30th June 2023

Diabetes

Relative insulin resistance and reduced glucose tolerance are normal for pregnancy. The placenta secretes anti-insulin hormones and so insulin production increases to overcome these changes. Low fasting glucose and high postprandial blood glucose are common.

Gestational diabetes

Gestational diabetes (GDM) is diabetes with the onset or first recognition in pregnancy; although the majority of these cases will be gestational diabetes, pregnancy can be the first time pre-existing diabetes is diagnosed.

Women with any risk factors for GDM should be screened by glucose tolerance testing between 24-28/40. Women with previous GDM should be screened as soon as practicable after booking the pregnancy. These risk factors for GDM are BMI >30, previous macrosomic baby >4.5kg, previous GDM, family history of diabetes, and ethnicity with a high prevalence of diabetes. Persistent glucosuria is also an indication for testing.

Testing should be performed using a 2-hour 75g oral glucose tolerance test, with fasting and 2-hour blood glucose levels taken. If positive, an HbA1c should be taken to screen for pre-existing diabetes.

All women who are diagnosed with gestational diabetes should be advised on how diet and exercise will improve their condition. If the fasting glucose level is under 7mmol/litre in the absence of fetal macrosomia, a trial of diet and exercise is offered.

Metformin and/or insulin should be offered to women with a fasting blood glucose of >7mmol/litre or between 6-6.9mmol/litre if there is fetal macrosomia or polyhydramnios.

Target levels for all women with diabetes in pregnancy are:

• Fasting: 5.3mmol/L
• 1hr after meals: 7.8mmol/L
• 2 hours after meals: 6.4mmol/L

Capillary plasma glucose should be kept above 4mmol/litre.

Growth scans are offered every four weeks from 28/40, with care being undertaken by joint diabetes and obstetric clinics. Women with uncomplicated gestational diabetes should be offered delivery by 40+6/40. Blood glucose measurements should be performed hourly in labour to keep levels between 4-7mmol/L.

Women with GDM should stop all blood glucose lowering therapy at delivery. Follow-up is with a fasting glucose or an HbA1c between 6-13 weeks post-delivery and an annual HbA1c thereafter.