Maternal weight gain before pregnancy and up to 18 weeks of gestation was associated with birth weight, but researchers found no association with weight gained after the 18th week.
The researchers found that a mother's weight status during the first half of gestation is "a key determinant of infant birth weight and highlight[s] the importance of the timing of weight gain in pregnancy." They conclude that interventions designed to affect birth weight might work best when targeted before and during the early stages of pregnancy.
Ravi Retnakaran, MD, from Mount Sinai Hospital in Toronto, Ontario, Canada, and colleagues published their findings online December 26 in JAMA Pediatrics.
Previous studies of early weight gain in pregnancy have produced conflicting results, the authors write. Many of those studies enrolled women during their second trimester and used unreliable self-reporting to identify a woman's weight at the start of pregnancy, they note.
The new research included outcomes from a group of women who were enrolled before pregnancy, thus allowing researchers to use actual pre-pregnancy weight, rather than self-reported weights.
The prospective, observational cohort study followed 1164 newly married women in Liuyang, China. The women were examined and weighed at a median of 19.9 weeks before a pregnancy. From 2009 to 2015, the researchers calculated maternal weight gain throughout the pregnancies of the women in the cohort. They used the following 10 points to monitor weight gain: from pre-pregnancy to less than 14 weeks and from 14 to 18, 19 to 23, 24 to 28, 29 to 30, 31 to 32, 33 to 34, 35 to 36, 37 to 38, and 39 to 40 weeks.
The mean age of the study participants was 25.3 (standard deviation, 3.1) years. Weight before pregnancy was consistently associated with infant birth weight. During the 10 "gestational intervals," only weight gain from pre-pregnancy to 14 weeks and from 14 to 18 weeks was associated with birth weight. Birth weight increased by 13.6 g/kg (95% confidence interval [CI], 3.2 - 24.1 g/kg) of maternal weight gain from before pregnancy to 14 weeks and by 26.1 g/kg (95% CI, 3.8 - 48.4 g/kg) of maternal weight gain from 14 to 18 weeks.
Past research has suggested that maternal weight gain during the second trimester is a key determinant of birth weight, the authors note. At the same time, research has also "implicated" weight gain in both the second and third trimesters. Other studies have found no link between first trimester weight gain and birth weight.
The underestimation of self-reported pre-pregnancy weight could have contributed to the conflicting findings about weight-gain timing, the researchers explain.
They conclude that the "preconception cohort" study design would allow for an objective evaluation of the timing of gestational weight gain.
"However, this design has generally not been implemented for practical reasons, owing to the potentially prohibitive cost of characterizing women and then waiting indefinitely for a subsequent pregnancy," they write.
The findings "lend support for suggestions calling for clinical emphasis on optimizing maternal health before pregnancy for the purpose of transgenerational benefit."
The results also suggest that interventions to limit weight gain during the latter half of pregnancy may have little impact on birth weight.
The authors note that a recent multinational study in eight geographically diverse regions suggests the timing of weight gain during pregnancy deserves more study.
That research showed the patterns of weight gain were similar in all regions: Brazil, China, India, Italy, Kenya, Oman, United Kingdom, and United States. The patterns persisted despite local differences in ethnicity, behaviors, and clinical practices.
The "apparent conservation of this pattern in the face of genetic and lifestyle differences" underscores the importance of the pattern of gestational weight gain, the authors write.
"Clinically, however, our understanding of the implications of the timing of weight gain in pregnancy remains limited."
This study was supported by operating grants from the Canadian Institutes of Health Research and Natural Science Foundation of China. Dr Retnakaran is supported by a Heart and Stroke Foundation of Ontario Mid-Career Investigator Award. The authors have disclosed no relevant financial relationships.
JAMA Pediatr. Published online December 26, 2017. Abstract
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