Often caregivers suggest diagnostic testing during the pregnancy to screen for complications or to determine the age, weight, or due date of the baby. Whenever a test is recommended, be sure to understand why the test is suggested, how it is done, and what the risks and benefits to the test may be. Some of the most common tests during pregnancy are Triple Screen , AFP (alpha-fetoprotein), Glucose Tolerance, Amniocentesis, Chorionic Villas Sampling (CVS), Non-Stress Test, Oxytocin Challenge Test, Biophysical Profile, and Ultrasound.

Triple Screen is a blood test performed between 15 and 18 weeks gestation and measures levels of hCG (human chorionic gonadotrophin), estriol, and alpha-fetoprotein. This screening can detect Down's Syndrome and is more accurate than the alpha-fetoprotein test alone. High levels of alpha-fetoprotein combined with low levels of estriol indicate the possibility of Down's Syndrome.

Alpha-fetoprotein screening is blood test done on the mother to screen for neural tube defects or Down's Syndrome in the baby during pregnancy. At 17 weeks, the production of alpha-fetoprotein by the baby's liver is at a detectable level in the mother's blood. A high level of AFP indicates possible neural tube defects such as spina bifida and anencephaly. A low level of AFP indicates the possibility of Down's Syndrome. AFP screening has a high rate of false positive readings and should be followed with another blood test, ultrasound, and possibly an amniocentesis.

An amniocentesis is a procedure whereby a needle is inserted into the abdominal wall and ultimately the uterus to retrieve a sample of amniotic fluid. This fluid contains fetal cells which are then assessed by the care giver. Possible complications include miscarriage, infection, and the need for RhoGam injection if mother is Rh negative. The procedure is performed between 13 and 16 weeks gestation and can detect certain birth defects and chromosome anomalies. An ultrasound is used to help place the needle in the optimal position to retrieve the sample, keeping the likelihood of complications to a minimum.

An ultrasound is high frequency sound waves through a transducer that is placed on the woman's abdomen. Through ultrasound, the care giver can view the baby's structure and internal organs and determine age, size, and position of the baby. Also, the care giver notes the position of the placenta and the volume of amniotic fluid. Ultrasounds can be performed anytime during the pregnancy and have very little risk to the mom or fetus. Accuracy varies and the tests require the mother have a full bladder which can be quite uncomfortable.

Perhaps the earliest genetic diagnostic screening is chorionic villi sampling, done at 10-12 weeks gestation. A needle is inserted into the abdomen and then into the placenta. A small tissue sample is removed and tested. The possible complications include bleeding, spontaneous abortion, and rupture of membranes. Risk to the pregnancy or baby is less than or equal to 0.5%. An ultrasound is used to guide the needle into the optimal position.

A glucose tolerance test is usually done at 28 weeks gestation to screen for gestational diabetes. The pregnant woman drinks a sugary drink and then a blood sample is drawn one hour later. An elevated reading requires the woman take a three-hour glucose tolerance test. For this test, the woman must consume at least 150 grams of carbohydrates per day for three days prior to the test and then must fast overnight. Blood is drawn every hour for three hours after she drinks a higher concentrated glucose solution than in the one-hour screening.

Towards the end of pregnancy, testing is often done to determine fetal well being, gestational age, or weight. A non-stress test assesses how the fetal heart rate responds to fetal movement. An electronic fetal monitor will record the fetal heart rate for 20-30 minutes and the mother will note when the baby moves. An oxytocin challenge test (OCT) assesses the fetal heart rate in relation to contractions. The mother is either given Pitocin (oxytocin) or she performs nipple stimulation to cause the contractions. OCT may cause preterm labor and may not always be accurate. A biophysical profile combines an ultrasound with a non-stress test to determine fetal movement, volume of amniotic fluid, fetal breathing, and fetal muscle tone.

For more information on these and other diagnostic screenings, refer to Maternity & Gynecologic Care: The Nurse and the Family by Bobak and Jensen, or Pregnancy, Childbirth and the Newborn by Simkin, Whalley, and Keppler.

References:

1. Bobak, I., Jensen, M. Maternity & Gynecologic Care: The Nurse and the Family. (1989) St. Louis: Mosby Publishers.
2. Nichols, F., Humenick, S. Childbirth Education: Practice, Research & Theory (2000) Saunders & Co.
3. Whitely, N. A Manual of Clinical Obstetrics (1985) Philadelphia: J.B. Lippincott Company.
4. Reeder, S., Martin, L., and Koniak-Griffin, D. Maternity Nursing: Family, Newborn, and Women's Health Care. (1997) Philadelphia: J.B. Lippincott Company.