2.4 Antenatal and Postnatal Screening

State 2 ultrasound scans

dating scan (8 - 14 weeks), anomaly scan (18-20 weeks)

State purpose of dating scan

determine stage of pregnancy, calculate/ predict date of birth

State purpose of anomaly scan

check of physical abnormalities in foetus

State 1 biochemical test

blood and urine test

State purpose of blood and urine test

check for marker chemicals concentrations, atypical results may suggest abnormalities

Name a marker chemical

HCG, AFP (alpha fetoprotein)

Name 3 tests for mother

renal, liver, thyroid function test
red/white blood cells count
glucose, calcium, urea, protein concentration

State the outcome if biochemical test is taken at a wrong time

may lead to false positive/negative result - different stages of pregnancy have different range of chemical concentrations

State the purpose of diagnostic tests

provide definitive answer

State 2 types of diagnostic tests

amniocentesis, chorionic villus sampling (CVS)

What does diagnostics test produce

karyotype

Define karyotype

complete chromosome complement arranged as homologous pairs

How does amniocentesis work

obtain cells from amniotic fluid, culture them to produce karyotype

How does CVS work

placenta cells removed through cervix, culture them and produce karyotype

State disadvantage of amniocentesis

risk of miscarriage

State advantage of CVS

can be done earlier - at 8 weeks instead of 14 - 16 weeks

State disadvantage of CVS

increased risk of miscarriage

State term used to describe x and y chromosomes

sex chromosomes

Define autosomes

all chromosomes except the sex chromosomes

State 4 characteristics of autosomal recessive inheritances and name an example

- affect male and female equally
- may skip generation
- express relatively rarely
- may express in consanguineous marriages (incest)
- sufferer (ff) non sufferer (Ff or FF)
- cystic fibrosis

State 4 characteristics of autosomal dominant inheritances and name an example

- affect male and female equally
- every sufferer has an affected parent
- expressed in every generation
- if a branch of tree fails to express the trait, it won't come back
- sufferer (Ff or FF) non sufferer (ff)
- huntington's disease

State 4 characteristics of autosomal incomplete dominance and name an example

- affect male and female equally
- fully expressed trait is relatively rare
- partially expressed trait relatively frequent
- each sufferer with fully expressed trait has 2 partially affected parents
- sufferer with fully expressed trait (SS) sufferer with partially expressed trait (SF) non sufferer (FF)
- sickle cell disease

State characteristics of sex-linked recessive trait and name an example

- affect males disproportionately more
- sufferer (XbY or XbXb), carrier (XBXb), non sufferer (XBY or XBXB)
- eg haemophilia, colour blindness

Define sex linked gene

surplus genes on the X chromosome and not on the Y