Multiple Pregnancies

Question 1

What two factors are most important to consider in multiple pregnancy?

Answer 1

Amnionicity

Chorionicity

Question 2

What is the diagnostic test required when making the diagnosis of twins, when is it done and why is this the best time for this testing?

Answer 2

Need U/S for amnionicity and chorionicity. Best in 1st trimester because the chorionic sac completely surrounds the amniotic sac so dichorionicity can be determined definitively. If testing is only completed in 2nd trimester, only way of ensuring dichorionicity is if there are differing genders because at this point the placental plates have come together.

Question 3

What are some fundamental risks for DC twins?

Answer 3

Minor: Increase in hyperemesis gravidum and MSK issues
Physiological: increased nutrional requirements, increased risk of gestational diabetes, increased surveillance

Question 4

Discuss Down’s Syndrome screening in the setting of twins.

Answer 4

In monozygotic twins, same as normal risk because one egg with one sperm but in dizygous twins, there is double the risk of downs because two eggs each with their own risk. 1st trimester combined screening is important because NIPT may not work because need individual analytes from each twin for individualised information.

Question 5

What are the 4 reasons congenital abnormalities are more common in twins?

Answer 5

1) Increase in monozygous twins than dizygous or singletons
2) Increased maternal age is a RF for twins and that population are more at risk of congenital abnormalities
3) Harder to scan twins morphology so detection rates are lower
4) More likely to let the twin go through to term because do not want issues with the other twin

Question 6

Discuss preterm birth in twin pregnancies and how management of preterm singleton pregnancies differs to multiple pregnancies

Answer 6

• Before 32 weeks –> 11%, before 37 weeks –> 60%
• Spontaneous with or without PPROM –> 2/3
• Iatrogenic for fetal and maternal well-being reasons –> 1/3
• In singletons –> cervical cerclage + progesterone supps will prevent preterm birth. This does NOT work in twins so need to focus on other strategies. Stop smoking etc but also work to prevent disease sequelae. MgSO4 for neuroprotection, Steriods to aid lung development and need to optimise mode/timing of delivery.

Question 7

Discuss Fetal Growth Surveillance in the context of growth discordance in twins.

Answer 7

More common in twins because uteroplacental insufficiency is present just by way of cirumstance in twins but also unequal placental sharing can occur leading to growth discordance. Assessment is by fetal biometry, umbilical doppler, amniotic fluid assessment.

Question 8

Explain the effects of Twin 1 being SMALLER than Twin 2 on delivery

Answer 8

Twin 1 smaller than Twin 2
When smaller twin 1 comes out –> uterus will compress and can get placental abruption given twin 1 is out –> twin 2 is in fetal distress and therefore there is a need to get twin 2 out fast –> if twin 2 is a big baby which it is, then not sure that the bigger baby will fit through the pelvis + the baby is in fetal distress. furthermore, if twin 2 is breech –> grab the feet and pull the baby out.

Question 9

Explain the effects of Twin 1 being BIGGER than Twin 2 on delivery

Answer 9

Twin 1 is BIGGER than Twin 2
Smaller twin is in fetal distress and is already gone through placental insufficiency –> 1/300 of twin 2 will die because of this.

Question 10

What are the risks of MCDA twins?

Answer 10

1) 15% TTTS
2) 15% sIUGR
3) Abnormalities
4) Death
+ all risks in DCDA twins

Question 11

Explain TTTS

Answer 11

In monochorionic twins, intertwin vascular communications exist which exist in equilibrium. In TTTS, this equilibrium is broken and the flow becomes unbalanced and a donor and recipient forms. The recipient receives all the fluid from the mother and the donor which leads to polyhydramnios –> cardiac failure –> fetal hydrops –> death. The donor becomes hypovolaemic and hypotensive which can lead to impairment of growth but also end organ asphyxia leading to fetal demise.

Question 12

How do you manage TTTS?

Answer 12

1) Terminate pregnancies
2) Expectant management
3) Amniotic Fluid Tap
4) Fetoscopic Surgery to create a dichorionic placenta

Question 13

In the management of TTTS, how do you choose between fetoscopic surgery and amniotic fluid tap?

Answer 13

Decision is based on gestational age. If early, then fetoscopic surgery and if late then amniotic fluid tap.

Question 14

Explain selective IUGR

Answer 14

Discordant growth of twins because of uneven sharing of the placenta. In this case, the smaller twin may not be viable/salvageable BUT if fetal demise then it is not good for the non-growth restricted baby. sIUGR baby holds a gun to the head of the normal baby saying that if they themselves die then they will take the healthy one down too. #ruthless

Question 15

How do you manage sIUGR twins?

Answer 15

With sIUGR twins, increased chance of preterm delivery. However, at early gestation when oreterm delivery is not possible, cord ligation of affected twin to stop chances of intertwin transfusion is preferred. Hard to explain this to parents because twin is not actually dead, it is “alive” but not salvageable BUT by clamping the cord, you are killing it. With TTTS, you can let the recipient twin die but cannot do that here and just wait and “see what happens” because there is an increased risk of co-twin death.

Question 16

Explain the difference between TTTS and sIUGR

Answer 16

Think of sIUGR as abnormality in the sharing of fuel. So the placenta is unequally sharing the fuel from the placenta to each twin. Hence why one is larger than the other one. In TTTS, think about it in terms of a abnormality in flow. An lack of balance in the intertwin anastomses mean that all the flow is going to one twin more than the other.

Question 17

What are 4 causes of fetal demise? Other than the death itself, why is it so bad that a twin dies?

Answer 17

Causes: 
1) Severe IUGR
2) Infection
3) Fetal Abnormality
4) Selective reduction of one twin
Due to placental anastamoses between twins --> demise of one twin --> hypotensive insult to the other twin as blood flows across anastomses to body of dead twin --> 25% chance of death and 25% chance of cerebral palsy

Question 18

Explain the risks associated with abnormalities in MCDA twins

Answer 18

Selective termination, if wanted, for DC twins can take place via intracardiac KCl injection into the unhealthy twin. However, cord ligation is required in MC twins which has an increased risk of pregnancy loss.

Question 19

What additional risk do MCMA twin have on top of all those in DCDA and MCDA twins? How do you manage MCMA twins?

Answer 19

Cord entanglement
- because both twins are in the same sac then just by way of a lack of space, cord can get tangled around a twin.
Mx –> early delivery via CS with repeated daily CTGs looking for decels

Question 20

Discuss the delivery of twins

Answer 20

• Overall increase chance of CS
• Mode of delivery is based on gestation, fetal size, presentation of twins
• Perinatal mortality increased earlier in twins than singletons. 37-39 for DC but 37 for MC
• NVD only when twin 1 is cephalic, no growth discordance and appropriately grown –> need weekly CTG + biophysical profile at 32 and 34 weeks.
• need elective manipulaiton with or without operative delivery of twin 2 but this leads to increased mortality/morbidity on twin 2 which leads to increased CS rate overall.

Question 21

What are the 4 types of twins, how long after fertilisation do each of them form and how common are they in monozygotic pregnancies?

Answer 21

Dichorionic diamniotic (DCDA) - less than 4 days (1/3)
Monochorionic Diamniotic (MCDA) - days 4-8 (2/3)
Monochorionic Monoamniotic (MCMA) - days 8-12 (1%)
Conjoined Twins - more than 12 days (rare)