Amniocentesis: Clear Answers, Step by Step

Amniocentesis is a procedure in which a specialist uses a thin needle, guided by ultrasound, to collect a small amount of fluid from the amniotic sac. That fluid is sent to a lab to test for genetic conditions and, when needed, infections. It’s typically performed between 16 and 22 weeks, most often after a screening result or an ultrasound finding that calls for a closer look.

What amniocentesis is, in plain language

During an amniocentesis, your specialist places a thin needle through the belly to reach the amniotic sac, then draws a small amount of fluid into a syringe. That fluid is transferred to a vial and sent to a lab, where it can be tested for genetic conditions and, in some cases, infections. The purpose is simple: to give you a clear, definitive answer rather than an estimate.

When it’s done

Amniocentesis is usually performed between 16 and 22 weeks of pregnancy. It can be done later if there’s a specific medical reason, which your specialist will explain.

Why you may have been referred

The most common reasons are an earlier genetic screening that came back outside the expected range, or a finding seen on a previous ultrasound that warrants a closer look. A screening tells you something is worth examining more carefully. Amniocentesis is one of the few tests that can give a definitive answer.

What to expect, start to finish

We want this to feel understood, not unknown, so here’s exactly how the appointment goes.

Before: Your doctor explains the procedure, answers your questions, and you sign a consent form.

During: Your doctor and the sonographer use ultrasound to find the safest location to collect the fluid. Once that spot is identified, your doctor cleans the area, guides the sonographer on where to place the probe, and inserts the needle. The sonographer follows the needle on the screen until it reaches the amniotic sac, and the doctor draws the fluid.

After: Your sonographer shows you the baby’s heartbeat, and we clean up and let you stay lying down until you feel ready to sit up. We give you another chance to ask questions, and we show you the labeled vial and confirm your information is correct before it goes to the lab.

The questions we hear most

“Do you use anesthesia?” No. We don’t use local anesthesia. The procedure is quick, and most patients feel only mild discomfort, similar to having blood drawn. Numbing the skin wouldn’t change what patients actually feel, because it can’t numb the uterus, which is where you might notice some pressure or cramping.

“Do you go through the belly button?” No, never. The exact location depends on where your baby, the placenta, and the fluid are positioned at the time of the procedure.

You won’t navigate the results alone

Whatever your results show, you’ll have a specialist who explains them in plain language and walks you through what comes next. This is something we navigate together.