Module 9.1 : Multiple Gestation

Question 1

what percentage of natural pregnancies are twins

Answer 1

3%

Question 2

how much higher mortality rate for twins than singleton

Answer 2

5-10 times higher

Question 3

twinning rate

Answer 3

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

Question 4

types of twins

Answer 4

• dizygotic

- monozygotic

Question 5

dizygotic

Answer 5

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

Question 6

monozygotic

Answer 6

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

Question 7

sharing rule

Answer 7

• less than babies share the better the outcome of survival

Question 8

dizygotic twins

Answer 8

• 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

Question 9

increasing chance of dizygotic twins

Answer 9

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

Question 10

monozygotic twins

Answer 10

• 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

Question 11

types of monozygotic twinning

Answer 11

• dichorionic diamniotic
• monochorionic diamniotic
• monochorionic monoamniotic
• conjoined twins

Question 12

chorionic

Answer 12

• placenta

Question 13

dichorionic diamniotic twins

Answer 13

- 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

Question 14

monochorionic diamniotic twins

Answer 14

• 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

Question 15

monochorionic monoamniotic twins

Answer 15

• 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

Question 16

conjoined twins

Answer 16

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

Question 17

scanning placentas - what to look for

Answer 17

• 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

Question 18

2 placentas

Answer 18

• 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

Question 19

twin peak / lambda sign

Answer 19

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

Question 20

t sign

Answer 20

• 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

Question 21

distinguishing between monozygotic DI/DI twins and dyzygotic twins

Answer 21

• can only tell if there is a boy and a girl

+ this means a dizygotic twin pregnancy

Question 22

clinical indication for twin scan

Answer 22

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

Question 23

protocol

Answer 23

• 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%)

Question 24

demised twin

Answer 24

• 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

Question 25

fetal reduction

Answer 25

- 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

Question 26

AFI on twin pregnancy

Answer 26

- 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