Twinning

Question 1

Hellin’s Law

Answer 1

in general, the approximate number of multiple births occurs in 1: 89n-1 pregnancies, where n is the number of fetuses

Question 2

Monozygotic twins

Answer 2

Twins that form from the splitting of one zygote

Question 3

Dizygotic twins

Answer 3

Twins that form from two separate zygotes– two separate oocytes produced during the same menstrual cycle, fertilised by two different sperm.

Question 4

Twins are dichorionic and diamniotic

Answer 4

the splitting occurs at the two cell stage to morula stage (approximately 0-4 days). Behave like dizygotic twins

Question 5

Twins are monochorionic and diamniotic

Answer 5

the splitting occurs at the early blastocyst stage (approximately 4-8 days)

Question 6

Twins are monochorionic and monoamniotic

Answer 6

the splitting occurs after the formation of the blastocyst with inner cell mass (late blastocyst stage - approximately 8-12 days)

Question 7

Conjoined twins

Answer 7

twins are formed by splitting of a bilaminar embryonic disc after the primitive streak started to form, but no separation

Question 8

Anastomosis of placental vessels increases risk of this disorder

Answer 8

TTTS (Twin to Twin Transfusion Syndrome), one twin gets more nutrients than the other… can cause death of both twins

Question 9

Answer 9

Question 10

In utero death of one twin

Answer 10

Can cause death of other twin because of drop in blood pressure – one heart attempts to pump both bodies, both die

Question 11

TRAP Sequence

Answer 11

one twin, the so-called pump twin, provides all of the blood flow to a second acardiac/acephalic twin through placental vascular anastomoses

Question 12

Cord entanglement

Answer 12

Occurs in monochorionic, monoamniotic twins, interrupts blood supply