Lecture 4.2: Prenatal Genetic Testing Flashcards
What is Screening?
A program applied to a whole population/ large numbers of asymptomatic, but potentially at risk individuals
What is Testing?
Is applied to either symptomatic individuals to establish diagnosis, or asymptomatic individuals with a positive screening test
Screening Target Audience
Foetus
Newborns
School Leavers
Adult Volunteers
Couples
Screening offered during pregnancy
• Infectious diseases
• Inherited conditions
• 11 physical conditions (20 week scan)
• Down’s syndrome, Edwards’ syndrome and
Patau’s syndrome
Screening offered for the newborn
• Newborn physical examination
• Newborn hearing screening
• Newborn Blood spot screening
The NHS young person and adult programmes
• Eye problems in people with diabetes
• Abdominal aortic aneurysms
Pre cancerous cell changes screening
• Breast
• Cervical
• Bowel
Newborn Blood Spot: when? by whom?
Day 5
Carried out by a Healthcare Professional:
• Heel prick
• 4 spots on special card
• Occasionally may need to be carried out later or second test
Newborn Blood Spot: what are they testing for? Name 5
Phenylketonuria (PKU)
Congenital hypothyroidism (CHT)
Sickle cell disease (SCD)
Cystic fibrosis (CF)
Medium-chain acyl-CoA dehydrogenase deficiency (MCADD)
Homocystinuria (HCU)
Maple Syrup Urine Disease (MSUD)
Glutaric Aciduria type 1 (GA1)
Isovaleric Aciduria (IVA)
Newborn Hearing Screening
The automated otoacoustic emission (AOAE) test
Quick, non invasive, a small soft-tipped earpiece is placed in baby’s ear and gentle clicking sounds are played
If results unclear offered a 2nd test. This may be repeat AOAE or another test called the automated auditory brainstem response (AABR) test
The AABR test involves placing 3 small sensors on baby’s head and neck. Soft
headphones are placed over baby’s ears and gentle clicking sounds are played
Newborn Physical Examination
Offered within 72hrs of birth
Examine:
• General health (colour, tone)
• Eyes
• Heart
• Hips
• Testicles
• Back
• Hands/feet
• Palate
• Anus
Maternal Health Screening
Looking for risk factors which may predispose to conditions which may impact pregnancy and baby’s health and/or maternal health
Risk assessed using information gathered from clinical history +/- examinations +/- investigations
If classified as high risk mother offered further intervention
Maternal Health Screening: Possible Conditions Detected
Gestational diabetes
Preeclampsia
Mental health disorders
Blood group and Rhesus factor
Screening for Infectious Diseases
Blood test
3 infectious diseases:
• Hepatitis B
• HIV
• Syphilis
Enables early treatment to prevent vertical transmission
Screening for Inherited Diseases
Sickle Cell
Thalassemia
Screening for Physical Conditions
20 Week Scan
Detailed look at bones, heart, brain, spinal cord, face, kidneys and abdomen
Cleft Lip/ Palate
The tissue that makes up the roof of the mouth does not join together completely during pregnancy
Diaphragmatic Hernia
A birth defect where there is a hole in the diaphragm
There are multiple air filled loops in the left hemi-thorax with mediastinal shift to the right and ipsilateral lung hypoplasia
Spina Bifida
A condition that affects the spine
Failure of closure of the vertebral arch
“Combined Test”
10-14 weeks pregnancy
Nuchal translucency (fluid at the back of the baby’s neck)
Blood test (Beta HCG, Serum pregnancy-associated plasma protein A)
Combined results of both tests calculate risk for all 3 condition (T13, T18, T21)
“Quadruple Test”
14-20w
Blood test (Alpha feta protein, BHCG, Unconjugated estriol and Inhibin A)
Down’s only
Less accurate
Outcome of Foetal Anomaly Screening
Higher-risk result: Offered a diagnostic test to find out for certain whether the baby has Down’s, Edwards’ or Patau’s syndrome or not
Screening for Neural Tube Defects
Levels of AFP tested
However, there is overlap of AFP levels in normal pregnancies and those with neural tube defects
What happens with high-risk individuals?
Genetic diagnostic tests (tests/biopsies of foetus, PCR, karyotyping)
Psychological support in prenatal screening (genetic counselling)
Foetal DNA Screening
Amniotic fluid cells
Chorion villus biopsy
Foetal DNA in mother’s blood
Amniocentesis
15–20 weeks of gestation
Ultrasound guidance
Cells must be recovered and may need to be cultured for 2 weeks
0.5–1.0% risk of causing miscarriage
Chorion Villus Biopsy
10–13 weeks gestation
Ultrasound guidance
Trans-cervical or transabdominal
Foetal villi must be separated from maternal tissue
2% risk of causing miscarriage
