Fetal heart rate patterns in red blood cell isoimmunized pregnancies

Abnormal fetal heart rate patterns caused by pathophysiologic processes other than fetal acidemia

Fetal acidemia is a common final pathway to fetal death, and in many cases, to fetal central nervous system injury. However, certain fetal pathophysiological processes are associated with significant category II or category III fetal heart rate changes before the development of or in the absence of fetal acidemia. The most frequent of these processes include fetal infection and/or inflammation, anemia, fetal congenital heart disease, and fetal central nervous system injury. In the presence of significant category II or category III fetal heart rate patterns, clinicians should consider the possibility of the aforementioned fetal processes depending on the clinical circumstances. The common characteristic of these pathophysiological processes is that their associated fetal heart rate patterns are linked to increased adverse neonatal outcomes despite the absence of acidemia at birth. Therefore, in these cases, the fetal heart rate patterns may provide more insight about the fetal condition and pathophysiology than the acid-base status at birth. In addition, as successful timing of intrapartum interventions on the basis of evolution of fetal heart rate patterns aims to prevent fetal acidemia, it may not be logical to continue to use the fetal acid-base status at birth as the gold standard outcome to determine the predictive ability of category II or III fetal heart rate patterns. A more reasonable approach may be to use the umbilical cord blood acid-base status at birth as the gold standard for determining the appropriateness of the timing of our interventions.

Prediction of fetal anemia by middle cerebral artery peak systolic velocity in pregnancies complicated by rhesus isoimmunization

OBJECTIVES

To study the correlation of peak systolic velocity in the middle cerebral artery with hemoglobin concentration in fetuses at risk of anemia due to Rhesus isoimmunization.

DESIGN

Peak systolic velocity of middle cerebral artery (MCA-PSV) was measured before 66 cordocentesis procedures in 20 isoimmunized fetuses. Reference values were derived from a study of 300 control fetuses. MCA-PSV values and hemoglobin concentrations were expressed as multiples of the median (MoM) for gestational age. The following hemoglobin concentration MoM thresholds defined degrees of anemia: mild, between 0.83 and 0.65; moderate, between 0.64 and 0.55; and severe, less than 0.55. Regression analysis was performed and receiver-operator-characteristic curves were constructed to determine the diagnostic accuracy of different thresholds of MCA-PSV for the prediction of moderate to severe anemia, either at the initial or repeat cordocentesis procedures.

RESULTS

The mean (+/-SD) gestational age at cordocentesis was 28.5+/-4.6 weeks. Moderate to severe anemia was observed on 29 (44%) and hydrops on 27 (41%) occasions. MCA-PSV correlated weakly with hemoglobin concentrations. At threshold values 1.50 MoM, the sensitivity, specificity, and negative predictive value for moderate to severe anemia were 9.0, 100, and 48.0% at the initial cordocentesis procedures, and 44.0, 96.0, and 73.0% at repeat cordocentesis procedures, respectively.

CONCLUSIONS

Although MCA-PSV is highly specific, negative values do not rule out fetal anemia. Further research is required before it can be recommended in clinical practice.

Computerized measurement of heart rate variation in fetal anemia caused by rhesus alloimmunization

OBJECTIVE

The purpose of this study was to examine the relationship between fetal heart rate variation and fetal hematocrit.

STUDY DESIGN

In 36 red-cell alloimmunized pregnancies (mean gestational age 30, range 25 to 36 weeks) 65 computerized fetal heart rate recordings were obtained before ultrasonographically guided fetal blood sampling for the measurement of fetal hematocrit. The recordings were captured and analyzed by a microcomputer on-line. Fetal heart rate variation in anemic fetuses was accurately measured.

RESULTS

Significant positive correlations between short-term or long-term heart rate variation and fetal hematocrit have been demonstrated even after adjusting for the effect of gestation (r = 0.60, n = 65, p less than 0.01, y = 19.264 + 0.913x - 0.003x2; r = 0.52, n = 65, p less than 0.01, y = 21.13 + 0.858x - 0.003x2, respectively). The relationship was best described by a quadratic model. When short-term variation was less than 5 milliseconds or long-term variation was less than 30 milliseconds, the positive predictive values for fetal hematocrit of less than 30 were 85% and 90%, and the negative predictive values 56% and 57%, respectively.

CONCLUSION

Computerized recording and analysis of fetal heart rate variation may prove to be a useful noninvasive tool for assessing fetal anemia in red-cell alloimmunization.

Management of immune haemolytic disease in the fetus

Although Rh alloimmunization has been successfully reduced in frequency and severity since the implementation of Rh immune globulin, cases still occur. The management of affected pregnancies requires the efforts of a team which includes obstetrics/fetal medicine, the blood transfusion service, haematological support, nursing assistance and neonatology. The aim of antenatal management is to predict whether or not the fetus is severely affected, to correct the fetal anaemia and to deliver the baby at the optimal time. The management has improved markedly with the introduction of high-resolution real-time ultrasound, fetal blood sampling, intravascular fetal blood transfusion and/or intraperitoneal transfusion and meticulous fetal surveillance. With appropriate and timely management in severely alloimmunized patient, the survival rate of affected fetuses in some centres is now about 90%. There is still a need for research into new methods of treatment such as high dose intravenous immunoglobulin, which might non-invasively diminish fetal red cell destruction. Due to the reduced frequency of severe disease, regionalized treatment centres are essential in order to maximize the experience and efficiency of the management teams.

Fetal heart rate responses to anemia in Rh isoimmunization

On 52 occasions 24 Rh immunized women were monitored with a nonstress test (NST) prior to fetal blood sampling. Cardiotocographic characteristics were recorded for each NST. Fetal blood was analysed for hemoglobin and hematocrit. Fetal hemoglobin and hematocrit were positively correlated to long-term variability, acceleration amplitude and negatively correlated to deceleration amplitude (linear regression analysis; p less than 0.05). Decelerations were almost without exception associated with low concentrations of hemoglobin and hematocrit. In fetuses of 32 weeks' gestation or more, a loss of variability (less than or equal to 5 bpm) was associated with severe anemia. Hemoglobin and hematocrit were significantly lower in the group with a pathological NST (n = 15) compared with the group with a normal NST (n = 37) (Mann-Whitney U test; p less than 0.05). The predictive value of a pathological test was 13/15 concerning hemoglobin and hematocrit; whereas, the predictive value of a normal test was poor. A pathological NST, especially when decelerative, is a good predictor of fetal anemia, but a normal NST is no guarantee for a normal blood status.