Assessment of fetal health: development, size, movement

Over the past thirty years, a number of different tests have been proposed for assessing the condition of the fetus, which are widely used in obstetric practice. Both biochemical studies (to monitor the endocrine function of the placenta or fetoplacental system) and biophysical monitoring methods (providing information on the development of the fetus and its physiological functions) are theoretically capable of detecting signs of such changes in the state of the fetus, which may occur only after a few hours , days or even weeks. However, none of the known methods can predict a sudden event, for example, a prolapse of the umbilical cord or placental abruption, which can cause severe disturbance or even death of the fetus.

The clinical relevance of antenatal monitoring is based on two main statements. The first is that the methods used in this case are able to identify or predict threatening conditions in the fetus, and second, with the correct interpretation of the data obtained and adequate follow-up actions, it is possible to reduce the frequency or severity of complications in the perinatal period or prevent unnecessary interventions.

Assessment of fetal development and size

Fetal assessment tests are used either as screening tests in order to prevent those sometimes unpredictable, dangerous fetal disorders that can occur from time to time during pregnancy, or according to indications, in special clinical situations, if the degree of risk to the fetus increases significantly. Complications of the course of pregnancy, which significantly increase the risk to the fetus, are: diabetes mellitus in the mother, preeclampsia, multiple pregnancy, post-term pregnancy, and most often - suspicion of fetal growth retardation. Since there is disagreement about the very concept of fetal growth retardation, and since suspicion of its presence is very often an indication for antenatal monitoring, it makes sense to revise the definition and pathophysiological concept of fetal development retardation.

In clinical practice, the terms “fetal size” and “fetal development” are often not distinguished. It is generally accepted to assess the standards of "body weight of a newborn for a given gestational age as a" scale of fetal development ", and body weight is lower relative to some, often arbitrarily chosen, percentiles to refer to" intrauterine growth retardation. " There are two main reasons why this confusion can lead to false conclusions. The first is that the body weight of a newborn at a given gestational age is not a sufficiently adequate reflection of the fetal body weight at the same gestational age. Second, some authors assess the development of the fetus by comparing with the average values ​​or medians of the body weight of children at birth at the corresponding stages of pregnancy. This approach is fraught with serious errors, since it does not account for the difference between "size" and "development". Newborns below a certain weight are often in fact “underweight for a given gestational age” and are unreasonably classified as having “developmental delay”. Fetal development cannot be assessed without determining two or more fetal sizes. The clinician would really like to know if there are any deviations in fetal development from its dynamics in an uncomplicated pregnancy.

The term "intrauterine growth retardation" should be applied only to those fetuses that have some evidence of a violation of the dynamics of its development. At the same time, newborns will not necessarily be "small for a given gestational age." A fetus whose relative body weight deviates from the 90th to 30th percentile in a short period of time in the dynamics of pregnancy is almost certainly in greater danger than a fetus whose weight is constantly at the 5th percentile as pregnancy progresses.

True fetal growth retardation is associated with insufficient supply of nutrients to it due to impaired placental function (or, more precisely, due to impaired uteroplacental hemodynamics). In response to this unfavorable circumstance, the fetus activates regulatory mechanisms that increase its chances of survival. There is a redistribution of fetal-placental blood flow (blood is mainly directed to the brain and heart, and to a lesser extent to the liver and kidneys) against the background of limiting the motor activity of the fetus. These manifestations of adaptation are the basis for tests to assess the condition of the fetus.

External assessment of the size and development of the fetus

The simplest clinical method for assessing fetal size - abdominal palpation - is very inaccurate and slightly better than the “eye” estimate: 20% of fetal weight determinations immediately before delivery do not fit within the error interval of 450 grams of the actual body weight of the newborn. Moreover, at earlier stages of pregnancy, when information about the weight of the fetus is most important, the relative error in its determination is even greater. A more accurate quantitative method for determining the weight of the fetus consists in assessing the dynamics of an increase in the size of the mother's abdomen, which should, to a certain extent, reflect the dynamics of an increase in the size of the uterus. In clinical practice, two methods are most widely used - measuring the height of the uterine fundus (the distance between the upper edge of the symphysis and the fundus of the uterus) and measuring the abdominal circumference at the level of the navel.

Several studies have been carried out in order to study the informative value of determining the height of the standing of the uterine fundus, as an indicator of the size of the fetus. At the same time, there are practically no studies to determine the value of this measurement for assessing fetal development. This is due to the significant variability in the results of repeated measurements of the height of the fundus of the uterus in the same patient, both in the same patient and among different researchers. Nevertheless, a number of studies have shown quite satisfactory sensitivity and specificity of the method for determining the height of the fundus of the uterus for diagnosing fetal weight as low for a given gestational period. The ability to predict low fetal weight does not mean a corresponding ability to detect delayed fetal development. However, the measurement of the height of the fundus of the uterus is likely to be applicable as a screening test, and can be confirmed in subsequent studies, which has been evaluated only in a few studies. The value of measuring the abdominal circumference of a pregnant patient has so far not been adequately assessed at all.

Assessment of the nature of fetal movements

Until now, the cause of sudden fetal death in late pregnancy remains unknown, and, therefore, at present, the ability to predict and prevent such a complication seems to be very limited. Screening for fetal movement by the mother has an advantage over other methods of assessing the condition of the fetus, since it is performed daily, which, due to practical considerations, is difficult or impossible to implement when using other methods of assessing the condition of the fetus.

There are data from two randomized controlled trials that included data from a survey of 68,000 women to determine whether pregnancy outcomes are improved by clinical interventions based on fetal motor activity. Based on the data of these studies, there is no reliable evidence that routine formalized counting of fetal movements reduces the incidence of fetal death at the end of pregnancy. Routine counting of the frequency of movements with a decrease in fetal motor activity led to more frequent use of additional methods for assessing the state of the fetus, to more frequent hospitalizations of pregnant women and an increase in the number of induced births, and, as a consequence of all this, to an increase in costs without a tangible improvement in perinatal outcomes. Practical observations do not support an increase or decrease in anxiety and anxiety in patients who routinely count fetal movements.

There is a certain probability that the assessment of the frequency of fetal movements can prevent fetal death in late pregnancy. However, before recommending to mothers an independent assessment of the motor activity of the fetus, the social, psychological and economic characteristics of the patients should be taken into account.

Biophysical tests

Ultrasound fetometry

Ultrasound examination helps in assessing the development and condition of the fetus, using various possibilities of the method: a single determination of fetometric parameters in order to confirm or exclude clinical data on the presence of a smaller fetus for its gestational age; determination of the relative volume of amniotic fluid (indirectly reflecting the intensity of fetal urine production); placentography; and, in addition, an assessment of the motor activity and behavioral responses of the fetus.

The use of ultrasound fetometry for assessing fetal development should be considered from a general perspective based on the criteria applied to any diagnostic methods that reflect efficacy - to determine its sensitivity, specificity and prognostic value. However, it is not entirely clear what exactly is the purpose of this method. There are no absolute postnatal criteria for developmental delay that could be used to assess the significance of this "test". In the absence of adequate postnatal indicators for evaluating the results of prenatal ultrasound examination, such evaluation criteria as “relatively low” body weight at birth or weight less than the 10th percentile for a given gestational period are often used.

It must be recognized that in order to create normative curves of fetometric indicators based on their measurements in dynamics in the same fetus as pregnancy progresses, a completely insufficient number of studies have been carried out. Information of this kind would reveal deeper criteria for assessing the nature of fetal development and convincing arguments for an effective diagnosis of delayed development. Such an approach to the use of ultrasound fetometry is especially valuable when the gestational age is unknown or not precisely defined. In this case, dynamic fetometry could be more justified than the assessment of the correspondence of weight to gestational age, be considered as the "gold standard" for determining the rate of fetal growth. And now, instead, evidence from controlled trials shows that routine ultrasound fetometry in late pregnancy leads to an increase in antenatal hospitalization rates and possibly induced labor without any significant improvement in perinatal outcomes. The available literature lacks information on adequate controlled studies regarding the value of ultrasound fetometry in high-risk pregnancies.

The so-called “low-weight-for-term” fruits form a heterogeneous group, within which the differences in the individual risk of perinatal complications are extremely large. Attempts were made to analyze the indicators of fetal development in the hope of identifying the pathogenesis underlying this feature of fetal development and determining the methods for calculating their individual risks. "Small for term" fruits can be divided into two groups: in the first, there is a sharp slowdown in the earlier normal dynamics of development, and in the second, the initially small size of the fetus remains so throughout pregnancy until delivery. The emergence of the first group is due to "uteroplacental insufficiency", and the second - a decrease in the potential for fetal development. The latter group includes fruits with hereditary abnormalities (especially with chromosomal abnormalities), in some cases - those affected by serious pathological effects, for example rubella, during a critical period of organogenesis, and in other cases - with their own genetic characteristics. A comparative assessment of the size of the fetal head and abdomen is proposed as a way to further differentiate between the two groups. While a higher incidence of fetal distress and operative delivery during labor occurs in the asymmetric group, perinatal mortality and low Apgar scores are equally high in both groups.

The value of ultrasound fetometry in order to assess the nature of fetal development requires further study, and identifying the correlation between fetometric and Doppler parameters would be especially interesting. The data available to date indicate a greater prognostic value of determining the abdominal circumference as compared to the head circumference as a criterion for predicting "low birth weight" fetuses, but there are still few data on serial measurements, and especially their relationship with neonatal outcomes.

The only study conducted in 1987 evaluated the value of ultrasound placentography. Information about the echostructure of the placenta made it possible for clinicians to adjust the tactics of pregnancy management. Compared with patients who did not have information about the echostructure of the placenta, its presence was combined with a decrease in the incidence of meconium impurities in the amniotic fluid during labor, with a decrease in the frequency of births of newborns with a low Apgar score at the 5th minute and, especially importantly, with a decrease in the incidence of death of newborns in the absence of congenital malformations. It can be assumed that preliminary information about the state of the placenta may lead to appropriate clinical interventions that can improve the outcome of pregnancy. Currently, it seems appropriate to use ultrasound to obtain information about the echo structure of the placenta in the third trimester of pregnancy.

Based on data from randomized trials, the assessment of amniotic fluid volume by ultrasound scanning is of clinical importance in the management of post-term pregnancy or in assessing the biophysical profile of the fetus (see above).

Doppler ultrasonography

The above is supported by clinical trial data. The evidence, summarized from the results of several clinical trials in high-risk pregnancies (mainly with fetal growth retardation or maternal arterial hypertension), suggests that if antenatal blood flow Doppler results are available to clinicians, it leads to a decrease in the incidence of stillbirth and the incidence of neonatal death of newborns in the absence of congenital malformations. The high frequency of death of fetuses and newborns in the control group in these studies was apparently due to the presence of uteroplacental insufficiency, the signs of which can be effectively detected using Dopplerometry and serve as the basis for the use of appropriate clinical interventions. The data available to date indicate that the use of Doppler in high-risk pregnancies leads to a decrease in the frequency of hospitalizations and to a decrease in the frequency of labor arousal. The effect of the use of Dopplerometry on the frequency of deliveries by caesarean section and on the condition of newborns was not revealed, with the exception of an increase in the likelihood for them to be born alive.

While highly effective in reducing perinatal mortality in high-risk pregnancies, Doppler is of limited value, if any, when used as a screening method. This is not surprising: in a low-risk population, the predictive value of any test is low, and the benefits of appropriate interventions based on the few true positive conclusions may be offset by the harm from unnecessary interventions in response to the inevitably high proportion of false positives.

Non-stress test

In 1969, for the first time, it was proposed to assess the cardiac activity of the fetus without regard to uterine contractions. Currently, this technique has found widespread use in antenatal management, both for screening and for diagnosing fetal disorders.

There is no universally accepted technique for performing non-stress antenatal cardiotocography. Various variants of the duration and frequency of fetal heart rate monitoring are used, which can be essential for the predictive value of the method. If fetal abnormalities were suspected, additional interventions were suggested or even used, such as transabdominal and sound stimulation of the fetus, glucose administration, repeated afternoon tests, and a subsequent oxytocin test. However, none of these effects increased the prognostic value of cardiotocography.

Many factors can make it difficult to interpret a non-stress test. Similar to the stress test, the non-stress test requires sophisticated medical equipment, the use of which requires sufficient skill to avoid technical malfunctions. Since the ultrasound probe of the heart monitor is very sensitive, fetal and maternal movements can cause artifacts in the recording of fetal heartbeats. During the period of a calm state of the fetus, which often lasts more than 30 minutes, a physiological decrease in heart rate variability can be mistaken for pathological disorders of the fetus. Medicines taken by the mother, especially those with a sedative effect on the central nervous system, can cause changes in the fetal heart rate curve on the cardiotocogram that can be interpreted as pathological. When interpreting a cardiotocogram, it is necessary to remember about the effect of gestational age on fetal heart rate variability, since fetuses often have a false positive areactive curve before full-term gestation.Taking into account all these facts, it turns out that 10-15% of all cardiotocograms can turn out to be incompletely interpretable.

Various methods of interpretation of non-stress cardiotocograms have been proposed. They usually include an assessment of all or some of the following: basal fetal heart rate, assessment of heart rate variability, acceleration (acceleration) of the fetal heart rate due to spontaneous and / or stimulated fetal movements, deceleration (deceleration) due to spontaneous contractions of the uterus. More sophisticated methods of interpretation involve calculating the sum of points of all or some of these parameters of the cardiotocogram. It is often used to differentiate the curves of the fetal heart rate into reactive (normal) and areactive (pathological); this division is based on the presence or absence of an adequate amount of variability and aceleration of the heart rate in connection with the motor activity of the fetus. However, it has been reliably shown that even when using a formalized technique, the interpretation of cardiotocograms can be different for the same researcher after a certain period of time, as well as the interpretation of one cardiotocogram by different researchers.

In addition to difficulties in interpretation, the use of cardiotocography as a screening method presents a certain danger inherent in any form of screening in a population in which the likelihood that the fetus is at risk is low, which, in turn, leads to a significant number of false positives. Interventions during pregnancy based on false positive non-stress test results at low risk are more likely to be harmful than beneficial to patients and their fetuses.

This harm is real, not just theoretical. In each of the four published clinical trials of the non-stress test, there was a higher perinatal mortality rate from causes not associated with congenital malformations in the group of patients whose test results were available to clinicians. In general, the increase in perinatal mortality was significant (more than threefold) and statistically significant among women who underwent a non-stress test. At the same time, there was no significant effect of antenatal cardiotocography on the frequency of cesarean sections, low Apgar scores, pathological neurological abnormalities or hospitalizations in neonatal intensive care units. Analysis of the data from these studies does not provide any grounds for using antenatal non-stress cardiotocography as it was used in these studies, that is, as an additional method for assessing the condition of the fetus in the absence of a high degree of risk. One can only wonder why cardiotocography in the absence of complications of pregnancy continues to be used so widely and why the results of the published four randomized trials are so persistently ignored by many obstetricians.

Antenatal cardiotocography is very valuable when an immediate assessment of the fetus is required. Unless additional indications arise, the clinical application of the method seems to be best limited to situations where acute fetal hypoxia can be suspected, for example, with a sudden decrease in fetal movements or prenatal bleeding.

Fetal biophysical profile

The biophysical profile of the fetus is determined on the basis of data from several sequential ultrasound examinations and antenatal cardiotocography (non-stress test) in high-risk pregnancies. The sum of the scores of five biophysical indicators (motor activity, respiratory movements and fetal tone, reactivity - non-stress test and amniotic fluid volume) is considered prognostically significant, and when compared with one non-stress test, it reduces the frequency of false-positive or false-negative results when examining the state of the fetus. An additional advantage of the biophysical profile in comparison with the non-stress test is that it performs ultrasound, which makes it possible to exclude the presence of gross malformations in the fetus, since this information can be important for choosing a method of delivery.

Only two controlled studies of the biophysical profile value are known. Both of these studies were carried out in clinics specializing in the biophysical assessment of the condition of the fetus. A comparison was made between two groups of patients: the management of one group was based on the results of determining the biophysical profile of the fetus, and in the other group of patients - on the results of one non-stress test. In both studies, the determination of the biophysical profile was more prognostically significant in relation to the decrease in the value of the newborn Apgar score at the 5th minute. In addition, the biophysical profile was both more sensitive and more specific in predicting the incidence of possible fetal complications compared with the non-stress test alone.

Despite the best predictive power, biophysical profiling was not associated with improved neonatal pregnancy outcomes compared with non-stress test alone. Outcomes were assessed by the frequency of the following indicators: perinatal mortality, fetal distress in labor, low Apgar scores, and low birth weight for gestational age. Compared with one cardiotocography, the determination of the biophysical profile of the fetus did not have a noticeable effect on these indicators (neither favorable nor negative). Data from controlled studies do not provide sufficient evidence to support the use of a biophysical profile as a means of assessing fetal health in high-risk pregnancies. However, the number of women included in these studies was so small that any calculations of the effectiveness of this method do not seem entirely correct.

Assessment of the state of the fetus on the basis of biochemical studies in the third trimester of pregnancy is currently only of historical interest. The enthusiasm for the study of estrogen concentration that took place in the 60s and 70s of the last century was based on the fact that the perinatal mortality rate was twice as high in women with low estriol excretion compared to the general population. However, the practical use of the test was associated with its low sensitivity in detecting the majority of pregnancies ending in an unfavorable outcome, and a high level of false-positive results among patients with uncomplicated pregnancies, unreasonably attributed to the high-risk group.

Among the large number of published studies, there is only one controlled randomized clinical trial. In this study, the determination of estriol levels had absolutely no effect on either the perinatal mortality rate or the elective delivery rate. Exactly the same results were obtained for pregnancy outcomes in the same institution over two consecutive time periods, with and without estriol testing in pregnant women. Thus, there is no evidence of any clinical benefit from the use of a biochemical test to determine the concentration of estriol.

Similar to the above, only one randomized study has been conducted to identify the clinical significance of determining the concentration of human placental lactogen. The results of this study, at first glance, indicate that intervention during pregnancy based on the results of determining the concentration of placental lactogen statistically significantly reduces the incidence of both antenatal and perinatal mortality. Although the results of this study are often cited to show that the determination of the concentration of human placental lactogen is favorable for improving outcomes in high-risk pregnancies, this conclusion applies only to 8% (4% in each group) of patients enrolled in the study with abnormalities. the level of human placental lactogen from the norm. Data on pregnancy outcomes in the vast majority of patients (92%) in whom the level of human placental lactogen was within the normal range are not published in this work and are not available for analysis. This does not exclude the possibility that the obvious benefit in a small sample of patients who had deviations in the concentration of human placental lactogen from the norm would be nullified by the negative consequences of pregnancy management based on normal values ​​of the concentration of placental lactogen, which took place in the vast majority of patients. in this study.

Today, biophysical tests are used with the same enthusiasm that was characteristic of biochemical tests in the recent past. These tests have greatly contributed to our understanding of fetal behavior and development, however, with the exception of umbilical artery Doppler blood flow in high-risk pregnancies and possibly placentography, the use of biophysical tests has not led to improved obstetric care for specific women and children. For this reason, despite their widespread clinical use, most biophysical methods for assessing the condition of the fetus should be considered as having only experimental value, but not as a tool with proven clinical efficacy. They should be recognized as such and, at the very least, their continued clinical use should be limited until evidence of a positive effect on maternal or neonatal outcomes is presented.

The value of non-stress cardiotocography for both screening and diagnosis seems questionable due to the relatively high cost of the study and its low predictive value. The biophysical profile may have great potential as a diagnostic test in women at high risk to the fetus, but the usefulness of this approach has not yet been fully established.

The value and effectiveness of dopplerometry have been assessed most widely and strictly in comparison with other methods of assessing the state of the fetus and the functional state of the fetoplacental system. The encouraging results from Doppler imaging suggest that more rational antenatal care can be provided with this method in high-risk pregnancies, but there is no evidence that there is any benefit from routine Doppler screening in the general population.