Introduction
Pregnancy loss is a common obstetric complication leading to significant economic and emotional burden for affected families and the health care system.1 Women experiencing pregnancy loss are at increased risk of its recurrence, as well as other obstetric complications in subsequent pregnancies.2-4 Recurrent pregnancy loss occurs in 1-2% of couples who are trying to conceive.5,6 Recurrent pregnancy loss is commonly defined by the American Society of Reproductive Medicine as ≥ 2 pregnancy losses,7 and because the etiologies of pregnancy loss vary across gestational age, more specific characterizations of losses by gestational age have been recommended.8 Thus, pregnancy loss can be divided into three epochs: embryonic loss (<10 weeks’ gestation), fetal death (10-20 weeks’ gestation) and/or stillbirth (≥20 weeks’ gestation).
Though known and suspected causes of recurrent pregnancy loss include autoimmune, endocrine, uterine, and genetic abnormalities, over half are not currently explained by these mechanisms.9-11 Among genetic abnormalities, the most clearly associated with recurrent pregnancy loss is parental balanced translocation.12However, this abnormality is found in fewer than 5% of couples with recurrent pregnancy loss.13,14 Embryonic losses (<10 weeks) are often due to spontaneously-occurring aneuploidy which result from errors in maternal meiosis.7 Such cases are identified by karyotype but often have a low recurrence risk.15
Many previous studies of pregnancy loss did not distinguish gestational ages of the losses and focused on sporadic losses <10 weeks.7,16 However, systematic evaluation of unexplained embryonic loss, fetal death and stillbirth cases is critical to identify genetic abnormalities that are not detected by karyotype and may influence specific developmental epochs. Whole-genome sequencing (WGS) allows identification of previously unrecognized genetic abnormalities (e.g., copy number changes, single gene mutations, single nucleotide variants [SNVs] and/or structural variants [SVs]) that may cause unexplained pregnancy loss.10 Few studies included DNA from parents, losses, and live births. The power of WGS technology can be further amplified by examining DNA from family pedigrees to clarify autosomal-dominant transmission of risk alleles and prove whether variants appeared in the germline of the probands asde novo , which will be critical for interpretation and determination of genetic causes of recurrent and sporadic pregnancy loss.
Therefore, we conducted a pilot WGS study of four families with several unexplained pregnancy losses, which included embryonic loss, fetal death and stillbirth. We applied best practice standards of WGS and analyses to identify variants using DNA from couples and their products of conception (pregnancy losses and live births). We hypothesized that pathogenic SNVs and/or SVs that may be inherited or occur de novoin the offspring will be relevant to the losses.