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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