Multiple Pregnancy

Question 1

What is meant by multiple pregnancy?

Answer 1

a pregnancy with more than one foetus

Question 2

What is the main factor in determing pregnancy outcome?

How is this identified?

Answer 2

• chorionicity is the main factor influencing pregnancy outcome
• this can be identified on US at 10-14 weeks

chorionicity = the number of placentas

Question 3

What is the difference between a monozygotic and dizygotic pregnancy?

Answer 3

monozygotic:

• identical twins that have come from the same zygote

dizygotic:

• non-identical twins that have come from 2 different zygotes

dizygotic - 2 eggs are fertilised by 2 different sperm

monozygotic - the fertilised ovum splits to develop into 2 embryos

Question 4

What is the difference between monoamniotic and diamniotic?

Answer 4

monoamniotic:

• there is a single amniotic sac

diamniotic:

• there are 2 separate amniotic sacs

Question 5

What is the difference between monochorionic and dichorionic?

Answer 5

monochorionic:

• there is a single placenta

dichorionic:

• there are 2 separate placentas

Question 6

What type of twin pregnancy has the best outcome?

Answer 6

diamniotic dichorionic

• this is because each fetus has their own nutrient supply

Question 7

What type of pregnancy is dizygotic pregnancy associated with?

Answer 7

• this involves the fertilisation of 2 separate oocytes with 2 different sperm
• this produces a diamniotic dichorionic pregnancy

Question 8

In a monozygotic pregnancy, how may a diamniotic dichorionic pregnancy result?

Answer 8

• this occurs if the zygote divides within the first 3 days of conception
• this results in each fetus having its own placenta and own amniotic cavity

Question 9

What is the most common outcome of monozygotic pregnancies?

How does this occur?

Answer 9

monochorionic diamniotic

• this accounts for 70% of monozygotic pregnancies
• there is sharing of a placenta, but each twin has its own amniotic sac

• this occurs when the blastocyst divides between day 4 to 7 after conception

Question 10

What are the other potential outcomes of monozygotic pregnancy and why do they occur?

Answer 10

monochorionic monoamniotic:

• occurs when the implanted blastocyst divides between day 8 and 13

conjoined twins:

• occurs when there is division of the formed embryonic disc after 13 days
• in both these cases there is sharing of the placenta and amniotic sac

Question 11

How is multiple pregnancy diagnosed?

Answer 11

• on the booking ultrasound scan
• US can also be used to identify the chorionicity (number of placentas) and amnionicity (number of amniotic sacs)

Question 12

What US sign is associated with dichorionic diamniotic twins?

Answer 12

lambda / twin peak sign

• this occurs as there is a membrane between the twins
• separation of the chorionic + amniotic sacs resembles a lambda

Question 13

What US sign is associated with monochorionic diamniotic twins?

Answer 13

T sign

• there is a membrane between the twins
• the T represents separation of the amniotic sacs

Question 14

What are the potential risks to the mother associated with multiple pregnancy?

Answer 14

• anaemia
• polyhydraminos
• hypertension / pre-eclampsia
• malpresentation
• spontaneous preterm birth
• instrumental delivery / CS
• antepartum / postpartum haemorrhage

Question 15

What are the major risks to foetuses associated with multiple pregnancy?

Answer 15

• miscarriage / stillbirth
• fetal growth restriction
• congenital abnormalities
• twin-twin transfusion syndrome
• twin anaemia polycythaemia sequence

structural abnormalities are 2-3x higher in monozygotic twins

Question 16

What must the circumstances be for twin-twin transfusion syndrome to occur?

Answer 16

it only occurs in monochorionic pregnancies in which the twins share the placenta

Question 17

What happens in twin-twin transfusion syndrome?

Answer 17

• there is a connection between the blood supplies of the 2 fetuses
• one fetus receives the majority of the blood from the placenta and is the “recipient”
• the other fetus is starved of blood and is the “donor”

Question 18

What are the consequences for the donor and recipient twin in TTTS?

Answer 18

donor twin:

• growth restriction
• anaemia
• oligohydraminos

recipient twin:

• polyhydraminos
• cardiac failure

Question 19

What is the management for TTTS?

Answer 19

laser ablation

• this may be used in severe cases to destroy the connection between the 2 blood supplies

Question 20

What is twin anaemia polycythaemia syndrome?

Answer 20

• it is similar to TTTS, but less acute
• one twin develops anaemia
• the other develops polycythaemia (raised Hb)

Question 21

What additional blood tests are required in multiple pregnancy?

Answer 21

• additional monitoring for anaemia is required
• FBC is performed at booking clinic
• and at 20 weeks and 28 weeks gestation

Question 22

What additional US scans are needed in multiple pregnancy?

Answer 22

monochorionic twins:

• US scans every 2 weeks from 16 weeks gestation

dichorionic twins:

• US scans every 4 weeks from 20 weeks gestation

Question 23

Why are additional US scans required in multiple pregnancy?

Answer 23

to assess for evidence of:

• fetal growth restriction
• unequal growth
• twin-twin transfusion syndrome

Question 24

What other additional tests are offered to women with multiple pregnancy?

Answer 24

regular BP measurements and urine dips to check for pre-eclampsia

Question 25

What additional medication is offered in multiple pregnancy?

Answer 25

* **folic acid 5mg** to reduce the risk of congenital abnormalities * **aspirin 75mg** as prophylaxis against pre-eclampsia * **oral iron** to prevent anaemia

Question 26

When is planned birth offered for DCDA twins?

Answer 26

between **37** and **37+6 weeks** gestation

Question 27

When is planned birth offered for MCDA twins?

Answer 27

between **36** and **36+6 weeks** gestation

Question 28

When is planned birth offered for MCMA twins?

Answer 28

between **32** and **33+6 weeks** gestation by ***planned caesarean-section***

Question 29

What are the delivery options for multiple pregnancies?

Answer 29

* if the presenting twin is **cephalic**, **vaginal delivery** is recommended * if the presenting twin is **breech / transverse lie**, **C-section** is performed

Question 30

Why is planned delivery performed in multiple pregnancy? What additional medication may be required?

Answer 30

* waiting beyond the recommended dates is associated with **increased risk of fetal death** * **corticosteroids** are given prior to delivery to mature the fetal lungs