Prepregnancy overweight/obesity, ART linked to twin births

Women who are overweight or obese prior to pregnancy are more likely to conceive twins, particularly those who undergo assisted reproductive technology (ART) treatment, according to a recent study.

“The prevalence of overweight and obesity (BMI ≥25 kg/m²) increased globally, and high BMI has been linked to higher rates of twin birth … However, temporal increases in twin deliveries represent a clinical and public health concern, as twin pregnancy is associated with elevated risks of maternal as well as foetal and infant complications,” said the researchers.

“Evidence from large population-based studies is lacking; the issue needs a careful study, as obese women are also more likely to use ART, which frequently results in twin pregnancy,” they noted.

Using data from the British Columbia Perinatal Database Registry, the researchers retrospectively analysed 392,046 women (median age 31.4 years) who had complete data on prepregnancy BMI, which was categorized as normal BMI (18.5–24.9 kg/m²), overweight (25–29.9 kg/m²), and obesity class I (30–34.9 kg/m²), class II (35–39.9 kg/m²), and class III (≥40 kg/m²). [JAMA Netw Open 2024;doi:10.1001/jamanetworkopen.2023.50934]

Overall, 8,295 women had twin pregnancies (15.8 per 1,000 deliveries).

Women with overweight (16 per 1,000 deliveries) and class I and II obesity (16 and 16.7 per 1,000 deliveries, respectively) achieved higher twin birth rates than those with normal BMI (14.4 per 1,000 deliveries).

Of note, women with class III obesity had the highest rate of twin deliveries (18.9 vs 14.4 per 1,000 deliveries).

Additionally, women with overweight and obesity class I and II had a higher likelihood of conceiving with ART (adjusted rate ratios [adjRRs], 1.09, 1.23, and 1.26, respectively) than women with a normal BMI.

In fact, ART led to a nearly twelvefold increase in twin deliveries (adjRR, 11.80).

“However, in women with obesity class III, who had the highest rate of twin birth, ART did not play any mediating role,” the researchers noted.

“Overall, women with higher BMI used ART at higher rates than those with normal BMI, and this partially mediated the association between high prepregnancy BMI and twin delivery in those with overweight or class I or II obesity,” said the researchers.

“Our assessment of ART conception as a potential mediator in the association between obesity and twin delivery is, to our knowledge, novel. Obesity is a known risk factor for subfertility and infertility leading to increased use of in vitro fertilization and other fertility treatments among women with overweight or obesity,” they noted.