An umbrella review and meta-analyses 6 studied associations between adiposity and risk of any type of obstetric or gynaecological conditions. Of the 144 meta-analyses that included cohort studies, only 11 (8%) had strong evidence for 8 outcomes: adiposity was associated with a higher risk of endometrial cancer, ovarian cancer, antenatal depression, total and emergency caesarean section, pre-eclampsia, fetal macrosomia, and low Apgar score. Caesarean section was more common wtih BMI over 35 versus under 25 (emergency RR 1.63, 95% CI 1.40 to 1.89; 6 studies, 2301cases/18 749 cohort and total RR 2.00, 95% CI 1.87 to 2.15; 16 studies, 8413/62 277). Pre-eclampsia was more common in women with BMI 25 to 30 vs BMI under <25 (RR 1.70, 95% CI 1.60 to 1.81; 12 studies, 30 001/1 091 624) and with BMI over 35 vs under 25 (RR 4.14, 95% CI 3.61 to 4.75; 5 studies with 12 614/901 409). With BMI over 30 vs under 25, antenatal depression (RR 1.48, 95% CI 1.32 to 1.66; 23 studies, 6370/46 182) and gestational diabetes (RR 3.78, 95% CI 3.31 to 4.32; 30 studies, 7941/3 613 404) were more common.
A cohort study 7 included 16 609 women (with known BMI) who delivered singleton babies in a 5-year period (2013-2017). Compared to women of normal weight (n = 9778), obese women (n = 2207) had a higher risk of pre-eclampsia (adjusted odds ratio [aOR] 2.199, 95% CI 1.46 to 3.29), rectovaginal group B streptococcus colonization (aOR 1.299, 95% CI 1.14 to 1.47), induction of labor (aOR 1.593, 95% CI: 1.44 to 1.75), caesarean section (aOR 2.755, 95% CI 2.46 to 3.08), fetal weight≥4000 g (aOR 2.090, 95% CI 1.80 to 2.42) and admission to the neonatal intensive care unit (NICU) (aOR 1.341, 95% CI 1.12 to 1.59). No association was found with preterm birth, stillbirth or neonatal mortality.
A population-based cohort study 5 using Perinatal Database in Canada compared obstetric outcomes in women with extreme obesity BMI (pre-pregnancy BMI ≥ 50.0 kg/m2; n=71) and those with a normal BMI (pre-pregnancy BMI under 25 kg/m2; n=5717) between years 2002 and 2011. Extremely obese women were more likely to have caesarean section (60.6% vs. 25.0%) (adjusted OR 1.46; 95% CI 1.29 to 1.65), gestational hypertension (aOR 1.56, 95% CI 1.33 to 1.82), gestational diabetes (aOR 2.04; 95% CI 1.74 to 2.38), shoulder dystocia (aOR 1.51; 95% CI 1.05 to 2.19), length of hospital stay more than five days (excluding caesarean section) (aOR 1.42; 95% CI 1.07 to 1.89), birth weight≥ 4000 g (aOR 1.58; 95% CI 1.38 to 1.80), birth weight ≥ 4500 g (aOR 1.87; 95% CI 1.57 to 2.23), neonatal metabolic abnormality (aOR 1.50; 95% CI 1.20 to 1.86), stillbirth (aOR 1.68; 95% CI 1.00 to 2.82) and composite adverse outcome (aOR 1.57; 95% CI 1.35 to 1.83).
In a prospective population-based cohort study in Sweden 1, 3 480 women with morbid obesity (BMI > 40), and 12 698 women with a BMI between 35.1 and 40 were compared with normal-weight women (BMI 19.8-26). In the group of morbidly obese mothers was an increased risk of caesarean delivery (adjusted odds ratio 2.69; 95% confidence interval 2.49, 2.90) and of instrumental delivery (OR 1.34; 95% CI 1.16, 1.56).
In a retrospective analysis 2 of a total of 287 213 completed singleton pregnancies in London, England, 176 923 (61.6%) normal weight (BMI 20-24.9), 79 014 (27.5%) moderately obese (BMI 25-29.9) and 31 276 (10.9%) very obese (BMI≥30) women were included. Compared to women with normal BMI, delivery by emergency caesarean section was significantly more common in obese pregnant women (odds ratio for moderately obese 1.30, 99% confidence interval 1.25-1.34, OR for very obese 1.83, 99% CI 1.74-1.93).
An analysis of a large prospective multicenter database in the United States 3 included 16 102 patients: 3 752 control, 1 473 obese (BMI 30 to 34.9), and 877 morbidly obese (BMI 35 or greater). For nulliparous patients, the cesarean delivery rate was 20.7% for the control group, 33.8% for obese, and 47.4% for morbidly obese patients.
In a population-based study 4 126 080 deliveries between the years 1988 and 2002 in a university hospital in Israel were analysed. Of the mothers, 1769 (1.4%) were obese (BMI≥30) before the pregnancy. Higher rates of caesarean deliveries were found among obese parturients (27.8% vs. 10.8%; OR = 3.2; [95% CI 2.9, 3.5]; P < 0.001). After controlling for possible confounders the association between maternal obesity and caesarean section remained significant. No significant differences were noted between the groups regarding perinatal complications such as perinatal mortality, congenital malformations, shoulder dystocia and low Apgar scores.
Comment: The quality of evidence is upgraded by strong association and by the fact that all plausible confounding factors would have reduced the effect.
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