Most women go through a battery of prenatal tests during the course of their pregnancy. But if you have diabetes, high blood pressure, or too much or too little of the fluid that bathes the fetus and serves as a shock absorber (known as amniotic fluid), extra monitoring is called for. If you have preeclampsia, a potentially serious condition marked by high blood pressure and excess protein in your urine after 20 weeks of pregnancy, or if your pregnancy is otherwise considered high-risk, you will also need special monitoring. Among other things, your doctor will probably order something called a biophysical profile in the third trimester of pregnancy.
By monitoring the heart rate, movements, muscle tone, breathing, and the amount of amniotic fluid, your doctor can assess whether your baby is healthy and growing normally. The results are used to determine whether you need special care or whether your baby should be delivered earlier than planned. Doctors may also use a biophysical profile to monitor your pregnancy if you are overdue and if it continues beyond the 42nd week.
What does a biophysical profile involve?
The assessment involves performing a nonstress test, which monitors the baby's heart rate when it moves. During the nonstress test, two belts are placed around your stomach. One is attached to a monitor that records your baby's heart rate and movement. Every time you feel the baby move, you push a button. The other belt records your contractions.
If the baby doesn't move during the 20- to 40-minute test, it's no cause for worry. He or she may just be asleep. Your doctor may try to wake the baby with a buzzer or by having you eat or drink to stimulate movement. The nonstress test is sometimes repeated if there is no change in heart rate in response to your baby's movements. It can also be skipped if the ultrasounds are normal.
Your doctor may also order a series of ultrasounds to monitor four factors over a half-hour period:
Breathing. Your baby should have one or more times where he's moving and breathing for 30 seconds or more.
Fetal movement. Your baby should be able to move three or more different limbs.
Fetal tone. Your baby should be able to flex a finger or toe or to open and close a hand.
Volume of amniotic fluid. There should be a pocket of amniotic fluid at least more than 2 centimeters wide.
Each of these four factors is recorded with a score of 0 to 2. A score of 8 is considered normal, while a score of 6 is borderline and may call for more monitoring or tests. A score of 4 or less is abnormal and requires further evaluation. Depending on the results, your doctor may recommend delivery of your baby.
If the amniotic fluid measure rates a 0, then your baby may need to be delivered right away, regardless of the scores for the other components.
Who should have a biophysical profile?
Your doctor may recommend a biophysical profile if your pregnancy is considered high risk because of conditions such as high blood pressure or diabetes. An assessment may also be ordered if your baby is too small or not growing, or if you have too little or too much amniotic fluid. The risk of stillbirth climbs significantly after your 42nd week of pregnancy.
In most practices, induction is routine at 42 weeks, regardless of a reassuring biophysical profile. And a biophysical profile should be performed on any mother who is overdue and in her 42nd week, but doesn't want to have the baby induced.
Your doctor may also perform a contraction stress test. This evaluates whether your baby can tolerate low oxygen levels that occur during contractions when you are in labor. Your practitioner may recommend subsequent weekly or twice-weekly biophysical profiles to keep close tabs on your baby before he is born.
Regular monitoring is a good way to discover problems long before they crop up. But ambiguous test results don't mean your baby has a problem. Talk to your doctor about what they mean, and how you can take the best possible care of yourself and your baby.
American Academy of Family Physicians. What to Expect After Your Due Date. http://www.acog.org/publications/patient_education/bp069.cfm
Johns Hopkins. Department of Gynecology and Obstetrics, Biophysical profile http://www.hopkinsmedicine.org/gynecology_obstetrics/specialty_areas/obstetrics_services/services/antepartum_testing_prenatal_diagnosis_treatment_center/biophysical_profile.html
American College of Obstetricians and Gynecologists. Special Tests for Monitoring Fetal Health.
University of Pittsburgh Medical Center. Pregnancy Non-Stress Test.