2.4 antenatal and postnatal screening
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What is the purpose of antenatal screening?
To identify the risk of a disorder, so further tests and a prenatal diagnosis can be offered.
How many ultrasound scans are typically given to pregnant women?
Two scans: a dating scan and an anomaly scan.
What is a dating scan, and when is it performed?
A scan to determine pregnancy stage and due date, performed between 8 and 14 weeks.
What is an anomaly scan, and when is it performed?
A scan to detect serious physical abnormalities in the fetus, performed between 18 and 20 weeks.
Why are blood and urine tests carried out throughout pregnancy?
To monitor the concentrations of marker chemicals.
What can happen if a chemical is measured at the wrong time during pregnancy?
It could lead to a false positive result.
What might an atypical concentration of a chemical indicate?
It may lead to diagnostic testing to determine if the fetus has a medical condition.
What is the purpose of a karyotype?
A karyotype shows an individual’s chromosomes arranged as homologous pairs and can detect chromosome abnormalities.
How are cells used in karyotyping?
Cells from samples are cultured to produce enough cells for a karyotype, which diagnoses a range of conditions.
What is chorionic villus sampling
CVS is a prenatal test where fetal cells are obtained from the placenta to test for genetic abnormalities.
When is chorionic villus sampling (CVS) performed compared to amniocentesis?
CVS is performed earlier in pregnancy than amniocentesis.
What is a key risk of chorionic villus sampling (CVS)?
CVS has a higher risk of miscarriage compared to amniocentesis.
What is amniocentesis?
Amniocentesis is a test where fetal cells are obtained from amniotic fluid for karyotyping to detect genetic conditions.
What is an allele?
Different forms of a gene, e.g., for hearing and non-hearing.
What does “dominant” mean in genetics?
A trait that always shows in a person’s phenotype if present
What does “recessive” mean in genetics?
A trait that only shows in a person’s phenotype if two recessive alleles are inherited.
What does “homozygous” mean?
Having two identical alleles present in a person’s genotype.
What does “heterozygous” mean?
Having two different alleles present in a person’s genotype.
Who is a “carrier” in genetic terms?
A person who has a recessive allele for a condition but does not show symptoms.
What is “genotype”?.
The alleles a person has for a trait
What is “phenotype”?
The physical expression of the alleles of a trait.
What does “sex-linked” mean in genetics?
It refers to alleles carried on the X sex chromosome.
How many alleles do females carry for a sex-linked trait?
Females carry two alleles (one on each X chromosome).
From whom do sons inherit their X chromosome?
Sons always inherit their X chromosome from their mother.