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Diabetes in Pregnancy
Gestational diabetes (GDM) is one of the most common medical complications of pregnancy affecting 5-10% of women, and has multiple consequences for the mother and fetus if undetected and untreated. We have discussed screening for gestational diabetes in our antenatal care module. You will also cover this topic in detail in Case 5. Women who develop diabetes in pregnancy have nearly all the same risks of complications as women with preexisting diabetes before pregnancy. But what are the risk factors for developing gestational diabetes in pregnancy?
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- Family history of type 2 diabetes, gestational diabetes or glucose intolerance
- Personal history of gestational dibabetes or glucose intolerance
- Previous large for gestational age baby
- Previous poor obstetric history (eg stillbirth)
- Belonging to a high risk ethnicity e.g. Polynesian, Indian, Middle Eastern, Asian, Mäori or Australian Aboriginal
- Being overweight or obese
- Maternal age > 30 years
- Previous abnormal glucose tolerance test
- Multiple pregnancy
- Glycosuria
- PCOS
Adapted from Goh & Flynn. 2011. Examination obstetrics and gynaecology, third edition. Elsevier Australia.
In 2014 the national guideline on gestational diabetes was published, Screening, Diagnosis and Management of Gestational Diabetes in New Zealand: A clinical practice guideline which recommended doing a HBA1c on all pregnant women at booking to detect women with undiagnosed diabetes. As you will recall, we do this routinely on our booking bloods. A result >49mmol/mol is indicative of diabetes and these women should be referred to the diabetes service.
In spite of the national guideline there is controversy as to optimum management for women with HbA1c between 41-49. The PINTO trial, which has not yet been published, may help answer this question. Women with risk factors for diabetes should have a OGTT, rather than a polycose test, even if their booking HbA1c is normal. There is international debate about which threshold to use to diagnose gestational diabetes with OGTTs and in NZ we currently use ≥5.5mmol/L fasting, ≥9.0 mmol/L at 2 hours (NSSD). Results from the GEMS trial will inform what is the best diagnostic criteria for NZ.
When GDM is diagnosed, intervention with dietary advice, the bio-feedback of home blood glucose testing and medication (metformin and/or insulin) helps reduce the risk of fetal macrosomia, fetal hyperglycaemia and need of neonatal unit admission.
