Pre-Natal Tests

What are the Different Prenatal Tests Women are Offered?

The following discussion is about tests conducted,
beyond the usual blood panel and vaginal cultures…

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DOPPLER OR ULTRASOUND

As with EFM, there have been questions raised regarding the use of Ultrasound, as to whether it is actually useful and if it is safe. Just like EFM it was in use before the safety of Ultrasound was confirmed. Now it is commonly used, expected by pregnant mothers.

With its use, are three ways in which women are exposed to ultrasound. First, the Doptone used in listening to the fetal heartbeat. Secondly when doctors order its use during exams, in order to check the fetal position and its growth along with the placenta (and take a picture of the baby within the womb). Third, Electronic Fetal Monitoring uses ultrasound to detect the fetal heartbeat.

So is it SAFE? Well, no one really knows for sure. The “problem lies in what happens when energy-containing sound waves strike growing fetal tissues (Sears & Sears, 82).” It is uncertain if the delicate tissues become damaged on a subtle level.

What happens is the sound-waves bombard the tissues, shaking up molecules causing heat. The heating up of the molecules cause gas bubbles of a microscopic size in the cell which are called cavitation. It is uncertain whether the heat or the bumbles damages the cells.

Not like EFM, Ultrasound has improved the practice of Obstetrics. Since it seems to be safer than X-rays, it can be used to give a more precise dating of gestational age of the fetal in early pregnancy. It also is helpful to determine if the placenta has any abnormalities, whether there is more than one fetus, and if there are abnormalities with the fetus.

Unfortunately, no study has been conducted to confirm whether there is an improvement in the outcome of mothers and their babies. Most likely, there never will be any studies, either.

Maternal Serum Alpha-Fetoprotein (MSAFP) Testing
(also known as: Alpha-Feto Protein (AFP) Screen)

The best time for this test is between 15 to 18 weeks gestation. This time frame seems to be best because the results are the most accurate.
(AFT) Alpha-fetoprotein is a substance that is produced by the liver of a fetus. It enters the bloodstream of the mother by way of amniotic fluid and placenta. It is found in the mother’s bloodstream in minute quantities. In pregnancy the level of AFP raises in progression with the duration of pregnancy. An abnormal low or high level is an indication of fetal anomalies.

MSAFP test does not harm a pregnant woman. It does seem to have an unusually high rate of false positives. If a woman has a very high level she may be referred for amniocentesis. She could be subjected to more tests that have higher risks for both herself and baby.

  • AFP increases as the baby grows.
  • It reads as “elevated” for multiples and for neural tube defects.
  • It reads low when the baby has Down’s Syndrome
  • If baby is found to have anomalies then the choices are: abortion, or keep the baby.


AMNIOCENTESIS

How the test is done:

The doctor inserts a long, sterile needle through the abdominal wall and the uterine wall, into the amniotic fluid. The test is conducted with an ultrasound, so that the fetus and placenta can be viewed.

What does the collected Amniotic fluid tell the Doctor?

The fluid contains cells from the fetus that would indicate certain birth defects. Such as: Down’s syndrome, hemolytic anemia (the destruction of red blood cells due to an Rh disease)metabolism disorders, Cystic Fibrosis, and many other diseases. It can tell the doctor the maturity of the lungs if an early labor or Cesarean is indicated.

What are the risks?

Puncture of other areas of the uterine area, such as the umbilical cord, placenta, or another area of the uterus. It can cause infection or miscarriages.

Not only that, but if an inadequate amount of fluid is collected, or the cells of the fetus do not grow in the culture, another test will be necessary.

What Happens then?

  • If the baby is found to have a disorder, then the mother needs to choose what to do next. Does she keep or abort the baby?
  • Is the test able to screen for all disorders of the fetus?No it does not. In fact it can damage the fetus.


CHORIONIC VILLI SAMPLING (CVS)

How is it done?

Tissues are removed from what will develop into the placenta. These tissues are gathered by one of two ways: either through the abdomen or the cervix, using an instrument to collect tissue while looking at the area.

At what point in the pregnancy is the test conducted?

The test is done at the nine to eleven weeks’ gestational point.

What would it indicate?

It would indicate whether there are any chromosomal abnormalities in the fetus. It is not able to detect all the abnormalities that can be seen in an Amniocentesis.

What are the risks of taking this test?

The risks include possible damage to the embryo, damage to the uterus, infection, hemorrhage, and miscarriage. It should not be conducted when an infection is already present, if there is a known Rh factor, or multiple gestations. It has a high false positive rate.


GLUCOSE TOLERANCE TEST (GTT)

This test is conducted around 24-28 weeks of pregnancy, and then repeated again at around 32-34 weeks for high risk mothers.

How is the test done?
A sweet liquid called glucola is given to her and then the blood sugar is checked an hour later. If positive, the doctor may then order the 3 hour test, which is more accurate. Only 15% of the women with abnormal results from the 1 hour test will have the same results in the 3 hour test.

Why would the test be important?

The hormones of pregnancy normally suppress insulin release, allowing more glucose to be released for the developing baby. Occasionally the blood sugar is too high (2-10% of pregnant women) causing blood sugar levels to be raised. This is condition called gestational glucose intolerance or gestational diabetes.

  • A lengthy exposure to the high blood sugar in pregnancy causes the infant to grow exceptionally large.
  • Babies of women with blood sugar issues also tend to be born prematurely and have respiratory problems.
  • The baby may manufacture too much of his / her own insulin instead. The manufacture of too much insulin would cause the baby’s blood sugar to drop quickly and dangerously once born.

Who would be at risk?

High blood sugar during pregnancy is more common in obese women, older women, and those who have a family history of diabetes, or in women who have delivered a baby weighing more than 9 pounds previously. If discovered early in pregnancy, by being tested, the pregnant woman can alter her diet to alleviate the issue of high blood glucose.


X-RAY PELVIMETRY AND / OR FETAL INDEX X-RAY (prelabor or labor)

How is it Done and why?

A series of x-rays are done in which the radiologist measures various dimensions of the pelvic passage in order to determine if it large enough for the baby to pass through safely. These measurements are compared to tables of “normals”.

  • The test is done on a mother whose baby is failing to descend during labor.
  • If delivery is contemplated for a breech birth
  • Or if there is a previous history of a difficult birth because of a presumed cephalopelvic disproportion (CPD)*

What Problems Can it Potentially Create?

The X Ray Pelvimetry is being used less often because of concerns over safety and accuracy. Studies have linked X Ray exposure of the fetus to higher odds of childhood cancers. This correlation is not determined accurate because of conflicting study results.

Considerations Regarding the Pelvic Opening:

What is not considered is that the process of labor is an amazing one, that changes of position such as using squatting, can increase the pelvic outlet by as much as 20%. This test also only considers the outlet, not the size of the baby itself.

A newer technique using measurements of the pelvis by X ray and the size of the baby by ultrasound, called the Fetal Pelvic Index (FPI). It considers the size of the whole baby, not just the head. It is useful for those mothers considering VBAC who have had a previous diagnosis of CPD based upon X rays.

 

* To be discussed in a future blog.  Next topic coming up: Teen Pregnancy and Nutrition

 

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