Partial hydatidiform mole

A partial hydatidiform mole (also called partial molar pregnancy or incomplete hydatidiform mole) is an abnormal form of pregnancy in which a non-viable fertilized egg implants in the uterus and develops into a mass of abnormal tissue rather than a healthy fetus. It occurs when a normal egg is fertilized by two sperm simultaneously (dispermy), resulting in a triploid karyotype (typically 69,XXX or 69,XXY), with two sets of paternal chromosomes and one set of maternal chromosomes. Unlike a complete hydatidiform mole, a partial mole may contain some identifiable fetal or embryonic tissue alongside the abnormal placental tissue characterized by focal swelling of chorionic villi and trophoblastic hyperplasia. The condition primarily affects the reproductive system. Key symptoms include vaginal bleeding during the first or second trimester, a uterus that may be smaller than expected for gestational age, abnormally elevated (though often less dramatically than in complete moles) levels of human chorionic gonadotropin (hCG), and ultrasound findings showing a mixture of cystic placental tissue and possible fetal parts. Patients may also experience nausea, vomiting, and pelvic discomfort. Pre-eclampsia may occasionally develop, though less commonly than with complete moles. Treatment involves surgical evacuation of the uterine contents, typically by suction curettage. Following evacuation, serial monitoring of serum hCG levels is essential to ensure complete resolution and to detect any persistent gestational trophoblastic disease. The risk of progression to gestational trophoblastic neoplasia (including invasive mole or, rarely, choriocarcinoma) is approximately 0.5–5%, which is lower than the risk associated with complete hydatidiform moles. Patients are generally advised to avoid pregnancy during the hCG monitoring period, which typically lasts six months to one year. Prognosis is generally excellent with appropriate follow-up, and most women can have successful subsequent pregnancies.

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