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Flashcards in Module 9.1 : Multiple Gestation Deck (26)
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what percentage of natural pregnancies are twins



how much higher mortality rate for twins than singleton

5-10 times higher


twinning rate

- higher earlier in pregnancy
+ one may die and reabsorbed in early pregnancy
- ART and IVF increasing rate of twins


types of twins

- dizygotic
- monozygotic



- fraternal twins
- zygote = number of eggs
- not sharing anything
- have their own placenta and amniotic sac
- dichorionic diamniotic
- as similar as siblings



- identical twins
- one egg
- chance of splitting early and not sharing anything
- or splitting late and sharing anything


sharing rule

- less than babies share the better the outcome of survival


dizygotic twins

- 70% of all natural births
- 1/80 births
- hereditary on maternal side
- fertilization of two separate ova
- genetic similarity sam as siblings
- have their own genetic mix


increasing chance of dizygotic twins

- maternal age
+ young ( < 15)
+ old (> 37)
+ parity (many children)
- hereditary
- racial background
- pharmaceutical agents
+ clomide and pergonal


monozygotic twins

- 30% of all natural twins
- 1/250 births
- random occurrence
- SINGLE fertilized ovum replicates during the early development
- genetically the same
- increased mortality rate is slightly higher than dizygotic twins


types of monozygotic twinning

- dichorionic diamniotic
- monochorionic diamniotic
- monochorionic monoamniotic
- conjoined twins



- placenta


dichorionic diamniotic twins

- occurs with ALL dizygotic twins
+ two placentas two amniotic sacs
- can occur in monozygotic twins
+ morula splits before it implants
+ 2 days post fertilization
+ each implants separately (2 of everything, 4 layer membrane)
- 18-30% of all monozygotic twins


monochorionic diamniotic twins

- division occurs at blastocyst stage after inner cell mass of embryo forms
- day 4-8 post fertilization
- 2 fetuses in separate amniotic sacs with single placenta
- 2 layer membrane 1 placenta
- 70% of all monozygotic twins
- possibility of twin to twin transfusion


monochorionic monoamniotic twins

- division occurs at embryonic disc stage after amnion's sac develops
- day 8-12 post fertilization
- 4% of all monozygotic twins (rare)
- increased risk of mortality due to cord entanglement


conjoined twins

- incomplete division at embryonic disc stage
- occurs after day 13 post fertilization
- no separating of membranes


scanning placentas - what to look for

- identify number of placentas
- identify presence or absence of a separating membrane
- identify presence of a peak sign or t sign where the membrane meets the placenta


2 placentas

- with dizygotic twins or di chorionic twins there will be 2 separate placentas
- or 2 placentas so close there appear fused looking like one placenta
- look for lambda or t sign


twin peak / lambda sign

- if 2 placentas implant close together some placenta tissue will grow up between the membranes creating a twin peak sign or lambda sign


t sign

- division occurring after implantation will result in one placenta
- one placenta with two membranes creates a t sign
- no placenta will grow between the membranes
- monochorionic diamniotic


distinguishing between monozygotic DI/DI twins and dyzygotic twins

- can only tell if there is a boy and a girl
+ this means a dizygotic twin pregnancy


clinical indication for twin scan

- strong family history
- large for gestational age
- increased maternal hCG
- two or more heart beats heard by doctor



- identify number of fetuses
- position of fetuses
- label presenting twin (closest to cervix) as A and label which side of the mom uterus baby is on
- identify presence of
+ membrane
+ number of placentas
+ presence of twin peak sign or t sign
- treat each fetus as a singleton and complete all documentation of one twin before moving on to the next
- show similar fetal parts to demonstrate multiple babies
- rule out polyhydroamnios (5-10%)


demised twin

- usually occurs in first trimester but can happen any time
- if this happens the boney remains of the demised fetus is termed PAPYRACEUS FETUS
- imaging of dead fetus only requires sag and trans image


fetal reduction

- increased rate of higher order multiples due to increased use of fertility treatment either with fertility drugs or IVF
- much higher rate of prematurity
- option is offered to have a fetal reduction (fetoscide) to improve outcome of pregnancy


AFI on twin pregnancy

- can't do a real AFI
- try to locate a 2x2 pocket of fluid anterior to each baby as close to membrane as you can