Invasive Prenatal Testing

Invasive prenatal procedures obtain a sample from within the uterus, or act on the pregnancy directly, under continuous ultrasound guidance.

They are only carried out where there is a clear clinical indication, after the reasons, alternatives and risks have been discussed with you. Genetic counselling usually forms part of that discussion.

Amniocentesis is the ultrasound-guided sampling of a small amount of amniotic fluid, which contains cells from the baby, for laboratory testing. A fine needle is passed through the abdomen under continuous ultrasound guidance.

It is usually performed from about 15 to 16 weeks onwards. The sample is sent for the specific tests your treating doctor has requested, and reporting time depends on which tests those are — some results return within a few days, others take longer.

CVS is the ultrasound-guided sampling of a small amount of placental tissue for laboratory testing.

It is usually performed between about 11 and 14 weeks. Because it can be carried out earlier in pregnancy than amniocentesis, it may be considered where an earlier answer matters. Which of the two is appropriate depends on how far along the pregnancy is and on the question being asked.

Fetal reduction is an ultrasound-guided procedure that may be discussed in a multiple pregnancy, where continuing with the current number of fetuses carries risk.

It is a considered decision with medical, personal and ethical dimensions. It is only undertaken after detailed counselling, and only where your treating doctor has advised that it should be discussed.

All invasive prenatal procedures carry a small risk, including a small risk of miscarriage. The specific risks, and how they apply to your pregnancy, are explained to you before written consent is taken.

A procedure is never the only option on the table. Choosing not to proceed is a legitimate decision, and you are free to decide against a procedure at any point — including after you have consented.

Please carry your referral, previous scan reports and any screening or laboratory results.

These procedures are scheduled in advance. Our team will confirm the appointment, the preparation required and what to plan for on the day. Arrange for someone to accompany you, and plan a quiet rest of the day rather than returning straight to work.