Longitudinal measurements of fetal breathing, body movements, heart rate, and heart rate accelerations and decelerations at 24 to 32 weeks of gestation

Fetal breathing, fetal body movements, fetal heart rate, and fetal heart rate accelerations and decelerations were studied longitudinally in healthy fetuses between 24 and 32 weeks' gestation in the second and third hour following an 800 kcal maternal meal. The expected increase in fetal breathing following a maternal meal was not seen until fetuses were at 30 to 32 weeks' gestation. The number of body movements decreased and the interaction between body movements and fetal heart rate accelerations became more evident as fetuses became older. Fetal heart rate decelerations increased with gestational age, and the relative proportion of total decelerations that were either associated with body movements or were part of a deceleration/acceleration/deceleration complex increased from 24 to 32 weeks' gestation. The data support the hypothesis that gestational age is an important variable to consider when interpreting biophysical measurements in the human fetus at 24 to 32 weeks' gestation. Fetal body movements may be the single most important measurement of fetal health at these gestational ages.     

Relationship between fetal heart rate and umbilical blood flow velocity in term human fetuses during labor

Fourteen pregnant women between 37 and 41 weeks' gestational age, who subsequently were delivered of healthy newborn infants, were studied to examine the effects of spontaneous changes in fetal heart rate on the flow-velocity waveforms in the umbilical artery. The women were in active labor and under epidural anesthesia at the time Doppler measurements were made. There was a significant positive relationship between end-diastolic flow velocity and fetal heart rate. The umbilical artery peak-systolic/end-diastolic ratio was best correlated with the negative reciprocal transformation of the instantaneous fetal heart rate value and end-diastolic flow velocity. No significant correlation was found between fetal heart rate, umbilical artery peak-systolic/end-diastolic ratio, and peak-systolic flow velocity. An upper limit of 3.0 for a normal umbilical artery peak-systolic/end-diastolic ratio was acceptable only if the instantaneous fetal heart rate was greater than or equal to 130 beats/min.     

Fetal loss in threatened abortion after embryonic/fetal heart activity.

OBJECTIVES: To study the incidence of fetal loss in threatened abortion after detection of embryonic/fetal heart activity. METHODS: A prospective study was performed on pregnant women with clinically diagnosed threatened abortion between 6 and 14 weeks of gestation. All had a good menstrual history and the calculated gestational age using crown-rump length in the first trimester ultrasound was in agreement. Embryonic/fetal heart rate measurements were obtained by a 5 MHz vaginal probe using M-mode and real-time B mode imaging. All cases were followed up with respect to pregnancy outcomes. The data were analyzed using the SPSS computer program. RESULTS: Eighty-seven pregnant women were included in the study. There were three pregnancies (3.4%) which resulted in fetal loss before 20 weeks of gestation. In viable pregnancies, the mean embryonic/fetal heart rate increased with advancing gestational age. The individual values of embryonic/fetal heart rate for fetal losses were within the reference range. CONCLUSIONS: The incidence of fetal loss in threatened abortion after detection of embryonic/fetal heart activity was 3.4%. There was no evident pattern of bradycardia or tachycardia that signaled the incipient of viability.     

Screening with Doppler velocimetry in labor

Doppler flow velocimetry was performed on 273 nonselected patients in labor. All patients were at least 2 cm dilated and 80% effaced (58% greater than 4 cm) and were delivered of infants within 24 hours. Fetal heart rate tracing performed at the same time was read by another observer and compared with Doppler flow velocity measurements (systolic/diastolic ratio, pulsatility index). A significant correlation was noted (r = 0.234, p less than 0.001) between the two modalities. Both fetal heart rate tracings and umbilical flow velocity measurements were correlated with fetal outcome. Significant associations were noted between the umbilical systolic/diastolic ratio and fetal distress. 5-minute Apgar scores, the need for intubation independent of gestational age, and umbilical arterial cord pH and base excess. It appears that the information obtained from flow velocimetry had additional benefits compared with that of fetal heart rate tracings alone.     

Clinical aspects of fetal heart auscultation

The widespread belief that fetal heart tones are first detected with an unamplified fetoscope at about 20 weeks' gestation has been studied prospectively only twice. Using data collection prospectively from 352 visits of 77 patients between 15 and 23 weeks' pregnancy, we studied various clinical aspects of fetal heart tone detection. We determined the gestational age at the time of initial auscultation of fetal heart tones with an ordinary fetoscope, and its relationship to quickening, parity, and placenta location. Fetal heart tones were first identified by auscultation at a mean gestational age of 19.4 weeks (range 17-22 weeks). Detection was possible in 81% of patients examined at 20 weeks and in virtually all patients examined at 21 weeks or later. Once heard, fetal heart tones were identified in every subsequent visit for all patients. Parity and placenta location were significant factors influencing initial fetal heart tone detection. Auscultation preceded quickening in only 12% of patients. Recommendations for using initial fetal heart tone detection in clinical practice are given.     

Catecholamine physiology in the ovine fetus. I. Gestational age variation in basal plasma concentrations

Fifty-five ewes with chronically catheterized singleton gestations were studied to assess changes in basal concentrations of fetal catecholamines with increasing gestational age. All pregnancies were time dated, and measurements of catecholamines were conducted at least 5 days after placement of fetal catheters when fetal metabolic parameters had normalized. Plasma concentrations of catecholamines were measured by radioenzymatic assay. Additionally, fetal heart rate (FHR) and corrected mean blood pressure were analyzed in 32 of the fetuses for correlation with plasma levels of catecholamines. Multiple regression analysis revealed significant inverse correlations of fetal plasma concentrations of catecholamines with gestational age, as follows: norepinephrine (p less than 0.001), epinephrine (p less than 0.05), and dopamine (p less than 0.01). FHR correlated inversely with gestational age (p less than 0.001) and positively with circulating levels of norepinephrine (p less than 0.001).     

Fetal heart rate and activity patterns in growth-retarded fetuses: changes after vibratory acoustic stimulation

Seventeen pregnant women who subsequently were delivered of infants with birth weights less than the third percentile were studied for examination of fetal heart rate and fetal activity patterns before and after a 5-second external vibratory acoustic stimulation. None of the fetuses was acidotic at birth. A reduced time was noted during which accelerations in heart rate occurred (50% less) and long-term fetal heart rate variability (25% less) in small for gestational age fetuses compared with age-matched, normally grown fetuses. The incidence of gross fetal body movements was significantly lower (40% less) in small for gestational age fetuses than in those who were appropriate for gestational age. Fetal heart rate and fetal activity patterns after stimulation with the electronic artificial larynx in small for gestational age fetuses were similar to those of appropriate for gestational age fetuses.     

Three-dimensional yolk and gestational sac volume. A prospective study of prognostic value

OBJECTIVE: To evaluate the relative prognostic value of ultrasound findings during the first-trimester scan by univariate and logistic regression analysis in a group of asymptomatic women. STUDY DESIGN: A total of 125 asymptomatic pregnant women with a singleton conceptus, concordance between menstrual age and crown-rump length, and documented fetal activity, 25 for each gestational age between 6 and 10 weeks, were enrolled in the study and underwent a transvaginal sonographic examination. The following data were collected: yolk sac mean diameter and volume, gestational sac mean diameter and volume, fetal heart rate, maternal age, gestational age and presence of a retrochorial hematoma. The outcome variable was abortion, defined as pregnancy loss at any time up to 20 weeks' gestation. Normograms were constructed for volumes, mean diameters and fetal heart rate. Receiver-operator characteristic curves were performed in order to dichotomize maternal and gestational age. Univeriate analysis was performed by Fisher's exact test. Logistic regression was performed to test the relationship between independent variables and pregnancy outcome. RESULTS: In univariate analysis, the variables significantly associated with spontaneous abortion were maternal age > 34 years, yolk sac volume outside the 5th to 95th percentile, gestational sac volume < the 5th percentile and fetal heart rate outside the 5th to 95th percentile. In regression analysis only maternal age > 34 years, gestational sac mean diameter < 5th percentile and fetal heart rate outside the 5th to 95th percentile were significant in predicting abortion. CONCLUSION: Our data suggest that new three-dimensional parameters are of no clinical benefit in the prediction of abortion in nonbleeding, first-trimester pregnancy, when conventional sonographic parameters are used.     

A prospective analysis of the influence of gestational age on the baseline fetal heart rate and reactivity in a low-risk population

The nonstress test is of recognized value for the antepartum assessment of fetal well-being. Less well defined, however, is the relationship between baseline fetal heart rate, reactivity, and the gestational age of the fetus. A prospective analysis of the nonstress test in a preterm, low-risk population was begun. Weekly tests were begun as early as 23 weeks and continued to term. A test was considered reactive if there were two or more fetal heart rate accelerations within a 20-minute period. A total of 128 nonstress tests were performed on 25 low-risk patients. Of these tests, 84 (64%) were considered reactive. With advancing gestational age, a progressive increase in the incidence of reactive tests was observed. However, no significant difference in baseline fetal heart rate could be identified between term and preterm fetuses. In addition, the frequency and amount of accelerations and decelerations were determined. Decelerations were not noted more frequently in the preterm population. Conversely, accelerations occurred more frequently with advancing gestational age. The pregnancy outcome was excellent for all study patients. It is concluded, therefore, that with advancing gestational age more reactive nonstress tests are seen. Baseline fetal heart rate and the frequency of decelerations appear to be unaffected by advancing gestational age. Finally, although the numbers are small, the nonstress test appears to be a suitable technique for assessing fetal well-being in the preterm fetus.     

Computerised evaluation of fetal heart rate in post-term fetuses: long term variation

Computerised fetal heart rate records were obtained between 1987 and 1993 using the Sonicaid System 8000 for a cross-sectional study of postdates fetal heart rate variation; 567 singleton pregnancies at 41 and 43 weeks provided 1502 records. In all cases gestational age had been verified by ultrasound examination in early pregnancy. The mean minute range of the long term pulse interval variation, which is known to be correlated with fetal oxygenation was found to decrease progressively from an average value of 48.5 ms at 41 weeks to 46.4 ms and 42.4 ms at 42 and 43 or more weeks, respectively. When conservative management of postdate pregnancies is chosen, accurate measurements are needed to follow the evolution of fetal condition. Reference values for calculated pulse interval variation at later gestational ages are now provided.     

Relationship of baseline fetal heart rate to gestational age and fetal sex

A study of 37 patients who underwent 365 antepartum fetal heart rate tests showed a significant difference in heart rate between 19 to 24 weeks' and 36 to 40 weeks' gestation. Baseline heart rate remained within the normal range, suggesting that an abnormal heart rate at any gestational age should prompt further fetal assessment. Baseline fetal heart rate was not significantly different between male and female fetuses.     

Biometry of the fetal heart between 10 and 17 weeks of gestation

OBJECTIVES: Assessment of the dimensions of the cardiac chambers and the great arteries in the human fetus may be helpful in the prenatal diagnosis of congenital heart disease. The purpose of this prospective cross-sectional study was to compile normative data in fetal cardiac measurements in early pregnancy. The structure of the fetal heart was examined in 136 normal singleton fetuses between 10 and 17 weeks of gestation. METHODS: The transversal heart diameter, both ventricular dimensions, interventricular septal thickness, heart area, heart circumference, thoracic diameter, thoracic circumference and thoracic area were measured in the four-chamber view during diastole. Diameters of the pulmonary trunk and ascending aorta were obtained in the short axis and long axis view during systole. Ultrasound examinations were performed with a 5.0-MHz transvaginal and/or transabdominal phased-array sector scanner. RESULTS: The four-chamber view and the cross-over of the pulmonary artery and the aorta were adequately visualized in 44% of the fetuses at 10 weeks of gestation, in 75% at 11 weeks of gestation, in 93% at 12 weeks of gestation and in 100% of the fetuses at 13-17 weeks of gestation. Before 14 weeks of gestation transvaginal sonography was superior to the transabdominal sonography in visualization of the fetal heart and great arteries. After 14 weeks of gestation transabdominal sonography accurately demonstrated the structure of the fetal heart. The ratio of right and left ventricle (RV/LV) and the ratio of the pulmonary trunk and aorta (PT/AO) were constant during this period of gestation (approximately 1.00 and 1. 10, respectively). The ratio of the cardiac and thoracic area showed only a slight increase with advancing gestational age, but with significant correlation. The fetal heart rate showed a slow decrease from 167 to 150 bpm in this period of gestation. The transversal heart diameter, both ventricular dimensions, interventricular septal thickness, heart area, cardiothoracic diameter ratio, aortic diameter and the pulmonary trunk diameter showed a highly significant linear correlation to the gestational age and the biparietal diameter. CONCLUSION: The advancing quality of ultrasound images allows fetal echocardiography in the first and early second trimester. Our normative data could be the basis of studying the development of cardiac structures in congenital heart disease and it might be helpful in the detection of some congenital heart defects in early pregnancy.     

The relationship between fetal activity and behavioral states and fetal breathing movements in normal and growth-retarded fetuses

The incidence of fetal breathing was studied during the course of behavioral state observations on 28 low-risk fetuses between 32 and 40 weeks' gestational age and on 12 growth-retarded fetuses between 36 and 40 weeks. Real-time ultrasound scanners were used to detect fetal eye, body, and breathing movements, and the fetal heart rate was recorded continuously. The mean duration of the observation sessions was 110 minutes. The mean incidence of fetal breathing was greater during periods of fetal activity (body and eye movements present, greater heart rate variability) than during quiescence (body and eye movements absent, narrowed heart rate variability) at all gestational ages studied in both low-risk and growth-retarded fetuses. During periods when one of the state variables (body movements, eye movements, heart rate pattern) was in its active condition while the other two were quiet, or the reverse, the incidence of fetal breathing was intermediate between those found when all three state variables were in agreement. After behavioral states had developed, at 38 and 40 weeks, the mean incidence of fetal breathing in the low-risk fetuses was greater during active states than during the quiet state. There was no apparent increase in the degree of linkage between fetal breathing and other expressions of fetal activity after the emergence of behavioral states.     

Sonographic appearance of the fetal heel ossification centers and foot length measurements provide independent markers for gestational age estimation

The sonographic measurement of fetal foot length and the assessment of fetal heel ossification centers were conducted as an additional method for the estimation of gestational age. Such an approach is particularly desirable in cases where measurements of other biometric parameters are precluded, for example, in diseases such as anencephaly, hydrocephalus, and short limb dysplasia. A significant correlation was found between fetal foot length and gestational age (r = 0.9, p less than 0.0001) and between fetal foot length and femur length (r = 0.9, p less than 0.0001). Ossification centers of the calcaneus and talus were all present by the twenty-second week of gestation. However, their measurements discriminated between gestational ages of 18 to 22 weeks. The utilization of fetal foot length and heel ossification centers will serve as a useful adjunct in the estimation of gestational age and possibly in the diagnosis of diseases affecting the fetal foot.     

Physiologic baroreceptor activity in the fetal lamb.

OBJECTIVE: We investigated the influences of gestational age and behavioral state on fetal baroreceptor activity. STUDY DESIGN: Two protocols were used to analyze low-voltage fast activity and high-voltage slow activity in eight chronically instrumented ovine fetuses at days 127 to 142. In protocol 1 correction of fetal heart rate to mean arterial blood pressure was assessed under physiologic conditions, and the linear regression slope of fetal heart rate on mean arterial pressure was calculated. In protocol 2 an injection of 7.5 micrograms of norepinephrine was given during consecutive behavioral cycles. The ratio of fetal heart rate decrease to mean arterial pressure increase was determined as representing baroreceptor activity. RESULTS: Under protocol 1 the slope was steeper in high-voltage slow activity (2.33 +/- 1.03) than in low-voltage fast activity (0.89 +/- 0.37) (n = 21, p less than 0.001), indicating that fetal heart rate changes are sensitive to blood pressure changes during high-voltage slow activity. Under protocol 2 inverse relationships were found between the ratio of fetal heart rate decrease to mean arterial pressure increase and gestational age in low-voltage fast activity and high-voltage slow activity. CONCLUSION: Fetal baroreceptor activity increased during high-voltage slow activity and decreased with gestational age.     

Nomogram of the fetal gastric size development in normal pregnancy

OBJECTIVE: To construct an ultrasonographic nomogram of the fetal gastric size with gestational age in normal singleton pregnancy. PATIENTS AND METHODS: Out of 17 000 outpatient pregnant women who were admitted to our hospital, a total of 250 fetal measurements were randomly collected from routine ultrasonographic examinations performed in women with normal singleton pregnancies between 13 and 39 weeks of gestation without medical or obstetric complications. None of the fetuses had detectable fetal malformations. The ultrasound plane which provided the largest stomach area including the pylorus on a transverse and oblique section was used for definition and measurement of gastric longitudinal dimensions. The transverse section at the center of the gastric corpus was used for transverse and anteroposterior dimensions. Biparietal diameter, abdominal circumference were also measured. RESULTS: The fetal gastric longitudinal, anteroposterior and transverse dimensions were significantly correlated with gestational age (r values 0.74, 0.71, and 0.49, respectively). There was a significant correlation measurements between gastric size and AC. The correlation coefficents for gastric dimensions with gestational age was larger than those with AC (r=0.732, 0.702 and 0.489, respectively). The ratio of fetal gastric anteroposterior dimension to fetal AC was a constant parameter calculated as 1/3. CONCLUSION: Fetal stomach dimensions in normal pregnancy correlate with gestational age and nomogram of fetal gastric development appears to be useful in assessment of normal fetal growth.     

Ultrasound biometry of the fetal heart]

We report on biometric measurements of the fetal heart with the TM-technique; these measurements were carried out between the 20th and 40th gestational week. The right and left endsystolic atrial and ventricular diameters were, measured, as well as the diameters of the large vessels, i.e. aorta and pulmonary artery; finally, the septal thickness was determined. Our measurements show a linear progression of the diameters in question, the right-left ratio of the atria and ventricles was close to one, so was the ratio between aorta and pulmonary artery. Our results are compared, as far as possible, to the literature.     

The three-vessel and tracheal view of the fetal heart: an in utero sonographic evaluation

OBJECTIVES: To establish a nomogram for fetal cardiac three-vessel view diameter changes during gestation. METHODS: The study is a prospective cross-sectional evaluation of 338 male and female fetuses between 14 and 38 weeks of normal singleton pregnancies. Measurements of fetal pulmonary artery, aorta and superior vena cava diameters, performed on a transverse view of the upper mediastinum were conducted using transvaginal ultrasonography between 14 to 18 weeks and transabdominal after 19 weeks' gestation. RESULTS: Adequate measurements of the three cardiac vessels were obtained in 338 fetuses. The regression equations for vessel diameters modeled as function of gestational age were pulmonary artery diameter (mm) = -2.275 + 0.273 x gestational age (week), aorta diameter (mm) = -1.77 + 0.227 x gestational age (week), and SVC diameter (mm) = -0.98 + 0.142 x gestational age (week). The correlation coefficients between gestational age and the diameter of the vessels were, r = 0.93, r = 0.93 and r = 0.86 for pulmonary artery, aorta and SVC respectively (all found to be highly statistically significant, p < 0.0001). The normal mean and 90% prediction limits were defined. CONCLUSION: Our data present the normal range of fetal heart three-vessel diameters during gestation. They may allow intrauterine assessment of their development and an adjunct in the detection and evaluation of great vessel pathology.     

Nuchal translucency and fetal cardiac defects: a pooled analysis of major fetal echocardiography centers

OBJECTIVE: Increased fetal nuchal translucency is associated with increased risk for congenital heart defects. In the present study, we aimed to investigate whether fetal nuchal translucency distribution differs among different types of congenital heart defects and whether it can lead to an earlier diagnosis. STUDY DESIGN: Four fetal echocardiography units provided data on fetuses with a congenital heart defect diagnosis in whom nuchal translucency thickness had been measured in the first trimester. Nuchal translucency data were compared per chromosomal status and type of congenital heart defect. Data on gestational age at diagnosis were also analyzed. RESULTS: Six hundred thirty-seven cases of congenital heart defect with known karyotype and exact nuchal translucency measurements were analyzed. Nuchal translucency was > or =3.5 mm in 22.9% of chromosomally normal fetuses (n = 397) and 58.8% of chromosomally abnormal cases (n = 240). Among fetuses with normal karyotype, the proportion of cases of congenital heart defect with increased nuchal translucency was similar in each of the subtypes of congenital heart defect (P = .96). Mean gestational age at diagnosis of congenital heart defect in fetuses with normal karyotype was 22.1 weeks with nuchal translucency of <3.5 mm and 16.1 weeks with nuchal translucency of > or =3.5 mm. CONCLUSION: Finding nuchal translucency of > or =3.5 mm may lead to an earlier diagnosis of all major types of congenital heart defects.