We conducted a genome-wide association meta-analysis (GWAMA) of mothers of naturally conceived dizygotic (DZ) twins (8,265 cases, 264,567 controls) and of independent DZ twin offspring (26,252 cases, 417,433 controls). Participants were carefully screened to exclude twins born after use of Medically Assisted Reproduction (MAR) technologies. Over 700.000 participants from Australia, New Zealand, Europe and USA were included. Genetic association analyses by cohort for being a mother of DZ twins and being a DZ twin were combined by fixed-effects inverse variance methods as implemented in METAL software meta-analysis. By enlarging sample size from previous efforts, both by including new cohorts and by combining through meta-analyses with independent DZ offspring, we identified 4 genome-wide significant loci, in addition to FSHB (follicle stimulating hormone subunit beta ) and SMAD3 (SMAD family member 3). Two novel loci GNRH1 (gonadotropin releasing hormone 1) and FSHR (follicle stimulating hormone receptor) have well-established roles in female reproduction. The 2 further novel genes were implicated by gene level enrichment analyses. Both ZFPM1 (Zinc Finger Protein, FOG Family Member 1) and IPO8 (Importin 8) have not previously been implicated. Significant genetic correlations were found with multiple aspects of female reproduction and body size as well as with a recent GWAMA of female infertility. The 26 top SNPs from our GWAMA in European-origin participants predicted the crude twinning rates in 47 non-European populations (r=0.23 between risk score and population prevalence, p=.058) indicating that GWAS are needed in African and Asian populations to explore the causes of their respectively high and low DZ twinning rates. A Phenome-wide association study (PheWAS) based on the GWAMA, linked SNPs predisposing to DZT with reduced risk of both ovarian dysfunction and polycystic ovaries.