Prenatal Screening Flashcards
(36 cards)
During screening when a woman becomes pregnant, they may have the combined test, what is the combined test?
- ultrasound scan of foetus
- blood test
- normally performed at 6 weeks
A blood test to assess for trisomy (3 chromosomes) is conducted on which week normally?
- weeks 12-13
A blood test to assess for trisomy (3 chromosomes) is conducted on weeks 12-13. What are the 3 most common chromosomes that are normally found in this blood test?
- 13, 18 and 21
What is a sensitising event in relation to blood?
- baby is rhesus + and mum is rhesus -
- a small amount of the baby’s blood enters the mother’s bloodstream during pregnancy or birth
- mother produces antibodies against the rhesus positive cells (known as ‘anti-D antibodies’)
- in a 2nd baby the antibodies can cross the placenta and attack the foetus RBCs
When screening a woman who is pregnant, we need to screen her for blood type, why?
- determine classification according to ABO (A, B, AB or O blood type)
- also determine if woman has D antigen which determine rhesus + or -
- 1st pregnancy is fine, but in 2nd pregnancy, maternal antibodies may attack babies RBCs
- screening identifies if this is an issue, and if so Anti-D immunoglobulin are provided
- performed around 20 weeks
During screening when a woman becomes pregnant, they may have the combined test:
- ultrasound scan of foetus
- blood test
- normally performed at 6 weeks
What 2 major things are they looking for on the ultrasound?
- growth patterns (foetal growth restriction or small gestational age)
- detection of trisomy (13, 18 and 21)
During screening when a woman becomes pregnant, they may have the combined test:
- ultrasound scan of foetus
- blood test
- normally performed at 6 weeks
On the ultrasound we are generally looking at growth patterns (foetal growth restriction or small gestational age) and for the detection of trisomy (13, 18 and 21). What syndromes is each of the 3 most common chromosomes affected linked with?
- 13 = patau syndrome
- 18 = edward syndrome
- 21 = down syndrome
When performing a blood test we are trying to detect if the female or baby have haemoglobinopathies, pathology of the blood. What are the 2 most common haemoglobinopathies that we are trying to detect?
1 - sickle cell disease
2 - thalassaemia
What is thalassaemia?
- disease where RBCs do not produce sufficient haemoglobin
- alpha and beta globin chains are affected
- patients may be anaemic causing them to be pale and tired
What is sickle cell disease?
- RBCs are moon shaped instead of like round donuts
- the odd shape and stickyness of the cells mean they get stuck in blood vessels
- blood vessels can become blocked or restricted limiting O2 to the body
Sickle cell disease causes RBCs to become moon shaped instead of like round donuts. The odd shape and stickyness of the cells mean they get stuck in blood vessels, causing blood vessels to become blocked or restricted limiting O2 to the body. Which populations are most likely to have sickle cell disease?
- African, Caribbean, Mediterranean, Indian or Asian backgrounds
What are the 3 main infectious diseases that mothers will be screening for when pregnant?
- HIV
- hepatitis B (specialist care is offered)
- syphylis
Generally, when can babies contract infectious diseases off their mothers?
- during birth
What is the nuchal translucency scan?
- part of ultrasound scan
- generally performed at week 12
During the nuchal translucency scan the sonographer will attempt to measure the crown rump length, what is this?
- measurement of greatest length in a straight line from the cranial to the caudal end of the body
During the nuchal translucency scan the sonographer will attempt to measure the crown rump length. In addition, 3 other measurements will try to be taken, what are they?
1 - femur length
2 - abdominal circumference
3 - cranial circumference
During the nuchal translucency scan the sonographer will attempt to measure fluid behind the babies neck. An increased volume of fluid here increases the risk of what?
- down syndrome
- has been linked with blockages in lymphatics
What % of woman have a miscarriage that is detected at the 12 week scan?
- 2-3%
The ultrasound scan can be useful for detecting the number of placenta and amniotic sacs. What are these 2 terms called?
- chorionicity = number of placentas (twins triplets etc..)
- amnionicity = number of amniotic sacs (twins triplets etc..)
During an ultrasound scan, what is used to predict gestation length, and therefore date of delivery, which can be useful when identifying if a women needs to be induced?
- last menstrual period
What are the 4 most common structural anomalies that can be detected at the 12 week scan?
1 - spina bifida (poor neural tube closing)
2 - anencephaly (absence of brain and/or skull)
3 - exomphalos and gastroschisis (internal organs on outside of the body)
4 - bladder outflow obstruction (reduced amniotic fluid around the foetus causing under development)
What screening scan is performed at weeks 18-20?
- foetal anomaly scan
- baby is big enough to detect abnormalities (brain, bladder, heart)
What happens to the risk of trisomy as a woman ages?
- risk of trisomy increases
What are 2 of the key markers that are measured in the blood during screening of a pregnancy?
- blood human chorionic gonadotrophin hormone
- Pregnancy Associated Plasma Protein-A (PAPP-A)
