A retrospective cohort study using national data and log binomial regression was done Among women undergoing IVF, prepregnancy  BMI affects pregnancy and obstetric outcomes. Underweight status may have a limited impact on pregnancy and live-birth rates, but it is associated with  increased preterm and low-birth-weight delivery risk. Obesity negatively impacts all ART and obstetric outcomes investigated.

A few studies till date which were evaluated showed impact of low BMI  on ART outcomes . A  statistically significant difference in  underweight  women  compared   to  normal women  counterpart. studies suggest both extrimites  of BMI underweight   and obesity is associated with diverse  sets of metabolic disorder & have reproductive consequence.  

The best outcomes were observed among women  of normal weight. For those of abnormal weight, obesity was associated with greater risk of adverse  obstetric outcomes than  underweight status.

Whenever feasible, particularly among the ART population, physicians should encourage women to reach a normal BMI before attempting conception.

To know more – study link