digynic

Digynic is an adjective relating to digyny, a form of triploidy in which two maternal genomes are present in the embryo and a single paternal genome. It contrasts with diandric triploidy, in which the extra chromosome set is paternal.

Most digynic triploidy cases arise when an oocyte that has not undergone normal meiosis is fertilized by a single sperm, producing a diploid maternal genome and a paternal haploid genome (two maternal sets and one paternal set). In rare instances, the extra maternal genome results from duplication after fertilization.

Clinical features typically include severe fetal growth restriction and a relatively small, underdeveloped placenta compared with diandric triploidy, which often shows molar changes and an enlarged placenta. Fetal anomalies, when present, vary and can involve the craniofacial region and the central nervous system.

Diagnosis is usually based on fetal karyotyping from chorionic villus sampling or amniocentesis, supplemented by placental and fetal imaging. Noninvasive testing can suggest an aneuploid or triploid conception, but confirmation requires genetic analysis. Common triploid karyotypes for digynic pregnancies are 69,XXX and 69,XXY, reflecting two maternal chromosome sets and one paternal set.

Prognosis is generally poor for digynic triploidy, with most pregnancies ending in miscarriage or early infancy with severe congenital anomalies. Triploidy, including digynic forms, remains a rare condition, representing a small fraction of embryonic and fetal losses.