Risks of pregnancy complications associated with obesity, according to five studies. Risks expressed as odds ratio (95% confidence interval) or percentage (US cohort study)

Study (by complication)	Risk of complication
Miscarriage
Meta-analysis (13 studies) in women with normogonadotrophic anovulatory infertility examined patient predictors for outcome of ovulation induction with gonadotrophins: obese v non-obese women	Rate of spontaneous miscarriage (3.05 (1.4 to 6.4))
Fetal anomalies
Case-control study of major birth defects in about 40 000 births/year in 1993-97	Spina bifida 3.5 (1.2 to 10.3), omphalocele 3.3 (1.0 to 10.3), heart defects 2.0 (1.2 to 3.4)
All complications
UK study of 287 213 singleton pregnancies (62% normal weight, 28% overweight, 11% obese): obese versus normal weight	Gestational diabetes 3.6 (3.25 to 3.98), pre-eclamptic toxaemia 2.14 (1.85 to 2.47), macrosomia 2.36 (2.23 to 2.50), intrauterine death 1.4 (1.14 to 1.71), induction of labour 1.70 (1.64 to 1.76), caesarean section 1.83 (1.74 to 1.93), postpartum haemorrhage 1.39 (1.32 to 1.46), genital infection 1.3 (1.1 to 1.6), urinary tract infection 1.4 (1.2 to 1.6), wound infection 2.2 (2.0 to 2.6)
US cohort study of 613 morbidly obese and 11 313 non-obese women	Gestational diabetes 14% v 4%, pre-eclamptic toxaemia 14% v 3.2%, fetal distress 12% v 8%, caesarean section 31% v 15%, endometritis 9% v 3%
Case control study from Middle East of 159 obese women and 300 women of normal weight, matched for age and parity	Gestational diabetes mellitus 26 (9 to 73), pregnancy induced hypertension 11 (5 to 24), caesarean section 1.9 (1.1 to 3.4), macrosomia 3.3 (2 to 5.5)