Pregnant women with various classes of obesity should not gain any weight until mid-pregnancy or later for optimal pregnancy outcomes, according to a new study in the journal Obesity.

Current gestational weight-gain guidelines by the Institute of Medicine do not recommend lower targets for women with more severe degrees of obesity due to a lack of sufficient data on short-term and long-term maternal and newborn outcomes. This study sought to create pregnancy weight-gain-for-gestational-age z-score charts for overweight and obese mothers based on severity of obesity.

The researchers evaluated serial weight gain measurements in 1,047, 1,202, 1,267, and 730 overweight, class I, II, and III obese women, respectively, who all had uncomplicated full-term pregnancies and deliveries from 1998–2010. Total gestational weight gain was 15.3kg (±6.8 SD), 12.8kg (±7.6 SD), 9.9kg (± 7.7 SD), and 7.7kg (± 8.6 SD) in these respective BMI groups.

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For all obesity categories, the median (50th percentile) of gestational weight gain was near zero (ie, little weight gain) until mid-pregnancy. Weight gain in the second half of pregnancy increased, with the rate of increase slowing as obesity increased. As obesity became more severe, no weight gain, or weight loss, became more common.

Based on these results, the researchers suggest that obese women should not gain any weight until mid-pregnancy or later based on obesity class. These charts can be used by healthcare professionals in antenatal care to monitor the progress of weight loss after additional research has been completed to confirm these optimal gestational weight gain z-scores.

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