What is Prenatal Chromosome Analysis?
Parents are often anxious about the condition of their unborn child. Some parents already have a child with a birth defect and may wish to test if the same condition is present in a subsequent pregnancy. While the majority of newborns are physically normal, 3 to 5 babies out of 100 births may have birth defects, and some of these defects are due to chromosomal abnormalities. Approximately 0.5% of all newborns have a chromosomal abnormality. Knowing the chromosomal status of their baby early in the pregnancy allows the parents to have a chance to plan, prepare and make definitive decisions.
Who needs prenatal screening for chromosomal abnormalities?
All expectant mothers can be tested during their pregnancy for chromosomal abnormalities. However the risks of invasive prenatal testing may outweigh the benefits, so prenatal diagnosis is normally recommended for higher-risk people.
Who is at risk?
Pregnant women with:
- Advanced maternal age
- Abnormal maternal serum markers
- Abnormal ultrasound markers (e.g. abnormal nuchal thickness in the foetus)
- Recurrent spontaneous abortions
- Known parental chromosomal abnormality
- Known or suspected chromosomal abnormality in a previous child
At present, conventional karyotype analysis still remains the gold standard for the evaluation of chromosome number and structural anomalies in prenatal diagnosis.
How are chromosomal abnormalities before birth diagnosed?
A diagnostic test such as amniocentesis or chorionic villus sampling can be recommended to confirm or exclude the presence of chromosomal anomalies. Before the test is done, it is important for the couple to consider how they might be affected if the test were to actually be positive for a chromosomal abnormality.