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Association of pre‐pregnancy weight and birth defects

We thank Dr Peek and Dr Nanan for their comment on our paper on the association of pre-pregnancy weight and birth defects. They raise two important issues. First, that identification of all cases of birth defects, particularly those that end in termination of pregnancy before 20-week gestation, is difficult. Secondly, identification of fetal anomalies by ultrasound examination is difficult in women who are obese. Peek and Nanan wonder whether these two issues may have led to many birth defects not being identified before 20-week gestation in obese women in our study. Hence, with termination of pregnancy being less likely for these women, this could have led to an overrepresentation of obese women in the group of cases with birth defects in our study. We do not believe this to have occurred in our study. We identified cases from the WA Birth Defects Registry, which has close to complete ascertainment of terminations of pregnancy for fetal anomaly. We acknowledge the less complete ascertainment from some other states, shown clearly for neural tube defects in a recent publication from the National Perinatal Statistics Unit. Furthermore, we have re-examined our data on outcome of the pregnancy (termination, stillbirth, live-birth) and body mass index for each of the birth defect groups in our study. A similar proportion of cases were stillborn, liveborn or terminations amongst obese women compared with non-obese women for each of the case groups – heart defects, facial clefts, limb