The relationship between perinatal outcome and daily glucose profile throughout pregnancy was assessed in 31 White Class B through R pregnant diabetic women. The study population was divided into two groups on the basis of perinatal outcome: 20 patients (Group I) without neonatal complications; 11 patients (Group II) with at least one form of neonatal complications. The overall capillary blood glucose average levels of Group I (98.53 +/- 22.33 mg/dl) and of Group II (110.14 +/- 20.77 mg/dl) was significantly different (ANOVA p < 0.0001). From the first trimester of pregnancy Group I showed significantly lower mean glycemic levels for daytime, evening and night (Bonferroni test p < 0.05) than Group II and both presented daily glycemic profiles with very extensive excursions. During the second trimester the groups continued to maintain these differences in mean glycemic levels (Bonferroni test p < 0.05) but a daily glycemic rthythm with relative nocturnal hypoglycemia with closer fluctuations. In contrast, during the third trimester the two groups presented both a daily rhythm of glucose and glycemic values for daytime, evening and night not statistically different (Bonferroni test p < 0.06). The distribution of women according to glucose levels reached during the night showed a mode of distribution in both Group I and II collocated in a range 70-100 mg/dl. These findings suggest that an optimum perinatal outcome can be achieved only if the pre-pregnancy diabetic women can achieve a metabolic equilibrium during the second trimester which matches the daily excursions of glycemia present in a non-diabetic pregnant women avoiding individual episodes of night-time hypoglycemia.