Long-term performance of biological prostheses and course of pregnancy, labor, and delivery were evaluated in women less than 35 years of age. Between 1975 and 1987, 87 female patients received a porcine (n = 86) or pericardial valve (n = 1); the mean patient age was 26.8 years, with a range of 8 to 35 years. A total of 17 of these patients experienced 37 pregnancies. A total of 25 babies were delivered, of which 19 were babies of normal birth weight born at term and six were born prematurely (two of these were stillborn). There were six spontaneous abortions and five therapeutic abortions. The mean time from primary operation to first delivery was 29 months. Of the 17 pregnant patients, 14 were in normal sinus rhythm and three were in atrial fibrillation. One of those in fibrillation had a therapeutic abortion while receiving warfarin therapy, and another was successfully delivered of her neonate after 7 months of warfarin therapy. The remaining 15 patients were treated through 35 pregnancies without anticoagulants or antiplatelet agents. Of the total population of 87 patients, 32 (36.8%) were treated for valve-related complications. Structural valve deterioration occurred in eight patients (47.1%) of the pregnancy group and 10 patients (14.3%) of the nonpregnancy group (p less than 0.05). The freedom from structural valve deterioration at 10 years was 23.3% +/- 14% for the pregnancy group and 74.2% +/- 8.5% for the nonpregnancy group (p less than 0.05, age as a determinant, p not significant). There were eight valve-related deaths (1.5%/patient-year). Reoperation was performed in 59% of the pregnancy group and 19% of the nonpregnancy group, primarily for structural valve deterioration manifested as valvular obstruction from aggressive calcification (p less than 0.05). The freedom from reoperation at 10 years parallels freedom from structural valve deterioration (20.3% +/- 12.4% and 64.3 +/- 9.1% for the pregnancy and nonpregnancy groups, respectively, with p less than 0.05; with age added as a determinant, p not significant). The overall reoperative mortality was 8.7% (two patients). The biologic prostheses afforded successful pregnancy without fetal wastage or congenital anomalies and without significant maternal morbidity or mortality.