Birthweight associations with parental obesity: retrospective analysis of 1,778 singleton term births following assisted reproductive treatment

OBJECTIVE: To determine the association of combined parental preconception overweight and obesity on infant birthweight. DESIGN: Retrospective study of fresh in vitro fertilization or intracytoplasmic sperm injection cycles (2009–2017). SETTING: Repromed, South Australia, assisted reproductive technology clinic. PATIENTS: Couples undergoing in vitro fertilization/intracytoplasmic sperm injection insemination with their own gametes and transfer of a fresh single blastocyst (N = 1,778). INTERVENTION(S): None. MAIN OUTCOME MEASURES: Parental body mass index (BMI) was recorded prior to cycle initiation. Infant birthweight was recorded at delivery. The impact of parental obesity and their interaction on first singleton term (≥37 weeks’ gestation) birthweight was assessed using linear regressions assessing nonlinearity and a pairwise linear interactions. RESULTS: In the base model where parental BMI is assumed linear, there was strong evidence for higher birthweight with increasing maternal BMI (11.2 g per maternal kg/m(2); 95% confidence interval, 7.2, 15.1) but not paternal BMI. The inclusion of a pairwise linear interaction indicated that paternal BMI attenuates the positive association between maternal BMI and infant birthweight (interaction −0.88; 95% confidence interval, −1.49, −0.27). The inclusion of nonlinear maternal BMI terms did not change the conclusions. CONCLUSIONS: Increases in the mean infant birthweight associated with maternal obesity are attenuated when the father is obese. While maternal BMI contributed more to the mean infant birthweight than paternal BMI, a couple-centered approach to preconception health advice is recommended, given the documented relationships between parental obesity and childhood weight beyond infancy. Further studies in both assisted reproductive technology and general population cohorts assessing the parental BMI interaction on infant birthweight are warranted.