The interaction between pre-eclampsia and diabetes mellitus (DM) is far from being completely understood. In this study, we compared normal pregnancies with those complicated with pre-eclampsia, gestational DM, and/or pre-existing diabetes to assess the effects of hyperglycemia on placental development. AnInstitutional Review Board (IRB) approved retrospective cross-sectional study with 621 subjects was performed. Statistical analysis was performed using Duncan's post hoc test and analysis of variance. Regardless of diabetes status, patients with pre-eclampsia delivered prematurely. Patients in the group with pre-eclampsia and pregestational diabetes delivered much earlier, at 35.0±0.4 weeks, when compared with the patients that had pre-eclampsia with gestational diabetes and pre-eclampsia with no diabetes (*P<0.05 for each). Additionally, patients with pre-existing diabetes who developed pre-eclampsia delivered smaller babies than those with pre-existing diabetes without pre-eclampsia (1.00±0.03, P<0.05 for each). Pre-existing diabetes with added insult of pre-eclampsia led to fetal growth restriction. This outcome validates the understanding that elevated glucose earlier in pregnancy alters placentogenesis and leads to fetal growth restriction.