Influence of pre-pregnancy BMI on gestational outcome: a retrospective study

Introduction: Analyse the association between pre-pregnancy BMI and different items of gestational outcome.

Materials and methods: A retrospective study of 14'287 patients with singleton pregnancies delivering at a Swiss perinatal centre including 1'046 obese patients with a BMI > 30.0 (8.7%) and 13'241 patients with a BMI up to 29.9 from 2005 to 2015. Women were divided in four groups (underweight, normal weight, overweight and obese) according to WHO obesity classification. Following items were analysed: mode of delivery, gestational age, birth weight and maternal pregnancy complications.

Results: Pre-existing obesity has an impact on the mode of delivery. Especially obese primiparous have a higher risk for a secondary C-section than normal weight primiparous (OR 2.4). Even multiparous with a history of vaginal delivery have a higher risk for a secondary C-section (OR 1.8). Both obese primiparous and multiparous have a higher risk of macrosomia at term (OR 1.8), of developing gestational diabetes (OR 4.9) and pregnancy induced hypertonia (OR 5.9). There is no difference in the rate of premature birth.

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Conclusion: Both primiparous and multiparous should be motivated to attain a normal BMI before pregnancy. In addition to all other negative impacts of obesity young women should be informed of the risks associated with gestational outcomes and pregnancy complications. Pregnant women with a BMI > 30.0 should be motivated to prevent a gain in weight more than 8 kg.