Twinning

Question 1

What is the general rule for determining the number of multiple births?

Answer 1

the approximate number of multiple births occurs in 1:89^(n-1) pregnancies, where n is the number of fetuses - Hellin’s law.

Question 2

Monozygotic

Answer 2

Twins that form by the splitting of a single original embryo

Question 3

For monozygotic twins, If splitting occurs at the two cell stage to morula stage (approximately 0-4 days) the twins will develop ____ chorions and amnions called ____, _____

Answer 3

separate, dichorionic, diamniotic

Question 4

For monozygotic twins, If the splitting occurs at the early blastocyst stage (approx 4-8 days), then embryos will share a ___ chorion and placenta but occupy separate amnions, termed ______, _______

Answer 4

Monochorionic, diamniotic

Question 5

For monozygotic twins, if the splitting occurs after the formation of the blastocyst with inner cell mass (late blastocyst stage, approximately 8-12 days) the embryos will be _____, ____

Answer 5

Mono chorionic, monoamniotic

Question 6

dizygotic twins arise from two separate ___ produced during the same menstrual cycle, fertilized by ____ ____ sperm

Answer 6

oocytes, two different

Question 7

Do dizygotic twin embryos implant separately and develop separate fetal membranes (i.e. amnion, chorion, placenta)?

Answer 7

You bethcya

Question 8

T or F: Dizygotic twins show a hereditary tendency

Answer 8

T

Question 9

What’s the most common type of twin?

Answer 9

Dizygotic, about 75-80% of twins

Question 10

Describe in utero death of one twin

Answer 10

If one twin dies late in gestation, the blood pressure of one twin drops significantly, and the remaining twin is at risk. The other twin may experience heart pressure as its heart attempts to fill both ciculatory systems at once. Also if one twin dies, the other twin may be killed by an embolism (blocked blood vessel) caused by bits of tissue that break off in the dead twin and enter the shared circulation

Question 11

Describe Twin-to-twin transfusion syndrome. What twin type does it most frequently occur in?

Answer 11

Occurs in 10% to 20% of all monochorionic, diamniotic twins)

in TTTS, vascular anastomoses occur between vessels in the two placentas that result in unbalanced blood flow between the twins. One twin, the donor twin, exhibits ologiohydramnios, grown restriction, and renal insufficiency, wheras the other, the so-called recipient twin, exhibits plyhdramnios and cardiac enlargement.

Question 12

Describe TRAP sequence

Answer 12

One twin, the pump twin, provides all the blood flow to a second, acardiac/acephalic twin through placental vascular anastomoses. Because of the addition stress placed on the pump twin’s heart, cardiac failure and the pump twins subsequent demise can occur in 50% to 75% of cases.

Question 13

Cord entanglement, what type of twin is most susceptible to this?

Answer 13

Most common complication in monochorionic, monoamnionic twins.

Usually occurs after 20 weeks, can cause the death of one twin, or both, if entanglement interrupts blood supply through umbilical cord. Overall risk is 10-15%

Question 14

How can triplets arise?

Answer 14

1 zygote and be identical, 2 zygotes and consist of identical twins and a singelton 3 zygotes and be the same sex or different sexes

Question 15

How is the risk of chromosomal abnormalities and fetal morbidity affected by multiple gestations?

Answer 15

The risk is higher in multiple gestations

Question 16

How is the risk of prematurity affected in multiple pregnancies?

Answer 16

The risk is higher in multiple pregnancies

Question 17

For monozygotic twins, if the twins are formed by splitting of a bilaminar embryonic disc after the primitive streak started to form, they will occupy the same ____. In rare cases, such twins may not separate, resulting in ___

Answer 17

amnion, conjoined twins

Question 18

What does this diagram illustrate?

Answer 18

Dichorionic, diamniotic twins developing from one zygote (monozygotic)

Question 19

What is most common twins, monozygotic or dizygotic?

Answer 19

Dizygotic

Question 20

What type of twin does this illustrate?

Answer 20

Monochorionic, diamniotic twins developing from one zygote (monozygotic)