FREQUENCY OF EARLY IN-UTERO HIV-1 INFECTION - A BLIND DNA-POLYMERASE CHAIN-REACTION STUDY ON 100 FETAL THYMUSES

Objective: To estimate the prevalence of in utero transmission of HIV- 1 through the second trimester. Material and methods: One hundred cons ecutive, unselected, intact fetuses, beyond 15 weeks gestational age ( mean, 22.4 weeks) were studied. These were obtained following spontane ous intrauterine deaths (n = 4), miscarriages (n = 4), and elective mi d-trimester terminations (n = 92), eight of which were fetuses with ma lformations from HIV-1-positive pregnancies. Coded DNA extracts from t he fetal thymuses were tested blindly by polymerase chain reaction in three laboratories using a total of six different primer pairs. Result s: Two thymuses tested positive [95% confidence interval (CI), 0.2-7]. Results from the three laboratories were consistent in all 100 cases. The two fetuses with HIV in the thymus both tested positive in other organs, demonstrating systemic HIV infection. The first fetus, whose m other had advanced AIDS, had died in utero and had diffuse toxoplasmos is. The second died following extremely premature delivery in a pregna ncy complicated by repeated bleeding. HIV infection was observed in no ne of the 92 fetuses that resulted from elective mid-trimester termina tions (95% CI, 0-4). Conclusion: The frequency of early in utero HIV i nfection appears to be low, compared with transmission rates in infant s born to HIV-l-infected mothers, suggesting that transmission occurs mostly later in pregnancy and/or at delivery. Specific risk factors ma y have implications in the occurrence of early as opposed to late tran smission.