Insulin-dependent diabetic women without adequate glucose control have a higher spontaneous abortion rate when compared with the general population. The present study examined whether the increased rate of spontaneous abortions in insulin-dependent diabetic women was associated with poor glycemic control in the early postconceptional period or close to the abortive event itself. Measurements of glycohemoglobin A1 at eight to nine weeks' gestation provide retrospective indexes of glucose control during the early postconceptional period, whereas measurement of glycosylated serum albumin and serum protein at the same time reflects short-term glycemic control before the abortive event. This study evaluated 84 consecutive pregnancies occurring in 68 insulin-dependent diabetic women; 66 pregnancies progressed beyond 20 weeks with no malformation or death, and 18 pregnancies terminated in spontaneous abortions before 20 weeks' gestation. The mean glycohemoglobin A1 concentrations of women experiencing spontaneous abortions were significantly greater than that of women who did not abort (P less than .05). In contrast, maternal glycosylated proteins and glycosylated albumin concentrations did not differ between groups. The authors suggest that poor control of diabetes in the early conceptional period, rather than that just before abortion, increases the risk of spontaneous abortion.