1. Department of Obstetrics and Gynaecology Shandong Provincial Hospital Affiliated to Shandong University Jinan China
2. Department of Obstetrics and Gynaecology Linyi People’s Hospital Linyi China
3. Department of Obstetrics and Gynaecology Maternal and Child Health Care of Shandong Province Jinan China
4. The Laboratory of Placenta‐Related Diseases Key Laboratory of Birth Regulation and Control Technology of National Health and Family Planning Commission of China Jinan China
5. Department of Central Laboratory Shandong Provincial Hospital Affiliated to Shandong University Jinan China