Twenty-one SNPs selected from the discovery meta-analysis were taken forward for either custom genotyping or analysis in studies with newly available genome-wide or CardioMetabochip array genotyping (the latter included 6 of the 21 SNPs). If the index SNP was unavailable, this was substituted with a closely correlated proxy from the HapMap (see Supplementary Table 12). Of a total of 25 available studies (maximum combined n = 42,519), there were 14 studies with custom genotyping (n = 22,569 individuals), of which 2 studies later acquired additional in silico data (ALSPAC (Replication), n = 6,315 with GWA; NFBC1986, n = 4,897 with CardioMetabochip). Eight further studies had in silico GWA data (n = 13,992 individuals) and 3 further studies had in silico CardioMetabochip array data (n = 5,958 individuals). Details of these studies are presented in Supplementary Table 3. Since resources for custom genotyping were limited, the total number of analyzed individuals varied by SNP, with 3 SNPs analysed in available in silico studies only (see Supplementary Table 2). Within each study, we analysed the association between each available SNP and birth weight z score in the same way as described above for Stage 1 studies.
