Chorionic villus sampling (CVS) is a prenatal test that diagnoses chromosomal abnormalities such as Down syndrome, as well as a host of other genetic disorders. The doctor takes cells from tiny fingerlike projections on your placenta called the chorionic villi and sends them to a lab for genetic analysis.
CVS and another test called amniocentesis produce a karyotype – a picture of your baby's chromosomes – so that your caregiver can see for sure if there are any problems.
Women who choose to have CVS or amniocentesis are often those at increased risk for genetic and chromosomal problems, in part because these tests are invasive and carry a small risk of miscarriage.
The main advantage of CVS over amniocentesis is that you can have it done earlier — generally between 10 and 13 weeks of pregnancy. For an amnio, you'll have to wait until you're at least 16 weeks pregnant.
Amniocentesis is a test you may be offered during pregnancy to check if your baby has a genetic disorder, such as Down's syndrome.
It involves removing and testing a small sample of cells from amniotic fluid, which surrounds the foetus in the womb (uterus).
Amniocentesis is usually carried out between the 15th and 20th weeks of pregnancy, but may be performed later than this if necessary.
Although it can be performed earlier, this may increase the risk of complications of amniocentesis and is usually avoided.
During the test, a long, thin needle is inserted through your abdominal wall, guided by an ultrasound image. The needle is passed into the amniotic sac that surrounds the foetus and a small sample of amniotic fluid is removed for analysis.
The test itself usually takes about 10 minutes, although the whole consultation may take about 30 minutes.
Amniocentesis is usually described as being uncomfortable rather than painful. Some women describe experiencing a pain similar to period pain or feeling pressure when the needle is taken out.
Fetal blood sampling (FBS) is the collecting of fetal blood directly from the umbilical cord or fetus. The fetal blood is tested for signs of anemia and other blood problems. FBS is also known as cordocentesis or percutaneous umbilical cord blood sampling.
FBS is usually used when a Doppler ultrasound and/or a series of amniocentesis tests have first shown moderate to severe anemia.
If you are Rh-sensitized and you are carrying an Rh-positive fetus, your immune system can attack the fetus's red blood cells. FBS is used to look at a fetus's red blood cell count and oxygen level, and it also looks for signs that your immune system is destroying fetal red blood cells.
When a high order multiple pregnancy (three or more fetuses present in the womb at the same time) is 'selectively reduced' to twin or singleton pregnancy by injecting a drug, the procedure is called 'selective embryo reduction'. It is an procedure whereby one or more fetuses are aborted so as to improve the outcome of the remaining fetuses.
The benefits of embryo reduction far outweigh the risks associated with the procedure. Embryo reduction substantially increases the duration of pregnancy, reduces the incidence of premature delivery which in turn has the benefit of increasing the baby’s birth weight and reducing neonatal mortality along with shortening the neonatal intensive care stay.
Most studies suggest an improved perinatal outcome for triplet pregnancies reduced to twins compared with non-reduced triplet pregnancies. Embryo reduction is associated with a lower incidence of premature delivery (54% versus 87% to 92%), higher birth weight (average increase of 380 to 450 g/fetus), shorter stay in neonatal intensive care (21 versus 8 days), and a lower rate of perinatal mortality (33 per 1,000 deliveries versus 51-93 per 1,000 births). The benefits are even more pronounced with quadruplets and other higher order multiple pregnancies.