The objective of this single-center prospective observational study is to clarify the trend of maternal serum 25(OH)D levels before pregnancy and during pregnancy, and to explore the correlation between serum 25(OH)D levels and subsequent pregnancy outcomes of patients with abortion, so as to provide certain scientific evidence for finding the optimal serum level of 25(OH)D and optimal vitamin D supplementation to maintain a healthy pregnancy.

Women of reproductive age who meet the inclusion criteria are recruited from the outpatient department of Renji Hospital from November 2022 to December 2023. Subjects fill in the basic information at the outpatient clinic. After being included in the study, peripheral blood is collected before and during the first trimester (< 10 weeks), second trimester (22-24 weeks) and third trimester (32 weeks) to detect 25(OH)D, calcium, phosphorus and PTH levels. B-ultrasound examination is performed before pregnancy to record endometrial thickness, endometrial hemodynamic index (PI, RI and S/D) and uterine arterial hemodynamic index (PI, RI and S/D) during the luteal phase. Data are comprehensively analyzed through questionnaire form filling, laboratory examination, and clinical information records including pregnancy outcomes (final live birth rate, cesarean section rate, pregnancy loss rate, etc.), obstetric complications, and neonatal delivery information.

Inclusion Criteria:

• ≥20 years old
• The chromosome karyotype of the couple is normal
• Color ultrasound examination results indicated that there was no organic disease related to reproductive tract
• No serious complications of surgery and medicine
• Agree and voluntarily sign informed consent

Exclusion Criteria:

• There are contraindications to pregnancy
• the initiative to give up pregnancy
• Severe medical and surgical complications, for example, liver disease was defined as serum alanine aminotransferase [ALT] or aspartic aminotransferase [AST]>3 x upper normal limit [ULN] after repeated testing
• Concomitant malignant tumor, malignant tumor developed in the last 5 years (except for the skin squamous basal cell carcinoma that has been removed and considered cured). Subjects who developed malignant tumors more than 5 years ago should provide evidence of remission or cure. Subjects with a history of cervical cancer were eligible if they could demonstrate that their cervical cancer had been cone removed or cured within the past 3 years
• Known human immunodeficiency virus (HIV) positive and/or hepatitis B surface antigen or hepatitis C virus antibody positive at screening visit
• With a history of chronic infections such as mycoplasma, chlamydia, cryptococcus, and invasive fungal infections should be discussed with the principal investigator

Women of childbearing age

Women of childbearing age who are ready to become pregnant or already pregnant.