A 30 y woman, G8P1 comes to the ED with vaginal bleeding. You notice two things in the uterus.

an apparently normal 7 wk gestation

and you also notice this mass;  what is it?

Our patient had a twin pregnancy where one twin was a molar pregnancy.  The term hydatidiform mole comes from the Greek hydatisia(a drop of water) and mola(from the Latin meaning millstone/false conception).  Molar pregnancies occur in 1 in 1000 pregnancies. They are more frequent in Mexico , SE Asia and the Phillipines.  They are more frequent in white women than black women. How a mole develops  is a subject of debate although it is thought to occur when an egg without DNA  is fertilized by a sperm which then creates a fetus with only male DNA patterned methylation and this stimulates syncytiotrophoblast growth.  If the egg DNA is present this rapid growth is normally curtailed.

molar twin pregnancy at 19 wks.

More than 80% of moles are benign and in those cases women are counseled to avoid pregnancy for 6 to 12 months after a D+C. In 10-15% of cases hydatidiform moles may develop into invasive moles. This is called persistent trophoblastic disease and can result in invasion of the uterine wall with hemorrhage.  In 2-3% of cases, moles develop into choreocarcinoma which is an aggressive malignancy resulting in widespread metastatic disease and death.

There are numerous reports of twin pregnancies where one “fetus” is a molar pregnancy.  It is estimated that 20% of these pregnancies will result in a viable term infant. On the other hand, the mole can be aggressive and cases have been presented where the HCG (which normally peaks at 100,000 in the 10th week of pregnancy) can be over 1,000,000 and widespread metastases occur.  HELLP syndrome can develop as well as hyperthyroidism and severe bleeding.

The ""bunch of grapes" appearance of a molar pregnancy

Our patient elected to undergo a D+C and had no complications.

Renard N, BijvankS, deGroot J, Verheijen R, et al. Aggressive complete hydatidiform mole coexistent with a normal fetus during pregnancy: is there a correlation between outcome and serum HCG levels? A report on 2 cases and review of the literature.  Obstetrics and Gynaecology cases=reviews 2016. 3(5) 089 ISSN : 2377-9004

Jones WB. Lauersen NH Hydatidform mole with coexistent fetus. Am J Obstet Gynecol 1975. 122:267-272.

Woo J, Hsu C, Fung L, Ma H. Partial hydatidiform mole: ultrasonograqphic features. 1983. Aust N Z J Obstet Gynaecol. 23 (2 ):103-7.