twinning

Question 1

How to determine chorionicity

Answer 1

1. dichorionic/ diamniotic: thick dividing membrane btw twins. Twin peak or lambda sign. 2. Monochorionic/Diamniotic: thin dividing membrane, T sign btw twins. 3. Monochorionic/ monoamniotic: no division btw twins

Question 2

List the layers surrounding the fetus

Answer 2

from closest to fetus out: amnion > chorion, extravillous trophoblast > decidua capsularis

Question 3

Histology of amnion

Answer 3

Closest to fetus. single layer of flat, cuboidal or columnar epithelial cells derived from fetal ectoderm. Passively attached to chorion by amniotic fluid pressure.

Question 4

Histology of chorion

Answer 4

tough fibrous layer that carries fetal blood vessels, often with atrophied villous remains (chorion frondosum)

Question 5

Histology of decidua capsularis

Answer 5

maternal contribution to membranes; macrophages, lymphocytes, decidualized endometrial stromal cells, rare maternal vessels

Question 6

Are dichorionic placentas mono or dizygotic twins

Answer 6

Can be either. Monozygotic- split at <3 days. All dichorionic placentas are diamniotic.

Question 7

histology of dichorionic placentA

Answer 7

amnion > chorion > amnion

Question 8

histology of monochorionic diamniotic placenta

Answer 8

amnion of one twin is right next to the amnion of the other twin.

Question 9

Are monochorionic placentas mono or dizygotic twins

Answer 9

monozygotic only- division at 3-8 days post conception

Question 10

Risks of twin pregnancies

Answer 10

miscarriage, hyperemesis (hCG), maternal anemia, gestational diabetes (hPL), gestational preeclampsia, intrauterine growth restriction, preterm birth, postpartum hemorrhage, perinatal mortality.

Question 11

perinatal mortality and type of twin

Answer 11

perinatal mortality increases the later the division occurs in monozygotic twins. Monoamniotic/ monochorionic has higher perinatal mortality than di/di

Question 12

Twin-Twin Transfusion Syndrome

Answer 12

•15-20% of monochorionic-diamnionic twins have unbalanced flow through connected vessels. Recipient twin (larger) increases urine production to reduce blood volume (polyhydramnios, large bladder). Donor twin (smaller) reduces urine production to retain blood volume (oligohydramnios).

Question 13

Why are monochorionic-diamnionic twins at the highest risk for TTTS

Answer 13

di/di don’t share any structures. Mono/mono have so many anastomoses. Mono/di twins are most likely to have unbalanced arteriovenous connections.

Question 14

TTTS implications

Answer 14

•Untreated, TTTS prior to 24 weeks gestational age leads to mortality of one or both twins in 80-90% of cases. After death of one twin, other twin at increased risk for brain damage in 1/3 of cases.

Question 15

What causes death of the donor twin in TTTS

Answer 15

decreased blood volume > lower urinary outpu > oligohydramnios. Small placental volume > not enough nutrients to support fetal growth

Question 16

What causes death of the recipient twin in TTTS

Answer 16

too much blood > strains babys heart to point of heart failure. Also too much urine > polyhydramnios (possibly leading to uterine distension and early delivery) and sometimes fetal hydrops (diffuse edema)

Question 17

TTTS treatment

Answer 17

1. reduction amniocentesis from recipient twin sac using needle through moms abd. Repeat every few days to weekly. Usually early delivery. Survival 18-83%. 2. Microseptostomy- create hole btw babies sac to equalize. If hole gets larger cords may entangle. 60% survival of both twins. 3. Laser ablation of communication. Higher complication rates. 35% survival of both