Safety of low weight gain or weight loss in pregnancies with class 1, 2, and 3 obesity: a population-based cohort study

Abstract

Background: There are concerns that current gestational weight gain recommendations for women with obesity are too high and that guidelines should differ on the basis of severity of obesity. In this study we investigated the safety of gestational weight gain below current recommendations or weight loss in pregnancies with obesity, and evaluated whether separate guidelines are needed for different obesity classes.

Methods: In this population-based cohort study, we used electronic medical records from the Stockholm-Gotland Perinatal Cohort study to identify pregnancies with obesity (early pregnancy BMI before 14 weeks' gestation ≥30 kg/m²) among singleton pregnancies that delivered between Jan 1, 2008, and Dec 31, 2015. The pregnancy records were linked with Swedish national health-care register data up to Dec 31, 2019. Gestational weight gain was calculated as the last measured weight before or at delivery minus early pregnancy weight (at <14 weeks' gestation), and standardised for gestational age into z-scores. We used Poisson regression to assess the association of gestational weight gain z-score with a composite outcome of: stillbirth, infant death, large for gestational age and small for gestational age at birth, preterm birth, unplanned caesarean delivery, gestational diabetes, pre-eclampsia, excess postpartum weight retention, and new-onset longer-term maternal cardiometabolic disease after pregnancy, weighted to account for event severity. We calculated rate ratios (RRs) for our composite adverse outcome along the weight gain z-score continuum, compared with a reference of the current lower limit for gestational weight gain recommended by the US Institute of Medicine (IOM; 5 kg at term). RRs were adjusted for confounding factors (maternal age, height, parity, early pregnancy BMI, early pregnancy smoking status, prepregnancy cardiovascular disease or diabetes, education, cohabitation status, and Nordic country of birth).

Findings: Our cohort comprised 15 760 pregnancies with obesity, followed up for a median of 7·9 years (IQR 5·8-9·4). 11 667 (74·0%) pregnancies had class 1 obesity, 3160 (20·1%) had class 2 obesity, and 933 (5·9%) had class 3 obesity. Among these pregnancies, 1623 (13·9%), 786 (24·9%), and 310 (33·2%), respectively, had weight gain during pregnancy below the lower limit of the IOM recommendation (5 kg). In pregnancies with class 1 or 2 obesity, gestational weight gain values below the lower limit of the IOM recommendation or weight loss did not increase risk of the adverse composite outcome (eg, at weight gain z-score -2·4, corresponding to 0 kg at 40 weeks: adjusted RR 0·97 [95% CI 0·89-1·06] in obesity class 1 and 0·96 [0·86-1·08] in obesity class 2). In pregnancies with class 3 obesity, weight gain values below the IOM limit or weight loss were associated with reduced risk of the adverse composite outcome (eg, adjusted RR 0·81 [0·71-0·89] at weight gain z-score -2·4, or 0 kg).

Interpretation: Our findings support calls to lower or remove the lower limit of current IOM recommendations for pregnant women with obesity, and suggest that separate guidelines for class 3 obesity might be warranted.

Funding: Karolinska Institutet and the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

Figure 1.. Pregnancy weight z-scores and adjusted rates with 95% CIs of adverse maternal (A) and infant (B) outcomes among 15,760 individual pregnancies with obesity class 1, 2 and 3 in the Stockholm-Gotland Perinatal cohort (SGPC), 2008-2015.

Predicted probabilities of each maternal and infant condition were adjusted for maternal age, height, continuous BMI, parity, education level, early-pregnancy smoking status, cohabitations status, country of birth, pre-pregnancy cardiovascular disease and pre-pregnancy diabetes. Perinatal death is not shown for class 3 obesity due to the small number of cases (n=5). The 95% CIs for some outcomes are not visible due to the range of the scale. Pregnancy weight gain z-scores for individuals with pre-eclampsia and gestational diabetes are based on last measured weight before diagnosis (for preeclampsia, median 36 weeks, interquartile range 32 to 37; for gestational diabetes, median 28 weeks, interquartile range 24 to 33).

Figure 1.. Pregnancy weight z-scores and adjusted rates with 95% CIs of adverse maternal (A) and infant (B) outcomes among 15,760 individual pregnancies with obesity class 1, 2 and 3 in the Stockholm-Gotland Perinatal cohort (SGPC), 2008-2015.

Predicted probabilities of each maternal and infant condition were adjusted for maternal age, height, continuous BMI, parity, education level, early-pregnancy smoking status, cohabitations status, country of birth, pre-pregnancy cardiovascular disease and pre-pregnancy diabetes. Perinatal death is not shown for class 3 obesity due to the small number of cases (n=5). The 95% CIs for some outcomes are not visible due to the range of the scale. Pregnancy weight gain z-scores for individuals with pre-eclampsia and gestational diabetes are based on last measured weight before diagnosis (for preeclampsia, median 36 weeks, interquartile range 32 to 37; for gestational diabetes, median 28 weeks, interquartile range 24 to 33).

Figure 2.. Association between pregnancy weight gain z-scores and a weighted composite of adverse maternal and infant health outcomes, compared with the lower limit of the IOM recommendation, in 15,760 individual pregnancies with early pregnancy obesity in the Stockholm-Gotland Perinatal cohort (SGPC), 2008-2015.

Models were adjusted for maternal age, height, continuous BMI, parity, education level, early-pregnancy smoking status, cohabitations status, country of birth, pre-pregnancy cardiovascular disease and pre-pregnancy diabetes. Outcomes in the weighted composite include: stillbirth (fetal death at ≥22 completed weeks of gestation), infant death (<365 days of life), large- and small-for-gestational-age birth (birthweight >90^th and <10^th percentile, respectively), preterm birth<37 weeks’ gestation, unplanned Cesarean delivery, gestational diabetes, pre-eclampsia, excess post-partum weight retention, and maternal cardiometabolic disease. The light blue markers indicate pregnancy weight gain values <0 kg (corresponding to a z-score value of −2.4). The vertical gray dotted line indicates the cut-points for the 2009 Institute of Medicine (IOM) pregnancy weight gain recommendations for obesity (5-9 kg, corresponding to z-score values of −1.1 to −0.4). The dark blue dot refers to reference value, the lower limit of the IOM recommendations (<5kg, corresponding to a z-score value of −1.1)