HIGHER HUMAN
BIOLOGY
Unit 2 Physiology and Health
1. Ante-natal Screening
Recap
• What are the two categories of contraception?
• Give examples of physical methods?
• What is the basis of chemical contraception?
What I need to know
• What is the purpose of antenatal screening?
• What are the two types of ultrasound scan?
• What are dating scans and chemical tests used to
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estimate?
What are anomaly scans used for?
What are biochemical tests and what are they for during
pregnancy?
Name two antenatal screening methods.
What are the advantages and disadvantages of the two
methods?
What is a karyotype and what are they used to
determine?
What is the Rhesus antibody and what are the risks
associated with this antigen during pregnancy?
What is the purpose of antenatal
screening?
• Antenatal screening is
carried out to monitor
the health of a pregnant
woman and her fetus
• Antenatal screening
identifies the risk of a
disorder so that further
tests can be carried out
and a prenatal diagnosis
given
What are the two types of ultrasound
scan?
• Dating scan
• Anomaly Scan
What are dating scans used to
determine?
• Carried out at 12
weeks
• Along with other
chemical tests used to
estimate how old the
fetus is i.e. stage of
pregnancy
• Also used to estimate
the due date
What are anomaly scans used for?
• Carried out at 20
weeks
• Used to determine any
abnormalities in the
development of the
fetus
• Also used to estimate
risk of Down’s
Syndrome
Biochemical tests
• Many physiological changes occur during
pregnancy
• Biochemical tests are used to monitor these
changes in order to highlight problems should
they occur
Tests Include
• Blood analysis to detect blood
Detect hypertension a
pre-cursor to preeclampsia
type (Rhesus)
• Hormone concentrations
(HCG)
• Thyroid (hyperthyroidism) liver
and kidney function
• Glucose analysis (gestational
diabetes)
False positives
• HCG increases up to
week 10 then
decreases in normal
pregnancy
• With a Down’s
syndrome pregnancy
HCG levels remain
high throughout
• False positive results
• Human chorionic
would be created if a
gonadotrophin levels in
blood sample was
normal pregnancy
taken at week 10
Diagnostic Screening
• These are procedures
• They include:
used to diagnose,
without doubt,
disorders associated
with the developing
fetus
• Offered if routine tests
have highlighted
problem or woman
belongs to high risk
category
• Amniocentesis
• Chorionic villus
sampling
Diagnostic testing
Amniocentesis
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Carried out at 18 weeks
Less risk of miscarriage
Amniotic fluid removed
Karyotype produced
Decision to proceed/terminate
Chorionic villus sampling
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Carried out at 8 weeks
Higher risk of miscarriage
Placental cells removed
Karyotype produced
Decision to proceed/terminate
How tests are used – Assessing risk of
Down’s syndrome
Step 1 – woman’s age/history
• Does she belong to high
risk group
Step 2 – Blood analysis
• Alpha-fetoprotein
concentration
• Levels are normal if within
0.5 – 2.49
• Low levels (less than 0.4)
can indicate high risk of
Down’s syndrome
• Baby may not have
Down’s syndrome even in
high risk
How tests used – Down’s syndrome diagnosis
Step 3a –Amniocentesis offered
• If high risk indicated
amniocentesis is offered
to confirm diagnosis
Step 3b – Nuchal translucency
Rhesus Antibody
Blood test Analysis
Second pregnancy
• Mother Rhesus negative
• If the baby is Rhesus
(no antigen for rhesus on
her blood cells)
• Causes problems if she is
carrying a Rhesus
positive baby
• Mother becomes
sensitised after birth and
produces Rhesus
antibodies
positive
• Rhesus antibodies from
mother cross placenta
and attack red blood cells
• Baby born severely
anaemic
• Prevention – Rhesus
negative expectant
mothers given Rhesus
antibody injections
Activities
• Make notes, summary on ante-natal screening
procedures
• Testing your Knowledge Qs
• p146 No’s 1-4