Gestational context
24 to 40 weeks
booking
12w
anatomy
24w
28w
36w
term
Maternal
- Glucose
- fasting under 5.3, 1 hour under 7.8, 2 hour under 6.7 mmol/L
- Weight and BP at each visit
- Weight and BP at each visit
- Ketones if unwell or restricting intake
- Ketones if unwell or restricting intake
- Postpartum
- repeat glucose tolerance at 6 to 12 weeks
Fetal
- Growth
- serial scans for macrosomia and polyhydramnios
- Movements
- ask at every visit
- Monitoring from 32 weeks if medication is needed
- Monitoring from 32 weeks if medication is needed
- Birth
- shoulder dystocia risk and neonatal hypoglycaemia planned for
Screening: two pathways, named
Diabetes Canada describes a preferred two-step approach and an alternative one-step approach. They use different thresholds and are not interchangeable; know which one your unit uses.
- Early screening (first visit) for those at high risk: prior GDM, BMI 30 or more, PCOS, prior macrosomic infant, high-risk ethnicity, corticosteroid use. An HbA1c of 6.5 percent or more or a fasting glucose of 7.0 or more in early pregnancy is pre-existing diabetes.
| Pathway | Test | Diagnostic thresholds |
|---|---|---|
| Preferred (two-step) | 50 g glucose challenge, non-fasting, 1-hour value | 11.1 mmol/L or more: GDM. 7.8 to 11.0: proceed to a 75 g OGTT. GDM if any one of fasting 5.3, 1-hour 10.6, 2-hour 9.0 or more. |
| Alternative (one-step) | 75 g OGTT, fasting | GDM if any one of fasting 5.1, 1-hour 10.0, 2-hour 8.5 or more (IADPSG thresholds). |
Diabetes Canada 2018. The alternative pathway diagnoses more patients; that is a known consequence of its thresholds.
Management
- Targets: fasting under 5.3, 1-hour postprandial under 7.8, 2-hour under 6.7 mmol/L.
- Nutrition and activity first; most reach targets without medication.
- Insulin is the standard when targets are not met (it does not cross the placenta). Metformin is an alternative after discussion; it crosses the placenta and long-term data continue to accumulate. Glyburide is used less.
- Fetal surveillance: growth scans in the third trimester; weekly monitoring from 36 weeks for those on medication, per local protocol.
- Delivery: offered at 38 to 40 weeks depending on control and treatment; earlier for poor control or macrosomia. Estimated fetal weight of 4500 g or more prompts a discussion of caesarean because of shoulder dystocia risk.
- Intrapartum: hourly glucose, insulin and dextrose infusion for those with significant insulin requirements. Neonatal hypoglycaemia is anticipated.
- Postpartum: stop insulin at delivery for GDM; 75 g OGTT at 6 weeks to 6 months; lifelong screening because the risk of type 2 diabetes is about 50 percent over the following decades.
Pre-existing diabetes
- Pre-conception care changes outcomes: HbA1c under 7 percent before conception, folic acid 5 mg, review of retinopathy and nephropathy, stop ACE inhibitors and statins.
- Congenital anomalies (cardiac, neural tube, caudal regression) track first-trimester control.
- Insulin requirements rise through the second and third trimester and fall abruptly after delivery.
- Aspirin from 12 to 16 weeks for preeclampsia prevention.
Check
A 50 g glucose challenge at 26 weeks returns 8.4 mmol/L. What next, on the preferred Canadian pathway?
On the modelPlacentaFundus and cornua