The purpose of antenatal testing is to ensure fetal well being. And when we say to reassure us or ensure fetal well being, we mean that there are no signs of fetal asphyxia.
ANTENATAL TESTING: Non-Stress test
Let’s first talk about the non-stress test.
- So the non-stress test is performed by doing the external fetal monitoring to look at the fetal heart rate.
- We then determined if the fetal heart rate is reactive which means fetal well being is reassured or is it non-reactive. Meaning there is additional testing needed to be done to assure fetal well being.
- Reactive and this is very important, means that there are two accelerations of greater than 15 beats per minute lasting at least 15 seconds over a 20 minute time period.
- So again you are looking at a 20 minute time period on the external fetal monitor and you’re looking to find two accelerations of greater than 15 beats per minute each lasting for at least 15 seconds.
ANTENATAL TESTING: Biophysical profile
So the next type of antenatal testing is the biophysical profile. Now with the biophysical profile, you’re looking at 5 different categories expecting to see certain things in this category. Patients are given a two if the fetus performs the manoeuvres that we’re looking for and 0 if they do not perform the manoeuvres. Again give 30 minutes to observe it. So we’re looking at fetal movement, we’re looking at fetal tone, fetal breathing, the amniotic fluid and again the non-stress test.
- So with the fetal movement, we’re looking to see three growth movements within that 30 minute time period.
- The fetal tone is looking for 5 movements, like the hands moving, the fingers, opening and closing the palm.
- Fetal breathing we’re looking for sustained breathing for 30 seconds over that 30 minute time period.
- Amniotic fluid volume, we’re really just looking at the maximum vertical pocket and we want that to be at least 2 centimetres and then we’ve already discussed the non-stress test.
Management of Biophysical profile
- So if we had a score of 8 that is reassuring. That means that the fetus is doing well and there are no signs of fetal asphyxia.
- If there is a score of 6, this is considered equivocal. So it doesn’t mean that we are reassured. But it also doesn’t mean that the baby is concerning for asphyxia. However, if the patient is term, meaning 37 weeks that means we need to deliver that fetus.
- At a score of 4, it is a little bit concerned as far as asphyxia and we do need to deliver at that point.
- So the biophysical profile can be used when the non-stress test is not reactive as a confirmation that the baby is doing okay.
ANTENATAL TESTING: Contraction stress test
The next antenatal testing that we use is a contraction stress test. So with a contraction stress test, we induce contractions and that can either be through nipple stimulation or can be induced by given Pitocin. And we’re looking to see that a patient has contractions over a 10-minute time frame.
- Now this test we do not want to be positive. So it’s a little different than a non-stress test. If the test is positive, that means that more than 50% of the contractions are associated with a late deceleration. The test is equivocal when there is intermittently decelerations but less than 50%.
- And the test is negative when there is less than 50% of the contractions associated with late decelerations. Again for the contraction stress test, we want a negative result to reassure that the fetus can tolerate labor.
ANTENATAL TESTING: Umbilical artery doppler
- This test is performed by doing an ultrasound looking at the Doppler of the umbilical artery. And we do this when we are suspecting fetal growth restriction. Now our results can show a normal SD, systolic diastolic ratio. Or it can show absent or even worse it can show reversal flow.
- If it is — if the flow is absent or reversal then that indicates that there is increased resistance in the placenta.
So let’s look at a question.
A 27-year-old gravida 1 para 0 female at 28 weeks and 3 days of gestation with a history of chronic hypertension presents for an antenatal visit. She has had no issues this pregnancy. All antenatal testing has been within normal limits. She takes labetol for her chronic hypertension. On physical exam, blood pressure is 140 over 95. Her heart rate –excuse me the fetal heart rate, is 150 beats per minute. And the fundal height for the mom is 23 centimeters.
So the next best step in her management is?
A fetal ultrasound
- Fetal Doppler of the umbilical artery.
- Contract stress test or
- Biophysical profile.
- So in this case, we first want to do the fetal ultrasound. Now there’s a lot of reasons, like the fundal height may be small. It could be because there is decreased amniotic fluid. It could be because the baby is small or it could be our measurements are not that great. So we want to confirm that the measurement is small, first by fetal ultrasound.
- If the fetus is indeed small, then the fetus will warrant, a fetal Doppler of the umbilical artery. So the next best step in her management is to perform the fetal ultrasound.