OBJECTIVE: This study was designed to determine whether pregnancy and increasing parity in women with insulin-dependent diabetes mellitus (1) increases the risk for diabetic nephropathy and (2) accelerates the progression of diabetic nephropathy. STUDY DESIGN: The study included women with insulin-dependent diabetes mellitus who enrolled in our diabetes-in-pregnancy trial with a pregnancy that continued beyond 20 weeks' gestation and who were delivered between 1978 and December 31, 1991, to allow for a minimum of 3 years' follow-up. Pregnancy and follow-up information was obtained from the medical records and from our computerized database. For patients followed up elsewhere, information was obtained from their current physicians. Life-table analysis was used to determine (1) the risk for nephropathy developing de novo as a function of duration of disease and the association of this risk with parity and (2) the risk of renal failure developing in women with preexisting nephropathy and its association with parity. RESULTS: The study population included 182 pregnant women with insulin-dependent diabetes mellitus: 46 with overt nephropathy (group F) and 136 without nephropathy (group NF). Pregnancy and increasing parity did not increase the overall risk for nephropathy (44% after 27 years of diabetes). In group NF 10% had nephropathy within 10.1 ± 4.2 years of the pregnancy. Proteinuria appearing during pregnancy and glycemic control during pregnancy were significantly associated with the subsequent development of nephropathy. In group F 26% had end-stage renal disease after a median period of 6 years from the pregnancy. Pregnancy or increasing parity did not increase the risk for renal failure in women with nephropathy. CONCLUSIONS: Our data support the premise that pregnancy in women with insulin-dependent diabetes mellitus does not increase the risk of subsequent nephropathy and does not accelerate progression of renal disease in women with preexisting nephropathy. (AM J OBSTET GYNECOL 1996;174:1180-91.)