Contribution of overweight and obesity to the occurrence of adverse pregnancy outcomes in a multi-ethnic cohort: population attributive fractions for Amsterdam

Objective To estimate the contribution of pre-pregnancy excessive weight to the occurrence of adverse pregnancy outcomes and to detect the differences in these contributions between different ethnic groups. Design Prospective multi-ethnic community-based cohort study. Setting The prevalence of excessive weight is increasing and in general higher in immigrant groups in many industrialised countries. Maternal excessive weight, like smoking during pregnancy, is an important risk factor for adverse pregnancy outcomes. Population A total of 8266 pregnant women, living in the Netherlands, were included in the ABCD study between January 2003 and March 2004. Methods After applying the exclusion criteria, the analysis included 7871 pregnancies. Binomial log-linear regression analyses were performed to estimate relative risks (RRs) expressing the association between overweight/obesity and small-for-gestational-age (SGA), large-for-gestational-age (LGA), preterm birth (PTB; <37 weeks of gestation) and extreme PTB (<32 weeks of gestation), controlling for parity, maternal age, education level and smoking. Next, the RRs were used to estimate population attributive fractions (PAF) for Amsterdam and separately for several ethnic groups. Main outcome measures The RRs and PAFs. Results The PAFs for overweight/obesity were: SGA -4.9%, LGA 15.3%, PTB 6.6% and extreme PTB 22.0%. In absolute terms, this corresponds to -47 SGA infants, 126 LGA infants, 35 PTB and 20 extreme PTB per year in Amsterdam. Except for SGA, these PAFs were higher than those for smoking (6.2%, -3.9%, 5.5% and 10.6%, respectively). The contribution of overweight/obesity to LGA and PTB was higher in non-Western immigrant groups. Conclusions Overweight/obesity has become an important contributor to the occurrence of adverse pregnancy outcomes in Amsterdam. For most outcomes, these contributions are larger than those for smoking. Development of special obesity prevention programmes for young women is required, especially focused on immigrant groups.