Affects approximately 5% of pregnant women, of whom over 80% have gestational diabetes and the rest had pre-existing DM of either type.
NICE recommends screening the following high-risk groups:
- BMI >30
- Previous baby 4.5 kg or over
- Previous gestational diabetes
- 1st-degree relative with diabetes
- Ethnic minorities with increased risk diabetes
Screening should be done with an oral GTT between 24 and 28 weeks. The exception is with women with previous gestational DM, who need more careful checking; they should be offered an oral GTT as soon as possible after booking, with a second between 24 and 28 weeks if the first is normal. As an alternative, they can be offered the option of self-checking their blood glucose from booking onwards (no details given on this).
Diagnostic thresholds for diabetes on the 2015 NICE guidelines are fasting glucose of 5.6 or greater, and/or 2-hour post-GTT of 7.8 or greater. (Which can be handily remembered as 5678, I suppose.) Note that these are different from both the 2008 guidelines and the WHO guidelines.
Women with gestational diabetes should be referred urgently to a specialist clinic and seen within 1 week. Women with fasting glucoses of 7.0 or greater should be started on insulin directly (plus or minus metformin).
Glycosuria can appear transiently in pregnancy in the absence of diabetes (due to changes in renal absorption), but women who have glycosuria of 2+, or of 1+ on more than one occasion, should be formally tested for gestational diabetes.
Some women can manage their glucose levels successfully with diet and exercise, but up to two-thirds require treatment with medication (metformin and/or insulin).
Women needing medication have to self-monitor at least four times daily – at least seven times if on hypoglycaemics. Aim to keep glucose levels above 4. Women will be at high risk of hypoglycaemia due to both the strict glucose control required and the metabolic changes of pregnancy. They should have quick-acting glucose available (not milk or chocolate – the fat slows down absorption) as well as glucagon, which partners should be trained to give in an emergency.
Insulin requirements may double; don’t be surprised if women in the latter half of pregnancy require much more frequent prescriptions (though this may plateau at around week 36). These will drop back to usual after birth, or possibly lower than usual in breastfeeding women.
HbA1c, despite its limitations in pregnancy, is of some use in estimating risk of complications, and should be checked at least once each trimester.
Women with Type 1 DM are at increased risk of ketosis, as pregnancy physiologically mimics a state of starvation. Ketone levels should be checked in any pregnant woman with Type 1 DM who becomes unwell, and if the results indicate ketoacidosis she should be admitted immediately to critical care. Ketosis can develop at normal blood glucose levels in pregnancy.
Women with pre-existing diabetes who are planning a pregnancy should ideally, where possible,
- be referred to a specialist clinic for advice
- aim for an HbA1c <48 mmol/l (often not possible; any progress towards this is nevertheless going to reduce risk). Their target BMs during the day should be the same as for anyone with Type 1 DM.
- take 5 mg folic acid daily
- stop any medications contraindicated in pregnancy
Obviously this ideal state of affairs often doesn’t happen. When a woman with diabetes presents already pregnant, refer urgently, start the folic acid, stop meds where needed, and request a urinary ACR.
Women with gestational DM should have a fasting glucose 6 – 13 weeks after birth and then annual HbA1c thereafter. Diabetes prevention measures (diet, exercise, weight loss), should be strongly advised.