Common Prenatal Tests
Today the number of prenatal care options is greater than at any other time in history. The introduction of technology into birth has undoubtedly saved many mothers and babies from severe illness or death. However, nearly all prenatal tests carry some risks, and these must be weighed on an individual basis for each woman, in each pregnancy. Often women are not fully informed of the benefits and risks of each prenatal test they are submitting to, and few women know that they have the right to refuse many routine tests during their pregnancies if they so choose.
This is not meant to be a comprehensive list of all routinely administed tests or procedures, nor is anything on these pages to be regarded as medical advice. This information is provided solely to help open the lines of communication between you and your doctor or midwife and to give you access to information, based on research, to discuss with him or her about some of the common tests you may be offered. I also highly recommend the book The Tentative Pregnancy by Barbara Katz Rothman.
Ultrasound (Sonogram, Doppler)
May be performed
at any time
Ultrasound is a diagnostic procedure used throughout
pregnancy in order to establish fetal viability, date the pregnancy, examine
the fetus for abnormalities, visualize or listen to the fetal heart, and
estimate the size of the fetus. Ultrasound is also used in concert with many
other diagnostic procedures such as CVS and Amniocentesis. Doppler fetoscopy, used commonly to hear
the fetal heart beat during prenatal visits starting as early as 8-10 weeks
from the last menstrual period, is also a form of ultrasound. External
Electronic Fetal Monitoring during labor also utilizes ultrasound
technology.
Obstetrical ultrasound has been in use for approximately 35 years, although its use was not nearly as widespread until approximately the last 10 years. The rate of exposure for many fetuses is extremely high when you take into account routine use of doppler fetoscopy, ultrasound scans for dating the pregnancy, estimating fetal size, predicting fetal gender, and (perhaps most disturbing) scans purely for entertainment and 'bonding.' Ultrasound exposure is generally considered risk-free by many medical professionals and scientists, but there is still some controversy over the benefits in normal pregnancies. Occasionally decisions about the pregnancy are based on ultrasound screening that later turns out to be in error due to improperly or inadequately trained technicians or due to the limitations of the equipment being used. All current recommendations make reference to the fact that, while no biological effects have thus far been conclusively linked to ultrasound exposure, the potential exists for these effects to become evident in future generations. Therefore it is wise to consider ultrasound only when a clear benefit exists during pregnancy. Ultrasound can be a highly beneficial obstetrical tool when applied properly.
Alphafetoprotein Testing (MSAFP, Triple Screen, Quad
Screen)
Usually performed between 15-18 weeks after LMP
This test is a screening measure for certain neural tube and genetic defects
such as spina bifida and Down's Syndrome. The test has a significant rate of
false positive results (meaning that the baby is healthy but the test comes
back abnormal). A positive result on this test does not guarantee
that your baby has a birth defect, but your care provider will likely offer
you further tests such as amniocentesis or high-level ultrasound
examination. A negative (normal) result does not guarantee that you will
have a healthy baby. For more information, this is an excellent FAQ
compiled by Dorothy Neville.
Chorionic Villus Sampling (CVS)
Usually
performed between 10-13 weeks after LMP
Chorionic Villus Sampling is
an invasive diagnostic procedure in which cells are collected from the
junction of the amniotic sac and the placenta. These cells are collected
either by inserting a catheter vaginally through the cervix and into the
uterus or by inserting a needle abdominally into the uterus and through the
placenta using ultrasound guidance for placement of the catheter or needle.
CVS is used to detect chromosomal abnormalities such as Down's Syndrome. It
cannot detect neural tube defects. There is a higher risk of pregnancy loss
associated with CVS procedures when compared to second trimester
amniocentesis. There is also an association between early CVS procedures and
birth defects involving missing or shortened fingers or toes.
Amniocentesis (Amnio)
Usually Performed
between 15-18 weeks after LMP; Early Amnio Available between 10-14
weeks
Amniocentesis is an ultrasound-guided procedure in which a
needle is inserted through the mother's abdomen into the uterine cavity
where a small amount of amniotic fluid is removed. Fetal cells from the
amniotic fluid are examined for chromosomal and genetic disorders such as
Down's Syndrome. Amnio can also aid in determining the presence of neural
tube defects. It is also used to determine fetal lung maturity later in
pregnancy.
Many studies have indicated that CVS is less risky in terms of pregnancy loss than amniocentesis performed before 15 weeks. The risk of miscarriage is generally considered to be around 1/200 pregnancies, but this varies widely with the skill of the practitioner. Other risks include leaking amniotic fluid, infection, vaginal bleeding, and fetal injury. There is also an increased incidence of club foot when amnio is performed before the 13th week. Amniocentesis results can take up to two weeks to obtain, although preliminary results can be acquired within 2 buisness days at some facilities.
Glucose Tolerance Testing (GTT, Glucose Challenge,
Gestational Diabetes Test)
Usually performed around 28 weeks from
LMP
The Glucose Tolerance Test is a screening measure for a
condition termed Gestational Diabetes (GD).
The test involves swallowing a 50 gram oral glucose solution (or an
equivalent) and then having blood drawn in order to test the blood glucose
level. There is a huge amount of controversy about Gestational Diabetes in the medical
community. Treatment protocols vary from care provider to care
provider, and there is no clear indication that treatment improves the
pregnancy outcomes of women or babies diagnosed with gestational diabetes.
For a very thorough and excellent source of information on GD, please visit
Kmom's Gestational Diabetes FAQ. It includes information
on the different tests available, interpretation of results, reasons to
avoid the test, and further resources for those who have already undergone
testing and been diagnosed as having GD.
Non-stress Test (NST)
May be performed at any
time during 3rd trimester;
Often performed if you go past your due date
Non-stress testing is indicated to
assess the well-being of the fetus in-utero if there is reason to
suspect that the baby may not be thriving. The situations in which an NST
will be recommended vary by care provider and most normal pregnancies will
never require this test. This test is called a "non-stress" test because
there is no stress placed on the baby as opposed to the
Oxytocin Challenge Test.
Non-stress testing involves monitoring the fetal heartrate elctronically for 20-30 minutes and seeing how the rhythm changes in response to stimulation such as fetal movement, sounds and vibrations, or uterine contractions that normally occur in late pregnancy. If the baby's heartrate increases from the baseline norm of 120-160 beats per minute by 15 bpm with movements or in response to a tuning fork being struck, it is said to be 'responsive' and this is indicative of fetal health. It is also normal for the baby's heartrate to decrease during contractions and then return to the baseline as the contraction ends. A baby with a heartrate that is non-responsive (no increases in heartrate over 40 minutes) may be preserving oxygen due to some kind of stress in the womb. However, a non-reactive heartrate can also just be because your baby is asleep at the time of the test, so it is a good idea to have some juice and lie on your left side to increase oxygen flow to the baby while repeating the test if possible. Babies younger than 32 weeks gestation are also normally less responsive.
Non-stress testing is often carried out routinely if a woman has not given birth by her due date. This testing is not recommended for women with healthy pregnancies before 42 completed weeks of pregnancy have passed.1 NST is often combined with Biophysical Profile or Amniotic Fluid Index testing. Some practitioners believe that Fetal Kick Counts done by the mother are as accurate at predicting fetal well-being as NST.
Amniotic Fluid Index (AFI)
May be performed at
any time during 3rd trimester;
Often performed if you go past your due date
Amniotic Fluid Index is an estimate of
the volume of amniotic fluid within the uterus. It is performed via
ultrasound. AFI is believed by many doctors to be a good indicator of
placental sufficiency. It is also used to assess fetal well-being since
amniotic fluid is primarily made of of fetal urine. If the fluid level is
too high (polyhydramnios) it can
indicate certain problems with the baby or mother. If the fluid level is too
low (oligohydramnios) it can also
signal problems with the baby or with the function of the placenta. Keep in
mind that most variations in amniotic fluid levels are
perfectly normal.
The amniotic fluid level normally reaches a peak at around 30-32 weeks and then remains fairly consistent until term, when it decreases slightly. Many women who have not gone into labor by their due date may be referred for AFI testing under the premise of assessing placental function, however AFI alone has never been shown to be a reliable factor in determining placental function or fetal health. Several studies2 3 4 5 have indicated that maternal hydration status plays a large part in amniotic fluid volume levels at term. Staying well-hydrated throughout pregnancy is important, but it is essential if you are referred for AFI testing, because low levels of amniotic fluid alone are often used to justify induction of labor. This practice is not supported by evidence-based medicine.
Another important factor in AFI testing is reliability. There are several different methods by which amniotic fluid volume is estimated and false diagnoses of oligohydramnios is higher when certain methods are used. 6 Many studies have shown that estimates vary about 15% depending on the sonographer performing the exam. Other studies have shown that the volume estimate varies depending on the pressure placed on the transducer during the ultrasound- with higher pressures resulting in lowered amniotic fluid volumes being reported. AFI is one factor used in the Biophysical Profile score.
Biophysical Profile (BPP)
May be performed at
any time during 3rd trimester;
Often performed if you go past your due date
A Biophysical Profile is used to assess
the health of the fetus by combining several different measures of
well-being, including information about heartrate
variability, amniotic fluid level, fetal breathing
movements, and frequency and type of body movements. Each parameter is
assigned 2 points. A score of 8-10 indicates that the baby is at low risk
and spontaneous labor can be awaited. A score of 6 is an indication for a
repeat BPP in 24 hours to verify the results. A score of 4 or lower suggests
the fetus may be deprived of oxygen and delivery is indicated if the baby is
over 36 weeks or if lung maturity has been determined by amniocentesis. A score of 0-2 requires continued
monitoring and immediate delivery if there is no improvement.
One controversial issue with BPP is the weight given to the amniotic fluid measurement. Even if the score is an 8, some care providers will recommend immediate delivery of the infant if the AFI is low. See the information above regarding Amniotic Fluid Index testing.
Oxytocin Challenge Test (OCT, Contraction Stress
Test)
Usually performed near term
The Oxytocin Challenge
Test, or Stress Test, is similar to the Non-Stress Test
except that it is performed by stimulating uterine contractions and then
assessing the fetal heart rate response to these contractions. Because of
the risk of starting labor, it is usually only performed at or near term.
The OCT may utilize either Pitocin via an intravenous (IV) or, less
commonly, the mother's own natural oxytocin released in response to nipple
stimulation.
The OCT is said to be negative (normal) if an adequate pattern of contractions is established and the baby shows a normal heartrate response. Contractions should be about 3-4 minutes apart, lasting at least 40 seconds. The baby's heart rate should not remain low following each contraction, although it is normal for the heartrate to decrease during contractions. The OCT is positive (abnormal) if the baby's heartrate remains decreased following the end of contractions. This can be a sign that the fetus is not receiving enough oxygen and may not tolerate labor well. It is important to determine whether this heartrate pattern is in response to uterine hyperstimulation (contractions that are too long, too strong, or too frequent) due to Pitocin, or attributable to true fetal compromise. If the test is normal, it is considered a reassuring sign of fetal well-being for the following 7 days. Daily Fetal Kick Counts may be suggested, and retesting usually scheduled within a week. If the test is positive, induction of labor or a cesarean delivery may be recommended immediately.
Fetal Kick Counts (Cardiff Count-to-Ten
Chart)
Performed by mother starting at anytime after 28
weeks
Fetal Kick Counts are a simple and effective way of assessing the health of the fetus during the
late third trimester. The observation should be done at approximately the
same time each day, preferably when the baby is usually very active or after
mom has had a meal or snack. The mother notes the starting time and begins
counting fetal movements (rolls, kicks, punches, turns), excluding hiccups,
and continues counting until 10 movements are noted. If 10 movements haven't
been recorded within 2 hours you should contact your midwife or doctor.
There are actually several different methods of counting fetal movement, so
if your midwife or doctor has given you different instructions you should
use them. You may also be given a Cardiff Count-to-Ten Chart. This
chart is usually used throughout the day over a 12 hour period instead of at
a set time over 1-2 hours.
Note: The information on this website should not be interpreted as medical advice. All of the information compiled here has been referenced where possible, and as with any information obtained from the internet you should verify the information for yourself. If you have questions please consult your health care provider.
1. American College of Obstetricians and Gynecologists. ACOG practice patterns. Management of postterm pregnancy. Int J Gynaecol Obstet. 1998 Jan;60(1):86-91.
2. Fait G, Pauzner D, Gull I, Lessing JB, Jaffa AJ, Wolman I. Effect of 1 week of oral hydration on the amniotic fluid index. J Reprod Med. 2003 Mar;48(3):187-90.
3. Hofmeyr GJ, Gulmezoglu AM. Maternal hydration for increasing amniotic fluid volume in oligohydramnios and normal amniotic fluid volume. Cochrane Database Syst Rev. 2002;(1):CD000134.
4. Flack NJ, Sepulveda W, Bower S, Fisk NM. Acute maternal hydration in third-trimester oligohydramnios: effects on amniotic fluid volume, uteroplacental perfusion, and fetal blood flow and urine output. Am J Obstet Gynecol. 1995 Oct;173(4):1186-91.
5. Magann EF, Doherty DA, Chauhan SP, Barrilleaux SP, Verity LA, Martin JN Jr. Effect of maternal hydration on amniotic fluid volume. Obstet Gynecol. 2003 Jun;101(6):1261-5.
6. Magann EF, Sanderson M, Martin JN, Chauhan S. The amniotic fluid index, single deepest pocket, and two-diameter pocket in normal human pregnancy. Am J Obstet Gynecol. 2000 Jun;182(6):1581-8.
7. Christensen FC, Rayburn WF. Fetal movement counts. Obstet Gynecol Clin North Am. 1999 Dec;26(4):607-21.
