BMI before pregnancy affects birth outcomes of ART twins

Prepregnancy maternal weight affects birth outcomes of twins conceived through assisted reproductive technology (ART), with maternal obesity tied to higher neonatal weight and the risk of preterm birth and maternal underweight linked to lower birthweight, a recent study has found.

Researchers examined a 10-year Chinese sample including 3,431 mothers who had given birth to twins through ART. Most of them (n=2,393) had normal weight before pregnancy, while 333, 576, and 129 were underweight, overweight, and obese, respectively.

Mothers who were underweight before ART pregnancy tended to give birth to infants with significantly lower birthweight (difference, –59.22 g, 95 percent confidence interval [CI], –93.16 to –25.27). Similarly, prepregnancy underweight was a significant risk factor for small for gestational age (SGA) infants (relative risk [RR], 1.25, 95 percent CI, 1.09–1.43).

Notably, the interaction between SGA and prepregnancy body mass index (BMI) was nonlinear. The risk of SGA decreased significantly with increasing BMI (RR, 0.90, 95 percent CI, 0.86–0.95), but only until the turning point of 21 kg/m², after which the correlation between the two tested nonsignificant (RR, 1.01, 95 percent CI, 0.98–1.04).

On the other hand, obese mothers prior to conception gave birth to significantly heavier infants (difference, 65.82 g, 95 percent CI, 10.66–120.99). Prepregnancy obesity increased the risk of preterm birth by nearly 20 percent (RR, 1.19, 95 percent CI, 1.03–1.37).

“These findings are important for the prevention of adverse neonatal outcomes for twin infants conceived by ART. An additional large-sample multicentre prospective cohort study is needed to confirm relationships between prepregnancy maternal BMI and perinatal outcomes,” the researchers said.