Prenatal Screening Flashcards
Screening in Pregnancy: Aims:
A process of identifying those who may be at risk of a disease or a condition.
to offer info, continue further testing and reduce risks/complications
Screening in Pregnancy:
- blood group screening
- infectious diseases: HIV, Hep B, syphilis
- haemoglobinopathie
- oral glucose tolerance test: gestational
diabetes - Down syndrome (trisomy 21)
- Edward Syndrome (Trisomy 18)
- Patau Syndrome (Trisomy 13)
- Dating ultrasound at 12 weeks
- anomaly ultrasound at 20 weeks
Screening Timeline:
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Blood Group Screening:
- determine maternal blood group: Rh+/-
- Rh- mother first pregnancy no issues
- second pregnancy; if first pregnancy had
Rh+ babe, antibodies are raises in mother
and cant target RBCs of a second Rh+ baby
in a following pregnancy - can result in an anemic baby or a baby
who develops jaundice after birth
= haemolytic disease of the newborn
IgM antibodies in first pregnancy are large so can not pass placenta
Second pregnancy, smaller IgGs can pass through the placenta
Haemoglobinopathies:
- all women offered thalassaemia screening,
high risk offered sickle cell disease
screening - test preferably before 10 weeks, if mother
is found to be carrier, father is offered
screening - most commonly seen in African, Carribean,
Mediterranean, Indian, Asian backgrounds
IDPS: Infectious Diseases in Pregnancy Screening:
- HIV: can be passed during pregnancy, birth
or breastfeeding if untreated - Hep B: if diagnosed, specialist care offered
complete course of vaccinations for
baby in first year to reduce risk - Syphilis: treated with antibiotics, earlier
treatment, lower risk of passing it
on to the baby
Dating Scan:
- ultrasound
- confirms viable pregnancy at 12 weeks
- 2-3% will have miscarried at this point
- confirms the number of foetuses and
chorionicity (one sac vs two) - measures foetus size to estimate gestation
of the pregnancy - checks for other conditions/structural
abnormalities
*part of combined screening test, to determine trisomy’s, only done between 10-14 weeks
Dating Scan: Other conditions/structural abnormalities:
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Combined Screening Test:
- ultrasound scan, screening for down
syndrome, edwards syndrome and pataus
syndrome - second part:
- blood test from mother, when foetus is
between 10-14 weeks (only this time
frame) - tests for bhCG (beta human chorionic
gonadotrophin) -> beta subunit of a
placenta produced protein (trophoblast
cells) - PAPP-A (pregnancy associated plasma
protein A) -> glycoprotein released soon
after implantation - nuchal translucency scan?
Which one is B-hCG and PAPP-A
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- normal starting point dependant on
maternal age and risk of developing
trisomy based on level
NT Scan: Nuchal Translucency Scan:
- between 11 and 14 weeks
- measures fluid at the back of the foetal
neck - associated with risk of trisomys
- per maternal age, and fluid accumulation,
risk is determined
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First Trimester Combined Screening Outcome:
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13, 18, 21 -> rest are fatal
incidence of trisomy is provided in ratio
Factors the can influence Combined Screening:
- maternal age
- gestational age
- ethnicity
- smoking (affects placenta)
- IVF
- multiple pregnancy
- weight: increased blood volume, dilute
marker conc in serum - diabetes
- past history of chromosome abnormality
- fetal sex
- analytical imprecision
For which trisomy is the quadruple screening test offered?
- screens for T21 only (down syndrome)
- if missed combined screening test
- lower detection rate than combined
- indications: NT measurements can’t be
obtained, CRL > 84, head circumference
between 101-173mm - test undergone between 14 -20 weeks
Checks:
- alpha fetoprotein (AFP): produced by yolk
sac, liver in foetal liver
- bhCG
- inhibin A: protein that regulates FSH
secretion
- unconjugated oestriol: steroid hormone
When is risk for trisomy considered high?
- 1:150
- 1:151 = low risk
- if high risk further screening tests are
offered
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NIPT: Non-invasive Prenatal Testing:
- for high risk trisomy
- FURTHER SCREENING TEST -> maternal
blood - cell free foetal DNA analysed in maternal
blood - looks at chromosomes 13,18,21
- increased detection compared to a normal
threshold indicates incidence of a trisomy
syndrome - test maternal blood from 10 weeks
- screening for T21 sensitivity and specificity
over 99% - less accurate in twins
- more accurate the combined/quadruple
- less accurate before 10 weeks
If NIPT shows high risk of trisomy then what tests are offered?
- diagnostic tests = invasive
- chorionic villous sampling (10-13 weeks)
- amiocentesis (15-20 weeks)
around 1% risk of miscarriage, higher in twins
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FASP: Fetal Anomaly Screening Programme:
- ultrasound scan between 18-26 weeks
- screening for 11 conditions:
- where baby may benefit from treatment
before/after birth - birth is advisable in an appropriate
hospital/center to optimise treatment
after the baby is born - baby may die shortly after birth
- where baby may benefit from treatment
What conditions are screened at 20 weeks in FASP?
- anencephaly
- open spina bifida
- cleft lip
- diaphragmatic hernia
- gastroschisis
- exomphalos
- serious cardiac anomalies
- bilateral renal agenesis
- lethal skeletal dysplasia
- edward’s syndrome
- patau’s syndrome
Meiosis:
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Chromosome Non-disjunction:
- mistake in chromosome separation during
meiosis - one daughter cells ends up with a
chromosome pair, other does not; one
daughter ends up with two sister
chromatid the other with none -> gametes
with incorrect chromosome numbers - Aneuploidy: one more or one less
chromosome (45/47) = non-viable - monsomies or trisomies
Down Syndrome:
- Trisomy 21
- some level of learning disabilities,
heart/septal defects, sight/hearing
problems - 1 in 1000 live births
- neurodevelopmental delay is variable
- 50% heart defects
- 95% due to non-disjunction
- 4% due to translocation of chromosome
21 to 14 - 1% due to mosaicism
Down Syndrome: Features:
- flat face, upward slant to eyes
- short neck
- abnormally shaped ears
- protruding tongue
- small head
- deep crease in the palm of the hand with
relatively short fingers - white spots in the iris of the eye
- poor muscle tone, loose ligaments,
excessive flexibility
Edward’s Syndrome:
- trisomy 18
- 1 in 8000 live births
- most die before or just after birth
- median survival rate is 2 weeks
- 10% survive up to 5 years
Edward’s Syndrome Characteristics:
- low birth weight
- microcephaly (small head)
- severe learning disability
- micrognathia (small jaw)
- malformations of heart and kidneys
- clenched fists and malformed feet
- feeding and breathing problems
- cleft lip/cleft palate
Patau’s Syndrome:
- trisomy 13
- heart defects, brain defects, spinal
abnormalities, physical abnormalities - low birth weight
- stillborn, die within few days
- 10% survive the first year
- 1 in 25,000
Patau’s Syndrome Characteristics:
- cleft lip/palate
- microphthalmis = abnormally small eye/s
- anopthalmia = absence of 1/both eyes
- hypetelorism = reduced distance between
eyes - nasal passage abnormal development
- cutis aplasia = skin missing from scalp
- ear malformations and deafness
- raised, red birthmarks = capillary
haemangiomas
Prevalence of Trisomies
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