Ch 14 Multiple Gestations Flashcards
What % of twins are MZ + DZ?
MZ: 30%
DZ: 70%
How are MZ twins formed?
From single ova
How are DZ twins formed?
From 2 ova (separately fertilized)
What factors cause MZ twins?
Random event
What factors cause DZ twins?
Genetics, environmental factors, advanced maternal age (over 35), and ART
Placental membranes are composed of what 2 layers?
Outer: chorion
Inner: amnion
What 3 structures do DZ twins ALWAYS have?
2 separate:
-placentas
-chorions
-amnions
What does the # of placentas, chorionicity + amnionicity depend on?
Depends on the day post-fertilization that the zygote divides on
What type of twins form when the zygote divides prior to day 4?
DC/DA (25%)
What type of twins form when the zygote divides b/w days 4-8?
MC/DA (75%)
What type of twins form when the zygote divides greater than 8 days?
MC/MA (less than 1%)
What type of twins form when the zygote divides greater than 13 days?
Conjoined twins (1/50,000-1/100,00)
What type twins the rarest?
Conjoined
What type of twins m/c?
MC/DA
What type of twins has the biggest risk?
MC/MA b/c they can get tangled + they share all the same structures
How many gest sacs, amniotic cavities, yolk sacs + # of embryos per sac are there with DC/DA twins?
GS: 2
AC: 2
YS: 2
Embryos/Sac: 1
How many gest sacs, amniotic cavities, yolk sacs + # of embryos per sac are there with MC/DA twins?
GS: 1
AC: 2
YS: 2
Embryos/Sac: 1 per amniotic cavity
How many gest sacs, amniotic cavities, yolk sacs + # of embryos per sac are there with MC/MA twins?
GS: 1
AC: 1
YS: 1
Embryos/Sac: 2
What type of twins are virtually always going to be different genders?
DC/DA
What type of twins have 2 discrete placentas?
DC/DA
What type of twins have the twin peak sign?
DC/DA
Another name for the twin peak sign?
The lambda sign
If we see 2 placentas, what is the pregnancy?
DC/DA
If we see 1 placenta, what is the pregnancy?
MC
What type of twins is it if there is there is a thick or thin intertwin membrane?
Thick: DC/DA
Thin: MC/DA
When can MC twins be detected on u/s?
100% sensitivity b/w 11-14 weeks gestation
If the T sign is present what does this indicate?
MC
If the lambda sign (inverted Y) is present what does this indicate?
DC
Difference b/w T sign + lambda sign?
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
Does the thickness of the intertwined membrane predict the chorionicity?
Yes!
What should we sonographically assess with multiple gestations?
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
Put in order from m/c to l/c of the different types of multiples.
Twins = 1 in 100
Triplets = 1 in 7,600
Quadruplets = 1 in 729,000
Quintuplets = 1 in 65,610,000
Can triplets + quads be MZ?
Yes
