Analysis of chromosome test results of 24,175 miscarried fetuses in Japan from 2000 to 2021.

Background: Fetal chromosome abnormalities, the most common cause of spontaneous abortion, were investigated pre-1980s. In recent years, chromosome testing has been outsourced to testing companies in Japan, and there have been few epidemiological studies of chromosome testing of miscarried fetuses on a nationwide scale.

Methods: We analyzed the chromosome test data of SRL, Inc., one of the largest clinical laboratories that has collected tissue specimens of products of conception derived from miscarried fetuses from hospitals throughout Japan from 2000.

Results: We collected and analyzed 24,175 cases, among which 8,726 (36.1%) were normal chromosomes, 1,298 (5.4%) were sex chromosome abnormalities, 9,735 (40.3%) were autosomal trisomies, 73 (0.3%) were autosomal monosomies, 840 (3.5%) were ploidy, 512 (2.1%) were chromosome structural abnormalities, and 2,991 (12.4%) were mosaics. The frequency of autosomal trisomy increased at the older maternal ages. By chromosome number, trisomies 22, 16, 21, and 15 were associated with advanced maternal age, but trisomies 13, 14, and 18 were not associated with advanced maternal age. The presence or absence of this maternal age effect was correlated with the chromosome segregation being due to maternal meiosis I or meiosis II. For the sex ratios of the fetuses, we focused on trisomies 22, 21, 18, 16, 15, 14, and 13, and found that only trisomy 16 was significantly more frequently seen in female fetuses.

Conclusion: The findings of this study provide insights into the basic understanding of miscarriage and will be useful in counseling and medical education.