Tests during Pregnancy

While ultrasound is currently the safest non-invasive method of examining fetal development, the number of ultrasounds appropriate for a pregnant woman is a hotly debated topic. Regardless of the debate, it is well known that ultrasound is priceless in its ability to see the fetus before it is born.

At 18-20 weeks, most physicians recommend an ultrasound for four main reasons:

i. To establish the due date - without an ultrasound, it is not possible to determine when a child will be born and how far along the pregnancy has progressed.

ii. To diagnose multiple pregnancies - ultrasound can be used to see if more than one baby is going to be born. Without this technique, many twin births are not diagnosed until delivery.

iii. To localize the placenta - an ultrasound can diagnose a condition known as placenta previa in which the placenta has attached too low in the uterus, providing a risk of bleeding late in pregnancy.

iv. To detect fetal abnormalities - scans can detect fetal abnormalities in mothers who have had no previous pregnancy problems.

Other specific reasons for carrying out an ultrasound include:

v. If there is bleeding in the 1st trimester. As well, couples planning to do a CVS or amniocentesis may use an ultrasound to determine the time at which these tests should be done. An ultrasound can also be used to diagnose Down syndrome at 10-13 weeks.

vi. If there is a concern about fetal growth in the 3rd trimester. While ultrasounds are not common in the 3rd trimester, they may be used if there are specific concerns.

An ultrasound can offer a variety of other types of information regarding the fetus. Most new parents are interested to know the sex of their child. It is important that the mother discuss with her partner before going to the ultrasound, whether or not she would like to know the sex of the baby. This will prevent conflict from arising while at the clinic.

Contrary to popular belief it is not possible to determine the sex of the fetus by monitoring fetal heart rate. To conclude on the sex of the fetus, the physician will look at the genitalia around 18 weeks into the pregnancy. However, what is seen on the ultrasound is not an absolute guarantee of the sex of the fetus. Depending on the stage of pregnancy, the experience of the physician and the position of the fetus, there is approximately a 98% accurate rate in determining the sex of the fetus.

A central goal in using ultrasound involves monitoring fetal growth. While growth assessments are usually done by palpating the abdomen, the ultrasound can also be a useful tool in determining the size of the fetus. The nutritional status of the fetus can also be assessed through detecting the amount of amniotic fluid present and the fatty tissue being laid down. Ultimately, the rationale behind monitoring fetal growth is to decide the most favorable time for delivery.

Finally, ultrasound can also be used to detect variations in the amount of amniotic fluid around the fetus. Excessive amounts of fluid may cause mothers to have increased discomfort and is at times associated with multiple pregnancies or fetal abnormalities. If there is an accumulation of fluid an obstetrician may contemplate further testing, such as fetal blood sampling or placental biopsy, to rule out a chromosomal abnormality. A deficiency in amniotic fluid may signal poor placental function and may be designate further fetal testing.

There are other tests that also use ultrasound equipment including cardiotocography (CTG), biophysical profiles and fetal Doppler studies. These tests will be covered in detail later on in this section.

Common Ultrasound Questions

The following is a list of common questions asked by mothers, regarding the procedure and results of an ultrasound:

Q. Is the ultrasound an X-ray?
A. No, the ultrasound involves the use of sound waves, much like those produced during speech, and does not contain X-rays at all.

Q. Are the sound waves going to hurt the baby?
A. At the levels used for diagnosis, ultrasound has not been found to damage the fetus in any way. As well, the baby's movements are not stimulated or caused by the ultrasound.

Q. Is the baby transparent?
A. When some people see the internal organs of the fetus during the ultrasound, they misinterpret this to mean that fetuses in early pregnancy are see-through. This is not the case, fetuses have thin skin and the ultrasound is able to penetrate this skin and supply images of the fetuses insides.

Q. In the picture, where are the baby's arms and legs?
A. Usually, the picture you receive of the ultrasound will include the baby's head and body. Since ultrasound pictures are taken in 'slices' one can not include the head, arms and legs all in one shot.

Q. Can I hear the baby's heartbeat?
A. Ultrasound equipment is able to hear the baby's heartbeat, however, it may be just projected onto a TV screen so the mother can see the heartbeat. Usually the physician does not listen to the heartbeat unless it is medically necessary.

Reasons for Testing with Amniocentesis or Chorionic Villus Sampling (CVS)

Amniocentesis and CVS are both carried out with the main intent of analyzing the genetic composition of the baby before he is born. Both amniocentesis and CVS involve sampling cells that contain the same genetic make-up as the baby. Amniocentesis involves taking a relatively large volume (~ 15 ml) of amniotic fluid to collect cells viable for chromosome analysis. Chorionic villus sampling involves investigation of the cells in the placenta, also known as the chorion.

The following is a list of reasons as to why the mother may be offered an amniocentesis or CVS:

Age - the major reason for testing pregnant women is their age. The mother may be offered a test if she is over 35 years of age, however it is generally believed that any couple should have access to counseling and prenatal testing if they need it.

Chromosomal abnormality in parent- if either the mother or the father has a chromosomal defect then the baby will be tested before he is born.

Past history - if a couple has a history of giving birth to a child with a chromosomal abnormality, they will be more likely to be tested in subsequent pregnancies.

Ultrasound Warnings - if the ultrasound provides any indication of chromosomal abnormality, ranging from subtle hints to major signs of fetal structural abnormalities, growth reductions or amniotic fluid volume deviations then appropriate testing will follow.

Biochemical test result irregularities - if there are abnormal levels of alpha fetoprotein (AFP) or other irregular results (see section on 'Other Tests').

Miscarriages - if the mother has a history of three or more previous miscarriages.

Neural tube defects - if couples are at risk of having a baby with neural tube defects, especially those who have given birth to a child with anencephaly or spina bifida. Also couples with raised maternal levels of AFP will be tested.

Single gene disorder - if either family of each parent has a history of single gene disorders, such as muscular dystrophy, hemophilia or thalassaemia.

Amniocentesis and CVS Questions

The following is a list of frequently asked questions regarding whether or not to conduct amniocentesis or CVS as a form of genetic counseling:

Q. Even though the mother is young she is still worried about giving birth to a baby with an abnormality. Is she allowed to have a CVS or amniocentesis to alleviate her fears?
A. While ideally every couple who wants prenatal testing should be able to get it, this is not always the case. Depending on the mother's location and the availability of resources, some centers may only reserve these expensive tests for couples who fit the aforementioned guidelines. As well, the mother must also consider the reasoning behind choosing an amniocentesis and what the mother would do if the tests showed an abnormality.

Q. What are the mother's chances of having a baby with Down syndrome if she has a close relative (e. g. brother, sister or cousin) with the condition?
A. The mother's chances of giving birth to a baby with Down syndrome are not increased above those of other women the mother's age. If an affected family member has the rare translocation type of Down syndrome, then parents and other family members may have a chromosomal rearrangement which increases their risk. In this case, it is probable that parents of the affected individual will know of the unusual condition.

Q. Early in pregnancy the mother took drugs/had an X-ray/was severely ill/drank alcohol heavily; should she have an amniocentesis or CVS?
A. None of the above external issues can increase the mother's chance of having a baby with a chromosome defect. It may be more suitable to carry out an ultrasound between 18-20 weeks. Amniocentesis and CVS do not test for impairments caused by any of the above substances or illnesses.

Q. Who should make the decision as to whether an amniocentesis or CVS is best?
A. The ultimate decision is up to the mother, though input from family and her partner may help in the decision making process. Remember, the mother's obstetrician and local counseling services are also available to help in making her choice.

Amniocentesis

Amniocentesis is the most common method of testing fetal chromosomes. The procedure involves inserting a needle through the mother's skin, the wall of her uterus and into the amniotic sac containing the amniotic fluid. While this test can be carried out at any stage in pregnancy, it is most commonly done between 15-17 weeks.

Amniocentesis is not considered a routine test and is usually only offered to women who are at risk of producing a baby with a specific abnormality such as Down syndrome. The reason for this is the small risk to the fetus and large financial expense associated with the procedure. The two main reasons for carrying out an amniocentesis involve checking for spina bifida and looking at the baby's chromosomes.

Alpha-fetoprotein (AFP) can be measured via amniocentesis to diagnose spina bifida. Interestingly enough, spina bifida can only be detected by amniocentesis and not by chorionic villus sampling.

Amniocentesis is usually performed between 15-17 weeks, when there is enough amniotic fluid accumulated for the test. Studies examining the safety of earlier stage amniocentesis (between 10-14 weeks) are not conclusive. Thus, physicians carry out the procedure at the traditional time as a safety precaution. While it is possible to carry out an amniocentesis beyond 17 weeks it takes up to three weeks for the laboratory to produce the results. If the bad results are received very late in pregnancy then it may be too late to terminate the pregnancy if that is what is wished. Depending on local laws, the latest time for an abortion can be as early as 20 weeks and as late as 24 weeks. Do not wait until longer than necessary, as the medical and emotional consequences of such action can be very detrimental.

Possible Complications of Amniocentesis

The most feared and severe complication of amniocentesis is miscarriage of the fetus. It is difficult to quantify the risk of miscarriage since it depends on the operator and the technique used. As well, one cannot ascertain whether the miscarriage was due to the amniocentesis or if it was meant to happen anyway. Most reports estimate that the risk of miscarriage with amniocentesis is about 0. 5 percent.

Parents are most afraid that the needle will pierce the fetus during the procedure. Before the use of ultrasound, around 1-3% of babies were touched by the needle and were born with dimples or skin scars. Today however, ultrasound allows for continuous monitoring of the needle and its closeness to the fetus, to ensure that contact is not made.

In terms of complications for the mother, there are few. In about 1% of amniocenteses there is leakage of amniotic fluid from the vagina. This happens usually a few days after the test and only lasts for a short time. If there is abdominal pain or blood lost through the vagina it should be reported to the physician.

Frequently Asked Amniocentesis Questions

The following is a list of questions regarding the procedure of amniocentesis and its possible complications:

Q. How does the physician ensure that the needle does not touch the baby?
A. The mother's doctor will watch the needle's location carefully using ultrasound. If for some reason the doctor accidentally nears the baby or the baby moves towards the needle, ultrasound will help the doctor guide the needle away. Even if the fetus did come into contact with the needle, it would not experience harm. The overall point of the amniocentesis is to collect a sample of amniotic fluid.

Q. How long does the needle stay inside the mother?
A. From the time the needle is inserted into the mother's skin to its removal the needle only spends about 30 seconds in the mother. Once the needle is in place and is withdrawing fluid from her uterus, the mother will feel no pain since the needle will not be moving.

Q. How much fluid is taken out of the amniotic sac?
A. About 15 ml will be taken from the sac, which comprises about 10% of the fluid present at 16 weeks gestation.

Q. How much time does it take for the removed fluid to be replaced in the sac?
A. At the end of pregnancy there will be about 1L of amniotic fluid that is continuously produced and removed by the baby. While it is hard to exactly pinpoint how long it takes for the fluid to be replaced, doctors estimate it occurs over the course of several days.

Q. Will the fluid leak out from the hole in my skin?
A. Because the needle that is used is so fine, the hole created closes right away and no fluid comes out of it later on.

Q. If a miscarriage occurred because of the amniocentesis, when would it happen?
A. The sad fact is there is no exact or simple answer to this question. The physician cannot tell whether a miscarriage happened because of the amniocentesis or because of other natural reasons. In general however, it is recognized that miscarriages occurring only a few weeks after amniocentesis are more likely due to the test than some other reason. Most importantly, the mother must remember that an amniocentesis is a relatively low risk test and miscarriage as a result of it is quite rare.

Q. If I have a brother or sister with spina bifida should I have an amniocentesis?
A. It is usually not recommended to carry out an amniocentesis in this case. At 13 weeks an ultrasound can detect all cases of anencephaly and about 95% of cases of spina bifida at 18 weeks. Thus, if the mother has a normal ultrasound at 18 weeks then her chances of having a baby with spina bifida are about 1/2000. Having an amniocentesis would be an added unnecessary risk.

Q. Is it possible to tell the sex of the fetus using amniocentesis?
A. Yes, analysis of the chromosomes shown in amniocentesis will automatically show the sex of the child. Let the obstetrician know in advance if the mother would like to know the sex of the baby.

Q. Will the test hurt?
A. If the procedure is carried out by an experienced physician, the mother should only experience mild discomfort. Most people compare the pain to that experienced during a blood test.

Q. Is it mandatory for the mother to have an amniocentesis if she is over 35?
A. While prenatal testing is not mandatory for everyone, amniocentesis is an option available to couples wishing to seek prenatal diagnosis. The ultimate decision is up to the mother.

Chorionic Villus Sampling (CVS)

Chorionic villus sampling, often called CVS, is a newer member of the family of procedures available in prenatal diagnosis. The greatest benefit of CVS is that the results are available much earlier than those of amniocentesis. However, the drawback to this technique is the fact that there is a slightly higher risk of miscarriage than amniocentesis.

The procedure involves passing a needle into the placenta to extract a small piece of tissue section for analysis. Currently, all CVS biopsies are carried out with the assistance of ultrasound. Under the care of an experienced physician, the miscarriage rate due to CVS is believed to be around 1 percent.

Like amniocentesis, CVS is a test used to assess women at risk of carrying a fetus with abnormalities. The CVS test is not used on the general population to see if the fetus is 'normal'. The most universal grounds for using CVS are to check for chromosomal abnormalities, usually because the mother is over the age of 35 and has an increased risk of giving birth to a child with Down syndrome. As well, if the woman has previously given birth to a child with a chromosomal abnormality, she is more likely to be tested.

Another drawback of CVS is that is cannot test for spina bifida. However, this is not a major concern since the incidence of spina bifida does not increase with age and it is a very rare condition. As well, ultrasound is now such a sensitive technique, it can be used to detect spina bifida in fetuses when scanned at week 18.

The best time to perform a CVS is between 10-12 weeks but technically the procedure can be carried out any time after 10 weeks. The reason why it is necessary to wait until 10 weeks of gestation is because by that time the placenta should be developed enough to locate its postitino, making it easier for the needle to access. If the tissue specimen is analyzed using the direct method of chromosome analysis, the mother may receive the results in a few days. Otherwise a laboratory will take about two weeks to process the sample. In the unfortunate event that an abnormality is detected, the pregnancy can be terminated at 12 weeks. By this time the mother will not have felt any fetal movements and the pregnancy will not show. The procedure will most probably involve a dilation and curettage operation which is quick and doesn't require an overnight stay.

Possible Complications of Chorionic Villus Sampling

The needle used in CVS does not penetrate the amniotic sac or near the fetus at all. As such, there is little risk of hurting the fetus directly through this procedure. Even passing a needle into the blood-rich placenta does not produce heavy bleeding as might be feared.

Immediate complications as a result of the test are rare. It is not often that pain is experienced or the physician is unable to obtain a tissue sample. A blood clot may form at the site of tissue extraction, however this is a very uncommon occurrence.

The most significant postponed complication of CVS is miscarriage. Miscarriage occurs in about 1% of post-CVS pregnancies and is similar to that experienced in rare instances after amniocentesis. There have also been some reports of fetuses being born with limb abnormalities. While this created controversy in its initial stages, it was discovered that the limb reduction defects were associated with very early sampling (at or before 8 weeks) and there was no data to suggest that CVS carried out after 8 weeks would increase the risk of the baby being born with physical deformities.

If a CVS fails it is usually for one of two reasons. Either there was technical failure and the physician failed to get an adequate sample or the laboratory failed to produce a satisfactory result. As well, maternal cells can contaminate the specimen and cells from the mother, not the fetus, will end up growing in culture. Overall, between 2. 2-10% of CVS cases will require further testing. This number largely depends on the proficiency of the physician, since technical failure is the main reason (1-6%) for CVS failure.

Frequently Asked CVS Questions

The following is a list of questions commonly asked regarding the chorionic villus sampling procedure:

Q. Is CVS as accurate as an amniocentesis?
A. The presentation of an abnormal result in either CVS or amniocentesis can be regarded as accurate. If CVS results are doubtful, they can be confirmed with the use of am amniocentesis.

Q. Is a CVS as sensitive as an amniocentesis?
A. Both tests are equal in their ability to diagnose chromosomal abnormalities. However, spina bifida cannot be diagnosed by CVS.

Q. What is more popular - CVS or amniocentesis?
A. The choices made depend on the expertise of local practioners. In places where CVS is a more developed technique, it appears that women favor this method.

Q. Does CVS cause the fetus to move or harm the fetus in any way?
A. During the procedure you may see the fetus moving, however, this isn't caused by the CVS itself. Since the needle is outside of the amniotic sac, the fetus is not aware of the needle's presence.

Q. Is it possible to have a CVS if there has been vaginal bleeding?
A. If there has been no bleeding one week before the CVS and the ultrasound shows a healthy pregnancy then it is unlikely that a CVS will cause an increased risk of miscarriage.

Q. If the CVS causes a miscarriage, when would it take place?
A. Since a miscarriage can occur at any time during pregnancy, it is difficult to pinpoint whether it was caused by CVS or if it occurred due to natural circumstances. To reduce your risk of miscarriage after CVS, rest for 12 to 24 hours after the procedure. After this time, any extra precautions will not offer much benefit.

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