Twin Pregnancies Flashcards
Definition of monozygous
Twins arising from a single fertilised egg that has divided into two growing embryos
Definition of dizygous
Twins arising from two separate fertilised eggs
Definition of chorionicity
Refers to the number of outer membranes surrounding the foetus and the corresponding placentation
Definition of amnionicity
Refers to the inner membrane layers that do or do not separate the gestational sacs of twins
Prevalence of twins in Australia
1-2% of pregnancies
Statistics of dizygotic v monozygotic v conjoined twins
70% of twins dizygotic
30% of twins monozygotic
- 1 in 200 of these will be conjoined
Definition of monochorionic monoamniotic
(MC/MA) no membranes separating the twins - they share a gestational sac
Definition of monochorionic diamniotic
(MC/DA) the membrane separating the twins is only two layers consisting of amnion, placenta is shared
Definition of dichorionic diamniotic
(DC/DA) membrane separating twins consists of layers of both amnion and chorion, they have separate placentae which may or may not fuse
Complications of twin pregnancy
Higher frequency and severity of pregnancy symptoms (hyperemesis, respiratory discomfort)
Preterm birth (less than 50% continue to 38 weeks)
IUGR
Increased incidence of complications (miscarriage, anaemia, polyhydramnios, PET, GDM, congenital anomalies, malpresentations, cord accidents, PPH)
TTTS - in monochorionic twins
Antepartum death of one twin
Increased risk of long term infant adverse outcomes e.g. CP
Complications specific to monochorionic twins
Twin to twin transfusion syndrome (twin oligohydramnios/polyjhydramnios sequence or twin anaemia/polycythaemia sequence)
Death of one twin
SPECIFIC TO MONOAMNIOTIC:
Cord entaglement in utero
Twin reversed arterial perfusion sequence
Complications specific to monoamniotic twins
Cord entanglement in utero
Twin reversed arterial perfusion sequence
Prevalence of twin to twin transfusion syndrome
develops in 15% of monochorionic twins (accounts for 15% perinatal mortality)
Clinical features of TOPS (classical) type of TTTS
Oligohydramnios, poor growth and abnormal umbilical artery Doppler in donor
Polyhydramnios progressing to cardiac dysfunction and failure in the recipient
Clinical features of TAPS type of TTTS
Slightly discordant middle cerebral artery peak systolic velocities (reflects anaemia and polycythaemia in donor and recipient respectively)
More common in later pregnancy
Can be associated with significant foetal anaemia and in utero compromise
Common cause of TAPS type of TTTS
Secondary to undergoing laser treatment for TOPS
Very slow transfusion from donor to recipient (thus fluid remains constant, but Hb slowly increases)
Surveillance of twins with TTTS
USS examination for:
- growth
- amniotic fluid volume in each sac
- bladder volume
- umbilical artery Doppler wave forms (after 24 weeks)
- MCA Doppler wave forms after 24 weeks
When is clinical suspicion of TTTS raised
Early discordance in foetal size or nuchal translucency
Discordance in foetal growth/size (+/- poly/oligo-hydramnios)
Rapid increase in maternal abdominal girth (rapid accumulation of polyhydramnios)
Treatment of TTTS
Serial amnioreduction via amniocentesis
OR
Fetoscopic laser ablation of placental vascular anastamoses in second trimester (higher survival rate and lower neurological morbidity postnatally than amniocentesis)
Additional monitoring of monoamniotic twins
Frequent CTG once reach viability
Delivery is indicated if cord compression is diagnosed
Changes in antenatal care in twin pregnancy v singleton
More frequent antenatal visits
Iron and folic acid supplements in all mothers (regardless of iron stores)
Second trimester screening for T21 is not applicable - NT is main test
USS every 3-4 weeks from 24w onwards
Screening and diagnosis of Down syndrome in twin pregnancies
Nuchal translucency is most useful parameter (thus second trimester screening basically useless)
Delivery of twin pregnancy
Must be at a higher level hospital (at least level 4)
Monochorionic from 36 weeks on
Dichorionic from 37 weeks on
Vaginal birth if meets conditions
C-section at 38 weeks if does not
Monoamniotic twins: c-section at 32 weeks
Conditions for vaginal delivery of twins
- Twins are diamniotic
- Twin 1 is cephalic
- Twin II is not more than 500g heavier than twin I
- Neither twin has evidence of foetal compromise
