Multiple Gestations
Twins have 4X increased risk of
congenital anomalies
Dizigotic: May have placental fusion, but never has vascular anastomoses
1:20 Nigerians, 1:80 Caucasians, 1:150 Japanese
Monozygotic (Incidence: 3.5/1000)
fused placenta always has some degree of arterial anastomosis
have increased risk of congenital abnormalities compared with dizygotes
1. Dichorionic-diamnionic (33%) with morula splitting prior to day 4.
degree of fusion variable, rarely separable.
Twin Monitoring
GA is best assessed early in pregnancy using composit of both. FL measurements are most reliable for determining GA later in pregnancy.
1st and 2nd trimester follows same grwth charts as singleton Then in 3rd trimester weight gein drops with resultant IUGR due to 3000g uterine max carrying capacity
Biophysical profile, sometimes performed up to 2x/wk with any signs of abnormality
A difference of 20mm in AC or 15% in EFW is evidence of significant growth discordance
Clubfoot and crowding is common in any type of twins
Twin-Twin Transfusion/Perfusion Issues
Twin-Twin Transfusion Syndrome
blood and nutrients are progressively shunted between a donor and a recipient twin, with the donor becoming anemic and growth restricted. Eventually the donor twin loses all of its amniotic fluid resulting in "stuck twin" where movement is restricted and the fetus is fixed in the nondependant portion of the uterus, while the recipient floats in polyhydramnios.
recipient: large and vigorous initially, then CHF, hydrops leading to death
donor: umbilical artery doppler demonstrates severe high resistance
Tx: selective amniocentesis of large twin can aid both with small twin regainign some fluid and circulation pressure.
Acardiac Parabiotic Syndrome ( Twin reversed arterial perfusion sequence)
pairing of arteries and veins between twins results in preferential perfusion to the lower body of an acardiac twin. (see normal fetal circulation ) Doppler shows reversal of blood flow with the umbilical artery (usually single) flow toward the acardiac twin by the "pump twin"
pump twin is usually normal, and if high output cardiac failure/hydrops absent or treated (by amniocentesis or ligation of acardiac twin) will survive normally.
Intrauterine demise of one Twin
early in pregancy occurs 50% of time (both mono/dichorionic)
one twin will vanish, or may become hyalinized as a fetal remnant (fetus papyraceous)
Monochorionic twins with vascular anastomoses can get twin-twin embolization syndrome where necrotic tissue is sent to healthy twin leading to DIC. Usually the brain, small intestine, kidneys affected
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Dizigotic: May have placental fusion, but never has vascular anastomoses
1:20 Nigerians, 1:80 Caucasians, 1:150 Japanese
Monozygotic (Incidence: 3.5/1000)
fused placenta always has some degree of arterial anastomosis
have increased risk of congenital abnormalities compared with dizygotes
1. Dichorionic-diamnionic (33%) with morula splitting prior to day 4.
- 10% risk of mortality
- 25% of placentas fuse
- thick (1-2mm) membrane separating two sacs indicates dichorionic twins in first trimester, and this with infiltrating placenta gives the "twin chorionic peak sign"
- 25% risk of mortality
- two yolk sacs, with thin whispy amnions between them. Single chorion prevents placenta from entering between amnions, with low signal at thin peak. The amnion may not be seen until 2nd trimester. But can use gravity and positioning to see if twin shifts into area.
- 75% have single placenta
- 50% mortality. C/S at 32 wks
- fuzed placenta with arterial anastomoses.
- single yolk sac
- If no definitive evidence of mono-mono with cord/limb entanglement, must confirm lack of amnion by dye injection into amnion with resulting concentration into gut (check by CT)
degree of fusion variable, rarely separable.
Twin Monitoring
GA is best assessed early in pregnancy using composit of both. FL measurements are most reliable for determining GA later in pregnancy.
1st and 2nd trimester follows same grwth charts as singleton Then in 3rd trimester weight gein drops with resultant IUGR due to 3000g uterine max carrying capacity
Biophysical profile, sometimes performed up to 2x/wk with any signs of abnormality
A difference of 20mm in AC or 15% in EFW is evidence of significant growth discordance
Clubfoot and crowding is common in any type of twins
Twin-Twin Transfusion/Perfusion Issues
- all monochorionic twins share some degree of placental vascular communication. Therefore never selectively terminate either of the monochorionic twins.
- amniotic fluid volume differences is the primary finding
Twin-Twin Transfusion Syndrome
blood and nutrients are progressively shunted between a donor and a recipient twin, with the donor becoming anemic and growth restricted. Eventually the donor twin loses all of its amniotic fluid resulting in "stuck twin" where movement is restricted and the fetus is fixed in the nondependant portion of the uterus, while the recipient floats in polyhydramnios.
recipient: large and vigorous initially, then CHF, hydrops leading to death
donor: umbilical artery doppler demonstrates severe high resistance
Tx: selective amniocentesis of large twin can aid both with small twin regainign some fluid and circulation pressure.
Acardiac Parabiotic Syndrome ( Twin reversed arterial perfusion sequence)
pairing of arteries and veins between twins results in preferential perfusion to the lower body of an acardiac twin. (see normal fetal circulation ) Doppler shows reversal of blood flow with the umbilical artery (usually single) flow toward the acardiac twin by the "pump twin"
pump twin is usually normal, and if high output cardiac failure/hydrops absent or treated (by amniocentesis or ligation of acardiac twin) will survive normally.
Intrauterine demise of one Twin
early in pregancy occurs 50% of time (both mono/dichorionic)
one twin will vanish, or may become hyalinized as a fetal remnant (fetus papyraceous)
Monochorionic twins with vascular anastomoses can get twin-twin embolization syndrome where necrotic tissue is sent to healthy twin leading to DIC. Usually the brain, small intestine, kidneys affected
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