Invasive Tests

Know the benefits and risks of invasive testing.

These are performed with the help of an ultrasound scan to determine the baby’s exact positioning in the womb.


This test can be carried out from 14-26 weeks and involves passing a fine, hollow needle through the abdominal wall into the womb. A sample of amniotic fluid that containing cells shed by the developing baby is taken and the cells are then cultured in a laboratory. This process can take up to three weeks and the results are considered accurate. Some women may have a little leakage or bleeding and it is also common to experience mild cramps on the day. It is recommended that you rest for 24 hours following the procedure. There is a one in 200 risk of miscarriage after the test, which is lower than for CVS.

Chorionic Villus Sampling

The advantage of CVS is that it can be carried out as early as 11 weeks. The basic procedure is similar to amniocentesis except fragments of the placenta are extracted. These are then sent off for detailed analysis and the results are ready in about 10-14 days.

The whole process will take about 30 minutes although the procedure itself takes only five minutes. You are likely to have this test if you are aged 30 or over, if you wish to be tested for chromosomal abnormalities or inherited disorders, or if there is reason to test sooner than is possible with amniocentesis.

CVS can be uncomfortable, some women have vaginal bleeding or cramping for a day. The risk of miscarriage is one in a hundred.


This test can be carried out relatively late in pregnancy from 18-24 weeks when the umbilical cord has developed. The doctor inserts a needle through your womb and into one of the blood vessels in the baby’s umbilical cord. A tiny sample of blood is taken and analysed.

Questions to ask yourself before having an invasive test

  • Are the results essential in deciding the course of my care?
  • If I decided not to have the test how would this affect my pregnancy?
  • If I am considered high risk and advised to have an invasive test, would I be willing to risk miscarriage to detect abnormality?
  • If a test reveals an abnormality, would I be prepared to terminate the pregnancy?
  • If I had a baby with mental or physical problems, could I deal with the extra demands placed upon me?

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