- Objective Recently, lower maternal plasma human leukocyte antigen (HLA)-G protein levels in preeclampsia (PE) in the first and second trimester was reported. Thus, we sought to evaluate the levels of HLA-G protein in patients with severe PE during the third trimester. Study Design In this prospective case control study, amniotic fluid and maternal and cord blood samples were aspirated from 50 pregnant women during the third trimester. The study group included 26 pregnant women diagnosed with severe PE and 24 women without PE serving as controls. A soluble HLA-G–specific enzyme-linked immunosorbent assay was used to measure protein levels. Statistical analysis included the Student t test and simple regression analysis. Results Maternal serum HLA-G levels in PE pregnancies were found to be significantly lower as compared with normal pregnancies (10.97 ± 6.55 vs 36.05 ± 34.53 μg/mL; P = .003). Conclusion A reduced level of maternal HLA-G protein was associated with severe PE during the third trimester. This finding may suggest an essential role for HLA-G in normal and preeclamptic pregnancies.