Objective: To assess the levels of pregnancy-associated plasma protein-A (PAPP-A) and β-human chorionic gonadotropin (fb-hCG) in cases of diabetic pregnancy, to determine whether these biomarkers can be considered significant predictors for macrosomia, preeclampsia (PE), intrauterine growth restriction (IUGR), and preterm birth in mothers with different types of pregestational diabetes mellitus (DM). Methods: It was a retrospective cohort study. Study groups were presented: type 1 DM (n = 100), type 2 DM (n = 50), and controls (n = 25). At 11 + 0 to 13 + 6 week’s gestation, we recorded maternal characteristics and medical history, and performed a combined test for the detection of risk of chromosomal abnormalities. To assess the performance of the markers in the prediction of the main obstetrical complications (PE, IUGR, preterm birth, and macrosomia), receiver-operating characteristic (ROC) curves were produced and area under the curves was calculated. Results: The study has shown that DM is associated with a high rate of perinatal complications: PE, IUGR, macrosomia, and preterm birth. The median level of PAPP-A was significantly lower in case of type 1 DM- 0.89 (inter quartile range (IQR), 0.51–1.1), and type 2 DM-0.88 (IQR, 0.42–1.15) compared to the unaffected group 1.03 (IQR, 0.96–1.12; p =.025). There were no significant differences in the fb-hCG multiples of the normal median (MoM; p =.14) between the diabetic and unaffected groups. More significant results were obtained when calculated by percentile: in diabetic pregnancies, PAPP-A and fb-hCG MoMs values were lower in the 5–10% ranges and higher in the 95% range, compared to the control group. ROC-analysis did not show any significant data that first-trimester PAPP-A and fb-hCG serum levels are predictors for PE, IUGR, macrosomia, and preterm birth. Conclusion: The routine first-trimester serum screening of fetal Down syndrome cannot be used as a tool of risk identification for PE, IUGR, macrosomia, and preterm birth in case of diabetic pregnancy.