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Flashcards in Triploidy Deck (15):
1

What is triploidy?

- Chromosomal anomaly seen in 1 - 2% of all conceptions and ~10% of spontaneous abortions
- 69,XXX or 69,XXY
- Most triploid conceptions end in the first trimester as spontaneous abortions, some reports of live births, with the longest reported survival of 10.5 months

2

Digyny

- Extra set of chromosomes = maternal
- Associated with asymmetric severe fetal growth restriction (FGR), pronounced wasting of body and sparing of head, normal NT-thickness and very low serum free beta-hCG & PAPP-A, and a very small placenta
- Usually occurs as a result of errors in meiosis I or meiosis II during oogenesis

3

Diandry

- Extra set of chromosomes = paternal
- Placenta = enlarged & partially molar
- Fetus = symmetric mild growth restriction or well grown fetus
- Fetal NT = high
- Maternal serum free beta-hCG = 10X higher than normal

- Diandric triploidy can also cause sever maternal complications, including severe early-onset preeclampsia and choriocarcinoma

4

Molar pregnancy

- When a non-viable fertilized egg implants in the uterus
- Can be complete or partial
- Tissue that normally would become a fetus instead becomes an abnormal growth in the uterus
- This growth triggers symptoms of pregnancy (occasionally *RARE* pregnancy that is though to be twins, one is molar and one is a real fetus)

5

Complete mole

- When either a single sperm or two sperm combine with an "empty" egg (without either a maternal nucleus or without maternal DNA)
- The sperm then reduplicates and forms a 46 chromosome set
- The tissue grows and looks similar to a cluster of grapes. It does not have fetal tissue.

6

Partial mole

2/3 of time: Two sperm fertilize an egg (dispermy) yielding paternal triploidy genotype --> results in abundant trophoblast and poor embryonic development

1/3 of time: Sperm fertilizes a diploid egg, yielding maternal triploidy genotype --> results in retardation of embryonic development and a small fibrocytic placenta

7

Risk factors for molar pregnancy

- Age >35
- Hx of molar pregnancy; especially 2 or more
- Hx of miscarriage
- Diet low in carotene (form of vitamin A) (women low in vitamin A have an increased rate of complete molar pregnancy)
- Certain ethnic groups (Filipinos)

8

Invasive Mole

- A hydatidiform mole that grew into the muscle layer of the uterus, can develop from complete or partial moles (more often complete)
- May spread to other parts of the body such as the vagina vulva and lung

9

Choriocarcinoma

malignant gestational trophoblastic cancer, usually of the placenta

10

Possible forms of inherited triploidy

There have been some reports of autosomal recessive triploidy and a susceptibility locus has been assigned to chromosome 19.

11

What method of NIPT would possibly pick up a case of triploidy?

DIANDRIC ORIGIN ONLY: Only the lab Natera, which uses targeted amplification and analysis of SNPs on chromosomes 21, 18, 13, X and Y in one reaction and determines the chromosomal copy number (cannot distinguish between twins and triploidy by this test alone)

Every other lab uses a counting method where the amounts of chromosomes 21, 18,13, X and Y are compared against other chromosome amounts as a reference and thus would not pick up triploidy.

12

Low fetal fraction on NIPT (through Natera), multiple congenital anomalies, and fetal growth restriction would be indicative of _________________

Digynic triploidy.

This is most likely due to the associated small placental mass.

13

If you have 2 maternal copies of a genome only, what kind of tissue would develop?

Fetal tissue only, "benign cystic teratoma"

14

With 2 paternal copies of a genome only, what kind of tissue would develop?

Placental tissue, no fetal tissue

15

Hydatidiform mole

Clump of growing tissue