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.     

Effect of gestational age on baseline fetal heart rate during the third trimester of pregnancy

Analysis of the fetal heart rate in 3,127 reactive nonstress tests revealed that the baseline rate decreased significantly between 28 and 41 weeks' gestation (6.4 beats per minute [4.5%]). Analysis of 235 women with two tests at least four weeks apart revealed that while the majority (51.1%) demonstrated a decrease, 26.8% experienced a rise in the baseline rate during the testing interval.     

Computerized analysis of fetal heart rate parameters by gestational age.

OBJECTIVE: The aim of this study is to define the reference ranges for fetal heart rate (FHR) parameters according to gestational age, by determining the relationship between the FHR and gestational age using a computerized FHR analysis system. METHODS: Using our own software developed by Hanyang University Hospital in Korea, non-stress tests were performed for 20 min. FHR parameters for 6455 subjects were analyzed for various gestational groups; <25 weeks, 25-28 weeks, 29-32 weeks, 33-36 weeks, 37-40 weeks, and >40 weeks. RESULTS: The FHR parameters were related to gestational age. The mean baseline FHR, signal loss, and fetal movements decreased significantly with gestation (P<0.0001). The variability and accelerations of FHR were highest for the 37-40 weeks gestational group (P<0.05). CONCLUSIONS: The results showed that overall, the differences in the FHR parameters between gestational groups were statistically significant, and the gestational age of the fetus should be considered when interpreting FHR patterns.     

Influence of gestational age and fetal heart rate on the fetal mechanical PR interval

Objective: The fetal mechanical PR interval obtained via pulsed Doppler has previously been demonstrated to correlate with electrocardiographic PR interval measured in the neonate. We sought to further analyze the influence of fetal heart rate and gestational age upon the fetal mechanical PR interval.

Methods: We searched our database for mechanical PR intervals, which were obtained during fetal echocardiography performed in our antenatal diagnostic unit. We included fetuses with a normal cardiac structural survey. The mechanical PR interval is measured from the A wave of the mitral valve to the beginning of ventricular systole corresponding to the opening of the aortic valve. Linear regression curves were generated to examine the correlation of mechanical PR interval with gestational age and fetal heart rate. Analysis of variance was used to compare the mean variation across three gestational age groups: 17–21.9 weeks (n?=?24), 22–25.9 weeks (n?=?52) and 26–38 weeks (n?=?20).

Results: Mechanical PR intervals were measured in 96 fetuses with normal fetal echocardiography. The mechanical PR interval was 123.9?±?10.3?ms (mean?±?SD), with a range of 90–150?ms. Linear regression curves correlating mechanical PR interval with fetal heart rate and gestational age demonstrated a flat slope with R²?=?0.016, p?=?0.22 and R²?=?0.0004, p?=?0.85, respectively. The mechanical PR interval measured over the three gestational ages was as follows (mean?±?SD): 122.3?±?10.5?ms for 17–21.9 weeks; 125.0?±?9.6?ms for 22–25.9 weeks; and 123.1?±?11.9?ms for 26–38 weeks. Analysis of variance revealed no difference among the mechanical PR interval means measured over the three gestational age groups (p?=?0.53).

Conclusions: Fetal mechanical PR interval ranges from 90 to 150?ms in fetuses with sonographically normal fetal cardiac structure and rate. The mechanical PR interval appears to be independent of gestational age and fetal heart rate.     

Influence of gestational age and fetal heart rate on the fetal mechanical PR interval.

OBJECTIVE: The fetal mechanical PR interval obtained via pulsed Doppler has previously been demonstrated to correlate with electrocardiographic PR interval measured in the neonate. We sought to further analyze the influence of fetal heart rate and gestational age upon the fetal mechanical PR interval. METHODS: We searched our database for mechanical PR intervals, which were obtained during fetal echocardiography performed in our antenatal diagnostic unit. We included fetuses with a normal cardiac structural survey. The mechanical PR interval is measured from the A wave of the mitral valve to the beginning of ventricular systole corresponding to the opening of the aortic valve. Linear regression curves were generated to examine the correlation of mechanical PR interval with gestational age and fetal heart rate. Analysis of variance was used to compare the mean variation across three gestational age groups: 17-21.9 weeks (n = 24), 22-25.9 weeks (n = 52) and 26-38 weeks (n = 20). RESULTS: Mechanical PR intervals were measured in 96 fetuses with normal fetal echocardiography. The mechanical PR interval was 123.9 +/- 10.3 ms (mean +/- SD), with a range of 90-150 ms. Linear regression curves correlating mechanical PR interval with fetal heart rate and gestational age demonstrated a flat slope with R2 = 0.016, p = 0.22 and R2 = 0.0004, p = 0.85, respectively. The mechanical PR interval measured over the three gestational ages was as follows (mean +/- SD): 122.3 +/- 10.5 ms for 17-21.9 weeks; 125.0 +/- 9.6 ms for 22-25.9 weeks; and 123.1 +/- 11.9 ms for 26-38 weeks. Analysis of variance revealed no difference among the mechanical PR interval means measured over the three gestational age groups (p = 0.53). CONCLUSIONS: Fetal mechanical PR interval ranges from 90 to 150 ms in fetuses with sonographically normal fetal cardiac structure and rate. The mechanical PR interval appears to be independent of gestational age and fetal heart rate.     

Comparison of the accuracy of gestational age estimation from fetal heart rate and crown-rump length

Objective: To compare the accuracy of gestational age (GA) estimation predicted by fetal heart rate (FHR) versus crown-rump length (CRL) measurements in early pregnancies.Methods: A total of 145 infertile women with singleton intrauterine pregnancies conceived through in vitro fertilization underwent vaginal ultrasonographic examination in early stage of pregnancy. We performed 197 FHR and 398 CRL measurements. The relationship between GA (counted with the day of oocyte retrieval used as day 14) and the FHR or CRL was explored with regression analysis by means of least squares. Polynomials up to the third order were analyzed, and the coefficient of determination (R²) was calculated.Results: Fetal cardiac activity could be detected as early as 38 days, gradually increased to 188 beats per minute at 62 days of gestation. Regression analysis with GA as dependent variable resulted in R² values of 0.906, 0.907, and 0.908 for the first, second, and third order polynomials, respectively. The standard deviations around the regression line were 2.90, 2.81, and 2.84 days, respectively. The second order polynomial to describe GA (days) estimated by FHR (beats per min): GA = 3.02E-41FHR² + 1.60E-11FHR + 2.22E+1. On the other hand, the CRL was measured at 38 days to 62 days of gestation. Regression analysis resulted in R² values of 0.827, 0.839, and 0.841, respectively. The deviations were 4.11, 3.83, and 3.89 days, respectively. The second order polynomial to describe GA estimated by CRL (mm): GA = −2.10E-21CRL² + 1.49E+01CRL + 3.86E+1. There was no difference between the R² values and no difference between the standard deviations around the regression lines.Conclusion: Our results indicate no statistically significant difference in the accuracy of GA estimation predicted by FHR versus CRL measurements. But better mathematical fits were obtained when the data of FHR were used for GA estimation. These findings suggest that the FHR measurement may be a new method for early ultrasound dating. This study mentions for the first time the possibility of “FHR dating” with functional data.     

Antepartum nonstress fetal heart rate monitoring: systematic analysis of baseline patterns and decelerations as an adjunct to reactivity in the prediction of fetal risks

A total of 1552 antepartum nonstress tests performed during the week before delivery are analyzed with respect to both reactivity and the presence of pathologic baseline patterns (tachycardia, bradycardia, diminished beat-to-beat variability) or decelerations. Correlation with mode of delivery and condition of the newborn infant shows that, irrespective of nonstress test reactivity, the presence of baseline anomalies and/or decelerations is associated with significantly increased perinatal morbidity and mortality. Nonstress test analysis, if systematic, that is, not restricted to reactivity alone, makes it possible to better detect fetuses at high perinatal risk, in which case closer surveillance would be indicated.     

小于胎龄早产儿产时胎心电子监护图形特征及其临床意义

目的探讨小于胎龄早产儿胎心电子监护图形(CTG)特征及其临床意义。方法回顾性分析303例32~36孕周、无妊娠合并症的单纯胎膜早破和原因不明早产孕妇的全产程CTG。其中,小于胎龄早产儿78例(PSGA组),适于胎龄早产儿225例(PAGA组)。比较宫缩时两组CTG特征,合并症情况及分娩结局。结果PSGA组及PAGA组出现单纯U型变异减速的胎儿分别为24例(308%)和10例(44%),两组比较,差异有统计学意义(P<001);U型变异减速合并其他异常CTG的胎儿分别为10例(128%)和1例(04%),两组比较,差异也有统计学意义(P<001)。PSGA组,出现单纯U型变异减速者的难产率(208%)与胎心电子监护无异常者的难产率(227%)比较,差异无统计学意义(P>005),但与U型变异减速合并其他异常CTG者的难产率(600%)比较,差异有统计学意义(P<005)。PSGA组中,34例出现U形变异减速,其中合并脐带异常15例(绕颈、绕身14例、脐带过短1例),PSGA组44例无U形变异减速者中,合并脐带异常9例(绕颈、绕身),两组比较,差异有统计学意义(P<005)。结论U形变异减速是小于胎龄早产儿分娩过程中的特征性胎儿监护图形,但不是胎儿缺氧的征象,如不合并其他异常CTG,不需特殊处理。     

The effect of scopolamine on fetal heart rate baseline variability

The effect on FHR baseline variability of intravenous scopolamine (0.43 mg.) administered alone and in combination with Demerol (50 mg.) and Largon (20 mg.) was evaluated. A decrease in baseline variability was found in nine of 19 patients given scopolamine (0.43 mg.). When scopolamine, Demerol, and Largon were infused simultaneously, a change in baseline variability was observed in nine of 12 patients. No change in variable or early deceleration FHR patterns was observed.     

Significance of echogenic foci in the left ventricle of the fetal heart in a low-risk population

OBJECTIVE: To determine if there exists a significant association between prenatally detected left ventricular echogenic foci and chromosomal abnormalities. METHODS: Over a 10-month period the presence of intracardiac echogenic foci was recorded on all low-risk patients referred for anatomical assessment. The study group consisted of 113 singleton fetuses and was compared to a control group with no foci. RESULTS: Among the study group with echogenic foci, 5 chromosomal abnormalities (three trisomies) were detected. In the control group only one chromosomal abnormality was diagnosed. CONCLUSION: An association exists between the finding of intracardiac echogenic foci in the fetus and the presence of chromosomal abnormalities.     

The effect of maternal hypocalcemia on fetal heart rate baseline variability

Marked decrease in fetal heart rate variability during labor was observed in a term fetus, borne by a mother with severe hypocalcemia due to idiopathic hypoparathyroidism and nutritional vitamin D deficiency. During the period of decreased baseline variability, fetal scalp pH was normal. A marked increase in fetal heart rate variability was observed within 5 minutes of intravenous administration of 1 gram calcium gluconate to the parturient. It seems that the recognition of the effect of maternal hypocalcemia on baseline fetal heart rate variability is important for accurate interpretation of fetal monitor tracing.     

Umbilical artery blood acid-base analysis and fetal heart rate baseline in the second stage of labor.

OBJECTIVE: To evaluate the correlation between umbilical arterial acidemia and second-stage baseline fetal heart rate (FHR) abnormalities in Japanese newborn infants. METHODS: Subjects were 365 newborns, born at term. Specimens were obtained from the umbilical artery as soon as possible after delivery and blood gas determinations were performed within 5 minutes of delivery. FHR monitoring was performed in the second stage. RESULTS: Umbilical arterial acidemia occurred in 54.1% of the newborns with moderate to severe bradycardia, in 27.3% with mild bradycardia, and in 19.3% with tachycardia, compared with only 1.3% of those with a normal FHR (p < 0.001). The mean umbilical arterial base excess was significantly greater in newborns with metabolic acidemia (-13.9+/-2.9 mmol/l) than in those with either mixed (-11.5+/-2.8 mmol/l) (p < 0.02) or respiratory (-9.1+/-3.2 mmol/l) (p < 0.01) acidemia. CONCLUSION: The second-stage baseline FHR abnormalities were highly correlated with an increased risk of umbilical arterial acidemia at delivery.     

The distribution of accelerations of the human fetal heart rate at 38 to 40 weeks' gestational age

In order to further understand the use of antepartum fetal heart rate monitoring we measured the distribution, in time, of two, three, or five fetal heart rate accelerations of greater than or equal to 15 bpm for greater than or equal to 15 seconds and of greater than or equal to 10 bpm for greater than or equal to 6 seconds in 12 healthy pregnant women at 38 to 40 weeks' gestation. The length of time necessary to measure 50% or 95% of intervals containing five accelerations would be substantially reduced by changing to a definition of two or three accelerations. However, an observation interval of at least 80 minutes is required to include the longest time interval of two, three, or five accelerations. These data may suggest new strategies for decreasing time and expense of fetal heart rate testing.     

Oscillation-frequency and baseline fetal heart rate in the last 30 minutes of labour.

The last 120 minutes of 394 intrapartum fetal heart rate (FHR) records of high technical quality were evaluated. Baseline FHR was estimated and oscillation frequency (OF) counted for each minute. There was a highly significant association between the baseline FHR and the number of oscillations/minute; an increase in baseline FHR of 10 beats/minute was associated with a fall of about one oscillation/minute. The highest mean OF (9.6 +/- 4.8 events/minute) was found in fetuses with an umbilical artery pH of between 7.20 and 7.25. The baseline FHR should be taken into account when assessing fetal condition.     

Ultrasonographic evaluation of fetal nasal bone in a low-risk population at 11-13 + 6 gestational weeks

OBJECTIVE: To evaluate the utility of determining the presence/absence of nasal bone in a low-risk fetal population. METHODS: Prospective study of the presence/absence of nasal bone among 1800 consecutive unselected fetuses, with complete follow-up of results. RESULTS: An adequate sonographic evaluation of nasal bone was obtained in 1682 (93.44%) of the fetuses. Nasal bone was considered absent in 19 (1.06%) of 1790 fetuses with a normal karyotype and in 2 (28.57%) of the seven recorded cases of Down syndrome (DS). The overall first-trimester sensitivity for DS to the absence of nasal bone was two of the six cases (33.3%) and the false-positive rate was 1.13%. The positive predictive value for DS of the absence of nasal bone was 2/21 (9.52%). CONCLUSIONS: In a low-risk population, the evaluation of the presence/absence of nasal bone in DS screening during the first trimester has a low sensitivity. First-trimester assessment of the nasal bone in population screening may play a lesser role than in the re-evaluation of high-risk pregnancies.     

Autonomic nervous system regulation of baseline heart rate in the fetal lamb.

OBJECTIVE: We examined 29 chronically instrumented fetal lambs from 125 to 143 days' gestation to investigate the effects of fetal behavioral states and autonomic nervous system maturation on baseline fetal heart rate. STUDY DESIGN: Behavioral states were defined from electrocorticographic analysis as low-voltage fast activity or high-voltage slow activity. Decrease and increase in baseline fetal heart rate subsequent to administration of propranolol and methylatropine represented beta-sympathetic and parasympathetic activity. RESULTS: Baseline fetal heart rate decreased with gestation in both states, with steeper regression in low-voltage fast activity (p less than 0.001). Positive correlation was noted between gestational age and percent decrease baseline fetal heart rate in both states with steeper regression in high-voltage slow activity (p less than 0.001), and between gestational age and percent increase baseline fetal heart rate with steeper regression in low-voltage fast activity (p less than 0.001). Fetal heart rate beta-sympathetic and parasympathetic tones increased with age in both states, with elevation of beta-sympathetic tone in high-voltage slow activity and parasympathetic tone in low-voltage fast activity. CONCLUSION: Sympathetic and parasympathetic systems influence baseline fetal heart rate in these behavioral states and with age.