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Cordocentesis, or fetal blood sample, is a prenatal diagnostic test, performed after 18 or 20 weeks of gestation, and consists of taking a sample of the baby's blood from the umbilical cord, to detect any chromosomal deficiency. in the baby, such as Down's Syndrome, or diseases such as toxoplasmosis, rubella, fetal anemia or cytomegalovirus, for example.
The main difference between cordocentesis and amniocentesis, which are 2 prenatal diagnostic tests, is that Cordocentesis analyzes the baby's umbilical cord blood, whereas Amniocentesis analyzes only the amniotic fluid. The karyotype result comes out in 2 or 3 days, which is one of the advantages over amniocentesis, which takes about 15 days.
Blood drawn between the cord and the placenta
When to do cordocentesis
Cordocentesis indications include the diagnosis of Down's Syndrome, when it cannot be obtained through amniocentesis, when the ultrasound results are inconclusive.
Cordocentesis allows the study of DNA, karyotype and diseases such as:
- Blood disorders: Thalassemia and sickle cell anemia;
- Blood clotting disorders: Hemophilia, Von Willebrand's Disease, Autoimmune Thrombocytopenia, Thrombocytopenic Purpura;
- Metabolic diseases such as Duchenne Muscular Dystrophy or Tay-Sachs Disease;
- To identify why the baby is stunted, and
- To identify fetal hydrops, for example.
In addition, it is also very useful for the diagnosis that the baby has some congenital infection and can also be indicated as a form of treatment for intrauterine blood transfusion or when it is necessary to administer drugs to treat fetal diseases, for example.
Learn other tests for the diagnosis of Down Syndrome.
How cordocentesis is made
No preparation is necessary before the exam, however the woman must have had an ultrasound exam and a blood test prior to cordocentesis to indicate her blood type and HR factor. This exam can be performed at the clinic or hospital, as follows:
- The pregnant woman lies on her back;
- The doctor applies local anesthesia;
- With the help of ultrasound, the doctor inserts a needle more specifically in the place where the umbilical cord and the placenta join;
- The doctor takes a small sample of the baby's blood with about 2 to 5 ml;
- The sample is taken to the laboratory for analysis.
During the examination, the pregnant woman may experience abdominal cramps and therefore should rest for 24 to 48 hours after the examination and not have intimate contact for 7 days after cordocentesis.
Symptoms such as fluid loss, vaginal bleeding, contractions, fever and pain in the belly may appear after the examination. For relief of pain and discomfort it may be useful to take a Buscopan tablet, under medical advice.
What are the risks of cordocentesis
Cordocentesis is a safe procedure, but it has risks, like any other invasive exam, and so the doctor only asks for it when there are more advantages than risks for the mother or baby. The risks of cordocentesis are low and manageable, but include:
- About 1 risk of miscarriage;
- Blood loss at the place where the needle is inserted;
- Decreased baby's heart rate;
- Premature rupture of the membranes, which may favor premature delivery.
Generally, the doctor orders cordocentesis when a genetic syndrome or disease is suspected that has not been identified through amniocentesis or ultrasound.