3.8 - Multiple Gestation

Question 1

what is Hellin’s law

Answer 1

Incidence of twins is 1:85 ^(X-1) where X = number of babies (e.g. twins =2)

Question 2

What are the 2 major risk factors that increase the incidence of multiple gestation?

Answer 2

1/3 - Older age
2/3 - Ovulation induction (Clomiphene citrate) and ART (artificial reproductive technologies) which also use ovulation induction

Question 3

Explain the pathophysiology of multiple gestation (go through it all like you would explain it to a consultant)

Answer 3

Dizygotic is when 2 eggs are fertilized by 2 sperms => genetically different fetuses => fraternal twins. => if the there is a boy and a girl then it is by definition Dizygotic

Now for monozygotic. The blastocyst is formed 5 days after fertilisation => if the split happens at days 2-3, 2 complete blastocysts are formed => Dichorionic, Diamniotic.
If it occurs between days the blastocyst splits into into an inner (foetus) and outer cell (placenta) mass. If the separation occurs between 4 and 8 days, only the inner cell mass is split => 1 placenta and 2 amniotic sacs. Monochorionic Diamniotic. If the split occurs between days 9-12, the embryonic disc is split => Monochorionic Monoamniotic.

Question 4

How many umbilical cords are in Monochorionic Diamniotic twins?

Answer 4

2

Question 5

How do you confirm the type of multiple pregnancy on the first trimester ultrasound that occurs between weeks 11-13? (and hence diagnose)

Are there any other methods that could be used to determine that?

Answer 5

DCDA: Different gender, 2 separate placentas, Thick dividing membrane between placentas, Twin peak sign/Lambda sign

MCDA: Thin dividing membrane between placentas, T-sign observed

Monoamniotic Twins: Absent dividing membranes

NIPT: determines zygosity

Question 6

How would you monitor Dichorionic and Monochorionic pregnancies in the antepartum period?

Answer 6

For both: Screen via NIPT for zygosity
Anomaly scan at 20 weeks
Foetal wellbeing
CTG monitoring for delivery

Dichorionic: Monthy US until 30 weeks before switching to 2x/month until delivery at 38/39 weeks

Monochorionic: US 2x/month until delivery at 36/37 weeks

Question 7

Pre-eclampsia is more common in multiple pregnancy. How do you prevent this?

Answer 7

Aspirin given before 16 weeks

Question 8

Can you vaginally deliver twins after a previous C-section?

Answer 8

Yes

Question 9

How would you determine the positon of both terms intrapartum?

Answer 9

First twin via normal obstetric examinatin. The second twin can be determined via US

Question 10

How would you deliver a Vertex-Vertex presentation?

Answer 10

Vertex-Vertex (45%): plan is to deliver both vaginally. Deliver twin A vaginally and then perform US to determine updated position of Twin B. If still cephalic, check CTG for distress. If any of them non-reassuring, expedite delivery (operative/Csection)

Question 11

How would you deliver a vertex-non-vertex presentation?

Answer 11

Vertex-Non-vertex (35%): Delivery twin A vaginally. check updates position of B on US again. Delivery depends on their weight. If >1.5kg delivery via breech extraction it is safe to do breech extraction/assisted breech. If <1.5kg, A C-section can be done instead

Question 12

How would you deliver Twin A if they are non-vertex?

Answer 12

Elective C-section

Question 13

Why would you opt for Elective C-section in cases where Twin A presents in Non-vertex form? (Breech-vertex/breech-breech)

Answer 13

Fear of interlocking chins if breech-vertex twins delivered vaginally

Question 14

What is the intrapartum management and delivery options?

Answer 14

Establish IV access
Administer Epidural for all multibirths
CTG monitoring in all cases
Intrapartum US to determine lie of both twins. Based on that:

Vertex-Vertex (45%): plan is to deliver both vaginally. Deliver twin A vaginally and then perform US to determine updated position of Twin B. If still cephalic, check CTG for distress. If any of them non-reassuring, expedite delivery (operative/Csection)

Vertex-Non-vertex (35%): Delivery twin A vaginally. check updates position of B on US again. Delivery depends on their weight. If >1.5kg delivery via breech extraction it is safe to do breech extraction/assisted breech. If <1.5kg, A C-section can be done instead

Non-vertex Twin A: Elective C-section

Question 15

When are triplets delivered?

Answer 15

33-34 weeks

Question 16

When are quads delivered?

Answer 16

28 weeks

Question 17

State 5 complications of multiple pregnancy

Answer 17

Preterm labour
IUGR
Pre-eclampsia/Gestational HTN
GDM
Anemia
Single demise
Selective growth restriction
TTTS

Question 18

How would you approach single foetal demise?

Answer 18

If one foetus dies it is important to know as to whether it is a mono or dichorionic pregnancy
Mono: Single shared placenta => 20% risk blood flows backwards from live foetus => deliver immediately

Di: No effect on other as there is no blood flow between them. Each has a placenta => no change to management

Question 19

Explain TTTS (Twin-to-Twin Transfusion Syndrome)

Answer 19

This can only occur in monochorionic and occurs in 10-20% of them. One foetus acts as the donor and the other acts as a recipient. This results in the donor having reduced flow whereas the other has increased flow

Question 20

What are the cardiac manifestations for the Recipient twin in TTTS?

Answer 20

High output cardiac failure leading to tricuspid regurg.

Question 21

List the US-findings in TTTS

Answer 21

Donor foetus: reduced flow
1) Anemia
2) Selective IUGR
3) Hypovolemic
4) Small bladder
5) => Oligohydramnios
6) “Stuck” Appearance (stuck to the wall whereas other is swimming in extra fluid)

Recipient Foetus: Increased flow => High output cardiac failure
1) Plethoric
2) LGA
3) Hypervolemic => Ascites
4) Large bladder
5) => Polyhydramnios

Question 22

90% of TTTS have complications. List 4 complications

Answer 22

Polyhydramnios
Severe preterm delivery
Miscarriage
Death

Question 23

What is a normal umbilical cord formed from?
What is the pathophysiology of TTTS?

Answer 23

Normally it is formed of 2 arteries (deoxygenated) and 1 vein (oxygenated) enclosed within whartons jelly.
Also, they would have AV anastomosis at the cotyledons in the placenta with blood flowing in both directions. In TTTS, the anastomosis is causing blood to only flow in one direction => AV shunt vessels!!.

Question 24

There are 3 types of anastomoses. Which type is associated with TTTS?

Answer 24

Arteriovenous flowing in 1 direction => AV shunt vessels!
In monochorionic twins, arteriovenous (AV) anastomoses within the shared placenta normally allow for balanced blood exchange between the twins. However, in Twin-to-Twin Transfusion Syndrome (TTTS), these AV connections become imbalanced, leading to unequal blood flow.

Question 25

How would you diagnose TTTS using Quintero staging

Answer 25

First you need to diagnose that it is a monochorionic twin pregnancy because it cannot happen in DCDA. Then you would need to compare

Stage 1: Donor bladder visible
Stage 2: Donor bladder not visible/oligohydramnios/stuck twin
Stage 3: Absent or reversed end-diastolic flow in Doppler US
Stage 4: Presence of foetal hydrops (Anemia)
Stage 5: Demise of one or both fetuses

Question 26

In terms of treatment, how would you manage TTTS

Answer 26

1) Reduction Amniocentesis
2) Fetoscopic Laser ablation of the AV shunt vessels (Done in conjunction with amniocentesis)

Question 27

How is reduction amniocentesis performed?
What are the benefits of this?

Answer 27

US-guided needle drainage of as much amniotic fluid as possible around recipient fetus. Repeat as much as needed to maintain normal amniotic fluid volume.
1) This relieves pressure from the recipient sac allowing for more perfusion
2) Reduces uterine over-distension which reduces the chances of pre-term delivery

Note that as with normal amniocentesis, this carries the risk of miscarriage, chorioamnionitis, damage to organs…

Question 28

How is Fetoscopic Laser Ablation performed?

Answer 28

Performed at the same time as reduction amniocentesis. It involves the injection of local anesthesia followed by insertion of a 2mm festoscope into maternal abdominal wall (through drainage site) into uterine cavity => !!Selective Photocoagulation of AV shunt vessels (laser)

Question 29

MCMA twins occur in <1% of multiple pregnancies. How do you diagnose monoamniotic Twins on US?

What is the main concern with MCMA twins?

How would you manage MCMA twins

Answer 29

Absent dividing membrane on US (Vs thin on MCDA and thick in DCDA).

The main concern is the fact that the twins share 1 amniotic sac with 2 chords =? they can become entangled => cord compression => death

Admit from viability
Daily CTG monitoring
Give Steroids (2x12mg IM dexamethasone 12 hours apart)
Elective C-section at 32-34 weeks