multiple pregnancies Flashcards
what is the incidence of twins?
1 in 89
monozygotic twins = 3.5/1000
what are dizygotic twins?
fertilisation of 2 eggs by 2 different sperm= 2 babies with a different genetic makeup
women have increased FSH and LH
80% of twins
what are the causes of dizygotic twins?
fertility drugs
dietary (yoruba tribe nigeria)
assisted conception techniques
what are monozygotic twins?
fertilisation of 1 egg by 1 sperm
same sex and genetically identical
occur due to lack of oxygen due to delayed implantation
20% of twins
what is zygosity?
refers to whether twins are monozygotic = identical or dizygotic = non-identical
when is chronicity?
refers to placentation
monochorionic = 1 placenta
dichorionic = 2 placentas
what is amniotity?
refers to how many amniotic sacs there are, if the babies are in separate ones or the same
what kind of twins are made if the cell division occurs at <4 days at the morula stage?
dichorionic diamniotic
what kind of twins do you gt if cell division occurs at 4-8 days at the blastocyst stage?
monochorionic diamniotic
what kind of twins do you get if cell division occurs at 8-13 days at the implanted blastocyst stage?
mono-chorionic monoamnitoic
what kind of twins do you get if cell division occurs >13 days once the embryonic disc is formed?
conjoined twins
how can chorionicity be determined?
number of placental sites plus inter-twin membrane placental insertion (lambda or T sign) inter-twin membrane thickness => DC - >2.4mm MC - <1.8mm counting membrane layers composite measures (placental masses, sex, number of gestational sacs and fetal pole)
what type of twins is the lambda sign seen in? when s best to see this?
dichorionic twins
10-14 wks (disappears by 20wks in 7%)
what type of twins is the T sign seen in?
monochorionic twins
= single placental mass, very thin dividing membrane, composed of 2 amniotic layers
what does 2 membrane layers mean? what does 4 membrane layers mean?
2 = 2 amnions -> monochorionic diamniotic 4 = 2 amnions and 2 chorions -> dichorionic diamniotic
why is chorionicity important?
perinatal mortality for twins 6x above singletons
perinatal mortality for MC twins increased 3-4x above DC twins
primarily due to TTTS = twin-to-twin transfusion syndrome
erly diagnosis and surveillance will increase potential for treatment and intervention
what complications are more frequent in twins then singletons?
miscarriage perinatal death IUGR preterm delivery major defects
what antenatal care is given for twin pregnancies?
scan 11-13wks for chorionicity and DSS
gestational age is based on larger twin
TA views ate poorer so use TV US
how is downs syndrome screened for?
1st trimester = nuchal translucency, PAPPA and hCG
2nd trimester = inhibit, hCG, estriol, AFP
DC twins have an individual risk for each baby - so risk is higher
MC twins have the same risk
what is the risk chromosomal defects affect twins?
DZ twins age related risk same as singletons but chance that at least one fetus is affected is 2x singletons
MZ twins same as singletons - usually both affected
what invasive procedures in twins is the risk?
only done is specialist centres CVS - MR = 1% amniocentesis - MR = 0.9% double MR for DC twins as 2 procedures is needed amniocentesis is preferred in MC twins
how can selective feticide be done in management of MCDA twins?
cord occlusive techniques
1st trimester = interstitial laser
2nd trimester = bipolar cord occlusion
late pregnancy = US guided cord ligation
why can single twin demise affect the other twin?
placental anastomoses intact risk of acute inter-twin transfusional event
acute haemodynamic changes at time of death with survivor losing 50% circulating volume into dead twin
risk of neurological handicap
how is discordant growth in twins defined?
birth weight different of >20-25%
associated with increased perinatal morbidity and mortality
how are MC twins managed?
determine chorionicity 11-13wks
gestational age determined by CRL larger fetus
scans 2 weekly from 16wks - DVP, UAPI, fetal bladder, EFW
label twins
what complications are associated with inter-twin vascular anastomoses?
twin to twin transfusion syndrome
TAPS - twin anaemia/polycythaemia sequence
selectie fetal growth restriction (sFGR)
TRAP - twin reversed arterial perfusion
why does twin to twin transfusion occur?
placental vascular anastomoses which allow communication of the two feet-placental circulations in 96%
one twin receives blood = recipient
other twin drains blood = donor
how is TTTS screened for?
women report increase abdominal size or SOB
2 weekly USS from 16 wks noting DVP, presence/absence of fetal bladders, UAPI, EFW
how is TTTS diagnosed/what are the stages?
I -> 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
what is the treatment for TTS?
<26 wks = fetoscopic laser
treat if QS 2 or more or QS 1 with DVP >8cm or cervical shortening <25mm
what is TAPS?
twin anaemia polycythaemia sequence signs of fetal anaemia in donor twin polycythaemia in recipient no oligo/polyhydrminos donor has increased MCA PI (middle cerebral artery pulsitile index) recipient has decreased MCA PI
what is the treatment for TAPS?
uncertain
fetoscopic laser reduces TAPS - difficult due to no polyhydraminos = only very small residual anastomoses to treat
how do TTTS and TAPS differ?
TTTS = large central artery to vein connections TAPS = tiny peripheral artery to vein connections
how is selective fetal growth restriction defined?
growth discordance of >20%
10-15% in MC twins
what are the different types of selective fatal growth restriction?
I = growth discordance, dopplers positive II = growth discordance with AREDV (absent or reversed end diastolic velocity) in one or both babies III = growth discordance with cyclical umbilical artery diastolic waveforms
how is selective fetal growth restriction managed?
tertiary fetal medicine centre
selective reduction can be offered in early onset cases with poor growth and abnormal dopplers
USS assessment min 2 wk
abnormal diastolic velocity should trigger delivery
type 1 = deliver 34-36wks
type 2-3 = deliver 32 wks
what is twin revered arterial perfusion (TRAP) sequence?
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 retrograde manner
how is TRAP seen on USS?
variable US appearances
absence of cardiac pulsation in one twin
poor definition of head, trunk and arms
deformed lower extremities with subcut oedema
how is TRAP managed?
conservative management
overall pump twin survival = 60%
in utero intervention is performed with cord occlusion or intrafetal ablation
what will all MCMA twins demonstrate?
cord entanglement on USS
how are MCMA twins managed?
serial scans 2 weekly consider sulindac (NSAID) in 2nd trimester elective delivery at 32 weeks with maternal steroid cover
what does the prognosis of conjoined twins depend on?
site and extent of conjoining
what are the NICE guidelines for aspirin in twins?
aspirin 75mg once daily if: age >40 pregnancy interval >10y BMI >35 family history of pre-eclampsia
how often are DCDA twins scanned?
4 weekly
MCDA and MCMA = 2 weekly
at what gestation does still birth increase in twins?
> 37 weeks
what is essential to plan management of twin pregnancy?
early and accurate diagnosis of chorionicity
