BACKGROUND: Abacavir-lamivudine (ABC/3TC) and tenofovir-emtricitabine (TDF/FTC) represent in the guidelines of several countries, including Italy and United States, the preferred nucleoside/nucleotide backbones of antiretroviral regimens. We assessed their profile in pregnancy using data from a national observational study.METHODS: Laboratory measures (CD4, HIV-RNA, lipid profile, glucose, hemoglobin, and alanine transferase) and pregnancy outcomes (preterm delivery, low birthweight, nonelective cesarean section, birthweight Z-score, congenital defects, HIV transmission, maternal weight gain, and pregnancy complications) were compared after prenatal exposure to ABC/3TC or TDF/FTC.RESULTS: The study evaluated 913 pregnancies (ABC/3TC: 252; TDF/FTC: 661). At entry in pregnancy, women on TDF/FTC were older (33.6 vs. 32.4 years, P = 0.005), less frequently on treatment (66.9% vs. 80.2%, P <0.001), and had lower CD4 counts (475/mm vs. 533/mm, P = 0.003) and higher plasma HIV-RNA levels (2.48 vs. 2.22 log10 copies/mL, P = 0.003). Women on ABC/3TC had more commonly hypertension/nephropathy (5.2% vs. 2.0%, P = 0.013). No major differences were observed in the main pregnancy outcomes and in rates of undetectable HIV-RNA at third trimester. In a subgroup analysis that evaluated at third trimester only cases with regular 3-drug treatment during pregnancy, women on TDF/FTC had lower hemoglobin levels (median: 11.1 vs. 11.8 g/dL, P = 0.002) and women on ABC/3TC had higher levels of total cholesterol (median: 230 vs. 216 mg/dL, P = 0.023) and low-density lipoprotein-cholesterol (133 vs. 111 mg/dL, P = 0.030).CONCLUSIONS: In this study, use of TDF/FTC and ABC/3TC in pregnancy was associated with similar pregnancy outcomes and with some differences in laboratory measures that might guide physicians' prescriptions in mothers with hematologic or metabolic risk factors.