Chorionic Villus Sampling (CVS)

CVS is an 'invasive' diagnostic test, meaning it involves entering the pregnancy environment to collect tissue. The chorionic villi are tiny, finger-like projections of placental tissue that share the same genetic code as the developing fetus. Because the placenta and the baby originate from the same initial cells, testing the placenta provides a reliable window into the baby's chromosomal health.

There are two methods of performing CVS: Transabdominal (through the mother's abdomen) and Transcervical (through the cervix). At the MFM Unit, we primarily use the transabdominal approach under continuous, high-resolution ultrasound guidance. This ensures the sampling needle remains precisely targeted within the thickest part of the placenta, well away from the baby. The procedure allows for a significantly earlier diagnosis than amniocentesis, which cannot typically be performed until 16 weeks.

CVS is not a routine test; it is offered when there is a clinical reason to seek definitive genetic information early in pregnancy. You may be considering CVS if:

• A High-Risk Screening Result: You have received a high-risk result from an NIPT or a First Trimester Combined Screen.
• Increased Nuchal Translucency (NT): An ultrasound has shown a measurement of 3.5mm or greater.
• Family History: You or your partner are known carriers of an inherited condition like Thalassaemia, Cystic Fibrosis, or Sickle Cell Disease.
• Previous Pregnancy: You have a history of a pregnancy affected by a chromosomal condition.

Because CVS can be performed as early as 11 weeks, it is the preferred choice for families who want to know the genetic status of their pregnancy at the earliest possible stage.

The procedure is performed between 11 weeks and 13 weeks 6 days. The team confirms fetal growth and maps the placenta, uses local anaesthetic where appropriate, and directs a fine needle into the placenta while monitoring its position and the fetus in real time with ultrasound. Laboratory analysis may include rapid testing for selected common trisomies, chromosomal microarray, or targeted testing for a known familial condition. Turnaround time and scope are confirmed during counselling.

Following CVS, mild cramping or light spotting can occur. The team provides written aftercare and warning signs. A result reported as normal lowers the chance of the conditions covered by the selected test, but it does not exclude every chromosomal, genetic, or structural condition; the detailed anatomy scan remains important. A pathogenic or uncertain result is reviewed with genetic counselling, and confirmatory amniocentesis may occasionally be discussed when placental mosaicism is suspected.

Miscarriage and other complications are uncommon, but the additional procedure-related risk is not zero and estimates vary with the population, indication, operator, and study method. CVS can provide an early diagnosis for conditions covered by the chosen laboratory test. The result may be diagnostic, uncertain, inconclusive, or occasionally reflect confined placental mosaicism, so counselling and clinical interpretation remain essential.

The usual CVS window is limited, so prompt specialist review is helpful after a high-chance screening result, increased NT, fetal finding, or known familial condition. The consultation should confirm whether CVS or amniocentesis better answers the question and should cover the procedure, laboratory scope, possible results, limitations, and risks before consent.