Unhealthy weight in parents before pregnancy tied to adverse birth outcomes

The preconception weight of parents, whether too low or too high, contributes to the risk of adverse birth outcomes, including perinatal death and birth defects, according to a study.

Researchers used data from the National Free Preconception Checkups Project and looked at 8,787,096 parent–child triads (average age of mothers 26.18 years, average age of fathers 27.83 years) with available data on parental preconception BMI and birth outcomes.

Outcomes included spontaneous abortion, medically induced abortion, preterm birth, small for gestational age (SGA), large for gestational age (LGA), birth defects, and perinatal death. Restricted cubic spline and Poisson regression analyses were performed.

Both maternal and paternal BMI were positively associated with the risk of LGA (when both parents had obesity: risk ratio [RR], 1.70, 95 percent CI, 1.65–1.74; when both parents were underweight: RR, 0.67, 95 percent CI, 0.66–0.69) and inversely associated with the risk of SGA (when both parents had obesity: RR, 0.73, 95 percent CI, 0.69–0.76; when both parents were underweight: RR, 1.57, 95 percent CI, 1.53–1.60).

J-shaped associations were observed between both maternal and paternal BMI and all other adverse birth outcomes examined.

Compared with a healthy BMI in both parents, preconception BMI categories of underweight, overweight, or obesity in either or both parents raised the risk of spontaneous abortion, medically induced abortion, perinatal death, preterm birth, birth defects, and composite adverse birth outcome. For instance, the risk of perinatal death increased by 17 percent when both parents had obesity (risk ratio [RR], 1.17, 95 percent confidence interval [CI], 1.03–1.33) and by 12 percent when both parents were underweight (RR, 1.12, 95 percent CI, 1.01–1.23).

However, when all the outcomes were combined as a composite, the risk increased by 10 percent (RR, 1.10, 95 percent CI, 1.08–1.11) when the mother had obesity and the father had a healthy BMI, by 4 percent (RR, 1.04, 95 percent CI, 1.04–1.05) when the mother had a healthy BMI and the father had obesity, and by 16 percent (RR, 1.16, 95 percent CI, 1.14–1.18) when both parents had obesity.

These findings point to the potential of maintaining a healthy weight for both parents before pregnancy as key to perinatal wellbeing.