Tools for Practice Outils pour la pratique

#148 Has insulin met its match? Metformin for gestational diabetes

Is metformin a reasonable alternative to insulin in gestational diabetes mellitus (GDM)?

Compared to insulin, metformin results in 1kg less maternal weight gain and less severe neonatal hypoglycaemia for one in 22 babies, but results in earlier delivery by about one day. Other clinical outcomes are unchanged and long-term safety of metformin in GDM appears reassuring. Metformin is a reasonable option in GDM requiring treatment.  

CFPCLearn Logo

Reading Tools for Practice Article can earn you MainPro+ Credits

La lecture d'articles d'outils de pratique peut vous permettre de gagner des crédits MainPro+

Join Now S’inscrire maintenant

Already a CFPCLearn Member? Log in

Déjà abonné à CMFCApprendre? Ouvrir une session

  • Three systematic reviews1-3 of up to six open-label, Randomized Controlled Trials (RCTs) of metformin or insulin in 1,372 women: Over half of patients from one RCT.4 
    • Metformin women had 
      • Less weight gain (1.1kg).1  
      • Less gestational hypertension: 
        • 3.6% versus 6.8%, Number Needed to Treat (NNT)=32.2  
      • More preterm births (<37 weeks) 
        • 10.1% versus 6.7%, Number Needed to Harm (NNH)=30.2 
        • Delivered ~1 day earlier (95% Confidence Interval: 0.14–2.1 days).1 
      • No difference in caesarean section rates or obstetrical trauma.1 
    • Metformin babies had:  
      • No difference in birth weight, macrosomia, hypoglycaemia (<2.6 mmol/l), shoulder dystocia, low APGAR scores, admission to level 2 or 3 nursery or mortality.1-4 
      • Less severe hypoglycaemia (<1.6 mmol/l):  
        • 3.3% versus 8.1% NNT=22.4 
    • 77% women preferred metformin for subsequent pregnancy.4  
    • ~1/3 of metformin users eventually required insulin.1 
  • Long-term follow-up: >400 children from RCTs4,5  followed up to two years found children born to mothers on metformin (compared to insulin) had: 
    • Similar6 or clinically insignificant differences in height and weight (example ~0.7kg heavier and 1.7cm taller7) or development at 18 months.6
  • GDM occurs in ~5% of pregnancies.8 
    • Risk factors include: Family/previous history of GDMhigher body mass index, and certain ethnicities.8,9 
  • Recent guidelines recommend either universal screening for GDM,8 or screening only those with risk factors.9 
  • For women with ‘mild’ GDM, advising mothers of diagnosis and treating (compared to not advising nor treatingreduces perinatal complications (death, shoulder dystocia, bone fracture, and nerve palsy) from 4% to 1% (NNT=34) but increases the likelihood of labour induction and admission to neonatal nursery (both NNHs=10).10 
  • Although off-label in pregnancy,11 UK guidelines9 recommend (in order) diet and exercise, then metformin, then insulin 

Latest Tools for Practice
Derniers outils pour la pratique

#370 Antibiotics or no antibiotics for acute diverticulitis, that is the question!

Do antibiotics change clinical outcomes for patients with acute uncomplicated diverticulitis?
Read Lire 0.25 credits available Crédits disponibles

#369 Remind me, do medications that target brain amyloid improve my dementia?

Are amyloid-targeting monoclonal antibodies safe and effective for mild cognitive impairment or Alzheimer’s dementia?
Read Lire 0.25 credits available Crédits disponibles

#368 Sodium Restriction in Heart Failure: Beneficial or pouring salt in the wound?

Does sodium restriction improve outcomes in patients with chronic heart failure?
Read Lire 0.25 credits available Crédits disponibles

This content is certified for MainPro+ Credits, log in to access

Ce contenu est certifié pour les crédits MainPro+, Ouvrir une session

  • Darryl Huang MD
  • Michael R Kolber BSc MD CCFP MSc

1. Balsells M, García-Patterson A, Solà I, et al. BMJ. 2015; 350:h102.

2. Poolsup N, Suksomboon N, Amin M. PLoS ONE. 2014; 9(10):e109985.

3. Gui J, Liu Q, Feng L. PLoS ONE 2013; 8(5):e64585.

4. Rowan JA, Hague WM, Gao W, et al. N Engl J Med. 2008; 358(19):2003-15.

5. Ijäs H, Vääräsmäki M, Morin-Papunen L, et al. BJOG. 2011; 118(7):880-5.

6. Rowan JA, Rush EC, Obolonkin V, et al. Diabetes Care. 2011; 34(10):2279-84.

7. Ijäs H, Vääräsmäki M, Saarela T, et al. BJOG. 2015; 122(7):994-1000.

8. Committee on Practice Bulletins—Obstetrics. Obstet Gynecol. 2013; 122(2):406-16.

9. National Institute for Health and Care Excellence (NICE). Diabetes in pregnancy: management of diabetes and its complications from preconception to the postnatal period. Published: 25 February 2015. Available at: Last accessed: June 4, 2015.

10. Crowther CA, Hiller JE, Moss JR, et al. N Engl J Med. 2005; 352:2477-86.

11. Sanofi-aventis Canada. Product Monograph Glucophage® (Metformin Hydrochloride). October 22, 2014. Available at: Last accessed: June 23, 2015.

Authors do not have any conflicts of interest to declare.

Les auteurs n’ont aucun conflit d’intérêts à déclarer.