Definition and Overview
Cordocentesis is one of the earliest methods used in prenatal diagnosis. Also referred to as percutaneous umbilical cord blood sampling (PUBS), this invasive procedure is performed to obtain fetal blood sample and test it for possible disorders or diseases, such as Down's syndrome, sickle cell anemia, Tay-Sachs disease, cleft palate, and other genetic disorders.
Today, prenatal diagnosis and screening can either be invasive or non-invasive. Being one of the earlier types, cordocentesis is an invasive method. Improvements in the procedure increased its popularity in 1983, but its roots can be traced all the way back to 1964. Back then, the procedure required major surgery, placing the lives and well-being of the mother and baby at a significant risk. With the assistance of ultrasound devices, the safety of the procedure has improved, minimizing its risks and possibilities of complications.
Cordocentesis is best performed between 20 and 24 weeks of gestation. By this time, the umbilical cord has already fully developed. If the procedure is performed later than 24 weeks, it would be more difficult to terminate the pregnancy in case serious problems are detected during the examinations.
In most countries, prenatal screening procedures, such as cordocentesis, are optional. While such provide many benefits, they also carry some risks that many parents would rather not take.
In addition to performing a risk versus benefit analysis prior to agreeing to such procedures, parents also need to consider other aspects of their lives, such as religious beliefs and personal preferences. Some parents have made the decision to accept the child no matter the outcome of the pregnancy so the benefits of prenatal screening would be nullified. Others may have religious beliefs that prevent them from intervening in the normal pregnancy and childbirth process.
Who should undergo and expected results
Cordocentesis is primarily recommended if the doctor needs to confirm abnormal test results, such as a prenatal ultrasound.
Below are the reasons why patients undergo the procedure:
- To have the choice to abort the pregnancy should the fetus shows signs of severe abnormalities
- To identify any problems ahead of time and be prepared to handle such problems as soon as the baby is born
- To allow for medical intervention to treat problems before the child is born or a shortly after childbirth
The procedure is expected to take anywhere between 30 minutes to an hour. Most cordocentesis procedures performed on the 20th week take place in an outpatient facility. If the procedure is to be performed on the 24th week or after, it is usually conducted in a hospital setting. In most cases, doctors prefer to perform the procedure at a location that is near a childbirth facility as complications can develop which would require an immediate C-section.
How the procedure works
Cordocentesis may be performed in an outpatient clinic or hospital setting. A day or two prior to the procedure, the mother will be given instructions on how to prepare. The specific instructions depend on the situation of the mother, but it will usually include abstaining from food or drinks for at least 12 hours before the procedure.
During a cordocentesis, the mother will be asked to lie on an examination table. The doctor will then use ultrasound to determine the exact position of the fetus before a small area on the abdomen is cleansed with antiseptic. In some cases, the doctor may opt to apply a local anesthetic to reduce the discomfort.
Guided by an ultrasound, the doctor will insert a syringe with a 5-inch needle into the abdomen and then to the umbilical cord to collect blood samples. The procedure may result in a bit of a discomfort, which is why the mother is usually advised to rest for a while before returning home. Some also experience a bit of cramping during and directly after the procedure.
Possible risks and complications
All invasive prenatal diagnostic procedures have associated risks and possibilities of complications. However, a cordocentesis procedure usually carries more risks than other types.
Some of the risks and complications can be serious, such as fetal death, fetal-maternal hemorrhage, preterm labor resulting in an immediate C-section, and cord hematoma. The mother may also experience bleeding, or infections although this rarely occurs.
It's important to note that cordocentesis does have a rather higher risk factor than other forms of prenatal diagnostic procedures. In fact, the risk of pregnancy loss is around 1.4 to 1.9 percent for normal pregnancies being tested for any abnormal conditions.
Grace D, et al. Training for percutaneous umbilical blood sampling during Maternal Fetal Medicine fellowship in the United States. Prenatal Diagnosis. 2009;29:790.
Cunningham FG, et al. Prenatal diagnosis. In: Williams Obstetrics. 24th ed. New York, N.Y.: The McGraw-Hill Companies; 2014. http://www.accessmedicine.com. Accessed Aug. 14, 2015.