Pathology of the Placenta

PLACENTA

The placenta provides food and oxygen for the baby. It is composed of 2 layers, the inner amnion and the outer chorion. 

The placenta can also tell you a lot about the events that occurred inside the body during pregnancy. It can reveal the etiology of why a baby was born prematurely, small, or as a stillbirth. (Autopsies don’t determine anything.) Apparently, the placenta can look and smell funny if something bad happened.

·         Maternal abnormalities

o        Hypertension or other pregnancy losses

·         Fetal abnormalities

o        Brain damage 

Placental exams can save OB-GYNs in law suits. When the doctor is blamed for not performing a C-section to save the baby, the pathologist can say that there was something wrong with the placenta for several months in the womb, thus saving the doctor from the poorhouse.
 

The placenta (chorionicity) can also tell the mother whether or not the twins are identical.

Dichorionic-Diamniotic Placenta

·         There are 2 sacs, one for each baby. Both placental layers (amnion and chorion) envelop both babies separately. 

·         You can have either identical or fraternal twines. 

Dichorionic-Diamniotic Fused Placenta

·         There are 2 chorion layers that are fused and 2 separate amnions.

·         You can have either identical or fraternal twins. 

Monochorionic-Diamniotic Placenta

·         There are 2 amnions and 1 chorion wrapping around both twins. There is no chorion in between the two babies.

·         Amnion – nothing - amnion 

Monochorionic-Monoamniotic Placenta

·         This is the least common abnormality. There is one placental bag with 2 babies.

·         There is a 40% risk of cord accidents in MoMo pregnancies. 

Monochorionic twins may have anastomoses of blood vasculature in the placenta. Bloodflow is diminished, and twin-twin transfusion results. The donor baby is anemic due to the loss of bloodflow, and the recipient baby suffers from congestive failure due to the increase in bloodflow.

Gestational Trophoblastic Disease 

The pathologic classification is:

·         Hydatidiform Mole (complete/partial)

o        The abnormal placenta may or may not have a baby.

o        This is a risk factor for cancer à choriocarcinoma.

·         Invasive Mole

·         Choriocarcinoma

·         Placental Site Trophoblastic Tumor 

GTD is found by elevated B-hCG levels in the blood.

Complete Hydatidiform Mole

·         This is the majority of hydatidiform moles.

·         It is genetically different from partial moles.

o        Diploid!

o        It is mostly 46xx with both components from the father. It’s like fertilization of an empty egg with no maternal genetic material.

·         The risk of progressing to choriocarcinoma is greater.

·         Incidence varies in the world – it’s more common in the Far East than in the US. It’s also more common in mothers at both ends of the reproductive spectrum (the young and the old).

·         Most complete moles (80-85%) spontaneously regress.

·         Some (2-3%) progress to choriocarcinoma.

·         There is a 1% recurrence rate with the next pregnancy.

·         Diagnosis (via ultrasound mostly)

o        The uterus is larger than the gestational age.

o        There are grape-like structures.

o        Bleeding

o        B-hCG is markedly elevated.

Partial Hydatidiform Mole

·         This is genetically different from complete moles.

o        Triploid!

o        It is mostly due to 2x more paternal genes than maternal.

o        There is no age-associated risk.

·         It occurs more in older patients.

·         The risk to choriocarcinoma is much less.

·         Diagnosis

o        The uterus is smaller or equal to gestational age.

o        The patient presents with symptoms of a dead pregnancy/abortion.

o        The B-hCG levels are of a lower elevation than complete moles and revert back to normal levels sooner.

o        There are less malignant sequelae.

Choriocarcinoma

This is the first cancer that was completely cured by chemotherapy in 1950. 

Background

·         50% is preceded by complete moles.

·         30% is preceded by abortions

·         20% is preceded by term pregnancies 

The cancer is followed by monitoring elevated B-hCG levels. When the patient has a mole, you have to make sure that the B-hCG levels return to normal. 

Pathology

·         There are not many tissue specimens of choriocarcinoma today.

·         These are considered to be hemorrhagic tumors. Therefore, the patient can bleed to death if she undergoes tissue biopsy.

·         Ovarian cysts may also be present due to B-hCG hormonal stimulation. 

Prognosis

·         Most patients do well with chemotherapy.

·         Poor prognostic factors include:

o        Longer time period since the index pregnancy

o        Higher B-hCG titers

o        Brain/liver metastases

o        Significant prior chemotherapy (more resistant)

o        Normal term index pregnancy

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