From the Journals

Supine sleep in late pregnancy may promote low birth weight



Sleeping supine during late pregnancy was independently associated with lower birth weight, but the number of women in this subgroup was small in the study.

Data from previous studies suggest that impaired uteroplacental flow can affect fetal growth, wrote Ngaire H. Anderson, PhD, of the University of Auckland, N.Z., and colleagues.

“The initial going-to-sleep position is the sleep position that women maintain for the longest duration throughout the night; therefore, going-to-sleep position is likely to have the greatest impact on blood flow to the developing fetus,” they said.

In a study published in JAMA Network Open, the researchers interviewed women with ongoing pregnancies at 28 weeks’ gestation or later to determine their sleeping positions. The mean age of the participants was 30 years. Of the 1,760 women, 3% reported that they usually slept supine during the past 1-4 weeks.

The adjusted mean birth weight was 3,410 g among supine sleepers and 3,554 g among nonsupine sleepers. The primary outcome was an adjusted mean difference in birth weight between infants of supine sleepers and nonsupine sleepers, which was a statistically significant 144 g (P = .009).

The study findings were limited by several factors including the small number of women who were reported supine sleepers, as well as the reliance on self-reports of sleep position, the researchers said.

However, women who had going-to-sleep data for the previous night and the previous month suggest that most women are consistent in their going-to-sleep position, they noted. “It is also biologically plausible that the association of decreased maternal blood flow on birth size with supine maternal position is cumulative over time,” but the researchers were not able to investigate how the duration of supine sleeping might further affect birth weight.

Although it might make additional studies more difficult, a public health campaign to encourage pregnant women to sleep on their side during the third trimester is a safe and easy opportunity to potentially optimize birth weight, they added.

The study was important because of the limited number of high-quality studies on the effects of maternal sleep on perinatal outcomes, Martina Badell, MD of Emory University in Atlanta said in an interview.

“The overall findings suggested a possible small increased risk of small-for-gestational-age babies with supine maternal sleeping, however, the absolute gram difference of 144 grams at term may not be clinically relevant,” she said. In addition, the relatively small number of women who reported supine sleep in late pregnancy suggests that broad public health campaigns or recommendations may not be indicated at this time.

“Also, the percentage of women who are supine sleepers at term is only approximately 3%, and this study didn’t assess reasons for supine sleeping in this small subset of women,” she said. “Further research is needed to assess whether there are specific maternal factors associated with supine sleeping, such as GI symptoms or respiratory difficulties, which could contribute to smaller fetal size rather than the sleep position itself.”

The study was supported by a Trans-Tasman Research Funding Grant by Cure Kids and Red Nose Australia. Six coauthors reported receiving numerous grants from a variety of organizations. Dr. Anderson and the remaining coauthors had no financial conflicts to disclose. Dr. Badell had no relevant financial disclosures.

SOURCE: Anderson NH et al. JAMA Network Open. 2019 Oct 2. doi: 10.1001/jamanetworkopen.2019.12614.

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