WRITE UPS - MISCELLANEOUS: (OB) - The Evolution Of Fetal Surveillance


Twenty years ago fetal health in the antepartum and intrapartum period was being assessed by a combination of clinical tests, largely nonspecific, which clinicians generally regarded as bearing some relation to fetal outcome and a scattering of newer, purportedly more specific tests relating to some objective measurement of the fetus. The clinical evaluations included categorization as “High” or “Low” risk pregnancy, estimates of fetal size or fundal height, passage of meconium, irregularity of auscultated fetal heart rate, and subjective evaluation of fetal movement. The more objective evaluations, just gaining degree of clinical use in the early 1970s, included continuous fetal heart rate monitoring, static ultrasound imaging (B-scans), hormonal tests, such as estriol and Human Chronic Somatomammotropin (HCS) levels and test of pulmonary maturity in amniotic fluid, such as the lecithin: sphingomyelin (L:S) ratio, creatinine concentration and the “shake” or “ foam” test.

There has been a remarkable refinement and enlargement (or extension) of many of these tests in the last two decades, primarily due to the development of reasonably priced, high resolution, real-time ultrasound and of an understanding of the relationship between aspects of fetal behavior or state and fetal health. Although “ intervention” and early delivery had been practiced for decades in certain pregnancies (e.g., Rh alloimmunization, maternal diabetes mellitus), the combination of a number of tests of fetal condition and of pulmonary maturity, has allowed the important concept of optimal timing of delivery in complicated pregnancies. This process allows the obstetric team to make decisions regarding the continued risk of remaining in utero versus the potential risk of sequelae of prematurity.


Clinical estimates of fetal weight and progression of fundal height measurements still have a place in management today, particularly as screening tools. The hormonal measurements (estriol and HCS) have all but disappeared.

The standard technique for ultimately determining fetal size today is to obtain sonographically determined fetal measurements: head diameter and circumference, abdominal circumference, and femur length. These are modern ultrasound imaging machines. The percentile based on either known menstrual dates or sonographically determined dates is also given.  Both the estimated fetal weight (EFW) and centiles are of value in confirming whether a fetus is small or large for gestational age. Serial measurements can be used to detect the appropriateness or otherwise of fetal growth. The EFW has a standard deviation of about 10 percent, relatively similar to that of age equivalents for each of the above four measurements allowing the clinician to look for internal consistency and also to note head/ abdomen discordance, which is usually seen with later gestational intrauterine growth restriction.


Many ultrasound machines are equipped with a device for measuring Doppler velocimetry in the fetal vessels, particularly the umbilical artery and middle cerebral artery. This device gives an index of vascular impedance in downstream beds and in the umbilical artery. Increased systolic: diastolic indices are related to decreased fetal placental blood flow. In the middle cerebral artery the resistance may decrease as the fetus compensates for nutrient or oxygen limitations, so indicating increased cerebral blood flow. There are many strong advocates of the use of Doppler velocimetry in clinical management, and abnormal tests have been related to increased stillbirth and other morbid outcomes. The role of Doppler velocimetry in clinical management utilizing other biophysical tests is still being established.


Soon after the introduction of continuous fetal heart rate monitoring for intrapartum assessment, the technique began to be used for antepartum assessment also.  The most popular test was the contraction stress test (CST or Oxytocin Challenge Test,) whereas a small group of Europeans concentrated on the presence of fetal heart rate variability in the monitor tracings, and thus foreshadowed the Non Stress Test (NST) by a decade or more. These tests served well for the 70’s. But many voiced concerns over the high false- positive (i.e. falsely abnormal) rates, upto 80 percent for the NST and 50 percent for the CST. The biophysical profile (BPP) was therefore a welcome introduction, with a false-positive rate less than the previous tests. The accuracy of this test is enhanced by combination of factors viz. fetal movement, fetal flexion tone, fetal breathing, amniotic fluid volume, and the NST.

There has now evolved a hierarchy of tests of fetal assessment, of increasing complexity and decreasing false- positive rates. The series consists of (a) fetal movement counting (kick counts), (b) the NST, and (c) the BPP, or modified BPP. On certain occasions the CST may be used as a follow-up to an abnormal or suspicious NST, or it may be used subsequent to an equivocal BPP.


Of great importance is the relatively recent realization that antepartum testing needs to be disease specific. For example, the volume of amniotic fluid can decrease over a period of days in postdate pregnancy. So evaluation needs to be done at least twice weekly for this indication. In the case of fetal anemia due to Rh problem the NST will be abnormally smoothed and lack accelerations, and one can usually provoke late decelerations with contractions. Again, in fulminant preeclampsia weekly NST testing may not be adequate to detect fetal deterioration when there is a rapid decrease in placental function.


The above tests for determining adequacy of fetal growth and fetal oxygenation have allowed many babies to be delivered before death or damage in utero has occurred. However, such successes would not have been possible without a number of other paralleled developments: (a) detection of fetal developmental defects by genetic testing and ultrasound imaging: (b) tertiary referral centers (c) neonatal intensive care units (d) tests of fetal pulmonary maturity such as the L: S ratio, phosphotidylglycerol, and rapid surfactant tests e) glucocorticoid treatment for accelerating fetal pulmonary maturity (primarily betamethasone) and more recently, (f) neonatal surfactant administration.

We are almost certainly not at the end of the evolutionary trail in the development and application of these technologies. There is no doubt however, that our ability to determine the condition of the fetus, and more accurately detect its state of health, and our ability to rationally intervene and optimally time delivery, has vastly improved in recent decades.

The most important challenges for the future are to refine these techniques to prevent over intervention due to the prevalence of false-positive results in many of the tests, and to ensure a proper understanding of these tests by the providers of obstetric health care.



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