Pregnancy & prenatal testing: Second trimester

Amniocentesis is usually performed at or after 15 weeks gestation. It is offered in women aged over 35, or where there is reason to suspect an increased risk of a particular genetic abnormality in their baby, no matter what the maternal age.

Amniotic fluid is removed from the mother’s womb using a needle inserted through the lower abdomen. The fluid contains skin cells from the developing baby and these can be tested for chromosomal and other genetic abnormalities. It can take two or three weeks to grow the small number of cells obtained in order to provide enough DNA to perform the necessary tests.

Amniocentesis is also used for other reasons in some women, for example to confirm or monitor infections affecting the baby.

Complications associated with amniocentesis 
There is a risk of miscarriage (approximately 1%) associated with the procedure. The procedure may cause an infection.

Limitation of testing
Not all genetic disorders can be detected.