Amniocentesis is the name given to the extraction of amniotic fluid for chromosomal analysis testing on the baby. Thgis is usually performed at around 16 weeks of pregnancy, when there is sufficient amni fluid to make its removal safe. An ultrasound is done first to located the fetus, placenta, and pool of fluid. The doctor inserts a hollow needle through the woman’s abdominal wall, and the amniotic fluid is drawn up through the needle into the vial. You will have to wait about seven to ten days (It used to be four to five weeks) for the results, while the cells are grown and the chromosomes are investigated.
It can be alarming for the pregnant woman, already entering her fifth month, to wprry about whether this will cause a miscarriage. Surprisingly, the procedure is not at all painful. Amniocentesis dose carry a small further risk of miscarriage, but this has lessened over the years as doctors become more and more skilled in the procedure. The risk factor can run from 1 in 200, to 1 in 400, with a doctor who perform amnios frequently.
Chorionic villus samping (CVS) is a new techonique, still considered at the research stage, whereby a small sample of chorionic (placental) tissue is taken at about the 9th or 10th week of pregnancy, by inserting a tube through the cervix or sometimes through the abdomen. Results are available within seven to ten days. The advantage of CVS is that it can be performed earlier in pregnancy, so that if a serious chromosomal defect is discovered, a termination could be performed earlier.
The advantage of CVS is that it still carries a higher risk of miscarriage than amnoocentesis. Currently the risk is given as 1 in 100. further, with CVS, confusion may arise if there is a mixture of chromosome karyotypes in the rapidly growing placenta cells.
Since both procedure carry a risk of miscarriage, women who have already suffered several pregnancy losses may find that putting this pregnancy at further risk is untenable. You and your partner will have to debate with each other and with your doctor the value of the test and its side effects very carefully. If you do have a history of recurrent miscarriage, amniocenesis is probably the safer procedure. It also offers alpha-fetoprotein (AFP) sampling from the fluid at the same time. With CVS, the test has a high incidence of false positives and needs to be repeated often, which may lead in some of the stories anxiety.)
As you will have read in some of the stories in this book, many women have had to go through this difficult decision process. Very often, despite their reluctance to terminate a pregnancy after years of struggling to save one, they do have the chromosomal testing because of their fear of not being able ever to have a normal healthy child.
