Antenatal Screening Tests



First Trimester Biochemical Testing
This is a blood test for the mother to be that is carried out between 9 and 13 weeks of pregnancy and also involves a nuchal scan (see below) at 12-13 weeks. However, some recent evidence indicates that it is better to do the biochemistry blood tests at 9-11 weeks, followed by the nuchal scan at 12-13 weeks. The pick up rate for certain problems in the baby is higher than scans or blood tests alone and your lead maternity carer will discuss these tests and the various issues involved in undertaking them e.g. falsely abnormal results or falsely normal results. This test is currently only available privately via a lab in Hamilton, or via Auckland Hospital and then Australia. Please discuss the details of this test further with your lead maternity carer.

 

Nuchal Translucency Ultrasound Scan

This scan is performed at 11 to 13 weeks and is a screening test for Down syndrome. The scan measures the thickness of the layer of fluid on the back of the baby's neck. This measurement is then combined with your age and number of weeks of pregnancy to provide an individual risk for you. This result tells you if your baby has a 'low risk' or 'high risk' for Down syndrome. This is not diagnostic or foolproof and women who are 'high risk' may consider further testing such as amniocentesis for accurate clarification. Risk is not a concept that everyone agrees on in any case; e.g. a risk of 1 in 300 may be a high risk to some couples and low risk to others.

 

Maternal Serum Screening

This test is done at 15-17 weeks and is a screening test for chromosomal abnormalities such as Down syndrome. The test measures the levels of 3 chemical substances in the pregnant woman's blood (which in turn are due to the baby and are influenced by the possibility of the baby having a problem). A risk is then estimated, also using information based on a woman's age, weight, race, and how far along her pregnancy is. Again, depending on the risk that is worked out, your next decision would be whether to have diagnostic testing, such as amniocentesis.

 

The Anatomy Ultrasound Scan

This is a detailed scan performed at 19 to 20 weeks, during which each part of your baby's body is examined. It screens for structural or physical abnormalities. This scan is able to detect 90% of babies with Spina bifida and 50-60% of babies with heart abnormalities. If it is normal then there is a high chance that the baby does not have any serious physical problems. It is this scan where couples can ask for the likely gender of the baby (if they wish to know).


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