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

AIMS: To test the common assumption that pregnant women who are sufficiently motivated to achieve very good HbA1c 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 HbA1c (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 HbA1c 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 HbA1c levels. These observations provide a hypothesis for understanding of the disappointing continuance of macrosomia despite excellent HbA1c levels throughout pregnancy.