Does a body mass index greater than 25kg/m increase maternal and neonatal morbidity? A French historical cohort study.

OBJECTIVES

To evaluate, in a French multicenter cohort, the risk of C-section based on a high pre-pregnancy body mass index (BMI). Secondary objectives were to assess the risk of elective C-section, severe post-partum hemorrhage (>1L), severe perineal tears (3rd and 4th degree) and neonatal complications according to pre-pregnancy BMI.

STUDY DESIGN

This historical cohort study analyzed records from the French AUDIPOG perinatal database. Inclusion criteria were deliveries≥22 weeks (or with a birth weight≥500g). Women with BMI<18.5kg/m (n=31,766) were excluded. After these exclusions, the study sample included 314,851 women between 1999 and 2009. Patients were classified among four BMI subgroups (normal: 18.5-24.9kg/m, overweight: 25-29.9kg/m, class I and II obesity: 30-39.9kg/m and class III obesity:≥40kg/m). BMI was calculated using pre-pregnancy self-reported weight. Results were expressed as crude and adjusted relative risks (aRR).

RESULTS

A C-section occurred in 16.4%, 22.7%, 28.8% and 39.4% of normal BMI, overweight, obese and class III obese women, respectively (P<10). aRR of C-section increased with BMI: 1.26 [95%CI: 1.22-1.30] for BMI between 25-29.9kg/m; 1.39 [95%CI: 1.34-1.45] for BMI between 30-39.9kg/m and 1.72 [95%CI: 1.57-1.90] for BMI≥40kg/m; but not the elective C-section. Neonatal complications were more frequent with increasing maternal BMI (BMI 25-29.9: aRR=1.09 [95%CI: 1.06-1.12]; BMI 30-39.9: aRR=1.20 [95%CI: 1.16-1.25]; BMI≥40: aRR=1.33 [95%CI: 1.21-1.45]).

CONCLUSION

Our study confirmed that pre-pregnancy BMI is an important factor to consider because its elevation is associated with adverse obstetrical outcomes, especially cesarean delivery and neonatal complications.