At what gestational age can a hydatidiform mole (molar pregnancy) be diagnosed?

From the Guidelines

A molar pregnancy can typically be diagnosed as early as 8-12 weeks of gestation. The diagnosis usually begins with symptoms such as abnormal vaginal bleeding, severe nausea and vomiting, or signs of preeclampsia before 20 weeks. Diagnosis is confirmed through ultrasound imaging, which can show characteristic "snowstorm" or "grape-like" appearances in the uterus instead of a normal gestational sac and embryo, as noted in the NCCN guidelines 1. Blood tests measuring human chorionic gonadotropin (hCG) levels are also crucial, as molar pregnancies often produce abnormally high levels of this hormone. Complete molar pregnancies (where no fetal tissue develops) may be detected earlier than partial molar pregnancies (where some fetal tissue exists alongside abnormal placental tissue).

Some key points to consider in the diagnosis of molar pregnancy include:

• Ultrasound findings, such as an enlarged uterus with a heterogenous mass, hydropic/swollen chorionic villi, and a vesicular pattern, are characteristic of complete molar pregnancies 1
• Quantitative hCG assay is an essential part of the workup, as marked elevations in hCG are often seen in complete molar pregnancies 1
• Pelvic ultrasound, complete blood count with platelets, liver, renal, and thyroid function tests, and blood type and screen are also recommended as part of the initial workup 1
• Early diagnosis is important because prompt treatment, typically through suction dilation and curettage (D&C), can prevent complications such as persistent gestational trophoblastic disease, as highlighted in the ESMO clinical practice guidelines 1.

Following treatment, patients require regular hCG monitoring for 6-12 months to ensure complete resolution and detect any recurrence or malignant transformation, with a plateaued or rising hCG on three and two consecutive samples, respectively, indicating potential malignant change 1.

From the Research

Diagnosis of Molar Pregnancy

• Molar pregnancy can be diagnosed as early as the first trimester of pregnancy, thanks to advances in ultrasound imaging 2, 3.
• The diagnosis of molar pregnancy is often made before the patient exhibits any symptoms, with vaginal bleeding being a common presenting symptom when symptoms are present 2.
• Expert histopathology coupled with ancillary molecular and genetic techniques is increasingly relied upon for accurate diagnosis, especially with earlier diagnosis 3.

Role of Ultrasound in Diagnosis

• Ultrasound examination can correctly identify molar changes in early pregnancy, and when combined with hCG level and uterine Doppler measurements, can establish the differential diagnosis in utero of various forms of placental molar transformations 4.
• The sensitivity of ultrasound for gestational trophoblastic disease is around 70.7%, with an estimated specificity of 99.88% 5.
• Detecting molar pregnancy by ultrasound remains a diagnostic challenge, particularly for partial moles, but the predictive value and sensitivity of ultrasound have increased over time 5.

Timing of Diagnosis

• With the wide availability of first-trimester ultrasound and serum human chorionic gonadotropin (hCG) measurement, the presentation of molar pregnancy has changed from a second-trimester to a first-trimester disease 3.
• Most patients with molar pregnancy have few symptoms at diagnosis due to earlier detection 3.
• Earlier diagnosis has not changed the risk of postmolar gestational trophoblastic neoplasia (GTN) 3.