[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Female genital tract](https://durgical.com/en/general-pathology/areas/female-genital/) › Hydatidiform mole: complete vs partial

# Hydatidiform mole: complete vs partial

- Lesion

A molar pregnancy is a placenta with too many paternal chromosomes: the villi swell like grapes, hCG soars, and a few cases become cancer.

Updated Nov 12, 2026

## Key points

- Complete mole: 46,XX (most) or 46,XY, all paternal; no embryo; diffuse villous swelling with cisterns and circumferential trophoblast proliferation; very high hCG.
- Partial mole: triploid (69,XXY, 69,XXX), one maternal and two paternal sets; fetal parts; only some villi swollen, scalloped with trophoblast inclusions; focal trophoblast proliferation.
- p57 (CDKN1C) is paternally imprinted and maternally expressed: negative in complete moles, positive in partial moles.
- Persistent gestational trophoblastic disease after a complete mole is common (roughly one in five); after a partial mole it is uncommon.
- Invasive mole: molar villi invade the myometrium and may reach the lungs; responds to chemotherapy.

On this page

- The basics Key points
- What it is
- Structure
- Step by step
- Complete vs partial hydatidiform mole
- Markers
- Memory aid
- Elsewhere in DurgiPedia

- Clinical Clinical notes

- Study Test yourself

- Connections Connections

## What it is

A hydatidiform mole is an abnormal pregnancy in which chorionic villi swell and the trophoblast proliferates because of an excess of paternal genes. A complete mole is diploid and entirely paternal, usually from an empty ovum fertilised by one sperm that duplicates; it has no embryo, all villi are swollen and it carries a real risk of persistent disease and choriocarcinoma. A partial mole is triploid, with one maternal and two paternal sets, has fetal tissue and a much lower risk. The p57 immunostain, made only from the maternal gene, separates them.

## Structure

- Complete mole: the uterus is filled with delicate thin-walled translucent grape-like vesicles; microscopically all villi are oedematous with central cisterns and surrounded by atypical cytotrophoblast and syncytiotrophoblast.
- Partial mole: a mixture of normal-sized and swollen villi with irregular scalloped outlines, focal trophoblast hyperplasia, and fetal tissue or nucleated fetal red cells.
- Invasive mole: molar villi within the myometrium or vessels, sometimes causing perforation and haemorrhage.

## Step by step

- An ovum that has lost its nucleus is fertilised by one sperm that duplicates, or by two sperm: a complete mole with only paternal genes.
- Or a normal ovum is fertilised by two sperm: a triploid partial mole.
- An excess of paternally expressed (imprinted) genes drives trophoblast growth and villous swelling.
- The proliferating trophoblast secretes large amounts of hCG.
- After evacuation, trophoblast that remains can persist, invade the myometrium or become choriocarcinoma.

## Complete vs partial hydatidiform mole

| Feature | Complete mole | Partial mole |
| --- | --- | --- |
| [Karyotype](https://durgical.com/en/conditions/molar-pregnancy/) | Diploid, all paternal (46,XX or 46,XY) | Triploid, two paternal and one maternal set |
| Embryo or fetal parts | Absent | Present |
| Villous swelling | All villi | Some villi |
| Trophoblast proliferation | Diffuse, circumferential | Focal, slight |
| p57 immunostain | Negative | Positive |
| Serum hCG | Very high | Often near normal for the stage |
| [Risk of persistent disease](https://durgical.com/en/conditions/gestational-trophoblastic-neoplasia/) | High; choriocarcinoma possible | Low; choriocarcinoma rare |

## Markers

- p57 (CDKN1C)
- Serum hCG
- Molecular genotyping (short tandem repeats)

## Clinical notes

- Presents with vaginal bleeding in early pregnancy, a uterus large for dates, hyperemesis, early preeclampsia, hyperthyroidism (hCG stimulates the TSH receptor) and theca lutein cysts.
- Ultrasound of a complete mole shows a snowstorm pattern; most are now diagnosed in the first trimester.
- Treatment is suction evacuation followed by serial hCG until it is undetectable; a plateau or rise means persistent disease.

## Memory aid

Complete means completely father's: no baby, no p57, all grapes. Partial shares the parents unequally and keeps a fetus.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the karyotype of a complete mole and where do its chromosomes come from?

Usually 46,XX, entirely paternal, from an empty ovum fertilised by a sperm that duplicates its DNA (or by two sperm).

## Why is p57 negative in a complete mole?

p57 is expressed only from the maternal allele; a complete mole has no maternal genome, so it does not stain.

## Which mole has fetal parts and a low risk of choriocarcinoma?

The partial mole, which is triploid.

## How is a patient followed after evacuation of a mole?

With serial serum hCG until it is undetectable; a plateau or rise indicates persistent gestational trophoblastic disease.

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## Elsewhere in DurgiPedia

- [Trophoblast and hCG; gestational trophoblastic disease](https://durgical.com/en/embryology/trophoblast-and-hcg-gestational-trophoblastic-disease/)
- [The placenta and pregnancy hormones](https://durgical.com/en/physiology/the-placenta-and-pregnancy-hormones/)
- [Placenta](https://durgical.com/en/histology/placenta/)

## Connections

## Related 7

- [Choriocarcinoma and trophoblastic tumours](https://durgical.com/en/general-pathology/choriocarcinoma-and-trophoblastic-tumours/)
- [Spontaneous abortion](https://durgical.com/en/general-pathology/spontaneous-abortion/)
- [Preeclampsia and eclampsia](https://durgical.com/en/general-pathology/preeclampsia-and-eclampsia/)
- [Non-neoplastic ovarian cysts and polycystic ovaries](https://durgical.com/en/general-pathology/non-neoplastic-ovarian-cysts-and-polycystic-ovaries/)
- [Genomic imprinting: Prader–Willi and Angelman](https://durgical.com/en/general-pathology/genomic-imprinting-prader-willi-and-angelman/)
- [Immunohistochemistry: the principle and the markers to know](https://durgical.com/en/general-pathology/immunohistochemistry-the-principle-and-the-markers-to-know/)
- [Chromosome abnormalities: number and structure](https://durgical.com/en/general-pathology/chromosome-abnormalities-number-and-structure/)

## Related conditions 6

- [Molar pregnancy (hydatidiform mole)](https://durgical.com/en/conditions/molar-pregnancy/)
- [Gestational trophoblastic neoplasia (choriocarcinoma)](https://durgical.com/en/conditions/gestational-trophoblastic-neoplasia/)
- [Hyperemesis gravidarum](https://durgical.com/en/conditions/hyperemesis-gravidarum/)
- [Preeclampsia](https://durgical.com/en/conditions/preeclampsia/)
- [Graves disease (hyperthyroidism)](https://durgical.com/en/conditions/graves-disease/)
- [Miscarriage (early pregnancy loss)](https://durgical.com/en/conditions/miscarriage/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Hydatidiform Mole](https://www.ncbi.nlm.nih.gov/books/NBK459155/) (StatPearls (NCBI Bookshelf), 2026); [Gestational Trophoblastic Disease Treatment (PDQ®)–Health Professional Version](https://www.cancer.gov/types/gestational-trophoblastic/hp/gtd-treatment-pdq) (National Cancer Institute, 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/hydatidiform-mole-complete-vs-partial/