The biophysical profile remains the most accurate way of assessing the fetal status in high-risk obstetric patients. It is simple yet powerful. It takes a maximum of 30 minutes. It can easily be reproduced and extremely performable in all clinical settings. Let’s get started.
The biophysical profile is an ultrasound-based assessment of fetal well-being in combination with a fetal heart rate tracing. It consists of a non-stress test, amniotic fluid index (AFI) assessment, fetal breathing movements, and total body movements and limb tone.
We demonstrate body movements and limb tone by flexion and extension movements.
We score a 2 or 0 for fetal heart rate tracing and four other parameters each. The maximum score is 10 – the lowest is 0, for normal fetal status and extremely worrying/ non-reassuring fetal state respectively.
A modified biophysical profile consists of a non-stress test and an amniotic fluid index. The amniotic fluid index is the most vital part of this assessment for reasons we shall get to know later.
Before looking at the details of each of the parameters, it’s worth knowing when to request or do a biophysical profile. Let’s get into it.
The most common indications for a biophysical profile are a non-reactive non-stress test and reduced fetal movements.
All high-risk pregnancies require a biophysical profile, and this is typically done from 32 weeks and beyond. However, the assessment may be done earlier than 32 weeks of gestation depending on the prevailing circumstances. We perform a modified BPP as part of the antenatal care contacts for other pregnancies.
In general, indications for a biophysical profile assessment are either entirely maternal or pregnancy-related.
Maternal conditions include;
-pregestational diabetes mellitus,
-systemic lupus erythematosus,
-chronic kidney disease,
-poorly controlled hyperthyroidism,
-hemoglobinopathies like sickle cell anaemia, and
-cyanotic heart disease.
Pregnancy-related conditions include;
-decreased fetal movements,
-gestational diabetes mellitus (poorly treated or medically treated),
-fetal growth restriction,
-late-term or post-term pregnancy,
-unexplained or recurrent previous fetal death, and
-monochorionic multiple gestations (with significant growth discrepancy).
We must consider several risk factors must in making a diagnosis based on the biophysical profile. The biophysical profile can only diagnose oligohydramnios or polyhydramnios. It is, however, an indicator of fetal well-being that reflects the blood pH.
As noted earlier on, the typical score is from 8 to 10, and this assures that the risk of fetal asphyxia in the next week is minute. The chances that this score is negatively false range from 0.00055% to 0.00083%. We regard a score of 6 as either equivocal or abnormal: we must repeat the assessment should within 24 hours.
We must reassess the patient after 24 hours if we diagnose oligohydramnios. We induce such a patient if she is at term with no contraindications to induction.
We regard the results as reassuring for a score of 6 if all the points lost relate to fetal movements: we should repeat the assessment within 24 hours or less.
A score of 2 to 4 considered non-reassuring and labour induction should be imminently planned or a cesarean delivery depending on the prevailing circumstances.
A score of 0 shows impending fetal asphyxia and delivery must be urgent by cesarean delivery at a hospital with neonatal intensive care unit services.
The amniotic fluid index should ideally be measured using a single deepest pool – we prefer this over the four-quadrant amniotic fluid index. The former usually prevents unnecessary interventions, including early labour induction due to oligohydramnios. Amniotic fluid volume is reassuring if the single deepest pool is between 2 cm and 8cm.
Abnormal fluid assessment is a rather chronic finding. It usually takes days for any pathology, maternal or fetal related to appear in the amniotic fluid. However, any abnormal fluid assessment, even if it is the only abnormality detected, should be followed up at short intervals to delineate the causes of the abnormal findings.
A non-stress test requires evaluation of a minimum of 2 accelerations of at least 15 bpm for a minimum of 15 seconds in a 30-minute interval for gestational age 32 weeks and above.
Fetal breathing patterns that are considered normal range from rapid, regular breathing, sighs, pauses while swallowing and intermittent long slow breaths while asleep. The changes in the rhythm of breathing coincide with the observed patterns of the typical beat to beat variability in a healthy fetal heart tracing. For the exam to be wonted, a minimum of one episode of 30 seconds of fetal breathing movements should occur in 30 minutes.
At least three movements of the body or limbs should occur in 30 minutes. Either an arm or a leg extends and flexes; a hand opens and closes during the test is considered normal. Note that we can omit the reactive fetal heart rate if all the other parameters are normal.
When fetal asphyxia occurs, fetal breathing movements are lost first, then body movements, extremity tone, and finally, loss of fetal heart rate variability.
A few interferences can affect or prolong the biophysical profile study. These include;
-fetal sleep cycles,
-drugs like corticosteroids, narcotics, magnesium sulfate, and tocolytics which reduce fetal movements, and
We note, though, that obstetric ultrasound is considered safe but, the rule “As Low As Reasonably Achievable” should be followed. A little caution rests on taking into account what is known as the thermal index. It is the unit of measure for the thermal energy released by the probe, and it usually shows in the margins of the display.
For curiosity, we define the thermal index as the ratio of the acoustic power emitted by the transducer to the one needed to raise the temperature of the tissue 1°C anywhere along the beam. As a precautionary measure, we recommend a lower thermal index.
In a nutshell, Biophysical profile remains the most accurate way of assessing the fetal status in high-risk obstetric patients. It is simple yet powerful. It takes a maximum of 30 minutes. It can easily be reproduced and extremely performable in all clinical settings.
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