multiple pregnancies Flashcards by Lauren Dixie

what is the incidence of twins?

1 in 89

monozygotic twins = 3.5/1000

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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

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what are the causes of dizygotic twins?

fertility drugs
dietary (yoruba tribe nigeria)
assisted conception techniques

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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

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what is zygosity?

refers to whether twins are monozygotic = identical or dizygotic = non-identical

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when is chronicity?

refers to placentation
monochorionic = 1 placenta
dichorionic = 2 placentas

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what is amniotity?

refers to how many amniotic sacs there are, if the babies are in separate ones or the same

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what kind of twins are made if the cell division occurs at <4 days at the morula stage?

dichorionic diamniotic

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what kind of twins do you gt if cell division occurs at 4-8 days at the blastocyst stage?

monochorionic diamniotic

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what kind of twins do you get if cell division occurs at 8-13 days at the implanted blastocyst stage?

mono-chorionic monoamnitoic

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what kind of twins do you get if cell division occurs >13 days once the embryonic disc is formed?

conjoined twins

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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)

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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%)

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what type of twins is the T sign seen in?

monochorionic twins

= single placental mass, very thin dividing membrane, composed of 2 amniotic layers

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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

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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

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what complications are more frequent in twins then singletons?

miscarriage 
perinatal death 
IUGR
preterm delivery 
major defects

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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

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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