Risk Factors and Outcomes of Recurrent Pregnancy Loss in Japan

Aim To clarify the risk factors and pregnancy outcomes for each risk factor of recurrent pregnancy loss (RPL) in Japan. Methods Using a prospective RPL database collected from 16 facilities in Japan, the prevalence of risk factors for RPL, their treatments and pregnancy outcomes were examined. Results Of 6663 patients registered in our database, 5708 patients had RPL. All examinations for risk factors were performed for 1340 patients (23.5%). The prevalences of positive antiphospholipid antibodies (aPL), malformation of the uterus, thyroid dysfunction, parental karyotype abnormality, factor XII deficiency, protein S deficiency and unknown risk factors were 8.7%, 7.9%, 9.5%, 3.7%, 7.6%, 4.3% and 65.1%, respectively. Although factor XII deficiency and protein S deficiency are not recognized as risk factors for RPL in general, low‐dose aspirin (LDA) or unfractionated heparin + LDA therapy improved live birth rates. In transiently aPL‐positive patients, the live birth rate with LDA therapy was similar to that with heparin + LDA. For unknown risk factors of RPL, the live birth rate in normal fetal karyotype in the none treatment group was similar to that in all other treatments group (81.3% vs 86.0%). Of 5708 RPL patients, pregnancy outcomes were known for 2261 patients and 1697 patients (75.1%) had at least one live birth. Conclusion The risk factors and pregnancy outcomes for each risk factor of RPL are useful for clinicians and patients. Factor XII deficiency and protein S deficiency may be risk factors of RPL.