1 Department of Obstetrics and Gynecology, University Medical Center Utrecht, Utrecht, The Netherlands.
2 Department of Obstetrics and Gynecology, Leiden University Medical Center, Leiden, The Netherlands.
3 Department of Obstetrics and Gynecology, University Medical Center Utrecht, 3508 AB, Utrecht, The Netherlands. Electronic address: m.n.bekker-3@umcutrecht.nl.