Computerized fetal heart rate analysis, Doppler ultrasound and biophysical profile score in the prediction of acid-base status of growth-restricted fetuses

Antepartum fetal testing: a critical appraisal

PURPOSE OF REVIEW

Recognition of the fetus at risk for death or damage in utero, quantifying the risk, balancing fetal risk against the risk of neonatal complications from immaturity and determining optimal time and mode of intervention, is a cornerstone of modern perinatal medicine. Antepartum fetal testing is essential in making these crucial decisions. The art and science of fetal assessment is fluid. In this treatise, the evolution of testing is reviewed, test accuracy results examined and suggestions for future applications are considered.

RECENT FINDINGS

Composite testing of a range of fetal biophysical variables is an excellent predictor of fetal acidemia and risk of death or damage. Confusion regarding the optimal means of measuring one of these variables, amniotic fluid volume, has been addressed in the literature and contemporary studies from several independent sources indicate that the amniotic fluid index method should be abandoned in favor of the maximal vertical pocket method. It is becoming increasingly more evident that a spectrum of fetal testing modalities based on interrogation of different aspects of fetal adaptive responses to adversity is preferable in fetal testing. Further it is evident that in some fetal diseases, such as intrauterine growth restriction, fetal condition may change acutely and accordingly best outcome is achieved by much more frequent testing. The question of whether intervention for fetal compromise can prevent subsequent neurological sequelae remains open.

SUMMARY

There has been remarkable advancement in identifying the fetus at risk. The concept of multispectral combined fetal testing including acute biophysical variables, amniotic fluid volume and arterial and venous Doppler flow velocity waveforms is established.

Computerized analysis of normal fetal heart rate pattern throughout gestation

OBJECTIVE

To analyze the evolution of computerized cardiotocography (cCTG) parameters throughout gestation in a large archive of traces from healthy fetuses.

METHODS

This was a cross-sectional study of the first cCTG record from 4412 singleton fetuses with good pregnancy outcome. Normal ranges of cCTG parameters for 25 to 42 weeks were derived from analysis of only one cCTG record per fetus, and the relationship between the parameters and gestational age was investigated.

RESULTS

Fetal heart rate (FHR) accelerations, short- and long-term variation overall, duration of episodes of high and low variation and variation in high episodes increased with advancing gestation. In contrast, maternal perception of fetal movements, basal FHR, variation in low episodes and the time until criteria for normality were met decreased with advancing gestation. Gestational age-related changes in FHR variation were less evident at the lowest percentiles. Episodes of high FHR variation were detected in most fetuses, even at 25 weeks. Opposite trends of basal FHR and variation were observed at 42 weeks. Large decelerations and the frequency and duration of low episodes were also higher at 42 weeks.

CONCLUSIONS

The characteristics of the normal FHR pattern are quite defined from early on in gestation, follow a continuous trend with advancing gestation and change abruptly at 42 weeks. Gestational age-related changes are less obvious at the lowest percentiles.

Intrauterine restriction (IUGR)

Perinatal mortality and morbidity is markedly increased in intrauterine growth restricted (IUGR) fetuses. Prenatal identification of IUGR is the first step in clinical management. For that purpose a uniform definition and criteria are required. The etiology of IUGR is multifactorial and whenever possible it should be assessed. When the cause is of placental origin, it is possible to identify the affected fetuses. The major complication is chronic fetal hypoxemia. By monitoring the changes of fetal vital functions it is thus possible to improve both management and outcome. The timing of delivery is crucial but the optimal management scheme has not yet been identified. When IUGR is identified at very early gestational ages, serial assessments of the risk of continuing the in utero fetal life under adverse conditions versus the risks of the prematurity should be performed. Delivery of IUGR fetuses should take place in centers where appropriate neonatal assistance can be provided. Careful monitoring of the IUGR fetus during labor is crucial as the IUGR fetus can quickly decompensate once uterine contractions have started.

Cardiac dysfunction and cell damage across clinical stages of severity in growth-restricted fetuses

OBJECTIVE

The purpose of this study was to assess cardiac function and cell damage in intrauterine growth-restricted (IUGR) fetuses across clinical Doppler stages of deterioration.

STUDY DESIGN

One hundred twenty appropriate-for-gestational-age and 81 IUGR fetuses were classified in stages 1/2/3 according umbilical artery present/absent/reversed end-diastolic blood flow, respectively. Cardiac function was assessed by modified-myocardial performance index, early-to-late diastolic filling ratios, cardiac output, and cord blood B-type natriuretic peptide; myocardial cell damage was assessed by heart fatty acid-binding protein, troponin-I, and high-sensitivity C-reactive protein.

RESULTS

Modified-myocardial performance index, blood B-type natriuretic peptide, and early-to-late diastolic filling ratios were increased in a stage-dependent manner in IUGR fetuses, compared with appropriate-for-gestational-age fetuses. Heart fatty acid-binding protein levels were higher in IUGR fetuses at stage 3, compared with control fetuses. Cardiac output, troponin-I, and high-sensitivity C-reactive protein did not increase in IUGR fetuses at any stage.

CONCLUSION

IUGR fetuses showed signs of cardiac dysfunction from early stages. Cardiac dysfunction deteriorates further with the progression of fetal compromise, together with the appearance of biochemical signs of cell damage.

Fetal growth restriction

Normal fetal growth is determined by the genetically predetermined growth potential and further modulated by maternal, fetal, placental, and external factors. Fetal growth restriction (FGR) is a failure to reach this potential and is clinically suspected if sonographic estimates of fetal weight, size, or symmetry are abnormal. Integration of fetal anatomy assessment, amniotic fluid dynamics, uterine, umbilical, and fetal middle cerebral artery Doppler is the most effective approach to differentiate potentially manageable placenta-based FGR from aneuploidy, nonaneuploid syndromes, and viral infection. Although placental dysfunction results in a multisystem fetal syndrome with impacts on short- and long-term outcome, only cardiovascular and behavioral responses are helpful to guide surveillance and intervention. Early-onset FGR before 34 weeks gestation is readily recognized but challenging to manage as questions about optimal delivery timing remain unanswered. In contrast, near-term FGR provides less of a management challenge but is often missed as clinical findings are more subtle. Once placenta-based FGR is diagnosed, integrating multivessel Doppler and biophysical profile score provides information on longitudinal progression of placental dysfunction and degree of fetal acidemia, respectively. Choosing appropriate monitoring intervals based on anticipated disease acceleration and intervention when fetal risks exceed neonatal risks are the prevailing current management approaches.

Integrated testing and management in fetal growth restriction

Growth-restricted fetuses are at higher risk for poor perinatal and long-term outcome than those who are appropriately grown. Multiple antenatal testing modalities can help document the sequence of fetal deterioration. The full extent of this compromise is best identified by a combination of fetal biometry, biophysical profile scoring, and arterial and venous Doppler. In the preterm growth-restricted fetus, timing of delivery is critically determined by the balance of fetal versus neonatal risks. In the near-term fetus, accurate diagnosis continues to be a challenge as unrecognized growth restriction contributes to a significant proportion of unexplained stillbirths. In this review, we present an integrated diagnostic and surveillance approach that accounts for these factors.