Amniocentesis: What to Expect During the Procedure

Amniocentesis is a prenatal diagnostic procedure that allows physicians to assess fetal health and detect genetic or chromosomal conditions before birth. It involves extracting a small amount of amniotic fluid from the uterus for analysis. This fluid contains fetal cells and various chemicals produced by the baby, offering valuable information about conditions such as Down syndrome, spina bifida, and cystic fibrosis. Early diagnosis through this procedure can assist parents and healthcare providers in making informed medical and personal decisions.¹Mayo Clinic. (2023). Amniocentesis. https://www.mayoclinic.org/tests-procedures/amniocentesis/about/pac-20392914

What is Amniocentesis?

Amniocentesis is typically performed between 15 and 20 weeks of gestation and is guided by ultrasound to ensure the safe removal of amniotic fluid. The extracted fluid is analyzed in a laboratory to detect abnormalities in chromosomes, neural tube defects, or infections.²American College of Obstetricians and Gynecologists. (2016). Screening for fetal aneuploidy (Practice Bulletin No. 163). Obstetrics & Gynecology, 127(5), e123-e137. This test is recommended for women who present certain risk factors, such as advanced maternal age or positive results from other prenatal screenings.

Why is Amniocentesis done?

Amniocentesis can be done for a number of reasons

Genetic Testing:

One of the most common reasons for amniocentesis is to test for genetic and chromosomal conditions. A sample of amniotic fluid is taken, and the fetal cells within are analyzed for abnormalities. This includes conditions like Down syndrome (trisomy 21), trisomy 18, neural tube defects like spina bifida, and other inherited disorders.³Maryam Rabiee, M., Zahra Jouhari, P., & Ashraf Pirasteh, P. (2019). Knowledge of Prenatal Screening, Down Syndrome, Amniocentesis, and Related Factors among Iranian Pregnant Women: A Cross-Sectional Study. International Journal of Community Based Nursing and Midwifery, 7(2), 150. https://doi.org/10.30476/IJCBNM.2019.44886
Carrier screening can also be done before or early in pregnancy using a blood or saliva sample. If both parents are carriers of the same condition, the baby has an increased risk of inheriting it. Amniocentesis can help confirm whether the baby is actually affected.

Diagnosis of Fetal Infection:

Amniocentesis can also help identify infections in the womb, such as cytomegalovirus (CMV) or toxoplasmosis. These infections can affect the baby’s health and development if not detected early.⁴Cavalcante, M. B., Cavalcante, C. T. M. B., Sarno, M., & Barini, R. (2021). Intrauterine infection and congenital anomalies: A review. Journal of Maternal-Fetal & Neonatal Medicine, 34(12), 1994–2001. https://doi.org/10.1080/14767058.2019.1653802

Fetal Lung Testing

In certain cases—especially if early delivery is being considered—amniocentesis is used in the third trimester to check if the baby’s lungs are mature enough to function well outside the womb. This is usually done between 32 and 39 weeks of pregnancy. Lungs typically mature by around the 35th to 36th week of gestation.⁵Miller, R. K., Haas, D. M., & Wisner, K. L. (2018). Assessing fetal lung maturity: New insights and old debates. Obstetrics & Gynecology Clinics, 45(2), 305–317. https://doi.org/10.1016/j.ogc.2018.01.009

Therapeutic Drainage (Treatment Purpose): 

Amniocentesis is also used therapeutically in cases where there is excessive amniotic fluid, such as in polyhydramnios. Draining some of this fluid helps relieve pressure in the uterus, reduce maternal discomfort, and prevent complications like preterm labor or damage to fetal organs.⁶Sinkin, R. A., Wallenstein, M. B., & Paul, D. A. (2019). Polyhydramnios: Etiology, diagnosis, and management. Neoreviews, 20(5), e260–e271. https://doi.org/10.1542/neo.20-5-e260

When is Amniocentesis done? 

It is usually performed between 15 and 20 weeks of pregnancy, with 16 to 18 weeks being the safest and most common window.⁷American College of Obstetricians and Gynecologists. (2020). ACOG Practice Bulletin No. 226: Screening for fetal chromosomal abnormalities. Obstetrics & Gynecology, 136(4), e48–e69. https://doi.org/10.1097/AOG.0000000000004084 Doing it earlier can increase the risk of complications. Since a sample of amniotic fluid is removed, performing it too early may reduce the already limited fluid, which could affect the baby’s development. However, it can also be done later in pregnancy if needed — for example, to check if the baby’s lungs are mature enough before an early delivery. The procedure is always done under ultrasound guidance to ensure safety.

Contraindications for Amniocentesis

Amniocentesis is generally safe when performed by experienced professionals, but there are certain situations where it may be avoided. Contraindications include active maternal infections such as HIV, hepatitis B or C (if not well-managed), or genital herpes, due to the risk of transmitting the infection to the fetus. It is also avoided in cases of low amniotic fluid (oligohydramnios), uterine abnormalities, or when the placenta is positioned in a way that blocks safe access to the fluid. Bleeding disorders or the use of anticoagulant medications may also increase the risk of complications. Each case is evaluated individually to weigh the risks and benefits before proceeding.⁸Cunningham, F. G., Leveno, K. J., Bloom, S. L., Spong, C. Y., Dashe, J. S., Hoffman, B. L., … & Sheffield, J. S. (2022). Williams Obstetrics (26th ed.). McGraw-Hill.

Amniocentesis Procedure

In this procedure, the doctor uses ultrasound guidance to insert a thin needle through the abdomen into the amniotic sac. A small amount of amniotic fluid, which contains fetal cells, is withdrawn for genetic and chromosomal testing. The sample is then sent to a lab in a syringe or container with appropriate culture media for analysis. Test results, such as fetal karyotyping, are usually available within 7 to 10 days.

It’s important to note that amniocentesis is different from chorionic villus sampling (CVS). CVS is done earlier, typically between 10 and 13 weeks, and involves collecting placental tissue rather than amniotic fluid. CVS can be done transabdominally or transcervically, depending on uterine and placental positioning, maternal anatomy, and other factors.

Amniocentesis is recommended in cases where there is a high risk of chromosomal abnormalities, genetic disorders, or neural tube defects. One potential challenge in early testing, particularly with CVS, is a condition known as placental mosaicism. This happens when the placenta has a different chromosomal makeup than the fetus. In some cases, the abnormal cells are only present in the placenta, while the baby’s cells are completely normal. This can lead to false-positive results, causing unnecessary anxiety. In other cases, the baby may have abnormal chromosomes that are not reflected in the placental sample, potentially giving a false sense of reassurance. For this reason, amniocentesis may be recommended to confirm or clarify CVS findings.

Steps of Procedure:

You don’t need to do anything special to prepare for amniocentesis. You can eat and drink as normal. Sometimes, your doctor may ask you not to empty your bladder for a few hours before the procedure, as a full bladder can make it easier to visualize the uterus during the ultrasound. Here’s how the procedure is typically done:

• You lie on your back while your abdomen is cleaned and a thin layer of ultrasound gel is applied.
• Your doctor moves an ultrasound wand (transducer) over your belly to locate the baby, the placenta, and the pocket of amniotic fluid.
• After identifying the right spot, your belly is cleaned with an antiseptic solution to reduce the risk of infection.
• A thin needle is inserted through your abdominal wall and into the uterus, guided by continuous ultrasound.
• A small amount (about 15–20 mL) of amniotic fluid is withdrawn. This fluid contains fetal cells used for testing.
• After the sample is taken, your baby’s heartbeat is checked again using ultrasound.

After the Procedure:

After the procedure, your doctor will continue to monitor your baby’s heartbeat. You might experience mild cramping or pelvic discomfort, which is usually temporary. It’s best to rest for the day and avoid any strenuous physical activity. Most people return to their normal routine within a day or two. However, you should call your doctor immediately if you notice:

• Vaginal bleeding or fluid leakage
• Cramping that lasts more than a few hours
• Fever, even if mild
• Redness or swelling at the needle insertion site
• Any change in fetal activity, such as reduced or absent movement

Getting your Results:

Once the lab analyzes your sample, your doctor will discuss the results with you. Amniocentesis can confirm or rule out many chromosomal abnormalities, including Down syndrome, trisomy 18, and neural tube defects. However, it can’t detect every possible genetic condition or birth defect.

If results show that your baby has a condition that may not be treatable, you may be faced with difficult decisions, including whether to continue the pregnancy. During such times, emotional support from your doctor and loved ones can help guide you through the next steps.

Risks Associated with Amniocentesis

In the past, amniocentesis was not routinely offered to all pregnant women. This was largely due to the increased risk of pregnancy loss associated with the procedure at a time when the likelihood of detecting a significant abnormality in the baby was relatively low.

Today, although the technique has improved, the procedure still carries some risks.⁹Nizard, J. (2010). Amniocentesis: technique and education. Current Opinion in Obstetrics and Gynecology, 22(2), 152–154.

• Miscarriage: The most well-known risk is miscarriage. However, this is rare. Fewer than 1 in 200 women (less than 0.5%) experience a miscarriage following amniocentesis.¹⁰Akolekar, R., Beta, J., Picciarelli, G., Ogilvie, C., & D’Antonio, F. (2015). Procedure-related risk of miscarriage following amniocentesis and chorionic villus sampling: a systematic review and meta-analysis. Ultrasound in Obstetrics & Gynecology, 45(1), 16–26. https://doi.org/10.1002/uog.14636
• Infection of the uterus: Though extremely uncommon, uterine infections can occur and may pose a serious risk to both mother and baby.
• Cramping, spotting, or leakage of amniotic fluid: These symptoms occur in about 1 to 2 in 100 women (1%–2%). While often mild and self-limiting, persistent symptoms require prompt medical attention.
• Transmission of infection to the baby: If the mother has a transmissible infection, such as HIV or toxoplasmosis, there is a slight risk of passing it to the fetus through the procedure. Toxoplasmosis is typically contracted through undercooked meat or exposure to cat feces.
• Rh incompatibility problems: During the procedure, there is a small chance that fetal blood may enter the mother’s bloodstream. If the mother is Rh-negative and the baby is Rh-positive, this could trigger an immune response. To prevent complications, Rh-negative women are usually given an Rh immune globulin injection after the procedure.

Conclusion

Amniocentesis has proven to be a valuable tool in the early diagnosis of genetic and neural tube disorders, allowing parents and healthcare providers to make informed decisions. It is particularly useful for detecting conditions like Down syndrome and spina bifida, which may have lifelong implications. Although the procedure carries some risks—such as cramping, bleeding, or a small risk of miscarriage—these are relatively rare, and in many cases, the potential benefits of early detection outweigh the risks.

Refrences

• 1
  Mayo Clinic. (2023). Amniocentesis. https://www.mayoclinic.org/tests-procedures/amniocentesis/about/pac-20392914
• 2
  American College of Obstetricians and Gynecologists. (2016). Screening for fetal aneuploidy (Practice Bulletin No. 163). Obstetrics & Gynecology, 127(5), e123-e137.
• 3
  Maryam Rabiee, M., Zahra Jouhari, P., & Ashraf Pirasteh, P. (2019). Knowledge of Prenatal Screening, Down Syndrome, Amniocentesis, and Related Factors among Iranian Pregnant Women: A Cross-Sectional Study. International Journal of Community Based Nursing and Midwifery, 7(2), 150. https://doi.org/10.30476/IJCBNM.2019.44886
• 4
  Cavalcante, M. B., Cavalcante, C. T. M. B., Sarno, M., & Barini, R. (2021). Intrauterine infection and congenital anomalies: A review. Journal of Maternal-Fetal & Neonatal Medicine, 34(12), 1994–2001. https://doi.org/10.1080/14767058.2019.1653802
• 5
  Miller, R. K., Haas, D. M., & Wisner, K. L. (2018). Assessing fetal lung maturity: New insights and old debates. Obstetrics & Gynecology Clinics, 45(2), 305–317. https://doi.org/10.1016/j.ogc.2018.01.009
• 6
  Sinkin, R. A., Wallenstein, M. B., & Paul, D. A. (2019). Polyhydramnios: Etiology, diagnosis, and management. Neoreviews, 20(5), e260–e271. https://doi.org/10.1542/neo.20-5-e260
• 7
  American College of Obstetricians and Gynecologists. (2020). ACOG Practice Bulletin No. 226: Screening for fetal chromosomal abnormalities. Obstetrics & Gynecology, 136(4), e48–e69. https://doi.org/10.1097/AOG.0000000000004084
• 8
  Cunningham, F. G., Leveno, K. J., Bloom, S. L., Spong, C. Y., Dashe, J. S., Hoffman, B. L., … & Sheffield, J. S. (2022). Williams Obstetrics (26th ed.). McGraw-Hill.
• 9
  Nizard, J. (2010). Amniocentesis: technique and education. Current Opinion in Obstetrics and Gynecology, 22(2), 152–154.
• 10
  Akolekar, R., Beta, J., Picciarelli, G., Ogilvie, C., & D’Antonio, F. (2015). Procedure-related risk of miscarriage following amniocentesis and chorionic villus sampling: a systematic review and meta-analysis. Ultrasound in Obstetrics & Gynecology, 45(1), 16–26. https://doi.org/10.1002/uog.14636