| Molar pregnancy | |
|---|---|
| Other names | Hydatid mole, hydatidiform mole |
_complete_type.jpg) | |
| Histopathologic image of hydatidiform mole (complete type).H&E stain. | |
| Specialty | Obstetrics |
Amolar pregnancy, also known as ahydatidiform mole, is an abnormal form ofpregnancy in which a non-viablefertilized eggimplants in theuterus. It falls under the category ofgestational trophoblastic diseases.[1] During a molar pregnancy, the uterus contains a growing mass characterized by swollenchorionic villi, resembling clusters of grapes.[2] The occurrence of a molar pregnancy can be attributed to the fertilized egg lacking an original maternalnucleus. As a result, theproducts of conception may or may not contain fetal tissue. These molar pregnancies are categorized into two types: partial moles and complete moles, where the term 'mole' simply denotes a clump of growing tissue or a 'growth'.
A complete mole is caused by either a singlesperm (90% of the time) or two sperm (10% of the time) combining with an egg that has lost itsDNA. In the former case, the sperm reduplicates, leading to the formation of a "complete" 46-chromosome set.[3] Typically, thegenotype is 46, XX (diploid) due to subsequentmitosis of the fertilizing sperm, but it can also be 46, XY (diploid).[3] However, 46, YY (diploid) is not observed. On the other hand, a partial mole occurs when a normal egg is fertilized by one or two sperm, which then reduplicates itself, resulting in genotypes of 69, XXY (triploid) or 92, XXXY (tetraploid).[3]
Complete moles carry a 2–4% risk, in Western countries, of developing intochoriocarcinoma and a higher risk of 10–15% in Eastern countries, with an additional 15% risk of becoming aninvasive mole. In contrast, incomplete moles can become invasive as well but are not associated with choriocarcinoma.[3] Notably, complete hydatidiform moles account for 50% of all cases of choriocarcinoma.
Molar pregnancies are relatively rare complications of pregnancy, occurring in approximately 1 in 1,000 pregnancies in the United States, while in Asia, the rates are considerably higher, reaching up to 1 in 100 pregnancies in countries like Indonesia.[4]
Molar pregnancies usually present with painless vaginal bleeding in the fourth to fifth months of pregnancy.[5] Theuterus may be larger than expected, or theovaries may be enlarged. There may also be more vomiting than would be expected (hyperemesis). Sometimes there is an increase inblood pressure along with protein in the urine. Blood tests will show very high levels ofhuman chorionic gonadotropin (hCG).[6]
The cause of this condition is not completely understood. Potential risk factors may include defects in the egg, abnormalities within theuterus, or nutritional deficiencies. Women under 20 or over 40 years of age have a higher risk. Other risk factors include diets low inprotein,folic acid, andcarotene.[7] The diploid set of sperm-only DNA means that all chromosomes have sperm-patternedmethylation suppression of genes. This leads to overgrowth of thesyncytiotrophoblast whereas dual egg-patterned methylation leads to a devotion of resources to the embryo, with an underdeveloped syncytiotrophoblast. This is considered to be the result ofevolutionary competition, with male genes driving for high investment into the fetus versus female genes driving for resource restriction to maximise the number of children.[8]
A hydatidiform mole is a pregnancy/conceptus in which theplacenta contains grapelike vesicles (small sacs) that are usually visible to the naked eye. The vesicles arise by distention of the chorionic villi by fluid. When inspected under the microscope,hyperplasia of thetrophoblastic tissue is noted. If left untreated, a hydatidiform mole will almost always end as aspontaneous abortion (miscarriage).
Based onmorphology, hydatidiform moles can be divided into two types: incomplete moles, all the chorionic villi are vesicular, and no sign ofembryonic orfetal development is present. Inpartial moles, some villi are vesicular, whereas others appear more normal, and embryonic/fetal development may be seen, but the fetus is always malformed and is never viable.
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In rare cases, a hydatidiform mole co-exists in the uterus with a normal, viable fetus. These cases are due totwinning. The uterus contains the products of two conceptions: one with an abnormal placenta and no viable fetus (the mole), and one with a normal placenta and a viable fetus. Under careful surveillance, it is often possible for the woman to give birth to a normal child and to be cured of the mole.[9]
In most complete moles, allnuclear genes are inherited from the father only (androgenesis). In approximately 80% of these androgenetic moles, the most probable mechanism is that anegg with an empty nucleus or no nucleus is fertilized by a singlesperm, followed by a duplication of allchromosomes/genes (a process calledendoreduplication). In approximately 20% of complete moles, the most probable mechanism is that an empty egg is fertilized by two sperm. In both cases, the moles arediploid (i.e., there are two copies of every chromosome). In all these cases, themitochondrial genes are inherited from the mother, as usual.
Most partial moles aretriploid (three chromosome sets). The nucleus contains one maternal set of genes and two paternal sets. The mechanism is usually the reduplication of the paternalhaploid set from a single sperm, but may also be the consequence of dispermic (two sperm)fertilization of the egg.[10]
In rare cases, hydatidiform moles aretetraploid (four chromosome sets) or have other chromosome abnormalities.
A small percentage of hydatidiform moles have biparental diploid genomes, as in normal living persons; they have two sets of chromosomes, one inherited from each biological parent. Some of these moles occur in women who carrymutations in the geneNLRP7, predisposing them towards molar pregnancy. These rare variants of hydatidiform mole may be complete or partial.[11][12][13]
The diagnosis is strongly suggested byultrasound (sonogram), but definitive diagnosis requireshistopathological examination. On ultrasound, the mole resembles abunch of grapes ("cluster of grapes" or "honeycombed uterus" or "snow-storm").[14] There is increasedtrophoblast proliferation and enlarging of thechorionic villi, andangiogenesis in the trophoblasts is impaired.[15]
Sometimes symptoms ofhyperthyroidism are seen, due to the extremely high levels of hCG, which can mimic the effects ofthyroid-stimulating hormone.[15]
| Complete Mole | Partial Mole | |
|---|---|---|
| Karyotype[16] | 46, XX or 46, XY | 69, XXY or 69, XXX |
| hCG | ↑↑↑↑ | ↑ |
| Uterine Size | ↑ | –[clarification needed] |
| Fetal Parts | No | Yes |
| Components[16] | 2 sperm + empty egg orEmpty egg + 1 sperm that duplicates | 2 sperm + 1 egg or1 sperm + 1 egg that duplicates |
| Risk of Choriocarcinoma[17] | 15% | 0.5% |
Hydatidiform moles should be treated by evacuating the uterus by uterine suction or by surgicalcurettage as soon as possible after diagnosis, to avoid the risks of choriocarcinoma.[18] Patients are followed up until their serumhuman chorionic gonadotrophin (hCG) level has fallen to an undetectable level.Invasive or metastatic moles (cancer) may requirechemotherapy and often respond well tomethotrexate. As they contain paternalantigens, the response to treatment is nearly 100%. Patients are advised not to conceive for half a year after hCG levels have normalized. The chances of having another molar pregnancy are approximately 1%.
Management is more complicated when the mole occurs together with one or more normalfetuses.
In some women, the growth can develop intogestational trophoblastic neoplasia. For women who have complete hydatidiform mole and are at high risk of this progression, evidence suggests that giving prophylactic chemotherapy (known as P-chem) may reduce the risk of this happening.[19] However P-chem may also increase toxic side effects, so more research is needed to explore its effects.[19]
The uterine curettage is generally done under the effect of anesthesia, preferablyspinal anesthesia in hemodynamically stable patients. The advantages of spinal anesthesia overgeneral anesthesia include ease of technique, favorable effects on the pulmonary system, safety in patients withhyperthyroidism, and non-tocolytic pharmacological properties. Additionally, by maintaining the patient's consciousness, one can diagnose complications likeuterine perforation, cardiopulmonary distress, andthyroid storm at an earlier stage than when the patient is sedated or is under general anesthesia.[20]
More than 80% of hydatidiform moles arebenign. The outcome after treatment is usually excellent. Close follow-up is essential to ensure that treatment has been successful.[21] Highly effective means ofcontraception are recommended to avoid pregnancy for at least 6 to 12 months. Women who have had a prior partial or complete mole have a slightly increased risk of a second hydatidiform mole in a subsequent pregnancy, meaning a future pregnancy will require an earlier ultrasound scan.[21]
In 10 to 15% of cases, hydatidiform moles may develop into invasive moles. This condition is namedpersistent trophoblastic disease (PTD). The moles may intrude so far into the uterine wall thathemorrhage or other complications develop. It is for this reason that a post-operative full abdominal and chestX-ray will often be requested.[citation needed]
In 2 to 3% of cases, hydatidiform moles may develop intochoriocarcinoma, which is a malignant, rapidly growing, andmetastatic (spreading) form of cancer. Despite these factors, which normally indicate a poor prognosis, the rate of cure after treatment with chemotherapy is high.[citation needed]
Over 90% of women with malignant, non-spreading cancer can survive and retain their ability to conceive and bear children. In those with metastatic (spreading) cancer, remission remains at 75 to 85%, although their childbearing ability is usually lost.[citation needed]
Theetymology is derived fromhydatisia (Greek "a drop of water"), referring to the watery contents of the cysts, andmole (fromLatinmola = millstone/false conception).[22] The term, however, comes from the similar appearance of the cyst to a hydatid cyst in anechinococcosis.[23]
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