Pbl 5 Fetal Development

Question 1

How common is it for a woman to be rhesus negative and why is it a potential problem during pregnancy?

Answer 1

Around 15% of the uk population are rhesus negative. It can be a problem in pregnancy if the father is rhesus positive resulting in the foetus having rhesus antigens on its red blood cells. This means that if the foetus blood mixes with the maternal blood then the mother produces antibodies against these antigens. This means in subsequent rhesus positive pregnancies the antibodies attack the foetus resulting in haemolytic disease in the foetus.

Question 2

What preventative measures are routinely used in rhesus negative pregnant mothers?

Answer 2

They are given an injection of Rhogam at 28 weeks and just before term. This is an anti-D immunoglobulin that works by destroying any rhesus positive cells that enter the maternal bloodstream. This prevents the mothers immune system having time to detect them and form an immune reaction.

Question 3

What is the basis of non-invasive foetal tests?

Answer 3

That there is a mix of maternal and foetal blood so foetal diseases may be able to be picked up from mothers blood samples.

Question 4

What are the pros and cons of non-invasive foetal tests?

Answer 4

Pros:
-current methods are invasive and bring risk of miscarriage
Cons:
-May not be ethically desirable as it could increase the number of women wanting terminations for minor abnormalities and other reasons.

Question 5

What are the effects on the baby of anti-D rhesus antibodies?

Answer 5

Will cause the baby to have rhesus disease resulting in haemolytic anaemia. Also causes extreme jaundice which can damage the brain.

Question 6

What is the pattern of inheritance of the rhesus D antigen?

Answer 6

it is dominant so if the father has homozygous for the antigen then the baby will definitely be rhesus positive.

Question 7

How does the risk of downs syndrome increase with maternal age? Is this true for all chromosomal anomalies?

Answer 7

The risk increases with maternal age as the first stage of meiosis occurs at 5 months gestation and then the second meiotic division does not occur until fertilisation. This time period can allow accumulation effects to damage the cells spindle formation predisposing to non-disjunction.

Question 8

how many chromosomes are there in a normal human cell?

Answer 8

46 chromosomes organised into 23 pairs.

Question 9

What are the 3 main ways that trisomy 21 may occur in a cell?

Answer 9

Nondisjunctiom of chromosomes (95%)
Robertsonian translocation (5%)
Mosacism (1%)

Question 10

what are the features of a downs syndrome baby?

Answer 10

physical:
-specific facial characteristics
-poor muscle tone
-single crease across palm of hand
Other issues:
-intellectual disability
-heart defects
-intestinal malformation

Question 11

How can downs syndrome be screened for in utero?

Answer 11

Ultrasound at 11-14 weeks for nuchal transluceny which is the thickness of fluid under skin at back of neck. Maternal blood test to determine the probability of downs