Michael Y. Divon

Identification of the small for gestational age fetus with the use of gestational age-independent indices of fetal growth

This study reviews the roles of sonographic assessment of the rate of growth of the fetal abdominal circumference, the femur length/abdominal circumference ratio, and qualitative determination of amniotic fluid volume as gestational age-independent indices for identification of the small for gestational age fetus. The sensitivity and specificity for single and combinations of test results were evaluated in 50 appropriate for gestational age and 40 small for gestational age fetuses. Positive and negative predictive values were derived for the general population. Our results indicate that either a rate of growth of the fetal abdominal circumference less than or equal to 10 mm/14 days or a femur length/abdominal circumference ratio greater than or equal to 23.5 correctly identifies most small for gestational age fetuses. When the general population is screened, only 15% of small for gestational age fetuses will be missed by this combination of criteria. The presence of a pocket of amniotic fluid less than or equal to 2.0 cm is highly suggestive of a small for gestational age fetus. However, the presence of a pocket of amniotic fluid greater than 2.0 cm does not guarantee an appropriate for gestational age fetus. We conclude that these gestational age-independent indices of fetal growth offer useful tools for differentiating between the small for gestational age and appropriate for gestational age fetus.

Evoked fetal startle response: A possible intrauterine neurological examination☆

The fetal startle reflex was studied in an attempt to provide an objective and quantitative estimate of the fetal neurological condition. This reflex is a normal response to a combined sound-vibratory stimulus in the healthy infant born after 30 weeks of gestation. It consists of a generalized paroxysmal motion that involves the whole body. Thirty women with uncomplicated pregnancies, who subsequently delivered healthy infants, were studied at term. Fetal movements were monitored by means of a real-time scanner. Placement of the transducer was such that it allowed for visualization of the long axis of the fetal forearm. A 3-second stimulus was delivered on the maternal abdomen over the fetal head with use of an artificial larynx. This device generates a mixed sound-vibratory output of 100 dB and 85 Hz. Sufficient visualization of the plane of forearm motion was possible 68% of the time, thus allowing for measurement of the duration of this motion. The results indicate that the mean duration of forearm motion in response to a 3-second sound-vibratory stimulus is 8.2 +/- 2.3 seconds (+/- SEM). Since an immediate forearm motion was detected each time that a stimulus was applied, we conclude that the startle reflex does indeed exist in the fetus. This simple means of assessing the neurological state of the fetus may provide a way to evaluate fetal tone as it applies to antenatal fetal assessment.

Respiratory sinus arrhythmia in the human fetus

This study explores the relationship between fetal heart rate variability and fetal breathing movements in the term fetus. Fourier analysis was applied to fetal heart rate variability during fetal breathing and nonbreathing episodes. A distinct component in the order of 0.7 to 0.95 Hz was demonstrated in fetal heart rate variability during breathing episodes. These frequencies have the same distribution as the corresponding rate of breathing and therefore indicate that respiratory sinus arrhythmia exists in the term fetus.

Autocorrelation techniques in fetal monitoring

Fetal monitors that feature autocorrelation have recently been introduced. This paper discusses autocorrelation and describes how it extracts periodic signals from a noisy background. An example of its performance under clinical conditions demonstrating advantages and limitations is discussed.

Diminished respiratory sinus arrhythmia in asphyxiated term infants.

Spectral analysis techniques were used to quantitate the association between respiration and heart rate variability in eight healthy and eight asphyxiated infants born at term gestation. Respiratory sinus arrhythmia was demonstrated in all healthy infants. This arrhythmia was significantly diminished in asphyxiated newborn infants. We conclude that newborn infants with low Apgar scores have a reduced respiratory sinus arrhythmia and that this reduction could account for the loss of short-term heart rate variability commonly associated with asphyxia.

Human fetal breathing: associated changes in heart rate and beat-to-beat variability.

A computerized quantification of fetal heart rate and beat-to-beat variability was performed during and between fetal breathing episodes. Sixteen healthy pregnant women at term participated in the study. The results indicate that fetal breathing is associated with a significant increase in beat-to-beat variability (from 4.48 +/- 1.66 between breathing episodes to 5.80 +/- 2.04 during breathing episodes, p less than 0.01) and a small but significant decrease in fetal heart rate (from 142.7 +/- 8.6 bpm between breathing episodes to 140.4 +/- 8.6 bpm during breathing episodes, p less than 0.05).

Increased beat-to-beat variability during uterine contractions: A common association in uncomplicated labor

A computerized system was used during labor to provide a quantitative and objective analysis of fetal heart rate, beat-to-beat variability, and uterine contractions. Twenty-nine healthy pregnant women at term participated in this study. Each woman was studied for a 40-minute period during the active phase of spontaneous labor. The results indicate that beat-to-beat variability rises from a value of 4.62 +/- 1.11 (mean +/- SD) between contractions to 6.86 +/- 1.53 during contractions. This rise is significant (p less than 0.01). At the same time, changes in fetal heart rate are small, inconsistent, and not significant. We conclude that an increased beat-to-beat variability is commonly associated with uterine contractions in normal fetuses. This increase is probably due to mild hypoxia caused by decreased perfusion of the placenta and to increased vagal tone caused by fetal head compression.

Missing hospital records: A confounding variable in retrospective studies

In retrospective chart reviews there are often a certain number of missing hospital records. To elucidate this variable we compared the outcomes of very low birth weight breech infants with respect to the method of collecting data. A prospective sampling, during the hospital stay, of data was performed in 1979 to 1980 and in 1983 to 1984, and the frequencies of very low birth weight were 1.89 and 1.90, respectively, per 1000 live births. For 1981 to 1982 a retrospective record search was performed with the use of the ordinary medical record search system at this institution. For this period 39 of 52 (75%) hospital records were recovered, giving an apparent frequency of 1.32/1000 live births, which differed significantly from either period studied prospectively. An analysis of demographic data of the three groups revealed that the mean gestational age and the mean birth weights were higher in the period studied retrospectively compared with both periods studied prospectively and that the neonatal mortality rates were higher in the periods studied prospectively (74.1% and 57.1%, respectively) than in the period studied retrospectively (28.2%). It is concluded that the more complicated a clinical case is, the more likely the record will not be found for retrospective chart review. This problem should be kept in mind, and it ought to be a requirement that the number of missing charts be stated in retrospective observational studies.