Partial molar pregnancy with coexisting fetus is an extremely rare variation of a molar pregnancy: it accounts for 0.005 to 0.01% of all pregnancies and usually derives from dispermic fertilization of a haploid normal oocyte and produces a triploid set of chromosomes [
1,
7]. An increased incidence could be explained by the greater use of assistive reproductive techniques [
8]. There are three types of molar pregnancy with coexisting normal live fetus: the most frequent case is a twin pregnancy with one normal fetus having a normal placenta and another complete mole; the second type is a twin pregnancy with regular fetus and placenta and another partial mole [
9]; the third and most uncommon occurrence reported only 19 times in the literature is a singleton normal fetus with partial molar placenta, which is similar to our case [
5]. The diagnosis of molar pregnancy with coexisting fetus is difficult. In fact, the diagnosis can be achieved with ultrasonography and sensitive measurement of serum hCG, usually on first trimester [
10]. Moreover, in molar pregnancy, symptoms are hyperemesis, heavy bleeding from the vagina, increased blood pressure and, sometimes, proteinuria that can lead to preeclampsia [
7,
10,
11]. Sometimes women with hydatidiform mole may experience symptoms typical of hyperthyroidism because of extremely high levels of hCG; in fact, this hormone can mimic the action of TSH [
12,
13]. High concentrations of hCG and suppressed levels of TSH can help to confirm the diagnosis. Interruption of pregnancy is common owing to congenital anomalies like triploidy of the fetuses and severe intrauterine fetal growth restriction due to limited normal functional placental circulation. If the pregnancy does not stop, management of molar pregnancies with an apparently normal fetus remains challenging [
5,
14]. The woman must be counseled regarding the maternal and fetal complications: late abortion, vaginal bleeding, mal presentations, preterm labor, persistent gestational trophoblastic disease, severe anemia in the fetus, hyperthyroidism, hypertensive disorders of pregnancy, pulmonary edema, and thromboembolic phenomena [
15,
16]. Therefore, pregnancy needs to be followed with regular ultrasound assessment of fetal anatomy and growth. A chorionic villous biopsy could be done if a live fetus is present, to confirm the diagnosis and to differentiate between a partial mole and complete mole: it has been reported that the latter has approximately 20% tendency to become an invasive mole or even a choriocarcinoma, while the risk was lower for partial moles [
15,
17].