[1] Vrije Univ Amsterdam, Med Ctr, Dept Obstet & Gynecol, NL-1081 HZ Amsterdam, Netherlands
[2] Univ Amsterdam, Acad Med Ctr, Dept Obstet & Gynecol, NL-1105 AZ Amsterdam, Netherlands
[3] Univ Amsterdam, Acad Med Ctr, Dept Clin Epidemiol, NL-1105 AZ Amsterdam, Netherlands
[4] Univ Adelaide, Robinson Res Inst, Sch Paediat & Reprod Hlth, Adelaide, SA 5005, Australia