Triploid dizygotic twin pregnancy: resolving meiotic error using SNP microarray

Triploidy is a common cause of first trimester pregnancy losses, but the underlying meiotic mechanism is often difficult to resolve using standard approaches. We report an extremely rare case of a dizygotic triploid twin pregnancy in which both fetuses demonstrated triploidy and evaluate the clinical utility of single nucleotide polymorphism (SNP) microarray to determine the origin and timing of the meiotic error. Products of conception (POC) from a twin pregnancy underwent pathological review, short tandem repeat (STR) analysis, and SNP microarray analysis. Pathology demonstrated a dichorionic twin pregnancy with two distinct embryos. SNP microarray identified triploidy in both fetuses (Twin A: 69,XXY; Twin B: 69,XXX). STR analysis supported a digynic origin for both twins, but was insufficient to determine the state of meiotic error. SNP analysis demonstrated a pattern of X chromosome pericentromeric homozygosity and telomeric heterozygosity consistent with a maternal meiosis II error with prior recombination in Twin A. The meiotic origin was unable to be determined for Twin B due to three X chromosomes. This case highlights the value of SNP microarray in distinguishing meiosis I from meiosis II mechanisms in the presence of recombination. These findings are important to delineate the genetic susceptibility factors associated with triploidy and inform maternal follow-up.