P–787 Impact of delaying ART to promote weight loss: a large multicentre study accounting for the combined effect of female/male age and body mass index (BMI)

Study question Is postponing the start of ART (to promote a reduction in female BMI) beneficial for cumulative live birth rates (CLBR) when accounting for the female/male ageing this delay will cause? Summary answer Postponing ART treatment in one year to promote female weight loss could be detrimental in women of advanced maternal age (AMA, >35 years-old). What is known already Overweight/obese couples are frequently encouraged to lose weight prior to infertility treatment to enhance ART outcomes. However, a meaningful weight loss is often difficult to achieve for these couples, frequently taking at least one year to accomplish. Given that both female and male ageing are also important for ART success, we were interested in understanding the combined impact on CLBR of BMI reduction and ageing following a one-year delay. Study design, size, duration A retrospective study including patients performing their first ART cycle using autologous gametes between 2013–2018 in one of 39 participating ART centres. Only GnRH antagonist cycles were included (n = 14260). CLBR was the primary outcome. Secondary outcomes included time-to-pregnancy, birthweight and gestational age. Participants/materials, setting, methods Patients were subdivided according to female BMI (Kg/m2) in either underweight (<18.5), normal-weight (18.5–24.9), overweight (BMI 25.0–29.9 kg/m2) and obese (≥30 kg/m2). Meaningful and extreme weight loss were defined as a reduction from obesity to either overweight or normal-weight, respectively. We performed multivariable regression analysis to account for potential confounding. Main results and the role of chance Overweight (36.8%) and obese (33.0%) women had significantly lower CLBR when compared to the underweight (42.6%) and normal-weight (41.4%). When assessing the confounder-adjusted net-effect of male/female age and BMI, the predicted benefit of promoting a meaningful BMI reduction was lower than the estimated hindrance due to male/female ageing as soon as women reached AMA (n = 8365, 58.6%). This absence of benefit was especially important in women >38 years-old, in which even extreme weight-loss did not compensate for the age-related reduction in CLBR caused by the one-year delay. Moreover, male weight-loss failed to provide any additional benefit when accounted for in the regression models. Finally, obesity was also associated with a modest but statistically significant one-month delay in time-to-pregnancy and a 96.1 g (95% confidence interval: 39.9–152.4) increase in birth weight. The diagram of predicted outcomes presented in this study may serve as a useful tool to counsel patients before treatment, namely when recommending treatment postponement to promote short-term (i.e. 3–6 months) or long-term (i.e. 1 year) weight loss. Limitations, reasons for caution Caution is recommended when extrapolating these results into everyday practice owing to the retrospective nature of the study and the fact that only GnRH antagonist cycles were included. Wider implications of the findings: Patients are frequently confronted with the dilemma to either postpone treatment (and promote weight loss) or start treatment immediately (to avoid further ageing). Our results seem to show that women in AMA may have hindered CLBR if recommended to delay treatment even if the desired weight loss is ultimately achieved. Trial registration number Not applicable