Inclusion Criteria:  (1) patients who were treated in the outpatient department of Zhejiang University Women's Hospital from January 1, 2018 to December 31, 2020; (2) With history of once spontaneous abortion; (3) Having fertility requirements but not yet pregnant; (4) Those who are willing to give birth again during the study period.  Exclusion Criteria:  (1) Previous history of multiple spontaneous abortion, inevitable abortion or missed abortion; (2) Re pregnancy after abortion, now in pregnancy or delivered; (3) Patients who are participating in other clinical studies or those who refuse to participate in the study; (4) The researchers consider that she is not suitable to participate in this study for other reasons.