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Fetus Module > multiple pregnancies > Flashcards

multiple pregnancies Flashcards

1
Q

what is the incidence of twins?

A

1 in 89

monozygotic twins = 3.5/1000

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2
Q

what are dizygotic twins?

A

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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3
Q

what are the causes of dizygotic twins?

A

fertility drugs
dietary (yoruba tribe nigeria)
assisted conception techniques

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4
Q

what are monozygotic twins?

A

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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5
Q

what is zygosity?

A

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

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6
Q

when is chronicity?

A

refers to placentation
monochorionic = 1 placenta
dichorionic = 2 placentas

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7
Q

what is amniotity?

A

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

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8
Q

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

A

dichorionic diamniotic

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9
Q

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

A

monochorionic diamniotic

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10
Q

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

A

mono-chorionic monoamnitoic

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11
Q

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

A

conjoined twins

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12
Q

how can chorionicity be determined?

A 
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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13
Q

what type of twins is the lambda sign seen in? when s best to see this?

A

dichorionic twins

10-14 wks (disappears by 20wks in 7%)

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14
Q

what type of twins is the T sign seen in?

A

monochorionic twins

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

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15
Q

what does 2 membrane layers mean? what does 4 membrane layers mean?

A 
2 = 2 amnions -> monochorionic diamniotic 
4 = 2 amnions and 2 chorions -> dichorionic diamniotic
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16
Q

why is chorionicity important?

A

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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17
Q

what complications are more frequent in twins then singletons?

A 
miscarriage 
perinatal death 
IUGR
preterm delivery 
major defects
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18
Q

what antenatal care is given for twin pregnancies?

A

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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19
Q

how is downs syndrome screened for?

A

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

20
Q

what is the risk chromosomal defects affect twins?

A

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

21
Q

what invasive procedures in twins is the risk?

A 
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
22
Q

how can selective feticide be done in management of MCDA twins?

A

cord occlusive techniques
1st trimester = interstitial laser
2nd trimester = bipolar cord occlusion
late pregnancy = US guided cord ligation

23
Q

why can single twin demise affect the other twin?

A

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

24
Q

how is discordant growth in twins defined?

A

birth weight different of >20-25%

associated with increased perinatal morbidity and mortality

25
Q

how are MC twins managed?

A

determine chorionicity 11-13wks
gestational age determined by CRL larger fetus
scans 2 weekly from 16wks - DVP, UAPI, fetal bladder, EFW
label twins

26
Q

what complications are associated with inter-twin vascular anastomoses?

A

twin to twin transfusion syndrome
TAPS - twin anaemia/polycythaemia sequence
selectie fetal growth restriction (sFGR)
TRAP - twin reversed arterial perfusion

27
Q

why does twin to twin transfusion occur?

A

placental vascular anastomoses which allow communication of the two feet-placental circulations in 96%
one twin receives blood = recipient
other twin drains blood = donor

28
Q

how is TTTS screened for?

A

women report increase abdominal size or SOB

2 weekly USS from 16 wks noting DVP, presence/absence of fetal bladders, UAPI, EFW

29
Q

how is TTTS diagnosed/what are the stages?

A

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

30
Q

what is the treatment for TTS?

A

<26 wks = fetoscopic laser

treat if QS 2 or more or QS 1 with DVP >8cm or cervical shortening <25mm

31
Q

what is TAPS?

A 
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
32
Q

what is the treatment for TAPS?

A

uncertain

fetoscopic laser reduces TAPS - difficult due to no polyhydraminos = only very small residual anastomoses to treat

33
Q

how do TTTS and TAPS differ?

A 
TTTS = large central artery to vein connections 
TAPS = tiny peripheral artery to vein connections
34
Q

how is selective fetal growth restriction defined?

A

growth discordance of >20%

10-15% in MC twins

35
Q

what are the different types of selective fatal growth restriction?

A 
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
36
Q

how is selective fetal growth restriction managed?

A

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

37
Q

what is twin revered arterial perfusion (TRAP) sequence?

A

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

38
Q

how is TRAP seen on USS?

A

variable US appearances
absence of cardiac pulsation in one twin
poor definition of head, trunk and arms
deformed lower extremities with subcut oedema

39
Q

how is TRAP managed?

A

conservative management
overall pump twin survival = 60%
in utero intervention is performed with cord occlusion or intrafetal ablation

40
Q

what will all MCMA twins demonstrate?

A

cord entanglement on USS

41
Q

how are MCMA twins managed?

A 
serial scans 2 weekly 
consider sulindac (NSAID) in 2nd trimester 
elective delivery at 32 weeks with maternal steroid cover
42
Q

what does the prognosis of conjoined twins depend on?

A

site and extent of conjoining

43
Q

what are the NICE guidelines for aspirin in twins?

A 
aspirin 75mg once daily if: 
age >40 
pregnancy interval >10y 
BMI >35 
family history of pre-eclampsia
44
Q

how often are DCDA twins scanned?

A

4 weekly

MCDA and MCMA = 2 weekly

45
Q

at what gestation does still birth increase in twins?

A

> 37 weeks

46
Q

what is essential to plan management of twin pregnancy?

A

early and accurate diagnosis of chorionicity

Fetus Module (18 decks)

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