Table 2.

Characteristics of recurrent hydatidiform moles

	Molar pregnancy	Cluster	Type	Genetic alteration	Risk of GTN	Future pregnancies and options
Recurrent HM	Complete HM	Familial	Biparental diploid	Single gene mutations [NLRP7 (48–80%) or KHDC3L (10–14% of NLRP7-negative patients)] with an autosomal recessive pattern of inheritance (imprinting defects) [19]	15–20% [2]	Subseq. molar pregnancies (ovum donation ± surrogation)
		Sporadic	Androgenetic diploid	Two paternal copies of the genome		May have subseq. normal pregnancies (IVF/PGD)
	Partial HM	Sporadic	Diandric triploid	Two paternal copies of the genome	< 5% [2]	May have subseq. normal pregnancies (IVF/PGD)

HM hydatidiform mole, IVF in vitro fertilisation, GTN gestational trophoblastic neoplasia, PGD preimplantation genetic diagnosis