Multiple pregnancy

Question 1

What is the incidence of twins

Answer 1

Hellin’s law- 1/89 twins, 1/89^2 for triplets etc
Monozygotic twins static- 3.5/1000 pregnancies
Dizygotic twins vary- age, ethnicity, ART, family history, parity

Question 2

What are dizygotic twins

Answer 2

80%
Fertilisation of two eggs by two different sperm
Each fetus has own genetic makeup
Increased FSH and LH
Multiple ovulation due to increased FSH
Dichorionic + Diamniotic but can have fused placenta

Question 3

What are monozygotic twins

Answer 3

20%
One egg, one sperm. Genetically identical
Can be due to oxygen lack + delayed implantation
Unrelated to hereditary factors
Can be mono/di chorionic, mono/di amniotic

Question 4

How does stage of splitting affect chroionicity

Answer 4

2 cell- separate amnion + chorion
Early blastocyst- separate amnion, common chorion
8-13 cells- common amnion + chorion
13+ conjoined twins

Question 5

How is chorionicity determined

Answer 5

Number of placental sites
Intertwin membrane placental insertion (lambda or T)
Intertwin membrane thickness
Counting membrane layers
Composite measures- placental mass, sex, number of gestational sacs, fetal poles

Question 6

What is the sign of dichorionic twins

Answer 6

Lambda

Optimal gestation 10-14 weeks

Question 7

What is the sign of monochorionic twins

Answer 7

T
Only 2 composite layers compared to dichorionic 4
Single placental mass
Thin dividing membrane

Question 8

Why is counting membranes difficult

Answer 8

Depends on resolution of ultrasound equipment + skill of operator
Difficult with high BMI

Question 9

How can membrane thickness be used to determine chorionicity

Answer 9

Dichorionic 2.4mm, <2mm

Monochorionic 1.4mm

Question 10

Why is chorionicity important

Answer 10

Perinatal mortality of twins 6x singletons
MC twins 4x DC twins
Risk of TTTS
Early diagnosis increases potential for treatment + intervention

Question 11

What happens if chorionicity cannot be determined

Answer 11

Treat as worst case scenario- MCDA

Question 12

How is downs syndrome screened for

Answer 12

First trimester NT PAPP-A, hCG

Second trimester inhibin, hCG, oestriol, AFP

Question 13

How does screening work in twins

Answer 13

DC twins have individual risk for each fetus
MC twins have same risk
Detection rate is lower in DC twins

Question 14

How do chromosomal defects affect twins

Answer 14

MZ twins same risk as singletons

DZ twins chance that one is affected 2x singletons

Question 15

How are invasive procedures done in twin pregnancies

Answer 15

Only in specialist centres
CVS + amniocentesis
Possible double miscarriage rate if DC- 2 procedures
Amniocentesis preferable to CVS- placenta already under pressure

Question 16

How are DCDA twins discordant for fetal abnormality managed

Answer 16

Selective feticide
If diagnosed at 20 weeks delay feticide to 30-32 weeks to allow survival of normal twin
Cord occlusive techniques
17-25 weeks bipolar cord occlusion
26+ ultrasound guided cord ligation

Question 17

What is single twin demise and how is it managed

Answer 17

Acute intertwin transfusional event
Haemodynamic changes at time of death with survivor losing 50% circulating volume to dead twin
Risk of neurological handicap to survivor
Refer to FMU
MRI at 4 weeks post fetal demise to scan brain for abnormal MRI- risk of cerebral palsy

Question 18

How is discordant growth in twins managed

Answer 18

Detection more difficult than singletons
Regular ultrasound- every 2 weeks from 16
Discordant growth = birth weight difference >25%
Increased perinatal morbidity + mortality
Monitoring with Doppler + liquor

Question 19

What are the RCOG guidelines for management of monochorionic twin pregnancy

Answer 19

Determine chorionicity 11-13 +6 weeks
Gestational age determined by CRL of larger fetus
Scans every 2 weeks from 16
Label twins laternal or vertical
Thermal image of chorionicity

Question 20

What are the complications associated with intertwin vascular anastomoses

Answer 20

Twin to twin transfusion syndrome
Twin anaemia/polycythaemia sequence
Selective fetal growth restriction
Twin reversed arterial perfusion

Question 21

What is TTTS

Answer 21

15% MCDA twins
Placental vascular anastmoses allow communication between two fetoplacental circulations
Imbalance between deep + superficial anastomoses- more deep- one twin can drain circulation of other
Larger baby makes more urine(amniotic fluid) causes uterine overdistention, preterm labour

Question 22

How is TTTS screened for

Answer 22

Nuchal translucency no longer
Increased abdominal size or SOB
Two weekly ultrasound from 16 weeks

Question 23

How is TTTS diagnosed

Answer 23

Quinterro score
1- oligo/poly sequence, donor has visible bladder
2- donor bladder not visualised
3- abnormal dopplers, umbilical arteries or ductus venosus
4- hydrops
5- fetal demise (1/both)

Question 24

What is the treatment for TTTS

Answer 24

<26 weeks then fetoscopic laser technique if QS 2+ or DVP >8cm with cervical shortening
Assessment of fetal heart post laser looking for functional abnormalities
Elective delivery 34-36 weeks
Amnioreduction after 26 weeks when fetoscopic laser not possible

Question 25

What is TAPS

Answer 25

2% uncomplicated MC twins, 13% post TTTS laser
Fetal anaemia in donor, polycythaemia in recipient
No oligo/polyhydramnios sequence
Donor has increased MCA PI, recipient decreased

Question 26

How is TAPS treated

Answer 26

Optimum management uncertain
Fetoscopic laser with solomon technique- at visible anastomoses
Selective feticide
Repeat laser treatment but difficult due to no polyhydramnios + very small residual anastomoses
Outcome varable with severity

Question 27

What is selective growth restiction

Answer 27

Growth discordance >20%
1- growth discordance, positive doppler
2- growth discordance, AREDV in one or both
3- growth discordance with cyclical umbilical artery diastolic waveforms

Question 28

How is selective fetal growth restriction managed

Answer 28

Tertiary FM centre
Selective reduction only offered in early onset cases with poor growth + abnormal dopplers
Ultrasound assessment every 2 weeks
Abnormal FV or CTG triggers delivery
Type 1 delivery 34-36 weeks
Tyepe 2+3 delivery 32 week

Question 29

What is TRAP

Answer 29

1% MC twins
Lack of cardiac structure in one fetus (acardiac), perfused by structurally normal cotwin
Single superficial artery anastomoses, arterial blood flow retrograde
Ultrasound appearance- variable, absence of cardiac pulsation, poor definition of head trunk + extremities, deformed lower extremities

Question 30

Management of TRAP

Answer 30

Conservative management when AC ratio <50%
Death of cotwin in 25%
Overall pump twin survival 60%
In utero intervention- cord occlusion or intrafetal ablation
Radiofrequency ablation >90% survival of pump twin

Question 31

What are monochorionic monoamniotic twins

Answer 31

Single amnion, single placenta
All babies demonstrate cord entanglement on ultrasound + doppler
Death due to congenital abnormalities up to 50%
Overall survival 60%

Question 32

How are MCMA twins managed

Answer 32

Serial scans 2 weeks
Poor outcomes mainly <24 weeks
Consider Sulindac in 2nd trimester
Inpatient monitoring
Twice daily CTGs
Elective delivery at 32 weeks with steroid cover

Question 33

What are conjoined twins

Answer 33

1/90-100,000
Classified according to interfetal body communication
Prognosis depends on site and extent of conjoining
20% termination, 10% IUD, 75% born alive have inoperable defects

Question 34

What are the NICE guidelines for twin pregnancy

Answer 34

Aspirin 75mg daily if >40, pregnancy interval >10y, BMI >35, family history of preeclampsia