Screening in pregnancy Flashcards
What are 4 types of fetal screening offered during pregnancy?
- Infectious diseases e.g. HIV, hepatitis B, syphilis
- Screening for inherited conditions affecting haemoglobin - thalassaemia, sickle cell disease
- Screening for chromosomal abnormalities
- Screening for physical anomalies on ultrasound
How are structural anomalies detected during pregnancy?
20 week (18-21 week) ultrasound ‘anomaly’ scan
What are 11 conditions that are looked for on a fetal anomaly scan at 20 weeks?
- Anencephaly
- Open spina bifida
- Cleft lip
- Diaphragmatic hernia
- Gastroschisis
- Exomphalos
- Serious cardiac abnormalities
- Bilateral renal agenesis
- Lethal skeletal dysplasia
- Edwards’ syndrome, or T18
- Patau’s syndrome, or T13
What proportion of fetuses have congenital malformations in the UK?
2.5%
What are 12 exampes of genetic disorders that can cause congenital abnormalities?
- Down syndrome (trisomy 21)
- Edwards syndrome (trisomy 18)
- Patau syndrome (trisomy 13)
- Triploidy
- Sex chromosome abnormalities
- XO (Turner syndrome)
- XXY (Klinefelter syndrome)
- XYY
- XXX
- Apparently balanced rearrangeemnts (translocations or inversions)
- Unbalanced chromosomal structural abnormlities
- Gene disorders e.g. fragile X syndrome, Huntington chorea, Tay-Sachs disease
What are 5 types of congenital structural disorders?
- Congenital heart disease
- Neural tube defects e.g. anencephaly, encephalocele, spina bifida
- Abdominal wall defects e.g. exomphalos, gastroschisis
- Genitourinary abnormalities
- Lung disorders
What are 5 examples of genitourinary structural disorders?
- renal dysplasia
- polycystic kidney disease
- pyelectasis
- posterior urethral valves
- Potter syndrome
What are 3 examples of structural lung disorders?
- Pulmonary hypoplasia
- Diaphragmatic herniae
- Cystic fibrosis
What are 12 examples of congenital infection?
- Toxoplasmosis
- Syphilis
- Rubella
- Cytomegalovrius
- Herpes simplex virus
- HIV
- Beta-haemolytic streptococci group B
- Chickenpox
- Erythrovirus
- Zika
- Hepatitis
- Listeria monocytogenes
What are 4 aims of prenatal diagnosis of congenital abnormalities?
- To identify early those which are incompatible with life or that are likely to result in significant handicap so as to prepare the parents, involve other specialist clinicians and offer option of termination of pregnancy if appropriate
- Identify conditions which may influence timing, site or mode of delivery
- Identify fetuses who may benefit from early neonatal paediatric intervention
- To identify fetuses who may benefit from in utero treatment
Why might couples opt to continue pregnancies in the face of severe defects which have resulted in either intrauterine or early neonatal death?
May find it easier to cope with their grief having held their child
What should our approach be when identifying conditions likely to cause long-term handicap and suffering for both the child and their parents?
parents must decide what is acceptable to them; we can only advise, guide and respect their final wishes, irrespective of our own personal opinions
provide written info for parents to absorb, may need to arrange follow up appointment a few days later
What increases the likelihood of autosomal trisomy, especially trisomy 21?
advancing maternal age
What are 6 factors that increase the risk of structural abnormalities?
- Increased maternal age
- Family history e.g. DMD, cysstic fibrosis, sickle cell disease
- Greater chance if parents have had previously affected child e.g. spina bifida
- Consanguinity - increases chance of single gene abnormalities, especially autosomal recessive
- Maternal pre-existing diabetes - increased risk of cardiac and neural tube defects
- Maternal epilepsy - increased chance of structural abnormalities (esp if taking teratogenic drugs)
What is the background risk of a child having spina bifida, and how is this affected if the mother has already had a child with spina bifida?
0.2%; increased to 2%
What are 2 conditions that a child is at increased risk of if the mother has pre-existing diabetes?
- Cardiac anomalies
- Neural tube defects (anencephaly, encephalocele, spina bifida)
What should counselling for screening involve?
make it clear most tests (especially those for chomosomal problems) will only identify those at ‘high or low risk’ for a condition, rather than whether condition is actually present
couple must understand that if they were placed in the ‘high risk’ group, further tests would then be offered and they should be aware of what that would involve
should ideally have given thought to what they would do should the pregnancy be affected
What type of screening test is the key one that is performed in the first trimester?
combined screening test for Down syndrome: measuring thickness of nuchal fluid behind fetal neck (nuchal translucency) + biochemistry (free beta-hCG and pregnancy-associated plasma protein A (PAPP-A)
What is the combined screening test in first trimester used to detect?
Risk of Down syndrome
What is the sensitivity of combined testing for Down’s syndrome?
up to 90% sensitivity when using cut off of 1 in 150 as high risk
but only identify those at increased risk, not absolute certainty
How does the combined screening test for Down syndrome work in dichorionic vs monochorionic twin pregnancies?
each twin given an individualised risk in dichorionic, but in monochorionic, risk is calculated as an average of that allocated to both twins
What are the 2 types of test which can be used to definitively diagnose Down syndrome?
- Amniocentesis
- Chorionic villous sampling
What are 2 reasons why it might not be possible to obtain a first trimester screening test?
- Poor fetal position
- Pregnancy already beyond 14 weeks’ gestation
In addition to informing about risk of Down syndrome, what else can nuchal translucency be used to indicate?
increased NT is a marker for structural defects e.g. cardiac malformations
What is the advantage of having the combined screening test in the first trimester?
allows surgical termination of pregnancy
At what point in the first trimester is the combined test performed?
11 - 13+6 weeks
What, in addition to Down syndrome, can be detected by the combined screening test in the first trimester?
all trisomies - Edward, Patau
What does measurement of nuchal translucency involve?
ultrasound of subcutaneous tissue between skin and soft tissue overlying cervical spine with the fetus in neutral position
In addition to the combined tests in the first trimester, what are 4 other types of tests for Down syndrome?
- Serum integrated test
- Integrated test
- Triple test
- Quadruple test
What does the serum integrated test for Down syndrome involve?
- dating scan (but not nuchal)
- PAPP-A at 10 weeks
- Quadruple test at 15 weeks measuring:
- oestriol
- hCG
- AFP
- inhibin A
What is a choroid plexus cyst?
a small, fluid-filled space that occurs in a gland in the brain called the choroid plexus. This gland is located on both the left and right side of the brain, and it makes fluid within the brain and spinal cord.
What does amniocentesis involve?
- Passing a thin needle transabdominally into the amniotic cavity, under continuous ultrasound guidance, to extract 10-15ml of amniotic fluid
- Previously, amniocyte culture was used to obtain karyotype results but this was replaced with quantitative fluorescence polymerase chain reaction (QFPCR) to exclude more common aneuploidies
- Most recently, micrarray analysis allows examination of many more segments of genome, may detect small changes not identified before
What does chorionic villous sampling involve?
passing a needle transabdominally, or occasionally transvaginally, under direct ultrasound guidance to take a sample of placental tissue
