• Collaborative Perinatal Project;
  • gestational weight gain;
  • infant;
  • obesity;
  • pre-pregnancy body mass index



Previous research on inadequate gestational weight gain among obese women and adverse outcomes has been mixed. The objective of this study was to examine associations between inadequate gain among obese women and antepartum, intrapartum, and infant outcomes.


Obese women from the U.S. Collaborative Perinatal Project were divided into obesity classes I (30.0–34.9 kg/m2) and II/III (> 35.0 kg/m2) and three weight gain categories (inadequate: < 5 kg, adequate: 5–9 kg, excessive: > 9 kg) as defined by the U.S. Institute of Medicine. Associations between 1-kg increments of inadequate gain (< 5 kg) and outcomes were examined. Women with inadequate gain were also compared with women gaining normal (5–9 kg) and excessive (> 9 kg) weight.


Each fewer 1-kg of weight gain increased small-for-gestational age (SGA) risk and reduced large-for-gestational age (LGA) risk by similar magnitude. Compared with excessive gain, inadequate gain reduced the odds of preeclampsia (OR: 0.56, CI: 0.37, 0.84), gestational hypertension (OR: 0.66, CI: 0.47, 0.92), and LGA (OR: 0.48, CI: 0.38, 060) and increased the odds of SGA (OR: 2.26, CI: 1.52, 3.35). Inadequate gain offered fewer advantages over adequate weight gain: lower odds of LGA (OR: 0.75, CI: 0.57, 0.99); increased odds of SGA (OR: 1.86, CI: 1.18, 2.91). Most associations applied to obesity class I but not class II/III women.


Inadequate weight gain poses benefits and risks to mothers and infants, but is preferable to excessive gain. The risks and benefits apply differently to class I versus class II/III obese women, indicating the need for weight gain recommendations by obesity class.