Maternal prepregnancy BMI and GWG, including period-specific GWG, were positively and independently associated with neonatal adiposity. Associations of early and midpregnancy weight gain with neonatal adiposity support the hypothesis that greater maternal weight gain during pregnancy, regardless of prepregnancy BMI, is directly related to offspring adiposity at birth. The Healthy Start study was registered as an observational study at clinicaltrials.gov as NCT02273297.

Many researchers favor repeated measures designs because they allow the detection of within-person change over time and typically have higher statistical power than cross-sectional designs. However, the plethora of inputs needed for repeated measures designs can make sample size selection, a critical step in designing a successful study, difficult. Using a dental pain study as a driving example, we provide guidance for selecting an appropriate sample size for testing a time by treatment interaction for studies with repeated measures. We describe how to (1) gather the required inputs for the sample size calculation, (2) choose appropriate software to perform the calculation, and (3) address practical considerations such as missing data, multiple aims, and continuous covariates.