Tuesday, 9 June 2015

16 to 20 weeks. Visits to your obstetrician

Q  I am now 16 weeks pregnant. what should I expect at my obstetrician?

Your baby will be fully formed, much larger and fingers and toes can be seen. The sex of the baby can be determined. He may want to do a blood test (triple test) for down's syndrome if the oscar test was not done earlier in the pregnancy.

What is a triple test?

This is a blood test to determine your risk of down's syndrome and other chromosome defects, detect spina bifida or other neural tube defects. The test measures 3 hormones and together with the mother's age and weeks of gestation, a risk factor is determined. A factor more than 1:250 would be positive. There are however false positives and negatives in this screen and it is not infallible. A positive test would indicate a need for an amniocentesis.

I have been told that I need an amniocentesis. How is this procedure done and what are the risks?

Approximately 15 mls of the babies waterbag fluid is extracted under local anaesthesia. This is usually done under ultrasound scan guidance. The fluid will contain the foetal cells from shed skin. These cells are harvested and examined . The procedure is relatively painless and takes about 20 minutes. The cell culture takes about 2 weeks and therefor the test should be done well before 20 weeks. It is a safe procedure with a less than 1% risk of complications. The main risk is that of miscarriage.

My obstetrician advised me to have an amniocentesis at 16 weeks rather than a chorionic villus biopsy at 9 weeks. Why is this so?

Chorionic villus biopsy is a procedure in which a biopsy is taken from the placenta under ultrasound guidance. The material is then undergoes DNA analysis to determine gene disorders. The risk of miscarriage is higher than amniocentesis, the results often inconsistent and a UK study has shown increased foetal abnormalities resulting from the procedure.

Both my husband and I are thalassaemia carriers. What tests should I do to determine if my baby is normal?

If both your husband and you are carriers, then you have a 1:4 chance of having a thalassaemia major child. This is fatal in childhood. This can be excluded by means of foetal blood sampling. the foetal cord is identified under ultrasound scan and a needle inserted to aspirate a small amount of cord blood and the blood then undergoes DNA analysis.

Q What is a foetal-DNA test and when should it be done?

This test may be done as early as 9 weeks. It tests the baby's DNA that passes into the mother's bloodstream. It is a very accurate test almost 99% and looks to replacing amniocentesis as the test of choice. It is non invasive and therefore does not carry the risks that are associated with an amniocentesis. This test is referred to as the Harmony test or Panorama test.

No comments:

Post a Comment