Due to the disappearance of microvessels in the trophoblastic stroma, fluid accumulates in the stroma, forming bubbles of varying sizes resembling grapes, hence the name hydatidiform mole. It is classified as complete or partial, with most cases being complete hydatidiform moles. So what causes hydatidiform moles? The exact cause remains unknown. Case-control studies suggest associations with nutritional status, socioeconomic factors, and age. Let's explore the potential causes of hydatidiform moles in detail.
Causes of Hydatidiform Mole
The exact cause of hydatidiform mole remains unknown. Case-control studies suggest associations with nutritional status, socioeconomic factors, and age. Age is a significant etiological factor: women over 40 have a 10-fold higher incidence than younger women, while those under 20 are at high risk for complete mole due to increased susceptibility to fertilization defects in both age groups.Partial molar pregnancies show no clear association with maternal age.
Cytogenetic and pathological studies confirm distinct genetic characteristics for each type. The chromosomal genome of a complete mole originates from the paternal lineage, developing when a sperm pronucleus fuses with an egg pronucleus that is either missing or non-viable.
The chromosomal karyotype is diploid, with 90% being 46, XX. This arises when an empty egg (an egg lacking genetic material) is fertilized by a haploid sperm (23, X). Through self-replication, it restores its diploid state (46, XX) and proceeds with growth and development. This is termed fertilization of an empty egg.A minority exhibit a 46,XY karyotype, resulting from simultaneous fertilization of an empty egg by two sperm with different sex chromosomes (23,X and 23,Y), termed double sperm fertilization.Partial molar pregnancy karyotypes are often triploid, with 80% being 69, XXY and the remainder 69, XXX or 69, XYY. This arises from a normal egg fertilized by two sperm, introducing an extra set of paternal chromosomes. It may also result from a normal haploid egg (or sperm) combining with a diploid gamete that failed meiosis.
Additional contributing factors include:
1. Poor nutrition:
Pregnant women in underdeveloped regions face higher pregnancy risks due to malnutrition or lack of timely prenatal care, making them more susceptible to molar pregnancies than the general population. Ensuring adequate maternal nutrition is crucial for prevention.
2. Maternal age: Pregnant women under 20 or over 40 are at higher risk due to immature or unhealthy eggs, which can lead to "empty sac pregnancies" and subsequently molar pregnancies. Conceiving at an appropriate age benefits both mother and fetus.
3. Previous History: Women who have previously experienced a molar pregnancy are considered high-risk for recurrence in subsequent pregnancies. Approximately 0.5–2.6% of molar pregnancies are recurrent, and these women also face an increased risk of developing invasive mole or choriocarcinoma later in life.
A peculiar phenomenon is that hydatidiform moles occur more frequently in women from Eastern countries, particularly in Southeast Asia and Taiwan. According to a research report by the Taiwan Medical Association, the average incidence rate in Taiwan is approximately 0.3%, which is 3 to 5 times higher than in Western countries. However, the exact reason for this disparity remains unclear.