Biguanide — Gestational Diabetes / PCOS
Pregnancy: Used in gestational diabetes and PCOS; long-term safety data reassuring but continue discussion with patient
Metformin (Gestational Diabetes / PCOS)
Brand names: Glucophage
Adult dose
Dose: 500-2000 mg/day in divided doses
Route: Oral (with meals)
Frequency: Two to three times daily
Max: 2500 mg/day
Gestational diabetes: NICE NG3 — metformin first-line pharmacological therapy when diet alone fails, before or alongside insulin. PCOS: off-label for ovulation induction and menstrual regulation
Paediatric dose
Dose: Not applicable in obstetric context N/A/kg
Route: Oral
Frequency: N/A
Max: N/A
Maternal medication
Dose adjustments
Renal
Avoid if eGFR under 30; reduce dose if eGFR 30-44; review at eGFR under 45
Hepatic
Avoid in hepatic impairment — lactic acidosis risk
Paediatric weight-based calculator
Maternal medication
Clinical pearls
- NICE NG3 (Diabetes in Pregnancy): Metformin crosses the placenta — long-term follow-up data from MiG trial shows no adverse fetal outcomes; however, some centres avoid and use insulin only due to limited long-term neonatal data
- PCOS: reduces insulin resistance, restores menstrual cycles in oligomenorrhoea, and improves ovulation rates — off-label use supported by ESHRE/ASRM PCOS guidelines
- Ovarian hyperstimulation syndrome (OHSS) prevention in PCOS: metformin during IVF stimulation reduces OHSS risk
- GI side effects: start at 500 mg once daily and titrate slowly over 4-8 weeks to improve tolerance; modified-release formulation better tolerated
- Post-partum: continue in women with T2DM or pre-diabetes; review in gestational diabetes — usually stopped after delivery as glucose normalises
Contraindications
- eGFR under 30
- Hepatic impairment
- Iodinated contrast media within 48 hours
Side effects
- GI upset (nausea, diarrhoea, abdominal discomfort — most common, usually transient)
- Lactic acidosis (rare, serious — predisposing factors: renal/hepatic impairment, dehydration)
- Vitamin B12 deficiency (long-term use)
- Metallic taste
Interactions
- Iodinated contrast (hold metformin before IV contrast; restart 48 hours after if renal function stable)
- Alcohol (increases lactic acidosis risk)
Monitoring
- Blood glucose (fasting and post-prandial)
- HbA1c
- eGFR annually
- Vitamin B12 (if long-term use)
Reference: BNFc; BNF 90; NICE NG3 (Diabetes in Pregnancy); MiG Trial (Rowan et al. NEJM 2008); ESHRE/ASRM PCOS Guidelines 2023. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.