PITTSBURGH, Oct. 10, 2019 - An old adage urges pregnant women to "eat for two." So with twins, is it "eat for three?" While that is likely bad advice, when it comes to twin pregnancies, clinicians don't have firm guidelines for ideal weight gain due to a lack of scientific study.
New research led by scientists at the University of Pittsburgh Graduate School of Public Health and published today in the journal Obstetrics & Gynecology is beginning to establish evidence-based guidelines for maternal weight gain while pregnant with twins. The researchers identified ranges above and below which the risk of adverse outcomes, such as preterm birth and infant death, increases.
"Twin pregnancies have high rates of complications, so it is important to identify factors that we can modify during pregnancy to lessen these risks," said lead author Lisa Bodnar, Ph.D., M.P.H., R.D., professor in Pitt Public Health's Department of Epidemiology. "Health care providers can work with women to maintain their weight gain within a targeted range, but previously, the lack of evidence on what that optimal range is left women and their doctors to make educated guesses or not to discuss weight gain at all."
Over the past 40 years, the number of twins born in the U.S. has nearly doubled. Compared with singletons, twins are more than twice as likely to die during pregnancy, and four times as likely to die in the first year of life. And while twins make up 3.3% of all births, they account for more than 20% of preterm births. Women pregnant with twins also are more likely to experience diabetes, preeclampsia and cesarean deliveries.
"At the initial prenatal visit for women pregnant with twins, we review a number of obstetrical complications that are more common with twins, emphasizing that gestational weight can decrease risk of some of these complications," said co-author Katherine Himes, M.D., M.S., assistant professor of obstetrics, gynecology and reproductive sciences at Pitt, and UPMC Magee-Womens Hospital obstetrician-gynecologist. "On top of all the other recommendations they are trying to digest, many women pregnant with twins are overwhelmed when they are counseled that they have to gain 40 to 50 pounds. We really need more robust data to inform this recommendation."
The research team gathered data from Pennsylvania infant birth and death vital statistics records on 27,723 twin pregnancies from 2003 to 2013. They matched the records with the mothers' pre-pregnancy height and weight, and weight at delivery. The mothers were classified as underweight, normal weight, overweight or obese, based on their pre-pregnancy height and weight.
From that data, the team calculated an increased risk of poor birth outcomes when weight gain was:
- Less than 31 pounds or greater than 60 pounds in underweight and normal weight women;
- Less than 24 pounds or greater than 62 pounds in overweight women;
- Less than 14 pounds or greater than 57 pounds in obese women.
"These are starting ranges," said Bodnar, who also is affiliated with the Magee-Womens Research Institute. "We are not saying that gaining within these weight ranges is necessarily best for the health of the mother and her babies, but simply that gaining above or below them carries greater risk of poor health. Women should talk with their health care providers to determine a safe amount of weight gain for them."
Bodnar and her team plan to conduct future research to further refine ideal weight gain ranges for women pregnant with single babies and twins.