twin pregnancies

Question 1

what percentage of births are twin pregnancies?

Answer 1

1.5%

they have a high percentage of still births

Question 2

what chance of twins being preterm?

Answer 2

50%

Question 3

how much more likely are they have to cerebral palsy

Answer 3

six times the risk

Question 4

how many monozygotic twins?

Answer 4

3.5/1000

Question 5

dyzgotic twins statistics?

Answer 5

Dyzgotic twins vary according to ethnicity, maternal age, ART, family history, parity

The highest rates of DZ twins worldwide are in Nigeria, estimated at 45%, lowest in Japan at 1.2%

Question 6

when was single embryo transfer brought in?

Answer 6

2009

reduced multiple pregnancy rates following IVF

Question 7

what are dizygotic twins

Answer 7

• 80% of twins
• Fertilisation of two eggs by two different sperm
• Two babies with a different genetic makeup
• Women with dizygotic twins have ↑ FSH and LH
• Multiple ovulation due to increased FSH
  - fertility drugs
  - dietary (Yoruba tribe Nigeria - they eat food rich in FSH)
  - assisted conception techniques

Question 8

Monozygotic twins

Answer 8

20% of twins; worldwide 3.5/1000 births
Fertilisation of one egg by one sperm
Same sex and genetically identical
Occur due to oxygen lack as a result of delayed implantation
Unrelated to hereditary factors

Question 9

what is the relationship between zygosity and chorionicity?

Answer 9

Zygosity refers to whether twins are monozygotic (identical) or dizygotic (non- identical)
Chorionicity refers to placentation: monochorionic (one placenta) dichorionic (two placentas)

Question 10

determination of chorionicity?

Answer 10

Number of placental sites plus inter-twin membrane placental insertion (Lambda or T sign)

Inter twin membrane thickness (> 2.4mms DC, <1.8 mms MC) Overall 99% sensitivity.

Counting membrane layers

Composite measures (placental masses, sex, number of gestation sacs and fetal poles)

Question 11

what is an uss sigh of dichorionic twins?

Answer 11

lambda sign

Optimal gestation 10 -14 weeks

Difficult to see with advanced gestation
Disappears by 20 weeks in 7% of DC twins

Question 12

monochorionic twins sign on uss?

Answer 12

T sign
single placental mass
very thin dividing membrane
composed of two amniotic layers

Question 13

what do you see in the second trimester in dichorionic diamniotic twins

Answer 13

• separate placentas

- discordant gender

Question 14

what do the number of membranes demonstarte?

Answer 14

2 layers demonstrated (2 amnions) Monochorionic diamniotic

4 layers demonstrated (2 amnions and chorions)
Dichorionic diamniotic

relies on excellent resolution of USS equipment.

Question 15

what does the membrane thickness mean?

Answer 15

Dichorionic membranes mean thickness of 2.4mms
Monochorionic membranes mean thickness 1.4mms

membrane thickness <2mm can predict MC placenta with sensitivity and specificity 90%

Question 16

what is chroionicity?

Answer 16

Chorionicity refers to placentation - monochorionic (one placenta) or dichorionic (two placentas)

Question 17

what time of devisions lead to which types of twins ?

Answer 17

<4 days - dichorionic diamniotic
4-8 days - monochrorionic diamniotic
8-13 days monochorionic monamniotic
>13 days - conjoined twins

Question 18

what are the risk of perinatal mortality associated with twins?

Answer 18

Perinatal mortality for twins 6 times increased above that for singletons

perinatal mortality for monochorionic twins further increases 3-4 times above DC twins

primarily due to twin to twin transfusion syndrome

Early diagnosis and surveillance will increase potential for treatment intervention.

Question 19

what are the risks of twins?

Answer 19

miscarriage 
perinatal death 
UUGR
Preterm delivery <32 weeks 
major defects

Question 20

what antenatal care is given for twin pregnancies?

Answer 20

offer scan 11-13 weeks for chronicity and DSS

Gestational age based on the larger twin

Chorionicity: placental masses, y or t sign, membrane thickness

> 14 weeks determine chorionicty asap with the above and fetal sex

if unsure treat as MCDA

Question 21

What do you look for in Down syndrome screening?

Answer 21

First trimester – NT, PAPPA and hCG

Second trimester – inhibin, hCG, oestriol, AFP

DC twins will have an individual risk for each baby

MC twins the same risk (average for both babies)

Question 22

what is the screening detection rates in twins?

Answer 22

Combined 1st trimester screening
- Singletons 85% DR for 3% FPR
- DC twins detection rate is lower (75-80% DR for 3% FPR)
- MC twins DR same as singletons, but FPR 8% per fetus or 14% combined due to association between increased NT and TTTS
Quad test – MC DR 80%, DC 40-50% cfDNA now available for twin pregnancies
- Detection rates 99% for T21 and 98% T18 and T13 for a 0.2% FPR

Question 23

what are the chances of chromosomal defects in twins?

Answer 23

DZ twins age related risk same as in singletons, but chance that at least one fetus is affected is 2x singletons
MZ twins same as singletons; usually both affected

Question 24

what is the management of DCDA twins discordant for petal abnormality

Answer 24

Selective feticide:
- 12/40 loss rate 5%
- 20/40 loss rate 10-15%
 Diagnosis at 20 weeks delay feticide until 30-32 weeks to allow survival of normal twin

Selective feticide is possible using cord occlusive techniques
First trimester – interstitial laser
Second trimester (17-25 weeks) – bipolar
cord occlusion
Late pregnancy (> 26 weeks) – ultrasound guided cord ligation

Question 25

what is single twin demise?

Answer 25

death of one of the twins Uncomplicated MCDA twins still at risk of single twin demise Placental anastomoses intact risk of acute inter-twin transfusional event Acute haemodynamic changes at time of death with survivor losing 50% circulating volume into the dead twin May be transient or persistent Risk of neurological handicap in survivor 15-26% Refer to FMU for management MRI at four weeks post fetal demise

Question 26

what is discordant growth in twins?

Answer 26

it is defined as a birth weight difference of >20%-25% associated with increased perinatal morbidity intensive monitory with doppler and liquor volumes

Question 27

what are the guidelines for monochorionic twin pregnancies?

Answer 27

Determine chorionicity 11-13+6 weeks Most accurate under 14 weeks Gestational age determined by CRL larger fetus Scans two weekly from 16 weeks – DVP, UAPI, fetal bladders, EFW Label twins (lateral or vertical) Thermal image of chorionicity

Question 28

what are complications associated with inter-twin vascular anastomoses

Answer 28

Twin to twin transfusion syndrome  TAPS – Twin anaemia/polycythaemia sequence  Selective fetal growth restriction (sFGR)  TRAP – Twin reversed arterial perfusion

Question 29

what is twin to twin transfusion syndrome?

Answer 29

5% MCDA twins (1 in 1600) Placental vascular anastomoses which allow communication of the two feto-placental circulations in 96% Superficial anastomoses: AAA 66% and VVA 20% Deep anastomoses AVA 90% - cotyledon receives blood from one twin and drains venous blood to the other Presence of AVA and absence of AAA lead to TTTS

Question 30

how do you screen for TTTS?

Answer 30

if woman report increase in abdominal size or shortness of breath two weekly USS from 16 weeks noting DVP, presence/absence of the fatal bladders, UAPI, EFW

Question 31

how is TTTS diagnosed?

Answer 31

– Oligo/poly sequence; donor has visible bladder II – Donor bladder not visualised III – Abnormal Dopplers umbilical artery or ductus venosus IV – Hydrops V – Fetal demise one/both one will have polyhydramnios one will have oligohydramnios

Question 32

how is TTTS treated?

Answer 32

TTTS occurring < 26 weeks should be treated by fetoscopic laser technique elective delivery between 34 and 36 weeks

Question 33

what is TAPS?

Answer 33

win anaemia polycythaemia sequence 2% of uncomplicated MC twins, 13% post laser TTTS Signs of fetal anaemia in the donor and polycythaemia in the recipient No oligo/polyhydramnios sequence Donor has increased MCA PI (>1.5 MoM) Recipient has decreased MCA PI (< 1.0 MoM)

Question 34

how is TAPS treated?

Answer 34

Optimum management uncertain Fetoscopic laser using Solomon technique reduces TAPS Expectant, delivery, transfusion, selective feticide, Repeat laser surgery only effective treatment, but difficult due to no polyhydramnios and only very small residual anastomoses to treat Outcome variable according to TAPS severity

Question 35

what is sFGR?

Answer 35

growth discordance of >20% 10-15% all MC twins 3 types : 1) growth discordance, positive dopplers 2) growth discordance with AREDV in one or both babies 3) Growth discordance with cyclical umbilical artery diastolic waveforms (positive, absent, reversed)

Question 36

how is sFGR managed

Answer 36

Tertiary FM centre Selective reduction can be offered in early onset cases with poor growth and abnormal Dopplers USS assessment minimum two weeks Abnormal DV flow or cCTG should trigger delivery Type 1 deliver 34 - 36 weeks Type 2 and 3 deliver 32 weeks

Question 37

what is twin reversed arterial perfusion sequence? (TRAP)

Answer 37

• 1% of MC twins • Lack of cardiac structure in one fetus (acardiac twin) • Perfused by structurally normal co-twin (pump twin) • Single superficial artery- artery anastomosis through which arterial blood flows in a retrograde manne

Question 38

whites seen on USS with TRAP?

Answer 38

Variable ultrasound appearances Absence of cardiac pulsation in one twin Poor definition of head, trunk and upper extremities Deformed lower extremities with subcutaneous oedema

Question 39

how is TRAP managed?

Answer 39

Conservative management recommended when AC ratio <50%: death of co-twin in 25%,- polyhydramnios 50% and PTD in 80% Overall pump twin survival 60% In utero intervention is performed with cord occlusion or intrafetal ablation Radiofrequency ablation > 90% survival of pump twin

Question 40

what are monochorionic mono amniotic twins

Answer 40

1% all twins: 5% MC twins Single amniotic cavity, single placenta All babies will demonstrate cord entanglement on USS and Doppler Recent studies suggest overall survival 60%

Question 41

how are mono amniotic twins managed

Answer 41

Serial scans two weekly Poor outcomes mainly occur < 24 weeks Consider sulindac in second trimester (evidence poor) Inpatient monitoring with twice daily CTG elective delivery at 32 weeks with maternal steroid cover

Question 42

what are the nice guidelines for twins?

Answer 42

Aspirin 75mgs once daily: Age > 40 years Pregnancy interval > 10 years BMI > 35 kg/m2 Family history of pre-eclampsia