Limited Availability of Short Tandem Repeat Genotype Testing in the United States for Diagnosis of Partial Hydatidiform Mole

The pathogenetic definition of a partial hydatidiform mole (PHM) is a diandric triploid gestation, thereby requiring short tandem repeat (STR) genotype testing for definitive diagnosis in formalin-fixed products of conception (POC) specimens. However, recent literature shows there is limited access to this test, even in high-income countries. Therefore, we hypothesized that in the United States, access to this test would be enriched in academic centers and commercial reference laboratories. We surveyed the Association for Molecular Pathology membership and directly queried selected commercial laboratories in the United States. The survey identified 13 laboratories (11 in academic centers, 2 in nonacademic centers, 0 commercial laboratories) that offered STR genotype testing for molar pregnancy diagnosis in formalin-fixed POC specimens. Four of the 13 laboratories did not accept specimens from pathologists outside of their health care system. Among the 9 who did, 8 first required that the specimen undergo formal diagnostic consultation in their surgical pathology department. Insufficient demand was the leading rationale reported by survey respondents from laboratories that did not offer this test at all. Separately, direct queries with client service representatives showed that only 1 of 16 selected commercial reference laboratories in the United States offered this test. Given the limited access to STR genotype testing, we propose a new reporting nomenclature system that reflects the level of diagnostic certainty for PHM, depending on whether the diagnosis is based on genotype analysis, ploidy analysis, or morphology alone. Further efforts are needed to educate pathologists who do have access to genotype analysis to select that test format rather than ploidy analysis to evaluate the concern for PHM.