Antenatal and postnatal screening U2

Assessing the health and general wellbeing of the mother and testing for diseases or conditions in an embryo before it is born, using a variety of techniques. Used to identify the risk of disorders such as Down’s syndrome, spina bifida, cystic fibrosis and muscular dystrophy so that further tests and prenatal diagnosis can be offered. Used to determine the sex of the baby.

Ultrasound imaging Blood & urine tests Amniocentesis Chorionic villus sampling (CVS)

Dating scans (8-14 weeks) • Determine pregnancy stage and due date. Used with tests for marker chemicals which vary normally during pregnancy. Anomaly scans (18-20 weeks) • May detect serious physical abnormalities in the fetus.

Carried out to detect marker chemicals that are produced during the normal physiological changes that take place during pregnancy.

In a normal pregnancy HCG increases during weeks 6-10 and then decreases to a steady low level later in gestation. However it remains at a high level if the fetus has down’s syndrome.

If a marker chemical was measured at an inappropriate point in the timescale and found to be high, significance could be attributed to it mistakenly, this would lead to a false positive result. If the test was carried out and found to be low at a time when the normal value is also low, this could give a false negative result. Biochemical tests are closely synchronised with information deduced from ultrasound dating scans to prevent this.

Affects a minority of pregnant women. Most common cause of several dangerous complications that can arise during pregnancy. Can display some or all of these conditions: • High blood pressure (hypertension) • Excess protein in blood plasma. • Changes to blood biochemistry caused by altered liver or renal functions.

Amniocentesis CVS

Produced from cells derived from amniocentesis or CVS to diagnose a range of conditions. An image of an individual’s chromosomes arranged in homologous pairs and used to identify anomalies in terms of the numbers or structure of chromosomes.

Carried out at 14-16 weeks. Involves the withdrawal of a little amniotic fluid containing fetal cells. These are cultured, stained and examined under a microscope. A full chromosome complement is photographed and the chromosomes are arranged into pairs to form the karyotype. Takes about 2 weeks and allows chromosomal abnormalities to be detected. Small risk of miscarriage. Gives results later in pregnancy.

Involves taking a tiny sample of placenta cells using a fine tube inserted into the mother’s reproductive tract. Cells are cultured and used for karyotyping. Can be carried out as early as 8 weeks. Higher risk of miscarriage. Gives results earlier in pregnancy.

Diagnose a person with a genetic condition. Help work out the chances of a person developing a condition. Determine whether a person is a carrier of a certain genetic mutation that could be inherited by their children.

Neither allele in the heterozygote is dominant over the other. This results in a combination of both alleles being expressed in the phenotype. Sickle cell disease. Males and females affected equally. Carriers have sickle cell trait. Affected have sickle cell anaemia.

Autosomal recessive Autosomal dominant Autosomal incomplete dominance Sex-linked recessive genes

Cystic fibrosis. Affects males and females equally. May skip generations.

Huntingtons disease. Affects males and females equally.

Always shown in the phenotype of males. Males affected more than females. Haemophilia.

Carries out after the birth of the baby. Aimed at detecting certain conditions or abnormalities. Used to detect metabolic disorders such as PKU, the heel prick is usually used for this. PKU is caused by an autosomal recessive genetic disorder, it is when the enzyme that converts phenylalanine into tyrosine is ineffective. The phenylalanine taking a different metabolic pathway affects the baby’s mental development.