[1] Univ Med Ctr Utrecht, Div Perinatol & Gynecol, Utrecht, Netherlands
[2] Univ Med Ctr Utrecht, Lab Clin Chem & Hematol, Utrecht, Netherlands
[3] Univ Med Ctr Utrecht, Julius Ctr Hlth Sci & Primary Care, Utrecht, Netherlands
[4] Univ Southampton, Div Human Dev & Hlth, Southampton SO16 5YA, Hants, England