Cytogenetic analysis of complete moles has shown a 46,XX chromosomal constitution. Ultrasonography discloses a snowstorm appearance . The partial mole differs from the complete mole in that the volume of the tissue is often less than 300 cc and only a proportion of the villi are vesicular. It is not uncommon for a fetus to be present, and it may be abnormal. Histologically a proportion of the villi are edematous with sometimes a central cistern.
Fetal vessels are usually present.
Some enlarged villi may show a degree of trophoblastic hyperplasia but usually less marked than that seen in a complete mole. The mechanism suggested in triploidy is either the fertilization of a single ovum by two different haploid sperm or by a diploid sperm. A rapid method for assaying ploidy in molar tissues is DNA cytometric analysis. This technique may serve as a useful complement to the pathologic interpretation. The biologic behaviour of partial moles is poorly known.