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Objective The safety of weight loss and low weight gain during pregnancy remains unclear. To determine how different patterns of gestational weight gain (GWG), including weight loss, stability, and low GWG relate to perinatal outcomes by prepregnancy obesity class. Study Design The study population included 29,408 singleton livebirths among pregnant people with obesity from Kaiser Permanente Northern California (2008–2013). Clinically measured GWG was grouped into meaningful categories (Adequate: reference, met 2009 National Academy of Medicine [NAM] Guidelines [5–9.1 kg], Excessive [>9.1 kg], Low [1–4.9 kg], Stable [±1 kg], Weight Loss [>1 kg]) or GWG Z-score quintiles. Modified Poisson regression was used to estimate risk of adverse outcomes, stratified by obesity class. Electronic health record data were used to define outcomes, including cesarean delivery, preterm birth, admission to the neonatal intensive care unit, small- and large-for-gestational age infants. Results Prevalence of weight stability and weight loss was 3.8 and 3.4%, respectively. Compared with those who gained within NAM, increased risk of small-for-gestational age was observed among those with weight loss among obesity class I (Risk Ratio (RR): 1.57, 95% confidence interval [CI]: 1.12, 2.19), obesity class II (RR: 2.18, 95% CI: 1.52, 3.13), and obesity class III (RR: 1.72, 95% CI: 1.21, 2.45). Weight loss was associated with a decreased risk of cesarean delivery among obesity class III, compared with NAM. Conclusion Weight loss during pregnancy is associated with increased risk of small-for-gestational age among all obesity classes, but not other adverse perinatal outcomes and may reduce risk of cesarean delivery. Low weight gain and weight stability are not associated with risk of adverse outcomes among those with class III obesity. GWG guidelines may need to vary by obesity class. Key Points Weight loss during pregnancy is associated with increased risk of small-for-gestational age among all obesity classes; but weight loss was not associated with other adverse perinatal outcomes. Among class III, low weight gain and weight stability are not associated with adverse perinatal outcomes. GWG guidelines may need to vary by obesity class. [ABSTRACT FROM AUTHOR]

Objective Despite an increase in twin pregnancies in recent decades, the Institute of Medicine twin weight gain recommendations remain provisional and provide no guidance for the pattern or timing of weight change. We sought to characterize gestational weight change trajectory patterns and examine associations with birth outcomes in a cohort of twin pregnancies. Study Design Prenatal and delivery records were examined for 320 twin pregnancies from a maternal–fetal medicine practice in Austin, TX 2011-2019. Prenatal weights for those with >1 measured weight in the first trimester and ≥3 prenatal weights were included in analyses. Trajectories were estimated to 32 weeks (mean delivery: 33.7 ± 3.3 weeks) using flexible latent class mixed models with low-rank thin-plate splines. Associations between trajectory classes and infant outcomes were analyzed using multivariable Poisson or linear regression. Results Weight change from prepregnancy to delivery was 15.4 ± 6.3 kg for people with an underweight body mass index, 15.4 ± 5.8 kg for healthy weight, 14.7 ± 6.9 kg for overweight, and 12.5 ± 6.4 kg for obesity. Three trajectory classes were identified: low (Class 1), moderate (Class 2), or high gain (Class 3). Class 1 (24.7%) maintained weight for 15 weeks and then gained an estimated 6.6 kg at 32 weeks. Class 2 (60.9%) exhibited steady gain with 13.5 kg predicted total gain, and Class 3 (14.4%) showed rapid gain across pregnancy with 21.3 kg predicted gain. Compared to Class 1, Class 3 was associated with higher birth weight z -score (β = 0.63, 95% confidence interval [CI]: 0.31,0.96), increased risk for large for gestational age (IRR = 5.60, 95% CI: 1.59, 19.67), and birth <32 weeks (IRR = 2.44, 95% CI: 1.10, 5.4) that was attenuated in sensitivity analyses. Class 2 was associated with moderately elevated birth weight z -score (β = 0.24, 95% CI: 0.00, 0.48, p = 0.050). Conclusion Gestational weight change followed a low, moderate, or high trajectory; both moderate and high gain patterns were associated with increased infant size outcomes. Optimal patterns of weight change that balance risk during the prenatal, perinatal, and neonatal periods require further investigation, particularly in high-risk twin pregnancies. Key Points A majority gained weight below IOM twin recommendations. Three patterns of GWC across pregnancy were identified. Moderate or high GWC was associated with infant size. [ABSTRACT FROM AUTHOR]