Antiretroviral therapy during pregnancy is critical to preventing human immunodeficiency virus vertical transmission. Physiological changes during pregnancy can alter drug kinetics. The aim of this study was to assess the pharmacokinetics (PK) of saquinavir (SQV) boosted with ritonavir during pregnancy and postpartum. Fourteen human immunodeficiency virus-positive pregnant women started SQV 500 mg new tablet formulation plus ritonavir at a dose of 1000/100 mg twice a day + 2 nucleoside retrotranscriptase inhibitors during pregnancy. At weeks 24 and 34 of pregnancy and 6 weeks postpartum, a 12-hour PK study was conducted. PK parameters were calculated using Win Nolin software version 4.1. At week 24, the geometric mean values for SQV area under the plasma concentration–time curve from 0–12 hours (AUC0–12), the maximum observed plasma concentration (Cmax), trough plasma concentration (Cmin), and the elimination half-life (t1/2) were 24.80 mg·h−1·mL−1, 4.66 mg/mL, 0.93 mg/mL, and 4.31 hours, respectively. At week 34, AUC0–12, Cmax, Cmin, and t1/2 were 12.71 mg·h−1·mL−1, 3.23 mg/mL, 0.26 mg/mL, and 4.06 hours, respectively. Finally, at 6 weeks postpartum, mean values for SQV AUC0–12, Cmax, Cmin, and t1/2 were 28.94 mg·h−1·mL−1, 3.92 mg/mL, 0.86 mg/mL, and 3.60 hours, respectively. Although PK parameters in week 24 and postpartum were very similar, those for week 34 showed an important reduction: −71.20%, −30.61%, −48.73%, and −5.81% in Cmin, Cmax, AUC0–12, and t1/2, respectively, compared with week 24, but no statistically significant differences were shown between patients. No vertical transmissions were reported. Therapeutic drug monitoring of SQV during pregnancy should be considered, mainly during the third trimester, to ensure adequate drug exposure throughout the entire pregnancy.