twin pregnancies Flashcards
what percentage of births are twin pregnancies?
1.5%
they have a high percentage of still births
what chance of twins being preterm?
50%
how much more likely are they have to cerebral palsy
six times the risk
how many monozygotic twins?
3.5/1000
dyzgotic twins statistics?
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%
when was single embryo transfer brought in?
2009
reduced multiple pregnancy rates following IVF
what are dizygotic twins
- 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
Monozygotic twins
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
what is the relationship between zygosity and chorionicity?
Zygosity refers to whether twins are monozygotic (identical) or dizygotic (non- identical)
Chorionicity refers to placentation: monochorionic (one placenta) dichorionic (two placentas)
determination of chorionicity?
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)
what is an uss sigh of dichorionic twins?
lambda sign
Optimal gestation 10 -14 weeks
Difficult to see with advanced gestation
Disappears by 20 weeks in 7% of DC twins
monochorionic twins sign on uss?
T sign
single placental mass
very thin dividing membrane
composed of two amniotic layers
what do you see in the second trimester in dichorionic diamniotic twins
- separate placentas
- discordant gender
what do the number of membranes demonstarte?
2 layers demonstrated (2 amnions) Monochorionic diamniotic
4 layers demonstrated (2 amnions and chorions)
Dichorionic diamniotic
relies on excellent resolution of USS equipment.
what does the membrane thickness mean?
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%
what is chroionicity?
Chorionicity refers to placentation - monochorionic (one placenta) or dichorionic (two placentas)
what time of devisions lead to which types of twins ?
<4 days - dichorionic diamniotic
4-8 days - monochrorionic diamniotic
8-13 days monochorionic monamniotic
>13 days - conjoined twins
what are the risk of perinatal mortality associated with twins?
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.
what are the risks of twins?
miscarriage perinatal death UUGR Preterm delivery <32 weeks major defects
what antenatal care is given for twin pregnancies?
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
What do you look for in Down syndrome screening?
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)
what is the screening detection rates in twins?
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
what are the chances of chromosomal defects in twins?
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
what is the management of DCDA twins discordant for petal abnormality
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
what is single twin demise?
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
what is discordant growth in twins?
it is defined as a birth weight difference of >20%-25%
associated with increased perinatal morbidity
intensive monitory with doppler and liquor volumes
what are the guidelines for monochorionic twin pregnancies?
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
what are complications associated with inter-twin vascular anastomoses
Twin to twin transfusion syndrome
TAPS – Twin anaemia/polycythaemia
sequence
Selective fetal growth restriction (sFGR) TRAP – Twin reversed arterial perfusion
what is twin to twin transfusion syndrome?
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
how do you screen for TTTS?
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
how is TTTS diagnosed?
– 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
how is TTTS treated?
TTTS occurring < 26 weeks should be treated by fetoscopic laser technique
elective delivery between 34 and 36 weeks
what is TAPS?
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)
how is TAPS treated?
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
what is sFGR?
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)
how is sFGR managed
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
what is twin reversed arterial perfusion sequence? (TRAP)
• 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
whites seen on USS with TRAP?
Variable ultrasound appearances
Absence of cardiac pulsation in one twin
Poor definition of head, trunk and upper extremities
Deformed lower extremities with subcutaneous oedema
how is TRAP managed?
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
what are monochorionic mono amniotic twins
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%
how are mono amniotic twins managed
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
what are the nice guidelines for twins?
Aspirin 75mgs once daily: Age > 40 years
Pregnancy interval > 10 years BMI > 35 kg/m2
Family history of pre-eclampsia
