GUIDE
Amniocentesis is a diagnostic test that analyzes amniotic fluid to definitively identify chromosomal conditions, genetic disorders, and certain infections.
Unlike screening tests such as NIPT, amniocentesis gives definitive results. It is typically performed between weeks 15 and 20, takes about 15 to 20 minutes, and carries a small risk of miscarriage (0.1 to 0.3 percent at experienced centers).
Be prepared from day one
Amniocentesis is a diagnostic procedure — meaning it gives definitive answers about your baby's chromosomes and genetic makeup. It is different from screening tests like the NIPT or nuchal translucency scan, which estimate risk but cannot confirm a diagnosis.
During the procedure, a thin needle is guided through your abdomen into the amniotic sac, and a small sample of fluid is withdrawn. This fluid contains fetal cells that can be analyzed for chromosomal abnormalities, genetic disorders, and certain infections.
Amniocentesis is typically performed between weeks 15 and 20 of pregnancy. It is not a routine test — it is recommended when there is a specific clinical indication, such as a positive screening result or a family history of a genetic condition.
Amniocentesis is always optional. Your provider will discuss the benefits, risks, and alternatives so you can make an informed decision.
The procedure is performed by a maternal-fetal medicine specialist or an experienced OB. Continuous ultrasound guidance ensures safety.
The primary risk of amniocentesis is miscarriage. Current data from experienced, high-volume centers places this risk at approximately 0.1 to 0.3 percent — meaning 1 in 300 to 1 in 1,000 procedures results in pregnancy loss attributable to the procedure. This is lower than the commonly cited older figure of 0.5 percent, which was based on studies from the 1970s and 1980s.
Other uncommon risks include temporary amniotic fluid leakage (about 1 to 2 percent of cases, usually self-resolving), uterine infection (very rare), and needle injury to the baby (extremely rare with ultrasound guidance).
If you are Rh-negative, you will receive a RhoGAM injection after the procedure to prevent Rh sensitization.
The experience of the provider matters. If amniocentesis is recommended, ask about the volume of procedures your center performs — higher volume is associated with lower complication rates.
| Test Type | Turnaround | What It Covers |
|---|---|---|
| FISH (rapid results) | 2–3 days | Checks for trisomies 21, 18, 13 and sex chromosomes. Preliminary but highly accurate. |
| Full karyotype | 10–14 days | Complete chromosomal analysis — detects all numerical and large structural chromosome abnormalities. |
| Chromosomal microarray | 2–3 weeks | Detects smaller deletions and duplications that karyotype cannot see. Increasingly used as standard. |
| Specific gene testing | 2–4 weeks | Tests for specific genetic conditions (CF, sickle cell, etc.) when there is a known risk. |
Most people feel fine by the next day. The amniotic fluid replenishes within 24-48 hours.
Talk to a genetic counselor. They specialize in explaining what tests can and cannot tell you, the meaning of positive and negative results, and how to weigh the risks of the procedure against the value of the information. Many people find this conversation clarifying and reassuring regardless of their decision.
Chorionic villus sampling (CVS) is the other diagnostic option. CVS can be performed earlier (weeks 10-13) and analyzes a tiny sample of placental tissue. It provides the same chromosomal and genetic information as amniocentesis with a similar risk profile.
The main advantage of CVS is timing — it gives results in the first trimester. The main advantage of amniocentesis is that it can also detect neural tube defects through alpha-fetoprotein (AFP) levels and can assess for fetal infections. Your provider and genetic counselor can help you choose the right option based on your specific situation and timing.
For a complete picture of prenatal testing, see our prenatal visit schedule, our pregnancy blood tests guide, and our overview of the anatomy scan.
This guide is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider with any questions about your pregnancy.
