What is the Difference Between Complete and Partial Mole

The main difference between complete and partial mole is that complete mole occurs with the fusion of one or two sperms with an egg that has lost its DNA whereas partial mole occurs with the reduplication of a fertilized egg with one or two sperms. Furthermore, in a complete mole, paternal DNA duplicates to form a diploid cell (46,XX), while in a partial mole, the reduplication of the fertilized egg results in a triploid cell (69,XXY).

Complete and partial mole are two forms of molar pregnancy, which is an abnormal form of pregnancy, implanting a non-viable fertilized egg in the uterus.

Key Areas Covered

1. What is Complete Mole
     – Definition, Formation, Characterization
2. What is Partial Mole
     – Definition, Formation, Characterization
3. What are the Similarities Between Complete and Partial Mole
     – Outline of Common Features
4. What is the Difference Between Complete and Partial Mole
     – Comparison of Key Differences

Key Terms

Complete Mole, hCG, Hydatidiform Mole, Malignancy, Molar Pregnancy, Partial Pregnancy

What is Complete Mole

Complete mole is a type of more common hydatiform mole that does not develop a fetus. During the formation of a complete mole, one or two sperms fuse with an enucleated egg. Then, the DNA in the nucleus duplicates, forming a diploid cell. There are two possible karyotypes in the complete mole: 46,XX (90%) and 46,XY (10%). Moreover, since an enucleated egg cell is involved in the formation, a complete mole does not contain maternal DNA; it only expresses paternal DNA.

Figure 1: Hydatidiform Mole – Complete Type

Another significant feature of the complete mole is that it causes the secretion of a higher level of hCG, which is the main clinical feature of this process. It occurs due to the over-proliferation of the chorionic villi and results in swelling. Also, these chorionic villi are diffusely hydropic and typically surrounded by hyperplastic trophoblasts. And, this causes the much rapid enlargement of the uterus when compared to a normal pregnancy.

Figure 2: Molar Pregnancy – Ultrasound

On the other hand, the commonest symptom of a complete mole is the vaginal bleeding that is a result of the separation of molar tissue from decidua. Moreover, hyperemesis (severe nausea and vomiting) is another symptom caused by the high levels of hCG in the blood. Besides, the late symptom of high hCG levels is hyperthyroidism.

What is Partial Mole

Partial mole is the other type of hydatiform mole involved in the development of a nonviable fetus. The formation of a partial mole can occur in two methods: the duplication of the haploid ovum with the subsequent fertilization by a single sperm or the fertilization of the haploid ovum by two sperms. However, the resulting fertilized egg is a triploid cell whose karyotypes can be either 69,XXX or 69,XXY. Also, a partial mole has both maternal and paternal DNA; hence, the expression of both types of DNA can be observed.

Figure 3: Molar Pregnancy

Moreover, the main histological difference between complete and partial mole is the development of embryonic/fetal tissue in the partial mole. However, partial moles develop normal chorionic villi. Furthermore, in a partial mole, the enlargement of the uterus is less dramatic as it involves in the secretion of comparatively low levels of hCG. More importantly, the risk of invasive disease in a partial mole is 1-5%, which is lesser than the risk in a complete mole.

Similarities Between Complete and Partial Mole

• Complete and partial mole are two types of molar pregnancies, which are forms of the gestational trophoblastic disease (GTD).
• They are tumors that develop from the gestational tissue.
• Both arise with the duplication of the fertilized egg. Therefore, the fertilized egg lacks the original maternal nucleus.
• Thus, they result in the implantation of a non-viable fertilized egg in the uterus.
• Furthermore, both forms of molar pregnancies give rise to a clump of growing tissue.
• Besides, some conceptions may develop fetal tissue.
• Moreover, this type of pregnancy is characterized by the presence of a hydatidiform mole. The two main characteristic features of a hydatidiform mole are abnormal hyperplastic trophoblasts and hydropic villi.
• ABoth forms of pregnancy manifest with vaginal bleeding accompanied by nausea and frequent vomiting, hyperemesis gravidarum, hyperthyroidism, and risk of spontaneous miscarriage.
• Usually, both types of hydatidiform moles are benign and premalignant, but they have the potential to become malignant and invasive.

Difference Between Complete and Partial Mole

Definition

Complete mole refers to a type of hydatiform mole that occurs due to the fertilization of an enucleated oocyte by one or two haploid spermatozoa while partial mole refers to a type of hydatiform mole that occurs due to the fertilization of a normal oocyte by two spermatozoa or one abnormal spermatozoon, allowing for some fetal development. Thus, this is the fundamental difference between complete and partial mole.

Frequency

Complete moles are more common while partial moles are less frequent.

Formation

The main difference between complete and partial mole is that a complete mole occurs with the fusion of one or two sperms with an egg that has lost its DNA whereas a partial mole occurs with the reduplication of a fertilized egg with one or two sperms.

Ploidy of the Fertilized Egg

Also, another difference between complete and partial mole is that complete mole results in a diploid fertilized egg while partial mole results in a triploid fertilized egg.

Karyotype

Moreover, the possible genotype in the complete mole is 46,XX while the possible genotypes in the partial mole are 69,XXY and 69,XXX.

Maternal DNA

Furthermore, a complete mole does not have and does not express maternal DNA while a partial mole has and expresses maternal DNA. Hence, this is another difference between complete and partial mole.

The Development of Fetal Tissue

While a complete mole does not develop a fetus, a partial mole may develop a deformed, nonviable fetus.

Chorionic Villi

Chorionic villi is another difference between complete and partial mole. Chorionic villi of a complete mole are diffusely hydropic and are typically surrounded by hyperplastic trophoblasts while a partial mole has normal chorionic villi and embryonic/fetal tissue mixed with hydropic villi.

Human Chorionic Gonadotropin (hCG) Levels

Complete mole results in the secretion of higher levels of hCG while partial mole results in the secretion of moderately high levels of hCG.

Risk of Choriocarcinoma

Besides, compete mole has the potential to develop choriocarcinoma due to high hCG levels while partial mole has a less risk to develop choriocarcinoma.

Uterine Size

Uterine size is also a difference between complete and partial mole. Complete mole results in the rapid enlargement of the uterus while in a partial mole, the uterus can be smaller than the suggested date.

Risk of Complications

Importantly, a complete mole has a 15-20% risk to develop malignant trophoblastic disease while a partial mole has a 5% risk to develop a malignancy.

Diagnosis

Diagnosis is another difference between complete and partial mole. A complete mole can be diagnosed during the first trimester with the use of ultrasonography while partial moles are diagnosed as spontaneous abortions discovered with the pathology report obtained from the fetal tissue.

Conclusion

A complete mole is a form of molar pregnancy caused by the fusion of one or two sperms with an enucleated egg cell. This causes the duplication of the sperm nucleus to form a diploid cell. Complete mole stimulates the secretion of significantly high levels of hCG and has a high risk of choriocarcinoma. In comparison, partial mole is the other form of molar pregnancy resulted by the reduplication of the DNA in the fertilized egg. However, a partial mole has a low risk of malignancy when compared to a complete mole. Therefore, the main difference between complete and partial mole is their formation and effect.

References:

1. Ghassemzadeh S, Kang M. Hydatidiform Mole. [Updated 2018 Dec 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2018 Jan-. Available Here

Image Courtesy:

1. “Hydatidiform mole (1) complete type” (CC BY-SA 3.0) via Commons Wikimedia  
2. “Molar pregnancy 0001” By Mme Mim – Own work (CC BY-SA 4.0) via Commons Wikimedia  
3. “Blasenmole Computertomographie axial” By Hellerhoff – Own work (CC BY-SA 3.0) via Commons Wikimedia