1. Norwegian National Advisory Unit on Women's Health; Oslo University Hospital; Rikshospitalet Oslo Norway
2. Department is Institute of population based research; Cancer Registry of Norway, Institute of Population-based Cancer Research; Oslo Norway
3. Section of Reproductive Medicine; Oslo University Hospital; Rikshospitalet Oslo Norway
4. National Cancer Institute; Division of Cancer Epidemiology and Genetics; Hormonal and Reproductive Epidemiology Branch; Bethesda MD