[Very preterm birth: should we be interested in maternal pre-pregnancy body mass index?]

Link between maternal body mass index (BMI) and pregnancy outcome is not clear.

To appreciate the impact of prepregnancy maternal BMI on very preterm birth (22-32 gestation's weeks).

To assess how maternal BMI does explain the mechanism of very preterm birth among live births.

Population-based study, including each mother with a live or stillborn baby was included in a geographically defined (Poitou-Charentes and Franche-comté, France) case-control study in 2004 to 2006. Leanness (BMI<18.5kg/m(2)) and overweight and obesity (BMI> or =25kg/m(2)) were defined according to World Health Organization's standards. Statistical analysis consisted in a polynomial regression on 832 mothers of very preterm babies and 431 mothers of full-term babies, taking account for confounders as maternal age, birth country, educational level, maternal work and smoking during the pregnancy.

Leanness is a risk factor for very preterm live birth (aOR=1.73 [1.12-2.68]), overweight is a risk factor for stillbirth. (aOR=1.71 [1.03-2.84]). Among mothers of live born babies, leanness is a risk factor for spontaneous preterm birth (aOR=2.12 [1.20-3.74]), whereas overweight is a risk factor for very preterm birth on medical decision due to gestational hypertension (aOR=2.85 [1.80-4.52]).

Morbid maternal stoutness before pregnancy is a complex risk factor for very preterm delivery. Women and couples should be informed and practitioners should be aware in order to prevent and manage this pathological status.