OBJECTIVE: To analyze the correlation between the genetic constitution and the phenotype in triploid pregnancies.

STUDY DESIGN: 158 triploid pregnancies identified in hospitals in Western Denmark from April 1986 to April 2010. Clinical data and karyotypes were collected retrospectively and archived samples were retrieved. The parental origin of the genome, either double paternal contribution (PPM) or double maternal contribution (MMP) was determined by analyzing methylation levels at imprinted sites.

RESULTS: There were significantly more PPM than MMP cases (p<0.01). In MMP cases the possible karyotypes had similar frequencies, whereas in PPM cases 43% had the karyotype 69,XXX, 51% the karyotype 69,XXY, and 6% the karyotype 69,XYY. Molar phenotype was only seen in PPM cases. However, PPM cases with a non-molar phenotype were also seen. For both parental genotypes, various fetal phenotypes were seen at autopsy. Levels of human chorionic gonadotropin in maternal serum (MS-hCG) were low in MMP cases and varying in PPM cases, some being as low as in the MMP cases.

CONCLUSIONS: In a triploid pregnancy, suspicion of hydatidiform mole at US, by macroscopic inspection of the evacuated tissue, at histology, or due to a high MS-hCG level each predict the parental type PPM with a very high specificity. In contrast the sensitivity of these observations is less than 100%.