2.4 - Antenatal and Postnatal screening

• antenatal screening is to identify the risk of disorders in the foetus
• antenatal screening can be used to determine the sex of the baby
• dating scans are carried out at 8-14 weeks
• dating scans determines the age of the foetus and the expected due date
• anomaly scan is carried out at 18-20 weeks
• anomaly scan is used to detect any physical abnormalities in the foetus
• routine blood and urine tests are used to monitor the health of the mother and foetus thought the pregnancy
• blood and urine tests include biochemical tests to monitor the concentration of marker chemicals
• measuring chemicals at the wrong time could lead to false positives
• diagnostic testing includes amniocentesis and chronic villus sampling
• cells from samples can be cultured to obtain sufficient cells to produce a karyotype to diagnose a range of conditions
• a karyotype shows an individuals chromosomes arranged in homologous pairs
• amniocentesis is caried out at 14-16 weeks
• amniocentesis is used to diagnose potential birth abnormalities
• amniocentesis examines cells found in the amniotic fluid
• amniocentesis can detect possible deflects in the development of the brain or spinal cord
• amniocentesis has a small risk of miscarriage
• amniocentesis gives results later in the pregnancy and takes longer to culture the cells
• CVS is used to diagnose genetic or chromosomal abnormalities
• cvs examines cells from the placenta
• cvs occurs at 8+ weeks
• cvs is offered to women who have a family history of genetic conditions
• cvs has a higher risk of miscarriage
• cvs doesn't detect neural defects
• cvs may carry risk of defects of fingers and toes if carried out too early
• cvs gives results earler in the pregancy and cultures cells very quickly
• the two types of ultrasound scans are dating scans and anomaly scans
• postnatal screening involves health checks that are carried out after the birth of the baby, aiming to detect certain conditions or abnormalities
• postnatal diagnosis is used to detect metabolic disorders like phenylketonuria (pku)
• pku is an inborn error caused by an autosomal recessive disorder
• pku involves a substitution mutation of the gene encoding the enzyme that converts the amino acid phenylalanine to tyrosine, this enzyme is non-functional
• those with pku cant metabolise phenylalanine
• those with pku are placed on a low phenylalanine diet
• autosomal recessive disorders are rarely expressed and skips generations
• autosomal recessive disorders can be carried by a heterozygous individual and can result from two unaffected carrier parents
• autosomal dominant disorders, autosomal recessive disorders and autosomal incomplete disorders affect males and females equally
• autosomal dominant disorders means that anyone with an effected parent will be affected
• autosomal dominant disorders means that those effected can either be heterozygous or homozygous
• autosomal incomplete disorders produces maximum expression in the homozygous state
• autosomal incomplete disorders are rarely expressed maximally and are usually mild