Multiple pregnancy Flashcards
What is the incidence of twins
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
What are dizygotic twins
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
What are monozygotic twins
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
How does stage of splitting affect chroionicity
2 cell- separate amnion + chorion
Early blastocyst- separate amnion, common chorion
8-13 cells- common amnion + chorion
13+ conjoined twins
How is chorionicity determined
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
What is the sign of dichorionic twins
Lambda
Optimal gestation 10-14 weeks
What is the sign of monochorionic twins
T
Only 2 composite layers compared to dichorionic 4
Single placental mass
Thin dividing membrane
Why is counting membranes difficult
Depends on resolution of ultrasound equipment + skill of operator
Difficult with high BMI
How can membrane thickness be used to determine chorionicity
Dichorionic 2.4mm, <2mm
Monochorionic 1.4mm
Why is chorionicity important
Perinatal mortality of twins 6x singletons
MC twins 4x DC twins
Risk of TTTS
Early diagnosis increases potential for treatment + intervention
What happens if chorionicity cannot be determined
Treat as worst case scenario- MCDA
How is downs syndrome screened for
First trimester NT PAPP-A, hCG
Second trimester inhibin, hCG, oestriol, AFP
How does screening work in twins
DC twins have individual risk for each fetus
MC twins have same risk
Detection rate is lower in DC twins
How do chromosomal defects affect twins
MZ twins same risk as singletons
DZ twins chance that one is affected 2x singletons
How are invasive procedures done in twin pregnancies
Only in specialist centres
CVS + amniocentesis
Possible double miscarriage rate if DC- 2 procedures
Amniocentesis preferable to CVS- placenta already under pressure
How are DCDA twins discordant for fetal abnormality managed
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
What is single twin demise and how is it managed
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
How is discordant growth in twins managed
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
What are the RCOG guidelines for management of monochorionic twin pregnancy
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
What are the complications associated with intertwin vascular anastomoses
Twin to twin transfusion syndrome
Twin anaemia/polycythaemia sequence
Selective fetal growth restriction
Twin reversed arterial perfusion
What is TTTS
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
How is TTTS screened for
Nuchal translucency no longer
Increased abdominal size or SOB
Two weekly ultrasound from 16 weeks
How is TTTS diagnosed
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)
What is the treatment for TTTS
<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
What is TAPS
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
How is TAPS treated
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
What is selective growth restiction
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
How is selective fetal growth restriction managed
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
What is TRAP
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
Management of TRAP
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
What are monochorionic monoamniotic twins
Single amnion, single placenta
All babies demonstrate cord entanglement on ultrasound + doppler
Death due to congenital abnormalities up to 50%
Overall survival 60%
How are MCMA twins managed
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
What are conjoined twins
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
What are the NICE guidelines for twin pregnancy
Aspirin 75mg daily if >40, pregnancy interval >10y, BMI >35, family history of preeclampsia
