Threshold values of maternal blood glucose in early diabetic pregnancy -: prediction of fetal malformations

Background. The prevention of congenital malformations in the newborns of diabetic mothers still constitutes one of the main problems in this group of patients. Aim. The aim of this study was to analyze the prevalence of fetal malformations in diabetic pregnancies, as well as detection of the cut-off points for the first-trimester glycemia levels, relating to diabetes-induced fetal malformations. Methods. The data for analysis were collected retrospectively from the case histories of diabetic pregnant women and their newborns, treated in our departments. For the evaluation of maternal diabetes control, the whole-day glycemia profiles as well as glycated hemoglobin (HbA(1C)) levels were registered. To establish the glucose cut-off values for malformations, we have used receiver operating characteristic (ROC) curves for fasting, 1-hr, and 2-hr postprandial glucose levels. To determine how metabolic control influences the risk of giving birth to a malformed infant, we followed 198 newborns of diabetic mothers and 4700 infants born of healthy mothers (control group). Results. We detected malformations in the infants of 8.6% (n = 17) of diabetic mothers and 3.8% of the control (odds ratio: 2.35, 95% CI = 1.40-3.96). We compared this group of diabetic patients to another diabetic pregnancy group, analyzed over a period of 1988-93 (n = 209), in which 13 newborns (6.2%) manifested congenital malformations (odds ratio: 1.41, 95% CI = 0.67-2.99) (the difference was statistically insignificant). HbA(1C) level during organogenesis was not significantly higher in women whose infants were malformed. We proved, however, that the risk of malformations was higher, when HbA(1C) value exceeded 9.3%. The malformation rate in diabetes classes D-H (according to White) was higher than in classes B and C, but the difference was not significant. A wide spectrum of anomalies has been observed in the newborns of diabetic mothers. Conclusions. Our results confirm the view that diabetic pregnancy, despite the improved metabolic control, is still a strong risk factor for alterations in fetal development, particularly in patients with a tendency to brittle glycemia during first trimester of pregnancy. It seems that keeping fasting glucose levels in first trimester below 5.8 mmol/l and postprandial glucose levels below 9.1 mmol/l can contribute to decreasing number of fetal malformations in pregestational diabetes mellitus (PGDM) pregnancy. The ROC curves appear to be useful and adequate tool for the analysis of factors influencing fetal development in diabetic pregnancy.