Handbook of Genetic Counseling/Percutaneous Umbilical Blood Sampling (PUBS)
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Percutaneous Umbilical Blood Sampling (PUBS)
- Welcome and acknowledge prior phone contact
- Discuss the reason for referral
- Elicit prior knowledge about Rh isoimmunization
- Assess questions and concerns
- Discuss overview of the session and explain relevance of each portion
- Medical information and family history
- Rh factor and isoimmunization
- Treatment options for the fetus
Explain Genes and Chromosomes
- Tell patient that we need to discuss genes and chromosomes so she can understand how we can tell that her baby is Rh negative
- Dominant vs. recessive alleles and autosomal dominant inheritance
Rh Factor and Rh Isoimmunization
- Rh refers to a protein that is sometimes present on the surface of red blood cells. If a person has this protein, they are Rh positive; if not, they are Rh negative
- A person with Rh negative blood can develop antibodies against Rh positive cells if they are exposed to Rh positive blood. This can happen during pregnancy with an Rh - mother and Rh + fetus.
- These antibodies attack the Rh + fetal cells
- A medication called RhoGAM can be given to an Rh - mother so that she will not produce antibodies against her Rh + fetus
- If the mother makes these antibodies, fetal blood cells will be destroyed and a serious condition called anemia can result. Another more life-threatening condition, immune hydrops fetalis, can also occur. This is the accumulation of water in the fetus, causing severe swelling. This can cause other organ systems in the baby to shut down or not develop correctly.
- Even though Rh is the most common blood protein to cause sensitization in mothers there are other blood proteins such as Kell that can cause isoimmunization.
- Percutaneous umbilical blood sampling is a technique used to collect a sample of blood from a fetus through an umbilical vessel
- "Percutaneous" refers to going through skin without puncturing or opening it
- We can use this technique to do a blood transfusion directly into a fetus to treat anemia
- Because of Rh incompatibility, we can't give the blood to the mother-it must be given directly to the baby
- PUBS can be done starting at 16 weeks gestation until birth
- The umbilical vessels connect the baby to the placenta (show on visual aid)
- A doctor and an ultrasound technician will typically be in the room during the procedure. The mother may have someone come in with her if she chooses.
- Mother will lie on an exam table on her back with her hands folded behind her head.
- An ultrasound will be done first to determine the location of the fetus and the placenta
- This is a special type of ultrasound, known as Color Doppler imaging. It allows the best view of the umbilical cord because it uses different colors to measure blood flow in the baby and allows the cord to be seen very easily.
- The physician and ultrasound technician will look for the best place to access the umbilical artery-this is usually where the umbilical cord meets the placenta, since it is farthest from the baby. This is not always possible, so the physician will look for the best spot available. This may include a loop in the umbilical cord, the place where the umbilical cord enters the fetus, or the hepatic vein (inside the fetal body)
- The entire procedure is done under ultrasound guidance
- Once the insertion site has been determined, the mother's abdomen will be sterilized with betadeine
- She will then be injected with a topical anesthetic at the insertion site
- The physician will then insert a special needle into the mother's abdomen, through the uterus and into the umbilical vein
- The needle is a 20 or 22-gauge needle (about the size used for drawing blood) and has a stylet inside of it
- Even though a topical anesthetic has been given, the mother will still feel some cramping when the needle passes through the uterus. Most women say this is the most painful part and compare it to a strong menstrual cramp.
- Once the needle has been inserted, the stylet will be removed and a syringe will be attached to the needle
- The syringe will have a drug in it (heparin) to help with blood clots
- A blood sample will then be taken to see if the baby is anemic. If that test (hematocrit) shows anemia, the procedure will continue.
- Hematocrit allows us to determine whether or not fetal blood cells are being destroyed due to Rh incompatibility.
- The baby will be given a neuromuscular blocking agent. This is to keep the baby from moving during the procedure.
- The blood transfusion will then be given to the baby
- The needle will then be removed and the physician will use ultrasound to check for fetal well-being
- The entire procedure will take less than ten minutes
- This procedure can reverse potentially detrimental conditions in a fetus. The overall survival rate for babies who have had a blood transfusion in utero is 84.7%. For babies without hydrops, the survival rate is 91.1%.
- If necessary, the procedure will be repeated at 2-to-3-week intervals until 34-35 weeks of gestation.
- If the mother is Rh negative, RhoGam needs to be administered within 72 hours.
- After the test, avoid any strenuous activity for 24 hours. This includes standing for long periods of time, lifting, and exercising. A woman may return to work if her job doesn't require physical activity.
- No sexual intercourse, douching, tub baths, or use of tampons for 72 hours.
- Some minor cramping after the procedure is normal. If the cramps become severe, call a doctor. Also, call a doctor if leakage of clear fluid (amniotic fluid) or blood from the vagina, fever, unusual fetal activity, or any other unusual feelings occur.
- A few days after the test, a mother should return for a follow-up ultrasound just to check on the baby. Also, serial ultrasounds are recommended to check for signs of hydrops.
- If the placenta is located closer to the abdominal wall than the fetus is, the needle will pass through the placenta. This can cause maternal-fetal blood mixing.
- RhoGAM will be given to the mother to prevent problems
- 1-2% risk for pregnancy loss (this is above the 3-5% background risk)
- Infection (chorioamnionitis) is another risk. Less common risks include blood clots in the umbilical cord, excessive bleeding (mother or baby), decreased fetal heart rate, and placental abruption. The overall risk of any of these things happening is between 1-6.7%, depending on the experience of the physician.
- Loss rates are higher in fetuses who have genetic conditions, structural anomalies, or IUGR. Maternal complications are uncommon.
Other Testing Options
- By using amnio, we can look at the amount of bilirubin in the amniotic fluid. This pigment is an indicator of hemolysis and can tell us if the baby is anemic. Also, we can measure the levels of DOD450 to tell if the fetus is anemic.
- This is accurate during the third trimester, but not accurate in the second trimester.
- This can diagnose anemia, but cannot treat it
Discuss Patient's Feelings About the Procedure
- Emphasize the fact that this is entirely her choice
Assess Understanding and Elicit Questions
The information in this outline was last updated in 2002.