Lisa M. Bodnar, PhD, and colleagues determined.
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The risks of cesarean section and neonatal death were elevated for those mothers who were overweight before pregnancy and then gained too much. But infants of underweight women who didn’t gain enough faced risks as well, wrote Dr. Bodnar of the University of Pittsburgh and associates in Obstetrics & Gynecology.
Among the most severely overweight women (obesity grade 2 or 3) who gained the most weight (43 kg) at 37 weeks’ gestation, there were 6 fewer small-for-gestational-age (SGA) infants per 100 births, but 14 more large-for-gestational-age (LGA) infants, 4 more cesarean deliveries, and 2 more neonatal deaths per 100 births. By contrast, among the most severely underweight women who gained the least amount of weight (9 kg), there were 18 more SGA infants, 3 fewer LGA infants, and 11 fewer cesareans, but 6 more preterm births before 32 weeks’ gestation.
The same U-shaped pattern also occurred within the individual weight categories. For example, compared with the outcomes among the most underweight women who gained least, among underweight women who gained the most (37 kg), there were eight fewer SGA infants, but four more LGA infants, 16 excess preterm births, and 9 excess infant deaths.
“If the associations we observed are even partially reflective of causality, targeted modification of pregnancy weight gain in women carrying twins might improve pregnancy outcomes,” wrote Dr. Bodnar and her team. “Data on a wide range of short- and long-term outcomes and information on the relative seriousness of these outcomes are needed to determine optimal gestational weight gain ranges for twin pregnancies.”
The cohort comprised 54,836 live-born twins from 27,723 twin pregnancies who were included in the MOMs database maintained by the University of Pennsylvania, Philadelphia. The population-based study tracks maternal obesity, gestational weight gain, and adverse birth outcomes. The information came from infant birth and death vital statistics records from 2003 to 2013.
However, this very source puts the findings in some degree of uncertainty, Ozhan Turan, MD, said in an interview.
Dr. Ozhan Turan
“It’s a very nice study, and the statistics are very well done,” said Dr. Turan, who is the director of fetal therapy and complex obstetric surgery at the University of Maryland School of Medicine. “But that kind of data has pitfalls that are unavoidable. For example, they don’t have access to maternal medical comorbidities which are mostly related to the outcome, particularly gestational diabetes and preeclampsia. They also don’t have the information on chorionicity – and we know that monochorionic twins face much greater risk for these outcomes than dichorionic twins.”
The investigators calculated total gestational weight gain by subtracting prepregnancy weight from maternal weight at delivery. The analysis controlled for race and ethnicity, education, neonatal care, level of birth facility, parity, payment at delivery, smoking during pregnancy, marital status, year of birth, height, maternal age, preexisting diabetes or hypertension, infertility treatment, neonatal sex, and racial composition of neighborhood, as a proxy of neighborhood-level socioeconomic status. Approximately 16% of mothers received infertility treatment.
Of the cohort, 3% were underweight, 48% were normal weight, 24% were overweight, 13% were grade 1 obese, 7% grade 2 obese, and 5% grade 3 obese.
“Pregnancy weight gain was negatively associated with SGA and positively associated with LGA and cesarean delivery in all [body mass index] groups. For example, among normal-weight women, compared with a pregnancy weight gain equivalent to 20 kg at 37 weeks’ of gestation, a weight gain of 27 kg at 37 weeks’ of gestation was associated with 2.2 fewer cases of SGA but 2.9 more cases of LGA and 3.7 more cases of cesarean delivery,” Dr. Bodnar and associates wrote.
The investigators found that “weight gains well above or well below the [Institute of Medicine] provisional guidelines (less than 14 kg or more than 27 kg in underweight or normal-weight women, less than 11 kg or more than 28 kg in overweight women, and less than 6.4 kg or more than 26 kg in women with obesity) were associated with the highest risk of adverse outcomes.”
“I would not say this is practice-changing information,” said Dr. Turan. “We already know all this. What would be very helpful is an algorithm to tell us, if a patient is pregnant with twins, this is the amount of weight you have to gain.”
For overweight patients, Dr. Turan tries to impart the key message of moderate or slight weight gain, according to prepregnancy body mass index. For underweight patients, the picture is a bit more complex.
“There are not that many who are underweight before pregnancy, so first thing I look for is the reason a woman is underweight. Is she just not eating properly? Is there a drug dependence issue, alcohol dependence, HIV? Is there smoking? A gut problem that causes malnutrition. You can’t just say ‘eat more.’ That does not solve the problem. We need to find out why she is underweight and fix that first,” said Dr. Turan.
Neither Dr. Bodnar nor Dr. Turan had any relevant financial disclosures. One coauthor disclosed her institution received funds from the University of Pittsburgh. The study was funded by National Institutes of Health grants.
SOURCE: Bodnar LM et al. Obstet Gynecol. 2019;134:1075-86.