Amniocentesis

Overview of the Procedure

Amniocentesis is an invasive prenatal diagnostic procedure that involves extracting amniotic fluid to analyze fetal cells for assessing the risk of genetic diseases or chromosomal abnormalities. This method is primarily used for pregnancies suspected of having chromosomal disorders such as Down syndrome, Edwards syndrome, or in cases where there is a family history of genetic diseases. The procedure is typically performed between 15 and 20 weeks of pregnancy and must be carried out by a qualified obstetrician under ultrasound guidance to ensure safety.

Types and Mechanisms of the Procedure

Amniocentesis is an invasive diagnostic technique involving three stages: first, locating the fetus via ultrasound; second, inserting a thin needle through the abdomen into the amniotic sac; and third, extracting approximately 20-30 cc of amniotic fluid. The collected fluid is cultured, and chromosomal analysis or gene sequencing is performed to detect hundreds of genetic defects, such as Down syndrome and trisomy 18. The diagnostic accuracy of this technique can reach up to 99%, but due to its invasive nature, it requires an assessment of the pregnant woman's risk tolerance.

Indications

This procedure is suitable for the following situations:

• Pregnant women aged 35 or older or those with high-risk results from non-invasive prenatal screening (e.g., NIPT)
• Family history of inherited metabolic disorders, muscular dystrophy, or other dominant genetic diseases
• Ultrasound findings indicating fetal structural abnormalities requiring further genetic analysis

When prenatal screening results are abnormal or when the clinician assesses the risk to be higher than 1/270, amniocentesis is usually recommended.

Usage and Dosage

The procedure is usually performed on an outpatient basis. The pregnant woman first undergoes ultrasound to confirm fetal position and amniotic fluid volume. Under local anesthesia, the physician inserts a fine needle through the abdomen and uterine wall to extract about 20 cc of amniotic fluid, which is then sent immediately to the laboratory for culture. The entire process takes approximately 15-20 minutes, and observation for 1-2 hours post-procedure is recommended. The volume extracted must be controlled within a safe range, as excessive removal can lead to oligohydramnios.

Benefits and Advantages

The main advantage is providing definitive genetic information:

• Detection of over 200 chromosomal abnormalities and genetic disorders
• Results serve as the ultimate diagnostic basis, avoiding unnecessary follow-up tests
• Compared to non-invasive testing, it offers more comprehensive chromosomal structural information

For pregnant women requiring a clear diagnosis, this method provides critical decision-making information.

Risks and Side Effects

Main risks include:

• Natural miscarriage rate increases by approximately 0.5-1%, directly related to the procedure
• Risks of amniotic fluid leakage, infection, or fetal injury are about 0.1-0.3%
• A small number of pregnant women may experience lower abdominal distension, pain, or bleeding

The medical team will administer antibiotics before and after the procedure to prevent infection and recommend avoiding strenuous activity for 24 hours post-operation.

Precautions and Contraindications

Contraindications include:

• Uterine bleeding, placenta previa, or history of preterm labor
• Suspected fetal infection or oligohydramnios
• Allergy to local anesthetics

Prior to the procedure, cervical length measurement and infection screening should be completed. Patients with hypertension or coagulation disorders should have their conditions managed beforehand.

Interactions with Other Treatments

This procedure is often combined with:

• Non-invasive prenatal screening (NIPT) as an initial screening tool
• Ultrasound anatomical scans to confirm fetal structure

If other invasive tests (such as chorionic villus sampling) are performed simultaneously, the interval between procedures should be evaluated to avoid repeated risks. Patients should inform their doctor about current medications, especially anticoagulants or immunosuppressants.

Effectiveness and Evidence

Studies show that amniocentesis has a diagnostic accuracy of 99.7% for chromosomal abnormalities and can detect microdeletions or duplications. However, due to its invasive nature, the American College of Obstetricians and Gynecologists recommends its use only in high-risk groups. Compared to NIPT's 99% sensitivity, its advantage lies in providing a comprehensive chromosomal map, but it carries a 0.5% risk of miscarriage.

Alternatives

Non-invasive options include:

• Non-invasive prenatal screening (NIPT): high accuracy but not diagnostic
• Chorionic villus sampling: suitable between 10-13 weeks of pregnancy, with a slightly higher miscarriage risk
• Ultrasound anatomical scan: only observes structural abnormalities and cannot detect chromosomal issues

The doctor will recommend the most appropriate method based on gestational age and risk assessment.

 

Frequently Asked Questions

Should I seek immediate medical attention if I experience light vaginal bleeding after amniocentesis?

Mild vaginal bleeding or blood-tinged discharge is common after the procedure and usually subsides within 24 hours. If bleeding exceeds the absorption capacity of a sanitary pad per hour or is accompanied by severe lower abdominal pain or fever, contact your healthcare provider immediately for assessment to rule out infection or preterm labor.

How long should I rest before resuming normal activities after amniocentesis?

It is recommended to avoid lifting heavy objects, standing for long periods, or vigorous exercise within 24 hours post-procedure. Mild household activities and short walks are generally acceptable. Usually, after three days, normal activities can gradually resume, but activities that increase abdominal pressure, such as intense exercise or sexual activity, should be avoided for at least one week.

How long does it take to receive the results of genetic testing after amniocentesis?

Results from chromosomal analysis (such as Down syndrome screening) typically take 7-10 working days, while detailed genetic mutation testing may require 3-4 weeks. The medical team will prioritize the reporting schedule based on the test items and will proactively contact the patient to explain the results once available.

Should I stop taking certain medications before undergoing amniocentesis?

It is advisable to discontinue anticoagulants (such as aspirin, fish oil) and blood-activating medications two weeks prior to the procedure to reduce bleeding risk. Patients with chronic conditions requiring long-term medication (e.g., antihypertensives) should inform their doctor in advance for possible dose adjustments or temporary cessation.

What are the main differences between amniocentesis and non-invasive prenatal screening (NIPT)?

Amniocentesis is an invasive diagnostic procedure that provides definitive results but carries a 0.5%-1% risk of miscarriage. NIPT is a non-invasive screening that offers high-risk or low-risk assessments with approximately 99% accuracy but cannot replace diagnostic testing. The doctor will recommend the most suitable option based on age, previous screening results, and other factors.