Chorionic Villus Sampling (CVS)
Chorionic villus sampling (CVS)
analyzes chorionic villus cells, which eventually become the placenta.
The test detects genetic abnormalities; sampling is done early in
pregnancy. The advantage of CVS is that a healthcare provider can
diagnose a problem earlier in pregnancy.
The test can be done at 9 to 11 weeks
instead of 16 to 18 weeks, as with amniocentesis. Some women choose CVS
so they can make a decision about their pregnancy earlier. If a woman
decides to terminate a pregnancy, the procedure may carry fewer risks
when performed earlier in pregnancy.
To perform the test, an instrument is
placed through the cervix or through the abdomen to remove a small
piece of tissue from the placenta. If your doctor recommends CVS, ask
about its risks. The test should be performed only by someone
experienced with the technique. The risk of miscarriage is
small—between 1 and 2%—and the test is considered as safe as
amniocentesis. If you have CVS and are Rh-negative, you should receive
RhoGAM after the procedure.
A special listening machine, called a doppler,
magnifies the sound of the baby’s heartbeat so it can be heard. It’s
usually possible to hear the baby’s heartbeat around your 12-week visit.
Because of advances in fiber optics, we
are able to look at a fetus or placenta as early as 10 weeks into its
development. Ultrasound cannot provide the same degree of detail. Fetoscopy enables the healthcare provider to look through a fetoscope to detect even subtle abnormalities and problems.
The healthcare provider makes a small
incision in the mother’s abdomen and places a small scope through the
abdomen and uterus. The healthcare provider uses the fetoscope to
examine the fetus and placenta.
The test is specialized and is not done
very often. It is usually recommended if you have given birth to a
child with a birth defect that cannot be detected by any other test. If
your healthcare provider suggests fetoscopy to you, discuss it with him
or her. The risk of miscarriage is 3 to 4%. Only someone experienced at
it should do the procedure.
Fetal Fibronectin (fFN)
It can be difficult to determine if a
woman is at risk of delivering a preterm baby. Many symptoms of preterm
labor mimic various discomforts of pregnancy. However, a test is
available that can help doctors make this determination.
Fetal fibronectin (fFN) is a protein
found in the amniotic sac and fetal membranes. After 22 weeks of
pregnancy, fFN is not normally present until around week 38.
When present in cervical-vaginal
secretions of a pregnant woman after 22 weeks (before week 38), it
indicates increased risk for preterm delivery. If absent, risk of
premature labor is low, and the woman probably won’t deliver within the
next 2 weeks. fFN can rule out early delivery with 99% accuracy.
The test is performed like a Pap
smear. A swab of vaginal secretions is taken from the top of the
vagina, behind the cervix. It is sent to the lab, and results are
available within 24 hours.
Percutaneous Umbilical Blood Sampling (PUBS)
Percutaneous umbilical blood sampling (PUBS), also called cordocentesis,
is a test done on the fetus while it is still inside the uterus. The
test has improved the diagnosis and treatment of Rh-incompatibility and
other blood disorders. Results can be available within a few days, but
it carries a slightly higher risk of miscarriage than amniocentesis
Guided by ultrasound, a fine needle is
inserted through the mother’s abdomen into a tiny vein in the umbilical
cord of the fetus. A small sample of the baby’s blood is removed for analysis. Blood disorders, infections and Rh-incompatibility are detectable with PUBS.
If the fetus is found to be
Rh-positive and its mother is Rh-negative, healthcare providers have
time to give it a blood transfusion, if necessary. This procedure can
help prevent life-threatening anemia that can develop if the mother is
isoimmunized (she has antibodies that attack her baby’s blood).If you are Rh-negative, you should receive RhoGAM after this procedure.