Pathology of Twinning

Question 1

95% of twins from fertility treatments are ___________.

Answer 1

dizygotic

Question 2

There are four kinds of monozygotic twins: ______________.

Answer 2

• Dichorionic diamnionic (division within 4 days of fertilization) • Monochorionic diamnionic (division between 4-8 days after fertilization) • Monochorionic monoamnionic (division between 8-12 days) • Monochorionic monoamnionic conjoined twins (division after 13 days)

Question 3

The most common type of monozygotic twins are ___________.

Answer 3

monochorionic dizygotic twins (70% of cases)

Question 4

Looking at an ultrasound, how can you distinguish a mono/di from a di/di?

Answer 4

The di/di show the lambda sign (chorion and amnion) and the mono/di show the T sign (because of the thinner amnion).

Question 5

Cord entanglement is a common problem in _____________.

Answer 5

monochorionic/monoamniotic

Question 6

What are some risks of twin pregnancies?

Answer 6

• Miscarriage • Hyperemesis • Increased risk of aneuploidy and anomalies • Diagnostic/screening protocols are less sensitive • Anemia • Diabetes • Preeclampsia • Preterm delivery • Hemorrhage • Growth restriction • Perinatal mortality (5x-7x rate of single pregnancies)

Question 7

When is a baby considered full-term?

Answer 7

37 weeks (even though most pregnancies are 40 weeks)

Question 8

Perinatal mortality increases with ________________.

Answer 8

later division (meaning conjoined twins have the worst mortality followed by mono/mono twins)

Question 9

What is twin-twin transfusion syndrome?

Answer 9

TTTS occurs in mono/di twins when anomalous blood connections develop across the amniotic sacs. One twin essentially gives their arterial blood to the other twin via the recipient’s veins.

Question 10

The _________ twin in TTTS develops a larger bladder to reduce blood flow.

Answer 10

recipient

increases urine production to reduce blood volume = polyhydraminos

Question 11

Arteries run ______ veins over the chorionic plate.

Answer 11

over

Question 12

Why are mono/di twins at the highest risk for TTTS?

Answer 12

Dichorionic twins have two placentas and thus have very few (if any) anastomoses. Monochorionic monoamnionic twins have so many connections that they likely balance out on the aggregate.

Question 13

How has the incidence of twins changed recently?

Answer 13

It was 1:53 gestations in 1980; now it is 1:30.

Question 14

The incidence of twinning is __________ in women using fertility treatment.

Answer 14

20x the spontaneous rate

Question 15

Why does the donor twin in TTTS develop oligohydramnios?

Answer 15

Because the fetus decreases its urine production to increase blood volume.

Question 16

How can TTTS be treated?

Answer 16

• Removal of the amniotic fluid from the recipient twin’s sac • Making a small hole in the amnions that separate the twins’ sacs (microseptostomy)

laser ablation of the cummunicating vessels, can even do this after one twin dies to lower the mortality rate of the surviving twin

early delivery (29-30 weeks)

Question 17

What causes death in TTTS?

Answer 17

• Donor twin: dehydration and anemia • Recipient twin: heart failure from volume overload

Question 18

name each arrow and whether it is maternal or fetal tissue

Answer 18

top to bottom

amnion (fetal)

chorion (fetal)

extravillous trophoblast (fetal)

decidua (maternal)

Question 19

what type of twins does this placenta belong to?

Answer 19

di/di twins, the thick pink with purple nuclei in the middle is the chorion with two amnions on the outside

Question 20

what type of twins does this placenta belong to?

Answer 20

mo/di twins, there is no chorion between the two amnions