Screening women who had diabetes mellitus in pregnancy

Women who had diabetes mellitus in pregnancy (as defined in Diagnostic thresholds for hyperglycaemia in pregnancy (including gestational diabetes)) at the time of diagnosis may have had undiagnosed diabetes before pregnancy. They need individual assessment regarding the appropriate timing and method of testing for diabetes. All women who had diabetes mellitus in pregnancy should be clinically reviewed within 8 weeks of delivery.

Glycated haemoglobin (HbA1c) of 53 mmol/mol (7%) or more at the time of diagnosis of diabetes mellitus in pregnancy suggests undiagnosed diabetes before pregnancy. These women should continue to monitor their blood glucose concentrations after delivery. Self-monitoring may only be needed on 1 or 2 days per week, and usually continues for the first 8 weeks. However, if blood glucose concentrations are more than 7 mmol/L fasting or more than 10 mmol/L postprandially, early review by a multidisciplinary diabetes team is required. This should include testing of fasting venous blood glucose concentrations for a possible diagnosis of diabetes. See Tests to diagnose diabetes for information about testing to diagnose diabetes.

If a diagnosis of diabetes has not been made within 8 weeks of delivery, and the woman’s fasting blood glucose concentrations from self-monitoring are high, a fasting venous blood glucose concentration can be taken to test for diabetes. It is preferable for women who had diabetes mellitus in pregnancy to be diagnosed using fasting blood glucose concentrations rather than results from an oral glucose tolerance test. If the result of a fasting venous blood glucose concentration is consistent with a diagnosis of diabetes (7 mmol/L or more), the test should be repeated on another occasion to confirm the diagnosis. However, if the result is below the threshold for diabetes (less than 7 mmol/L), perform an oral glucose tolerance test.

If the oral glucose tolerance test is normal, it is recommended that the woman has a fasting venous blood glucose concentration and HbA1c measured every year, or an oral glucose tolerance test every 2 to 3 years; if further pregnancy is considered or planned, oral glucose tolerance testing is preferred. An oral glucose tolerance test should also be performed before any planned pregnancies.

If an HbA1c test is used for ongoing screening of women who had diabetes mellitus in pregnancy, consider the following when interpreting the result:

• if further pregnancy is considered or planned and the HbA1c is 37 to 46 mmol/mol (5.5 to 6.4%), additional testing with an oral glucose tolerance test is required to detect impaired glucose tolerance, so that it can be managed appropriately before conception
• if there is no likelihood of another pregnancy and the HbA1c is less than 48 mmol/mol (6.5%), ongoing screening for type 2 diabetes should follow the usual schedule for screening people at risk of developing type 2 diabetes (see Screening for type 2 diabetes in asymptomatic adults). Patients with an HbA1c of 42 to 46 mmol/mol (6.0 to 6.4%) may require additional testing to determine if they have impaired fasting glucose or impaired glucose tolerance; see Interpreting HbA1c diagnostic tests.

Do not use HbA1c for diagnosis of diabetes or monitoring blood glucose concentrations within the first 3 months after delivery. HbA1c will be falsely low because of the lower blood glucose concentrations during pregnancy (due to haemodilution of pregnancy), the increased red blood cell turnover and/or shorter red cell lifespan in pregnancy, and peripartum blood loss.