Fig. 1From: Risk estimates of recurrent congenital anomalies in the UK: a population-based register studyDetails and derivation of the study population and sample. aEstimated from the mean percentage of first and second births in England and Wales during 1990 and 2000 [27]. bEstimated from the mean parity progression ratios for England and Wales during 1990 and 2000 [27]Back to article page