Episodic hyperglycaemia in pregnant women with well‐controlled Type 1 diabetes mellitus: a major potential factor underlying macrosomia

Abstract

Aims To test the common assumption that pregnant women who are sufficiently motivated to achieve very good HbA_1c levels will record home blood glucose data accurately. Methods A new device was used to download information from electronic blood glucose meters to assess the extent of selectivity in patient glucose diary‐keeping. Results In an index case, a woman with excellent ambient HbA_1c (5.9%; upper limit of normal 6.1%) was observed to have 68% of preprandial blood glucose readings above the target range of 3.5–6.5 mmol/l and a mean (± sd) level of 8.9 ± 3.9 mmol/l in the corresponding period. No such impression was conveyed by the home monitoring diary. Six pregnant women with well controlled Type 1 diabetes (mean HbA_1c 6.6 ± 0.2%) exhibited between 42 and 68% of preprandial readings above the target range. Conclusions The frequency of hyperglycaemia has hitherto been underestimated in well controlled pregnant women whose near‐perfect home monitoring record is apparently corroborated by near‐normal HbA_1c levels. These observations provide a hypothesis for understanding of the disappointing continuance of macrosomia despite excellent HbA_1c levels throughout pregnancy.