Aim. - This study retrospectively evaluated the complications associated with prepregnancy overweight (OW) or obesity (OB) and gestational weight gain (GWG) in women with or without universally screened and treated gestational diabetes mellitus (GDM). Methods. - A total of 15,551 non-Asian women without pregravid diabetes or hypertension who delivered singleton babies (2002-2010) were classified according to GDM (13.5%), pregestational body mass index (BMI; normal range: 18.5-24.9 kg/m(2)), OW (26.2%), OB (13.9%; BMI >= 30 kg/m(2)) and GWG (<7 kg: 32%; 7-11.5 kg: 37%; 11.6-16 kg: 23%; > 16 kg: 8%). Main outcome measures were large/small for gestational age (LGA/SGA), caesarean section, preeclampsia, preterm delivery and shoulder dystocia. Results. - GDM was associated with more LGA babies [Odds Ratio (OR): 2.12, 95% confidence interval (CI): 1.85-2.43], caesarean section (OR: 1.49, 95% CI: 1.34-1.65) and preeclampsia (OR: 1.59, 95% CI: 1.21-2.09). OW/OB and GWG were associated with LGA infants whatever the GDM status, and with SGA babies only in women without GDM. LGA status was independently associated with GWG in women with GDM (11.6-16 kg: OR: 1.74, 95% CI: 1.49-2.03 and > 16 kg OR: 3.42, 95% CI: 2.83-4.13 vs 7-11.5 kg) and in women without GDM (OR: 2.14, 95% CI: 1.54-2.97 or OR: 2.65, 95% CI: 1.68-4.17, respectively), and with BMI only in women without GDM (OR: 1.12, 95% CI: 1.00-1.24, per 10 kg/m2). SGA status was independently associated with OW (OR: 0.86, 95% CI: 0.77-0.98), OB (OR: 0.84, 95% CI: 0.72-0.98) and GWG <7 kg (1.14, 95% CI: 1.01-1.29) only in women without GDM. Conclusion. - In our European cohort and considering the triumvirate of GDM, BMI and GWG, GDM was the main contributor to caesarean section and preeclampsia. OW/OB and GWG contributed to LGA and SGA infants mainly in women without GDM.