MIAMI BEACH — Contrary to prior reports, very-low-birth-weight multiples have significantly greater morbidity and mortality than weight-matched singleton fetuses, according to a study presented at the annual meeting of the Society for Maternal-Fetal Medicine.
Researchers assessed outcomes for 1,779 infants born between July 1993 and July 2004 who weighed less than 1,500 g at birth.
They compared risk of death and severe intraventricular hemorrhage (IVH) among 475 infants from multiple gestations and 1,304 singletons.
When the researchers examined the data for multiple fetuses, “we saw increased neonatal death and/or severe IVH,” Dr. Edward Hayes, of Thomas Jefferson University Hospital in Philadelphia, said during a poster presentation. The risk of death for a VLBW infant born as part of a multiple pregnancy was higher than that of a VLBW singleton (odds ratio 1.3).
The risk increased as birth weights decreased, Dr. Hayes said. The multiples group included 206 infants born weighing less than 1,000 g and 86 weighing less than 750 g.
Mortality risk among multiples below 1,000 g carried an odds ratio of 1.5, and below 750 g the odds ratio was 1.9, compared with weight-matched singletons. “The risk was twice as high when you're a multiple [below 750 g],” Dr. Hayes said. The singletons group included 578 born weighing less than 1,000 g and 262 weighing less than 750 g.
The mean gestational age at birth was 28 weeks in both groups; the mean birth weight was 1,039 g in the multiple group and 1,035 g among singletons. There were no significant differences between the groups in mean gestational age or mean birth weight.
However, significant differences existed between mothers in the two groups. For example, the percentage who were white differed (68% of mothers of multiples vs. 43% of mothers of singletons); as did mean maternal age (29 years vs. 26 years); birth at the facility (95% vs. 86%); use of prenatal steroids (74% vs. 58%); preeclampsia (14% vs. 24%), and preterm labor (74% vs. 62%). The investigators used a multivariate analysis to control for these differences and then compared groups for neonatal morbidity and mortality.
The risk of severe, grade 3–4 intraventricular hemorrhage was higher among VLBW infants born as part of a multiple pregnancy (odds ratio 1.2) versus similar singletons. The risk of this outcome was similar for neonates in the multiple groups below 1,000 g or 750 g (odds ratio 1.1 for both).
The etiology of the higher risk among multiple gestation VLBW infants remains unknown, Dr. Hayes said. Researchers have theorized that multiples are more stressed than singletons because they share the same space in utero. “But I don't agree,” he said. He instead proposed that prenatal steroids play a role. “More data are coming out showing it's just the number of fetuses—you're giving the same dose of medicine to more. It's 12 mg of betamethasone whether you have one or more fetuses.”
The practice of giving the same dosage of prenatal steroids despite the number of fetuses is not likely to change soon, Dr. Hayes said. “There is no evidence in the literature for giving multiples a higher dose of steroids.”