Introduction
Recurrent pregnancy loss (RPL) is defined as two or more pregnancy losses before 20 weeks with a 1-3% incidence rate from ESHRE in 2018 [1]. In addition to unexplained miscarriage accounting for 50% of RPL [2], other factors, such as female age, uterine anomalies, endocrine disturbances, autoimmune antibodies, thrombophilia and chromosomal aberrations, are known risks of RPL[3]. Parental chromosomal aberrant couples, called carriers, account for 2-4% of the recurrent pregnancy loss population[4, 5]. Unbalanced gametes generated from chromosomal aberrant parents are associated with RPL, but no direct causal relationship has been proven between the parental chromosome and RPL, because foetal chromosomal abnormalities of abortion tissue are common not only in carriers but also in noncarriers[6, 7]. No consensus exists regarding the difference in pregnancy outcomes between carriers and noncarriers with RPL to date. Additionally preimplantation genetic diagnosis (PGD) has been performed increasingly at several centres worldwide, and has been applied for patients with chromosomal aberrations. Can PGD improve live birth rates compared with natural conception or expectant management (NC or EM) in RPL carriers? However, no evidence has substantiated the reproductive outcome benefit of these carriers after EM or after PGD. Recurrent pregnancy loss with abnormal chromosomes is a frustrating challenge for clinicians because no convincing evidence of effective therapy exists for these patients. The present study aimed to systematically analyse the best evidence from the efficacy literature to illustrate these associative questions.