Correction to: BMC Pregnancy Childbirth 21, 568 (2021)

https://doi.org/10.1186/s12884-021-04017-8

Following publication of the original article [1], the authors reported an error in correspondence field of the PDF file. Corresponding affiliation in the bottom left corner of the first page for author Xiaokui Yang should be ‘Department of Human Reproductive Medicine, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing 100,026, China’.

The original article [1] has been updated.