Gestational diabetes mellitus

Red Flags

Severe hyperglycaemia (random glucose >250 mg/dL or HbA1c >8.5%) at any antenatal visit — admit; insulin start; rule out pre-existing T1/T2DM^[1]
Diabetic ketoacidosis in pregnancy — emergency obstetric and endocrine; IV fluids, insulin, electrolytes; high fetal mortality risk^[1]
Polyhydramnios, large-for-gestational-age fetus, or maternal hypertension on GDM — escalate surveillance; consider earlier delivery and joint clinic^[1]
Postpartum persistent hyperglycaemia (fasting >100 or random >200 mg/dL) — likely undiagnosed type 2 diabetes; investigate and treat^[1]

First-line treatment

Interventions

Medical nutrition therapy^[1]
First-line for all GDM; carbohydrate counting and even distribution across meals and snacks; complex carbohydrates with low glycaemic index; protein and fibre to reduce postprandial peaks; total intake 1800–2400 kcal/day per BMI
Physical activity^[1]
Moderate aerobic activity 30 min/day, ≥5 days/week (walking, swimming, prenatal yoga); resistance training adjunct; tailor to obstetric risk profile
Glycaemic targets and pharmacotherapy if not met in 1–2 weeks of MNT^[1]
Targets: fasting <95 mg/dL, 1-h post-meal <140 mg/dL, 2-h post-meal <120 mg/dL. If fasting or post-meal exceeds target on ≥30% readings within 1 week — start pharmacotherapy
Fetal surveillance and delivery planning^[1]
Growth scan + amniotic fluid index from 28 weeks every 4 weeks; CTG weekly from 36 weeks if pharmacotherapy; deliver at 39 weeks if uncomplicated GDM, 38 weeks if poor control or macrosomia
Postpartum management^[1]
Stop GDM-specific therapy at delivery; encourage breastfeeding (reduces future T2DM risk); 75 g OGTT at 6–12 weeks; annual diabetes screening; preconception counselling for next pregnancy

First-line drug therapy

Drug	Class	Adult	Paediatric	Notes
Insulin (basal ± rapid)^[1]	Insulin therapy	Start NPH 0.1 U/kg/day at night ± rapid analogue 0.05 U/kg per meal; titrate by SMBG. Total dose typically increases 50% by third trimester	Not applicable — pregnancy use only	First-line pharmacotherapy in GDM; aspart, lispro, glargine, detemir all safe in pregnancy; teach self-administration and hypoglycaemia recognition
Metformin^[1]	Biguanide	500 mg PO BD, titrate to 1000 mg BD as tolerated	Not applicable — pregnancy use only	Acceptable alternative or adjunct to insulin (FOGSI 2023, NICE NG3); long-term safety good but crosses placenta — counsel on uncertainties; ~30–50% require insulin addition
Glyburide (alternative — not preferred)^[1]	Sulfonylurea	2.5–5 mg PO BD; max 20 mg/day	—	Less preferred than insulin or metformin due to neonatal hypoglycaemia and macrosomia signal; reserve for cases where insulin and metformin both unsuitable

Insulin (basal ± rapid)^[1]

Insulin therapy

Adult: Start NPH 0.1 U/kg/day at night ± rapid analogue 0.05 U/kg per meal; titrate by SMBG. Total dose typically increases 50% by third trimester
Paediatric: Not applicable — pregnancy use only

First-line pharmacotherapy in GDM; aspart, lispro, glargine, detemir all safe in pregnancy; teach self-administration and hypoglycaemia recognition

Metformin^[1]

Biguanide

Adult: 500 mg PO BD, titrate to 1000 mg BD as tolerated
Paediatric: Not applicable — pregnancy use only

Acceptable alternative or adjunct to insulin (FOGSI 2023, NICE NG3); long-term safety good but crosses placenta — counsel on uncertainties; ~30–50% require insulin addition

Glyburide (alternative — not preferred)^[1]

Sulfonylurea

Adult: 2.5–5 mg PO BD; max 20 mg/day
Paediatric: —

Less preferred than insulin or metformin due to neonatal hypoglycaemia and macrosomia signal; reserve for cases where insulin and metformin both unsuitable

Safety-net

Test blood sugar as instructed and bring the log to every appointment — adjustments depend on the actual numbers^[1]
Sick-day rules — keep eating and drinking small amounts; check sugar more often; if vomiting, ketones present, or sugars erratic — call for review^[1]
After delivery, do not skip the 6-week glucose test — this is when undiagnosed type 2 diabetes is caught early^[1]

Referral criteria

All women with GDMJoint obstetric and diabetes/endocrine clinic^[1]
Severe hyperglycaemia (HbA1c >8.5% or DKA)Endocrine same-day; consider admission^[1]
Macrosomia, polyhydramnios, or fetal compromise on surveillanceMaternal-fetal medicine and obstetrics^[1]
Persistent postpartum hyperglycaemia or HbA1c ≥6.5% at 6–12 weeksDiabetes clinic^[1]

Clinical summary

Screening, glycaemic targets, lifestyle and pharmacological therapy for hyperglycaemia first detected in pregnancy and postpartum follow-up.

References

1.FOGSI Guidelines for Gestational Diabetes Mellitus (2023); DIPSI Criteria; ADA Standards of Care in Diabetes — Section 15 Pregnancy (2023)