overweight and obese patients, respectively. A rate of gestational weight gain , rather than an absolute number, was utilized to define inadequate gestational weight gain to account for the different gestational age time points at which the patients’ weights were measured. The primary outcome was preterm birth at o32 weeks. Secondary maternal outcomes included the rates of indicated and spontaneous preterm birth at
o32 weeks, gestational diabetes, gestational hypertension, preeclampsia
and cesarean delivery. Secondary neonatal outcomes included the rates
of small-for-gestational age infants, neonatal intensive care admissions,
multiple morbidities associated with preterm birth and neonatal length of stay.
Based on previous research, we estimated that the rate of preterm birth at
o32 weeks would be 4% in the adequate gestational weight gain group and 13.3% in the inadequate gestational weight gain group. After sampling of the population, it was determined that the ratio of adequate to inadequate gestational weight gain patients collected at 20 to 28 weeks would be approximately 4:1. Using a two-sided
α = 0.05 and 80% power, we estimated that we would need to include 89
patients with inadequate gestational weight gain at 20 to 28 weeks and 357 patients with adequate gestational weight gain at 20 to 28 weeks.
All data were analyzed using SPSS (SPSS, Version 22; Armonk, NY, USA).
All tests were two-sided and a P-value o0.05 was considered significant.
Continuous variables were analyzed with Student’s t-test and categorical
data with the χ2 or Fischer’s exact tests. Stepwise logistic regression
analysis was performed to assess the association between adequacy of
gestational weight gain and preterm birth at o32 weeks, after controlling a history of a prior preterm birth, short cervical length and chorionicity