Chorionic Villus Sampling

Indications

According to the American College of Obstetrics and Gynecology, women of all ages should be offered prenatal assessment for aneuploidy through either screening or diagnostic testing, regardless of maternal age or other risk factors.[1][2] Prenatal genetic testing cannot identify all abnormalities, so testing should be focused on the patient's risk, reproductive goals, and preferences. Ideally, genetic testing should be discussed during the first obstetric visit.

Indications for chorionic villus sampling include the following:

• Abnormal early genetic screening on a noninvasive prenatal screening, first-trimester combined screening, or abnormalities on ultrasound
• A prior child with a structural birth defect 
• A prior child with autosomal trisomy or sex chromosome aneuploidy 
• Advanced maternal or paternal age 
• Parental carrier of a chromosomal rearrangement 
• Parental aneuploidy or aneuploidy mosaicism 
• Parental carrier of a genetic disorder such as Tay-Sachs disease, sickle cell disease, or neurofibromatosis [1][3]

Contraindications

Chorionic villus sampling carries some potential complications that clinicians should carefully consider. Caution is advised in patients on anticoagulation therapy due to an increased risk of bleeding. Maternal alloimmunization is a relative contraindication, as chorionic villus sampling may lead to fetal hemolytic disease by disrupting placental villi, resulting in fetomaternal blood mixing.[4] In addition, patients with bloodborne infectious diseases, such as HIV and hepatitis, should be informed about the potential risk of vertical transmission during prenatal diagnostic testing. As with any invasive procedure, careful patient selection, informed counseling, and appropriate precautions are essential to minimize risks.

Equipment

Before performing chorionic villus sampling, it is essential to ensure that all necessary equipment is available and appropriately prepared. The required equipment may vary slightly depending on whether the transabdominal or transcervical approach is used; however, both methods require precision instruments and sterile technique to ensure patient safety and diagnostic accuracy. The procedure is performed under continuous ultrasound guidance using an aseptic technique.[5]

Transabdominal Approach

• Sterile drape 
• Sterile ultrasound probe cover
• Chlorhexidine or iodine preparation 
• Local anesthetic (optional)
• 10 and 20 cc syringes
• 18- or 20-gauge spinal needle 
• Sample collection container with transport media 

Transcervical Approach

• Sterile speculum
• Single-tooth tenaculum
• Iodine preparation 
• 10 cc and 20 cc syringes 
• Transcervical chorionic villus sampling catheter
• Sample collection container with transport media

Personnel

Chorionic villus sampling should be performed by a trained obstetrician or maternal-fetal medicine subspecialist with expertise in ultrasound-guided procedures. A skilled sonographer is essential for real-time imaging and guidance during the procedure. In addition, nursing staff or medical assistants may be required to assist with patient preparation, provide support during the procedure, and ensure the proper handling and transportation of the specimen to the genetics laboratory.

Preparation

Proper preparation for chorionic villus sampling is critical to ensure a safe and effective procedure. Preparation includes patient counseling, assessment of clinical indications, and selection of the appropriate approach based on gestational age and placental location. Clear communication and thorough planning help optimize outcomes and minimize risks for both the patient and fetus.

Pre-Procedure Steps

• Formal consultation with an maternal-fetal medicine subspecialist is conducted.
• If possible, referral for prenatal genetic counseling is made.
• Informed consent is obtained after a thorough discussion of risks and benefits, with patients having the opportunity to ask questions.
• Evaluation of the need for Rhogam in Rh-negative patients is performed.
• An ultrasound is performed to confirm fetal cardiac activity, gestational age assessment with crown-rump length measurement, and location of the placenta.
• All necessary materials, including transport media, are available

At the Time of the Procedure

• A skilled healthcare provider and ultrasonographer are present.
• The patient is made comfortable on the examination table.
• Appropriate lighting is ensured.
• The abdomen or cervix, depending on the chosen approach, is prepared.
• The steps of the procedure are explained to the patient, if desired, to help alleviate anxiety.

Technique or Treatment

The choice of procedural route is generally based on the healthcare provider's preference, but the placental location may also influence the decision.[6] In the transabdominal approach, the optimal site for exposing the longest axis of the placenta is identified. The patient is supine, and the abdomen is cleaned with a chlorhexidine or iodine solution. Sterile drapes are placed to create a sterile field. A local anesthetic may be used. An 18- or 20-gauge spinal needle is inserted into the placenta under continuous ultrasound guidance. A 20 cc syringe containing collection media is attached to the end of the needle once the stylet is removed. Negative pressure is created, and the needle is moved up and down through the placenta, collecting the tissue. Once the sample is collected, it is evaluated to ensure sufficient chorionic villi are aspirated.

In the transcervical approach, the patient is placed in the dorsal lithotomy position, and a sterile speculum is inserted into the vagina. The cervix is cleaned with an iodine solution. A single tooth tenaculum may be applied to the anterior lip of the cervix to facilitate the passage of the catheter. Under continuous ultrasound guidance, a transcervical chorionic villus sampling catheter is inserted into the placenta. The catheter contains a malleable guidewire with an echogenic tip, which can be identified on ultrasound. Once in the proper location, the stylet is removed, a 20 cc syringe containing media is attached to the end of the catheter, and negative pressure is created. The sample is evaluated for adequacy before ending the procedure. Transcervical chorionic villus sampling can also be performed using small biopsy forceps.[7] Tissue samples are sent to the laboratory for culturing and further testing, including conventional karyotype, fluorescence in situ hybridization, and chromosomal microarray. Rapid assessment results return in 2 to 4 days, and cultured samples result in 1 to 2 weeks. Once results are available, families should meet with their healthcare providers to discuss next steps in management

Whether the transcervical or transvaginal approach is chosen, care must be taken to avoid entry into the amniotic sac. Inadvertent puncture increases the risk of complications such as amniotic fluid leakage or infection. 

Complications

There are limited data directly comparing the risks of transcervical versus transabdominal chorionic villus sampling. However, current evidence does not suggest a significant difference in complication rates between the 2 approaches.[1][1] The risks associated with chorionic villus sampling are similar to those of amniocentesis and may include pregnancy loss, bleeding, infection, rupture of membranes, and uncertain results. The pregnancy loss rate has decreased with the use of ultrasound guidance and improvements in skill and technique.

A systematic review of the complications of chorionic villus sampling found a total fetal loss of 0.7% within 14 days, 1.3% within 30 days, and 2% for loss anytime during pregnancy using a transabdominal approach. In the amniocentesis group, the total rate of fetal loss within 14 days was 0.6%.[8] A more recent cohort study found that pregnancy loss rates following chorionic villus sampling were comparable to those in pregnancies without chorionic villus sampling, confirming that the risk of this procedure is low.[9] 

Predictors of increased fetal loss include the number of times the needle or catheter is introduced, the experience and skill of the operator, pregnancies after assisted reproductive techniques, and the use of a transcervical cannula instead of biopsy forceps.[10][11] With chorionic villus sampling, there is a possibility of identifying confined placental mosaicism, which occurs in 1% to 2% of cases.[12] This possibility arises when there is a discrepancy between the chromosomal makeup of the placenta and that of the fetus. The fetus is truly mosaic in 10% of cases. Mosaicism identified by chorionic villus sampling should be followed by amniocentesis in the second trimester to determine the genetic makeup of the amniocytes, which contain fetal cells. The finding of mosaicism is associated with an increased risk of poor placental function and perinatal complications, including fetal growth restriction and maternal hypertension.[13] 

In addition, limb reduction defects and oromandibular hypogenesis have been described in the literature as potential risks associated with chorionic villus sampling.[14] Early chorionic villus sampling (before 10 weeks of gestation) has been identified as a risk factor for these complications. The World Health Organization estimates the risk of limb defects to be approximately 6 per 10,000, which is comparable to the risk in the general population.[1][15] Although the risk is low, it is essential to inform patients about the data when considering chorionic villus sampling before 10 weeks. Vaginal spotting has been reported in up to 32% of women and is more common after transcervical chorionic villus sampling.[1][16] The incidence of culture failure, leakage of amniotic fluid, or infection after chorionic villus sampling is reported to be less than 0.5%.

When discussing genetic diagnostic testing in the setting of multiple gestations, counseling should include a thorough discussion of management options if only 1 fetus has aneuploidy. Such options include continuing the pregnancy, terminating the pregnancy, and selective second-trimester termination of the affected fetus.[1] There are limited data concerning the risk of fetal loss with chorionic villus sampling or amniocentesis in twin gestations. In a recent systematic review, the procedure-related loss rate for chorionic villus sampling and amniocentesis in twin pregnancies was estimated at 1%. With chorionic villus sampling, there is also a 1% chance for cross-contamination, or inadvertent sampling of both fetuses, which can lead to misinterpreted results.[17] In addition, the results from a recent multicenter study involving 8583 twin pregnancies showed that pregnancies undergoing chorionic villus sampling have a 2-fold increased risk of fetal loss before 24 weeks of gestation compared to those not undergoing chorionic villus sampling. This study also identified factors that provide an independent contribution to the increased risk of miscarriage or fetal loss in twin pregnancy. These factors include increased maternal weight, Black race, monochorionicity, monoamnionicity, large intertwin discordance in crown-rump length, and increased fetal nuchal translucency. After adjustment for maternal and pregnancy characteristics, the chorionic villus sampling procedure itself did not provide a significant contribution to the risk of fetal loss in twin pregnancies undergoing chorionic villus sampling, suggesting that the procedure itself is not the cause of the increased fetal loss risk.[18]

Clinical Significance

Chorionic villus sampling is a safe and established option for early prenatal genetic testing. With a skilled healthcare provider and the advancement of ultrasound, complications are minimal. The results can help families make informed decisions about their pregnancy.

The laboratory test ordered for diagnosing a fetal genetic disorder depends on the clinical scenario. Patients at increased risk of aneuploidy should be offered genetic diagnostic testing with chorionic villus sampling or amniocentesis. The collected sample should be sent for karyotyping for chromosomal analysis.[19] If a pregnancy is at risk of being affected by a particular genetic disorder that has been identified in other family members, chorionic villus sampling or amniocentesis can be completed, with the sample sent for DNA testing for the specific mutation in question. If a structural abnormality is noted during an ultrasound, the patient should be offered chorionic villus sampling or amniocentesis, and the sample should be sent for chromosomal microarray analysis, as the diagnostic yield is higher than with karyotype analysis alone.[1]

Enhancing Healthcare Team Outcomes

Effective performance of chorionic villus sampling requires a high level of skill, strategic planning, ethical decision-making, and interprofessional collaboration to ensure patient-centered care and optimal outcomes. Maternal-fetal medicine subspecialists must possess technical expertise in both transcervical and transabdominal approaches, applying careful procedural strategies guided by real-time ultrasound to minimize risk. Given the specific time frame in which chorionic villus sampling can be performed, early referral to maternal-fetal medicine is a key factor in ensuring patients have access to the procedure.

Ethical responsibilities include ensuring informed consent through clear and compassionate communication about the risks, benefits, and alternatives, thereby allowing patients to make decisions that align with their values. Genetic counselors are an additional resource for families, helping them understand risks and options for prenatal testing. Nurses play a critical role in patient education, emotional support, and post-procedural care, whereas pharmacists contribute by reviewing medications such as anticoagulants that may affect procedural safety.

Interprofessional communication facilitates the seamless exchange of clinical information and coordinated decision-making among maternal-fetal medicine subspecialists, genetic counselors, pediatric subspecialists, and primary obstetric providers. Effective care coordination ensures timely referrals, accurate specimen handling, and follow-up on results, all of which contribute to improved patient safety, satisfaction, and overall team performance. Through a shared commitment to collaboration and patient advocacy, healthcare teams can enhance the quality and effectiveness of prenatal diagnostic care involving chorionic villus sampling.