Ch 14 Multiple Gestations

Question 1

What % of twins are MZ + DZ?

Answer 1

MZ: 30%
DZ: 70%

Question 2

How are MZ twins formed?

Answer 2

From single ova

Question 3

How are DZ twins formed?

Answer 3

From 2 ova (separately fertilized)

Question 4

What factors cause MZ twins?

Answer 4

Random event

Question 5

What factors cause DZ twins?

Answer 5

Genetics, environmental factors, advanced maternal age (over 35), and ART

Question 6

Placental membranes are composed of what 2 layers?

Answer 6

Outer: chorion
Inner: amnion

Question 7

What 3 structures do DZ twins ALWAYS have?

Answer 7

2 separate:
-placentas
-chorions
-amnions

Question 8

What does the # of placentas, chorionicity + amnionicity depend on?

Answer 8

Depends on the day post-fertilization that the zygote divides on

Question 9

What type of twins form when the zygote divides prior to day 4?

Answer 9

DC/DA (25%)

Question 10

What type of twins form when the zygote divides b/w days 4-8?

Answer 10

MC/DA (75%)

Question 11

What type of twins form when the zygote divides greater than 8 days?

Answer 11

MC/MA (less than 1%)

Question 12

What type of twins form when the zygote divides greater than 13 days?

Answer 12

Conjoined twins (1/50,000-1/100,00)

Question 13

What type twins the rarest?

Answer 13

Conjoined

Question 14

What type of twins m/c?

Answer 14

MC/DA

Question 15

What type of twins has the biggest risk?

Answer 15

MC/MA b/c they can get tangled + they share all the same structures

Question 16

How many gest sacs, amniotic cavities, yolk sacs + # of embryos per sac are there with DC/DA twins?

Answer 16

GS: 2
AC: 2
YS: 2
Embryos/Sac: 1

Question 17

How many gest sacs, amniotic cavities, yolk sacs + # of embryos per sac are there with MC/DA twins?

Answer 17

GS: 1
AC: 2
YS: 2
Embryos/Sac: 1 per amniotic cavity

Question 18

How many gest sacs, amniotic cavities, yolk sacs + # of embryos per sac are there with MC/MA twins?

Answer 18

GS: 1
AC: 1
YS: 1
Embryos/Sac: 2

Question 19

What type of twins are virtually always going to be different genders?

Answer 19

DC/DA

Question 20

What type of twins have 2 discrete placentas?

Answer 20

DC/DA

Question 21

What type of twins have the twin peak sign?

Answer 21

DC/DA

Question 22

Another name for the twin peak sign?

Answer 22

The lambda sign

Question 23

If we see 2 placentas, what is the pregnancy?

Answer 23

DC/DA

Question 24

If we see 1 placenta, what is the pregnancy?

Answer 24

MC

Question 25

What type of twins is it if there is there is a thick or thin intertwin membrane?

Answer 25

Thick: DC/DA
Thin: MC/DA

Question 26

When can MC twins be detected on u/s?

Answer 26

100% sensitivity b/w 11-14 weeks gestation

Question 27

If the T sign is present what does this indicate?

Answer 27

MC

Question 28

If the lambda sign (inverted Y) is present what does this indicate?

Answer 28

DC

Question 29

Difference b/w T sign + lambda sign?

Answer 29

T sign: looks like thin line/membrane coming from placenta

Lambda sign: looks like thick line/membrane with inverted Y appearance coming from placenta, the chorion forms a wedge shape

Question 30

Does the thickness of the intertwined membrane predict the chorionicity?

Answer 30

Yes!

Question 31

What should we sonographically assess with multiple gestations?

Answer 31

1st trimester:
-# fetuses
-fetal lie
-# placentas
-presence/absence of membranes
-standard biometry/anatomy

2nd/3rd trimester:
-qualitative assessment of amniotic fluid or MVP, SDP/DVP in BC
-CD + pulsed doppler if indicated

Question 32

Put in order from m/c to l/c of the different types of multiples.

Answer 32

Twins = 1 in 100
Triplets = 1 in 7,600
Quadruplets = 1 in 729,000
Quintuplets = 1 in 65,610,000

Question 33

Can triplets + quads be MZ?

Answer 33

Yes