In women with pre-existing diabetes, the contribution to pregnancy outcomes of gestational weight gain as defined by IOM guidelines, differs when adjustment for gestational age is used.

Aims: To investigate the association between gestational weight gain (GWG) as per Institute of Medicine 2009 (IOM) and pregnancy outcomes in women with gestational (GDM) or preexisting diabetes mellitus (PDM), when applying or not a correction for gestational age (IOM-CGWG and IOM-GWG respectively).

Methods: We conducted a retrospective analysis of pregnant women with either GDM or PDM attended in our center. Exposure variables: IOM-GWG and IOM-CGWG.

Outcome variables: Maternal and fetal/neonatal clinical outcomes.

Statistics: Logistic regression with adjustment for other potential independent variables.

Results: In women with GDM, correction for gestational age did not affect the distribution of weight gain or the association with clinical outcomes (pregnancy-induced hypertension, preeclampsia, cesarean delivery, large-for-gestational age newborns (LGA), macrosomia and small-for-gestational age newborns (SGA)). In women with PDM, correction for gestational age, caused a shift in the distribution to a higher rate of excessive weight gain. In the adjusted analysis, IOM-GWG was significantly associated with cesarean delivery, preterm birth, LGA, macrosomia, SGA and neonatal respiratory distress. With IOM-CGWG, the association with preterm birth disappeared while an association with PIH emerged. Population-attributable and preventive fraction were substantial for both women with GDM and PDM.

Conclusions: We conclude that the associations of IOM-GWG and IOM-CGWG are substantial in both women with GDM and PDM, indicating an area for potential intervention. In women with PDM, the modification of associations when gestational age is accounted for is relevant, highlighting the importance of considering this variable.