A hydatidiform mole is an abnormal pregnancy characterized by hydropic placental villi, trophoblastic hyperplasia, and poor fetal development. Familial recurrent hydatidiform mole is an autosomal recessive condition in which women experience recurrent pregnancy losses, predominantly complete hydatidiform mole (CHM). However, unlike sporadic CHMs, which are androgenetic with 2 paternal chromosome complements, CHMs associated with familial recurrence are genetically biparental in origin with both a maternal and a paternal contribution to the genome. Other pregnancy losses in this condition include partial hydatidiform mole, stillbirths, ectopic pregnancies, early neonatal deaths, and miscarriages, some of which may be undiagnosed molar pregnancies. Normal pregnancies are extremely rare in families with this condition (summary by Fallahian et al., 2013). For a discussion of genetic heterogeneity of recurrent hydatidiform mole, see HYDM1 (231090).

The first symptom of a hydatidiform mole is often vaginal bleeding in the first trimester of pregnancy. During an ultrasound examination, the abnormal placenta appears as numerous small sacs, often described as resembling a bunch of grapes.\n\nHydatidiform moles are not naturally discharged from the body and must be surgically removed, typically by the end of the first trimester. After removal, there is up to a 20 percent risk that any tissue left behind will continue to grow and become a cancerous (malignant) tumor called a persistent mole. If the tumor invades the surrounding tissue of the uterus, it is called an invasive mole. In rare cases, this malignant tumor can transform into a different form of cancer called gestational choriocarcinoma that can spread (metastasize) to other tissues such as the liver, lungs, or brain.\n\nRecurrent hydatidiform mole is a condition that affects women and is characterized by the occurrence of at least two abnormal pregnancies that result in the formation of hydatidiform moles. A hydatidiform mole is a mass that forms early in pregnancy and is made up of cells from an abnormally developed embryo and placenta. Normally, the embryo would develop into a fetus and the placenta would grow to provide nutrients to the growing fetus. When a hydatidiform mole occurs once, it is known as sporadic hydatidiform mole; if it happens again, the condition is known as recurrent hydatidiform mole.

Hydatidiform mole is a human pregnancy with abnormal or no embryonic development and excessive trophoblastic proliferation. Partial hydatidiform moles have a triploid dispermic genome, with 2 sets of paternal chromosomes and 1 set of maternal chromosomes; complete hydatidiform moles have a diploid androgenetic genome with all chromosomes originating from 1 (monospermic) or 2 (dispermic) sperms, and no maternal chromosomes (summary by Nguyen et al., 2018). For a discussion of genetic heterogeneity of recurrent hydatidiform mole, see HYDM1 (231090).

Hydatidiform mole is a human pregnancy with abnormal or no embryonic development and excessive trophoblastic proliferation. Partial hydatidiform moles have a triploid dispermic genome, with 2 sets of paternal chromosomes and 1 set of maternal chromosomes; complete hydatidiform moles have a diploid androgenetic genome with all chromosomes originating from 1 (monospermic) or 2 (dispermic) sperms, and no maternal chromosomes (summary by Nguyen et al., 2018). For a discussion of genetic heterogeneity of recurrent hydatidiform mole, see HYDM1 (231090).