Fifty-nine of 94 pregnant women with juvenile-onset insulin-dependent diabetes who attended a preconceptional clinic were periodically examined by a diabetologic team. Glycemic control was obtained by intensified insulin therapy and monitored by blood glucose self-monitoring. These women were compared with the 35 pregnant women who did not receive preconceptual glycemic control. The initial glucose and maternal hemoglobin A1 values of the latter group experiencing spontaneous abortions were significantly higher (p less than 0.001) when compared with women receiving preconceptional diabetologic counseling whose pregnancies continued beyond 22 weeks' gestation. The frequency of spontaneous abortions among patients not seen before pregnancy was significantly higher (p less than 0.001), in contrast to attending women, whose rate represented the normal rate in the general population. We confirm the evidence accumulated in the recent literature that poor metabolic control around conception and in the early weeks of pregnancy may be the determining factor favoring abortion.