Introduction
Fetal blood sampling (FBS), also known as cordocentesis, is a prenatal diagnostic procedure used to obtain a small sample of fetal blood from the umbilical cord for testing. It is an invasive procedure that is performed in the second or third trimester of pregnancy. It provides valuable information for the diagnosis and treatment of certain fetal conditions.
How Is Fetal Blood Sampling Done?
Fetal blood sampling (FBS) involves withdrawing a small sample of blood from the umbilical cord or a fetal vessel for diagnostic testing. The procedure is performed under ultrasound guidance. The procedure for fetal blood sampling involves the following steps:
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Preparation: Before the procedure, the mother’s blood type is checked to detect if there is a risk of Rh incompatibility. If the mother is Rh-negative and the father is Rh-positive, she may require Rh immunoglobulin injections to prevent Rh sensitization. The fetal position and location of the umbilical cord are determined using ultrasound.
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Anesthesia: Local anesthesia is administered to the mother’s abdomen to numb the skin and the uterus.
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Fetal Blood Sample Collection: Using ultrasound guidance, a small amount of fetal blood is drawn and sent to the laboratory for testing.
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Monitoring: The fetal heart rate is observed throughout the procedure for the safety of the fetus.
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Post-Procedure Care: After the procedure, the mother is observed for any complications such as bleeding, infection, or preterm labor.
What To Do After a Fetal Blood Sampling Procedure?
Some general instructions to be followed after a fetal blood sampling procedure include
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Rest: After the procedure, it is important to rest completely for at least 24 hours. This will reduce the risk of bleeding or injury at the puncture site.
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Avoiding Medications: Patients may be advised to avoid taking medications like blood thinners (Aspirin or Ibuprofen) after the procedure.
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Monitor for Signs of Infection: Patients should monitor the puncture site for signs of infection, such as redness, swelling, or drainage.
What Are the Indications of Fetal Blood Sampling?
Fetal Blood Sampling (FBS) can be used to diagnose a variety of conditions, including:
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Chromosomal Abnormalities: FBS can be used to diagnose chromosomal abnormalities such as Down syndrome, Turner syndrome, and Klinefelter syndrome.
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Fetal Anemia: FBS can be used to diagnose fetal anemia, a condition in which the fetus has a low hemoglobin level or red blood cell count. This can occur in cases of Rh sensitization, where the mother is Rh-negative and the fetus is Rh-positive or in cases of fetal-maternal blood group incompatibility.
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Evaluation of Fetal Infection: FBS can be used to evaluate for fetal infection, such as in cases of congenital cytomegalovirus (CMV) or toxoplasmosis.
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Assessment of Fetal Lung Maturity: FBS can be used to assess fetal lung maturity in situations where preterm delivery is anticipated.
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Evaluation of Fetal Acid-Base Status: FBS can be used to evaluate the fetal acid-base status, which can help healthcare providers determine whether fetal distress is present and whether delivery is necessary.
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Assessment of Fetal Hemoglobinopathies: FBS can be used to assess for fetal hemoglobinopathies, such as sickle cell disease or thalassemia.
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Evaluation of Fetal Thrombocytopenia: FBS can be used to evaluate for fetal thrombocytopenia, a condition in which the fetus has a low platelet count.
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Fetal Metabolic Disorders: FBS can be used to diagnose fetal metabolic disorders such as phenylketonuria and maple syrup urine disease.
What Are the Contraindications of Fetal Blood Sampling?
There are certain situations in which fetal blood sampling (FBS) is contraindicated, including:
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Placenta Previa: FBS should not be performed if the placenta is covering the cervix (placenta previa) because there is a risk of bleeding and injury to the placenta.
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Active Labor: FBS is not performed during active labor because there is a risk of injury to the fetus and complications during delivery.
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Premature Rupture of Membranes: If the mother's membranes have ruptured prematurely, there is a risk of infection.
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Fetal Distress: FBS should not be performed if the fetus is in distress because the procedure may further compromise the fetal condition.
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Maternal Coagulopathy: If the mother has a bleeding disorder or is taking anticoagulant medication, there is a risk of bleeding and injury. Hence, fetal blood sampling is not indicated in such cases.
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Maternal Infection: FBS should not be performed if the mother has an active infection, such as chorioamnionitis because there is a risk of infection transmission to the fetus.
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Fetal Hydrops: FBS should not be performed if the fetus has hydrops, a condition in which there is an abnormal collection of fluid in two or more fetal compartments, because the procedure may exacerbate the condition.
What Are the Benefits of Fetal Blood Sampling?
The benefits of fetal blood sampling include the following:
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Accurate Diagnosis: FBS can provide an accurate diagnosis of fetal conditions that cannot be diagnosed by other non-invasive tests such as ultrasound, maternal blood tests, or amniocentesis.
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Early Diagnosis: FBS can detect fetal conditions earlier in pregnancy, which can allow for earlier intervention and treatment.
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Tailored Treatment: FBS can provide information that allows for tailored treatment of fetal conditions, such as blood transfusions for fetal anemia.
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Improved Outcomes: Early diagnosis and tailored treatment of fetal conditions can lead to improved outcomes for both the mother and the fetus.
What Are the Complications of Fetal Blood Sampling?
The most common complications of fetal blood sampling (FBS) include:
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Fetal Bradycardia: FBS can cause a temporary slowing of the fetal heart rate (bradycardia).
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Maternal Discomfort: FBS involves inserting a needle through the mother's abdomen and into the uterus, which can cause discomfort and pain.
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Bleeding: FBS can cause bleeding from the puncture site, although the risk of significant bleeding is low.
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Infection: FBS carries a small risk of infection, particularly if the procedure is performed under unsterile conditions.
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Injury to the Fetus: FBS carries a small risk of injury to the fetus, including puncture of the umbilical cord or placenta, although this is rare.
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Preterm Labor: FBS can cause preterm labor in rare cases.
Conclusion
Fetal blood sampling is a useful diagnostic tool for the management of high-risk pregnancies. It is always advisable to follow the instructions provided by medical professionals to prevent any risk of complications and ensure better outcomes.
