1. What is amniocentesis? Under ultrasound guidance, a long thin needle is passed through the abdominal wall and uterine wall of the pregnant woman to enter the amniotic fluid cavity and extract some amniotic fluid is called amniocentesis.
2.What kind of fetal diseases can be detected by using amniotic fluid? Amniotic fluid is taken to analyze the chromosomal composition of the fetus, the most important and common of which is Down’s syndrome. Some single gene disorders, such as beta marine anemia and hemophilia, can be diagnosed by testing the genes (DNA composition) in the amniotic fluid cells. In addition, there are some major defects on the fetal body surface, such as spina bifida, meningocele, umbilical bulge, abdominal wall dehiscence, etc., can also quantify the alpha-fetoprotein in the amniotic fluid and get a pretty good reference value.
3.What is the best time for amniocentesis? The best time is around 16 weeks of pregnancy, i.e. 14 to 18 weeks. If it is less than 14 weeks, the amount of amniotic fluid is low and the difficulty of amniocentesis is higher; if the number of weeks is too large, for example, after 22 weeks, the fetus may be too pregnant at the time of diagnosis, which may cause a lot of trouble and more harm if the pregnancy is aborted.
4. Will the amount of amniotic fluid decrease after amniocentesis and will it affect the development of the fetus? Most of the amniotic fluid comes from the fetus’ urine. In the middle of pregnancy, the amniotic fluid volume is at least 250 cc or more. During amniocentesis, about 20 cc of amniotic fluid is usually extracted, accounting for less than 8% of the overall amniotic fluid volume, and it will be replenished soon, so there is no need to worry about the above problem.
5.Is amniocentesis painful and do I need anesthetic injection? The needle used for amniocentesis is long (about 10 cm) but the diameter of the tube is very small, thinner than the needle used for general blood sampling. Generally speaking, amniocentesis is at most as painful as drawing blood, so there is no need for local anesthesia. Even if anesthesia is needed, the first injection will still be painful. Therefore, local anesthesia is superfluous and may sometimes increase the risk of drug allergy or infection.
6.What is the chance of fetal miscarriage after amniocentesis? No more than 3 per 1,000. A large scale survey was conducted in the UK and the US and the results were obtained. NTU Hospital has also performed more than 15,000 amniocentesis cases so far, and the results are similar to those reported in the United Kingdom and the United States.
7.After amniocentesis, besides the extremely low miscarriage rate, will the fetus be injured? Amniocentesis performed under continuous ultrasound guidance will not harm the baby, although pregnant women may still be concerned. The main reason for this is that some pregnant women have had friends or relatives who have given birth to defective children after undergoing amniocentesis. Many people have the misconception that “all fetal abnormalities are caused by amniocentesis”. In fact, this idea is completely illogical. Even if the chromosomes are normal, about 2% of newborns have some kind of defect. These problems have nothing to do with chromosomes, and there is no way to diagnose them using amniotic fluid analysis. Even if the mother had not undergone amniocentesis, these defects would still be present. It is unreasonable for people to blame all newborns’ abnormalities on a specific test.
8. What are the discomforts that may occur after amniocentesis? There may be some pain at the site of the needle, which is the same as a shot or blood draw. Very few pregnant women have a little vaginal bleeding or a little more discharge, which usually disappears naturally after a little rest or within a few days. However, if you have severe abdominal pain or fever, or if your water breaks significantly, you should seek medical attention. The chance of having these serious complications is not more than 3 in 1000.
9.After amniocentesis, is there anything that needs special attention? Generally speaking, except for heavy work, you can continue to work as usual, and you do not need to take any injections or medication, and you can work and rest as usual.
10.How long does it take to get the results of chromosome analysis after amniocentesis? About two to three weeks. The chromosome analysis of amniotic fluid cells is not like a normal test, where the results are available as soon as the amniotic fluid is put into the machine. The extracted cells must be cultured before they divide to a sufficient number, a process that usually takes about five to ten days. After that, the chromosomes have to be stained, observed, photographed, enlarged, cut and pasted, and reviewed, so it takes this long time.
Is it true that there are reports that chromosomal abnormalities can be detected in the mother’s blood without amniocentesis? The direct use of maternal blood to detect chromosomal abnormalities in the fetus is the ultimate goal that scientists pray for day and night. However, so far, this goal is still largely unattainable, except for a very few exceptional cases. Although the scientific community has long confirmed that maternal blood contains fetal cells, the number is extremely rare. It may be more difficult to detect these cells than to find a needle in a haystack. It should also be noted that maternal blood screening for Down’s syndrome is very different from amniocentesis. Maternal blood screening can only calculate the chance of the fetus having Down’s syndrome, while amniocentesis can diagnose Down’s syndrome, which is a far cry from each other.
12.After amniocentesis, if the result is normal, does it mean that everything is fine with the fetus? Generally speaking, amniocentesis is only for chromosomal examination and a normal result only means that the chromosomes (the most common and important one is Down’s syndrome) are fine, but it does not exclude other non-chromosomal disorders such as most congenital heart diseases, mental retardation, cleft lip and palate, and genetic problems. In other words, even if the chromosomal test results are normal, about 2% of babies are still found to have some abnormality at birth.
13. What is the success rate and correctness of the chromosome test with amniotic fluid cells? The success rate of the test is higher than 99%. A few amniotic fluid tests are not able to grow because the mother’s blood is heavily contaminated. Also, due to other factors, the chromosomes of the cells may not be available. In this case, the amniotic fluid may have to be re-drawn. The correctness of chromosome results is up to 99.8% or more. In a few cases, there will be a very small percentage of errors due to contamination of the mother’s blood cells and the abnormal nature of the chromosomes.
14.Why do some people who have undergone amniocentesis have to be advised by the physician to come back and take blood from both spouses for comparison? In a few cases, the amniotic fluid cells may have structural abnormalities. For example, the A and B chromosomes are each broken at one point; the broken A chromosome is attached to the B chromosome, and similarly, the broken B chromosome is attached to the A chromosome. During the process of chromosome breakage and reassembly, some important genes may be damaged, causing certain defects, most commonly mental retardation. However, some chromosome breaks and recombinations do not harm the genes, so there is no harm to the baby. If a similar phenomenon is found during the amniotic fluid examination, the physician must first understand the chromosomal composition of the parents. If the father or mother has the same abnormality as the fetus, but the parents themselves do not have the abnormality, it means that this chromosomal variation will not cause problems in the family and the pregnancy can continue intermittently. On the other hand, if the chromosomes of both spouses are normal, but the chromosomes of the fetus are structurally abnormal, there is a 5% to 10% chance that the fetus will have some defects, especially mental problems. When a physician encounters such chromosomal recombination, he or she will first examine the chromosomal composition of the parents to assess the possible effects on the fetus.
15.What is called chorionic villus sampling? The placental tissue looks like villi after magnification, so villi are the smallest unit that makes up the placenta. Under ultrasound guidance, a catheter or a thin needle is inserted into the placental tissue through the cervix or abdomen and a small amount of villi is aspirated for chromosomal, genetic or enzyme analysis to diagnose fetal chromosomal or genetic abnormalities, a method called chorionic villus sampling.
When is the appropriate time for chorionic villus sampling? According to many studies worldwide, chorionic villus sampling can be performed after 10 weeks of pregnancy (calculated from the start of the last menstrual period). The World Health Organization has tracked more than 210,000 pregnant women who have undergone chorionic villus sampling and found that chorionic villus sampling after 10 weeks of pregnancy does not increase the chance of miscarriage (about 1%) and does not cause malformations in the newborn, such as limb defects.
17.What are the two types of chorionic villus sampling? What are the main differences? Due to the different sampling routes, there are two types of sampling: trans-cervical and trans-abdominal. When sampling through the cervix, the pregnant woman’s bladder usually has to urinate, as in the case of an internal examination, and the pregnant woman must remove her pants and lie on the examination table while the physician opens the vagina with a vaginal opener. The timing for this route is between 10 and 13 weeks of pregnancy. For transabdominal sampling, the pregnant woman simply lies flat on a normal examination table and the physician passes a long, thin needle through her belly and uterine wall to access the placenta to collect the villi. It can be used from 10 weeks to full term. Transabdominal chorionic villus sampling can be used in most cases, but only in rare cases because the entire placenta is located in the posterior wall of the uterus, making it technically less likely that chorionic villus can be collected.
18. What diseases can be detected by chorionic villus sampling? Chromosomal abnormalities and single gene disorders of the fetus. Basically, chorionic villus sampling can detect similar diseases as amniocentesis. However, some genetic disorders require a larger amount of DNA for diagnosis, for example, marital anemia A. In such cases, chorionic villus is preferable to amniocentesis.
19. Do I need anesthesia for chorionic villus sampling? Neither cervical nor abdominal sampling requires anesthesia. If the sample is taken through the cervix, the bladder has to be raised, so there will be a sensation of urine, but the sample will not be painful. For abdominal sampling, although the needle used is slightly thicker than that used for amniocentesis, it is not very painful and there is nothing to worry about.
20.Can I use chorionic villus sampling or amniocentesis to check the health of the fetus if I take medication or X-ray in early pregnancy? Basically, only 1 to 2% of all fetal abnormalities are caused by drugs or x-rays. Even if there is an effect, it usually does not change the chromosomal or genetic composition, so chorionic villus sampling or amniocentesis is not helpful in these cases.
21. Is there any special attention needed for pregnant women who undergo chorionic villus sampling afterwards? Generally speaking, no special attention is needed; daily activities can be carried out as usual. For those who undergo transcervical sampling, there will almost always be a small amount of vaginal bleeding for the first few days after the procedure. For those who undergo transabdominal sampling, there is more or less pain at the site of the needle prick, and a few people may also experience some vaginal bleeding, which is normal and not a cause for concern. If there are some special symptoms, such as heavy bleeding, premature rupture of membranes, severe pain in the lower abdomen, or chills and fever, you should consult a doctor as soon as possible.
22.How long does it take to get the report after chorionic villus sampling? It varies depending on the test. If the test is for chromosomal examination, like amniotic fluid cells, chorionic villus cells have to be cultured and analyzed, and it usually takes about two weeks to get the chromosomal diagnosis. If the test is for a single gene disorder, it can take as short as one week or as long as three weeks for a report to be available.
23. What is the chance that a person who undergoes amniocentesis or chorionic villus sampling will have an abnormal test report? Generally speaking, the rate of chromosomal abnormalities is about 2-4%, while the rate of recessive genetic disorders is 25% and the rate of dominant genetic disorders is 50%.
24. How many genes are there in humans? How many genetic diseases can be diagnosed at present? There are approximately 100,000 genes in humans, distributed over 23 pairs of chromosomes. Unfortunately, the number of genes that are well understood by the scientific community worldwide is not large, but only a few hundred, so many genetic diseases cannot be diagnosed prenatally at present. Europe, the United States and Japan are actively engaged in research projects on the human genome, and it is expected that the full sequence of human DNA will be known in the next few years. Once this project is completed, it will be a great contribution to the research and diagnosis of single genes.
How many single gene diseases can be diagnosed by amniocentesis or chorionic villus sampling in China at present? Some single gene disorders are very rare and some are not severe enough to require prenatal diagnosis. Currently, there are more than 10 single gene disorders that are more commonly diagnosed prenatally in China, such as marine anemia type A and B, hemophilia type A and B, Juvenile muscular dystrophy, fragile X chromosome disorder, hepatic glucose storage disorders type I and II, congenital adrenal hyperplasia, male feminization, Huntington’s chorea, phenylketonuria, spinal muscular dystrophy, neurofibromatosis type I, adult polycystic kidney disease and a few mucopolysaccharidoses. Although amniotic fluid diagnosis is almost 100% accurate in detecting chromosomes, it cannot detect structural disorders like deformed feet or heart disease.