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Post-term birth a risk factor for neonatal morbidity in low-risk cases

Post-term pregnancy is an independent risk factor for adverse neonatal outcomes, even in low-risk cases, according to data published in Archives of Disease in Childhood.

“Post-term pregnancy is defined as pregnancy reaching to or extending beyond 42 weeks of gestation from the last menstrual period,” Nehama Linder, MD, of the department of neonatology at The Helen Schneider Hospital for Women, Rabin Medical Center, in Petah Tikva, Israel, and colleagues wrote. “… The American College of Obstetricians and Gynecologists recommended that labor be induced after 42+0 gestational weeks and no later than 42+6 gestational weeks. However, many of the available studies were limited by lack of differentiation between low-risk and high-risk populations, and some reported only a few selected neonatal outcomes. Therefore, the independent association of post-term pregnancy and neonatal outcome in the low-risk population remains unclear.”

To analyze the association of post-term pregnancy with neonatal outcomes in low-risk populations, the researchers conducted a retrospective cohort study at a tertiary university-affiliated medical center, including all newborns of low-risk, singleton pregnancies over the course of 5 years. Outcome measures included admission to the neonatal intensive care unit (NICU), length of stay in the hospital, 5-minute Apgar score, birth trauma, respiratory, neurological, metabolic and infectious morbidities and neonatal mortality.

The researchers compared the adverse outcome rate among groups: those born post-term (42+0 or more weeks), late-term (41+0 to 41+6 weeks) and full-term (39+0 to 40+6 weeks). Of the 23,524 eligible cases, 3.2% were born post-term, 19.7% were late-term and 77.1% were full-term.

According to the researchers, women in the post-term group had a rate of caesarean section births of 8.9%, compared with a rate of 5.6% in the late-term group. The post-term group also reported an operative vaginal delivery rate of 9.6%, compared with a 7.4% rate in the late-term group.

Compared with full-term pregnancy, those in the post-term group had an increased risk for NICU admission (OR = 2; 95% CI, 1.4-2.8), respiratory morbidity (OR = 2.2; 95% CI, 1.3-3.8) and infectious morbidity (OR = 1.88; 95% CI, 1.32-2.69). In addition, post-term pregnancy, compared with late-term pregnancy, was associated with in increased risk for NICU admission (OR = 2; 95% CI, 1.4-2.9), respiratory morbidity (OR = 2.7; 95% CI, 1.5-5), infectious morbidity (OR = 1.8; 95% CI, 1.2-2.7) and hypoglycemia (OR = 2.6; 95% CI, 1.2-5.4). There was no association between post-term pregnancy and neonatal mortality.

“Post-term pregnancy appears to be independently associated with adverse neonatal outcome even in low-risk singleton pregnancies,” Linder and colleagues wrote. “This information should be considered by obstetricians when counseling women regarding the management of post-term pregnancy as well as by pediatricians who need to be aware of the higher rate of complications in post-term neonates.” – by Jason Laday

Disclosure: The authors report no relevant financial disclosures.