Published on in Vol 7 , No 4 (2019) :April
Preprints (earlier versions) of this paper are
available at
https://preprints.jmir.org/preprint/11664, first published
.

1 Erasmus MC, Department of Obstetrics and Gynecology, University Medical Center Rotterdam, Rotterdam, NL
2 Erasmus MC, Department of Biostatistics, University Medical Center Rotterdam, Rotterdam, NL