Novel approaches to examining weight change in pregnancies affected by obesity.

BACKGROUND: Current gestational weight change (GWC) recommendations for those with obesity were established with limited evidence of the pattern and timing of weight change across pregnancy. Likewise, the recommendation of 5-9kg does not differentiate by obesity severity.

OBJECTIVES: We sought to describe GWC trajectory classes by obesity grade and associated infant outcomes among a large, diverse cohort.

METHODS: The study population included 22,355 singleton pregnancies individuals with obesity (BMI≥30.0kg/m2 ) and normal glucose tolerance who delivered at Kaiser Permanente Northern California between 2008-2013. Obesity grade specific GWC trajectories were modeled to 38wk using flexible latent class mixed modeling (package lcmm) in R. Multivariable Poisson or linear regression models estimated associations between GWC trajectory class and infant outcomes (size for gestational age and preterm birth) by obesity grade.

RESULTS: Five GWC trajectory classes were identified for each obesity grade, each with a distinct pattern of weight change before 15wk (including loss, stability, gain) followed by weight gain thereafter (low, moderate, and high). Two classes with high gain overall were associated with increased risk for large for gestational age (LGA) in obesity grade 1 (IRR=1.27 95%CI 1.10,1.46; IRR=1.47 95%CI 1.24,1.74). Both high (IRR=2.02 95%CI 1.61,2.52; IRR=1.98 95%CI 1.52, 2.58) and two moderate gain classes (IRR=1.40 95%CI 1.14,1.71; IRR=1.51 95%CI 1.20, 1.90) were associated with LGA in grade 2; and only early loss/late moderate gain class 3 (IRR=1.30 95%CI 1.04, 1.62) was associated in grade 3. This class was also associated with preterm birth in grade 2. No associations were detected between GWC and small for gestational age (SGA).

CONCLUSIONS: Among pregnancies affected by obesity, GWC was not linear or uniform. Different patterns of high gain were associated with increased risk for LGA with the greatest magnitude in obesity grade 2, while GWC patterns were not associated with SGA.

RESEARCH REGISTRATION: This research does not require registration at clinicaltrials.gov.