriver National Institute of Child Health and Human Development and her colleagues.
The investigators also found that different precursors for late preterm deliveries were associated with differing rates of neonatal morbidity in the study, a factor that has implications for counseling patients about the risks and benefits of late preterm delivery, they reported in November in Obstetrics & Gynecology.
Nearly 66% of preterm deliveries were late preterm deliveries in this study, which compared 15,136 singleton gestations delivered late preterm (between 34 weeks and 36 weeks 6 days) vs. 170,593 gestations delivered between 37 weeks and 41 weeks 6 days.
The investigators used data from the Consortium on Safe Labor, a study that included 228,668 deliveries from 12 clinical centers and 19 hospitals representing nine American College of Obstetricians and Gynecologists districts in 2002-2008.
Precursors for late preterm birth included spontaneous labor in 30% of cases, preterm premature rupture of membranes (PPROM) in 32% of cases, and medical indications for an obstetric, maternal, or fetal condition in 32% of cases. The cause of late preterm birth was unknown in 6% of cases, the investigators said (Obstet. Gynecol. 2010;116:1047-55).
Of the medical indications for late preterm delivery, hypertensive disease was most common (48% of indicated deliveries), followed by a maternal condition (32%), and a fetal condition (30%).
With advancing gestational age, the incidence of respiratory morbidity and neonatal sepsis decreased, as did neonatal intensive care unit admissions and median NICU length of stay, regardless of the reason for late preterm delivery, the investigators noted.
PPROM-related late preterm deliveries were associated with decreased severe respiratory morbidity, compared with those delivered for other reasons. Medically indicated late preterm deliveries were associated with a higher incidence of newborn sepsis and neonatal death at 35 and 36 weeks, compared with the other precursors. Indicated deliveries also were associated with a higher incidence of admission to the NICU at every gestational age, compared with the other categories.
The investigators found that among the "indicated" categories, 18% were for soft – or potentially avoidable – precursors. Additionally, in the "unknown" category there were 175 elective deliveries with no other maternal-fetal or obstetric complications, "and together these 1,044 soft or elective precursors made up 6.9%, or approximately 1 in 15, of all late preterm deliveries," they noted, adding that the "adjusted risk of oxygen use, transient tachypnea of the newborn, mechanical ventilation, respiratory distress syndrome, pneumonia or newborn sepsis, and admission to the NICU all were significantly decreased for neonates with soft or elective precursors delivered at 37, 38, 39, and 40 weeks of gestation compared with late preterm."
No increase in the risk of stillbirth or neonatal mortality was seen with expectant management of these soft precursors, suggesting that at least 1 in 15 of the deliveries with soft precursors could have been expectantly managed until 39 weeks’ gestation, Dr. Laughon and her associates said.
Furthermore, the differences in neonatal outcomes based on precursor type suggest that "the underlying pathology for precursors is an important determining factor in neonatal morbidity."
Based on these findings, the investigators recommended that elective deliveries be postponed until 39 weeks’ gestation. As for soft precursors, additional study is needed, they said. "More prospective data are needed and guidelines should be developed to help providers and women decide which soft precursors can be managed expectantly," Dr. Laughon and her associates concluded.
The authors said they had no relevant financial disclosures.