Table 5.

Methodologic considerations to guide the design of studies on gestational weight gain in twin pregnancies

Use a large enough sample size to provide sufficient statistical power to examine the study’s primary outcome. Calculate gestational weight gain using the last measured weight before delivery and a reliable reporting of prepregnancy weight (1). Describe gestational weight gain in relation to chorionicity and assisted reproductive technologies and control for these variables if they are confounders. In observational studies, control for key confounders, including prepregnancy BMI, gestational age at delivery, maternal race/ethnicity, smoking, parity, maternal age, and socioeconomic indicators. Stratify results by prepregnancy BMI category, including severe obesity. Confirm gestational age using ultrasound. When studying gestational diabetes and/or hypertensive disorders of pregnancy, study gestational weight gain before diagnosis.