Ultrasound Diagnosis of Molar Pregnancy

This article is a retrospective observational study that looked at ultrasound evidence of suspected molar pregnancy or other gestational trophoblastic disease [such as invasive moles, choriocarcinomas, and placental site trophoblastic tumors] compared with their histopathology, spanning a period of 11 years with a total of 65,536 pregnancies. The primary aims were to establish what proportion of suspected molar pregnancies on ultrasound were confirmed on histological examination and what proportion of histologically diagnosed molar pregnancies were identified by ultrasound pre-operatively.

Molar pregnancies are the most common type of gestational trophoblastic disease and can be either complete or partial. They typically present with vaginal bleeding, hyperemesis gravidarum, early embryonic demise, an enlarged uterus, early preeclampsia, hyperthyroidism, and abdominal distention. On ultrasound, molar pregnancies characteristically appear as a “uterus full of dots” or a “snowstorm” in the second trimester. Ultrasound criteria for suspected molar pregnancy includes cystic changes, irregularity, or increased echogenicity in the decidua, chorionic tissue, or myometrium.

On pre-op ultrasound, 60 out of 68 complete molar pregnancies were suspected compared with 42 out of 75 partial molar pregnancies that were suspected. Overall, 102 out of 143 molar pregnancies were suspected on pre-op ultrasound. Ultrasound findings either showed cystic changes in the chorionic tissue typical of molar pregnancies, more subtle changes, small cysts in the chorionic tissue and a relatively high proportion of trophoblast for a small gestational sac, abundant chorionic tissue with loss of the normal sac-like architecture, or small irregular gestational sac only with inability to see any features that could indicate a complete mole.

Ultimately, over half of the pregnancies that were suspected to be molar on ultrasound were proven to be so, and a higher proportion of molar pregnancies were detected by pre-op ultrasound than previously reported in the literature. Since modern transvaginal ultrasound has been used routinely for the assessment of early pregnancies, the proportion of molar pregnancies suspected pre-op has risen. The main diagnostic difficulty was found to be in distinguishing partial molar pregnancy from uncomplicated first trimester miscarriage [i.e. early embryonic demise]. Thus, detecting molar pregnancy by ultrasound remains a diagnostic challenge, particularly for partial molar pregnancy compared to complete molar pregnancy.