Hydatidiform mole (ORPHA:99927)
A rare, benign gestational trophoblastic disease that develops during pregnancy and is characterized by the abnormal fertilization, trophoblastic proliferation, and abnormal or absent embryo development. Hydatidiform moles can be either complete or partial.
Epidemiology
In Europe, the condition occurs in approximately 1/1,000 pregnancies.
Clinical description
Complete moles are asymptomatic in 40% of cases. Most often, a mole is detected upon suspicion of miscarriage in the first trimester, with bleeding and pelvic pain. The clinical signs in the second trimester (vomiting, metrorrhagia, abnormal increase in the size of the uterus, and more rarely anemia or preeclampsia) are observed less often, due to early detection by ultrasound examination. Hyperthyroidism is exceptional. The clinical signs of a partial mole (metrorrhagia, vomiting, etc.) are rare. A mole is usually detected histologically on analysis of aspiration samples from a suspected miscarriage.
Etiology
The moles are caused by abnormal fertilization with an excess of paternal chromosome material. Complete moles result from fertilization of an enucleated ovocyte by one or two haploid spermatozoa. The karyotype is 46,XX (75% of cases) or 46,XY (25%). The mole is characterized by trophoblastic hyperplasia associated with generalized degeneration of chorionic villi and absence of an amniotic cavity and embryonal tissue. Partial moles result from fertilization of a normal ovocyte by two spermatozoa or one abnormal spermatozoon. This type of mole is characterized by focal trophoblastic hyperplasia, localized degeneration of chorionic villi and identifiable embryonal tissue. The karyotype is triploid in 99% of cases.
Diagnostic methods
Ultrasound of a complete mole may show a classic ''snow storm'' appearance (solid, hyperechoic areas of varying forms interspersed with liquid areas of various sizes) occupying the entire uterine cavity. Earlier ultrasound before 9-10 weeks of pregnancy can show a limited vesicular appearance of the placenta. Ultrasound of a partial mole may sometimes show focal vesicular change. Embryonic structures without an increase in uterine size are commonly found. Diagnosis is based on histological examination of the product of fertilization. Expert pathology review is often useful. When hydatidiform mole is suspected, determination of total chorionic gonadotropin (hCG) must be performed.
Differential diagnosis
Moles may be, but should not be, confused with gestational trophoblastic neoplasms or with prolonged retention of a ''classic'' spontaneous miscarriage.
Genetic counseling
Aside from very rare cases of recurrent moles in the same patient or in the same family (1% of cases, in which a mutation in the NLRP7, KHDC3L, MEI1 or C11orf80 genes have sometimes been found), genetic counseling is not required.
Management and treatment
Treatment of moles consists of suction evacuation of the uterine contents. Ultrasound guidance may be useful. Evacuation must be scheduled rapidly due to the risk of complications which increases with gestational age. Due to possible progression to gestational trophoblastic neoplasia (GTN), plasma hCG should be monitored until the levels normalize. Diagnosis of GTN warrants disease staging and appropriate chemotherapy.
Prognosis
After removal, the prognosis is excellent. The main risk is retention by incomplete aspiration (up 25% of cases) which may justify ultrasound follow-up in the weeks following aspiration. Retention (ultrasound image of more than 17 mm in anteroposterior diameter) may require a repeated aspiration in certain clinical circumstances. In about 15 % of cases of complete moles and in 0.5 to 5% of partial moles, the condition leads to gestational trophoblastic neoplasia in the weeks and months following mole evacuation.

                            Last update: 
                            June 2022


                            - Expert reviewer(s): 
                            Dr John COULTER