Re: Pregnancies in women with Turner syndrome: A retrospective multicentre UK study

Sir, We are grateful to Tomoyuki Kawada for his interest in our article about tobacco exposure in pregnancy and neurodevelopment at 10 years of age among infants born extremely preterm. They identify several characteristics of our study in their opening paragraph, including the high coprevalence of tobacco exposure in pregnancy and neurological disorders in infants born extremely preterm. In their second paragraph they address the issue of ‘mechanism’. As conservative and cautious epidemiologists we are reluctant to invoke a mechanism. We describe relationships and try to show to what extent they are statistically and biologically relevant. Nothing more. Their third concern appears to be the potential confounding resulting from relationships among low socioeconomic status, maternal overweight and obesity status, and epilepsy. We have tried to tease these apart as best we could. We certainly agree that this topic is worthy of continued prospective study in contemporary cohorts, including further characterisation of tobacco use by intensity and pattern, in addition to the concurrent use of other prevalent substances in pregnancy, which may impact child neurodevelopment. C ON F L IC T OF I N T E R E S T S None declared. Completed disclosure of interests form available to view online as supporting information.