Forty‐eight‐hour first‐trimester glucose profiles in women with type 1 diabetes mellitus: a report of three cases of congenital malformation

Objective Despite modern methods of treatment and near‐normal HbA 1c levels, women with type 1 diabetes mellitus are still at risk of having an infant with a congenital malformation (CM). We hypothesised that HbA 1c levels are too gross a measure of glycaemic control and used a continuous glucose monitoring system (CGMS) to determine the diurnal glucose profiles during the first trimester of pregnancy. We present three cases of infants with a CM. Methods Fifty‐three women with type 1 diabetes used the CGMS for 48 h in the first trimester of pregnancy. Three of them gave birth to infants with a CM. HbA 1c levels were determined at the time of the CGMS measurement and 6 to 8 weeks later. Results The HbA 1c levels at the time of the CGMS measurement were 6.0, 6.5 and 7.8% (normal range 4.0–6.0%) in the three women. The 48‐h diurnal glucose profiles of these women showed a large variability with frequent hyperglycaemic episodes. Conclusions HbA 1c levels are too gross a measure of glycaemic control to identify women at risk of giving birth to an infant with a CM. Even in women with normal or near‐normal HbA 1c levels, the diurnal glucose profiles reveal intermittent hyperglycaemic episodes that may cause the CM. Copyright © 2006 John Wiley & Sons, Ltd.