Fetal Heart Rate Accelerations Research Articles

Fetal responses to maternal strength conditioning exercises in late gestation.

Cardiovascular responses to strength conditioning exercises were examined in 12 healthy pregnant women and their unborn fetuses during the third trimester. A group of 12 healthy nonpregnant women of similar ages, parity, body height, and pre-pregnant body mass was also studied. Maternal heart rate and blood pressure and fetal heart rate (FHR) responses were measured in both the supine (30 degrees tilt) and seated postures during handgrip (HG), single-leg extension (SL), and double-leg extension (DL) exercise. Subjects performed 3 sets of 10 reps at 50, 70, and 90% of their 10-repetition maximum (10-RM) for each exercise in both postures. Pregnant subjects exhibited higher heart rates but similar blood pressure responses to control subjects under all experimental conditions. Significant increases were observed for the frequency of FHR accelerations (0.10 to 0.27/min) from rest to DL in the sitting posture at 90% RM. Moderate fetal bradycardia was observed occasionally in the tilted supine posture at rest and both during (SL, DL) and following (HG, SL, DL) exercise, suggesting that this posture should be avoided in late gestation. The results support the safety of moderate strength conditioning exercises in healthy pregnancy.

Fetal behavior in diabetic and nondiabetic pregnant women: An exploratory study

To characterize differential behavior and the relationship between maternal blood glucose levels and behavior in fetuses of diabetic (n = 10) and nondiabetic (n = 20) women at 33 and 36 weeks gestational age (GA), spontaneous changes in fetal heart rate (FHR), body and breathing movements, and vibroacoustic stimulus elicited (3 stimulus/3 no-stimulus control trials) FHR changes and body movements were compared. Measures of maternal blood glucose levels were obtained immediately following testing; measures varied within normal range. Spontaneous behaviors showed no differences between groups and no relationship to maternal blood glucose levels. Sensory stimulation elicited similar average peak FHR accelerations (M = 17.1/20.0 BPM) and average movement scores (2.0/2.6) across groups. In the diabetic group at 33 weeks GA, the nature of the FHR change over time, showed more varied patterns of response, a shorter latency to peak acceleration, was less organized, and less mature; as average maternal blood glucose levels increased, elicited body movements decreased. These findings suggest immaturity and differential functional development of sensory–motor response systems in fetuses of diabetic mothers. © 1999 John Wiley & Sons, Inc. Dev Psychobiol 35: 69–80, 1999

Fetal behavior in diabetic and nondiabetic pregnant women: An exploratory study

To characterize differential behavior and the relationship between maternal blood glucose levels and behavior in fetuses of diabetic (n = 10) and nondiabetic (n = 20) women at 33 and 36 weeks gestational age (GA), spontaneous changes in fetal heart rate (FHR), body and breathing movements, and vibroacoustic stimulus elicited (3 stimulus/3 no-stimulus control trials) FHR changes and body movements were compared. Measures of maternal blood glucose levels were obtained immediately following testing; measures varied within normal range. Spontaneous behaviors showed no differences between groups and no relationship to maternal blood glucose levels. Sensory stimulation elicited similar average peak FHR accelerations (M = 17. 1/20.0 BPM) and average movement scores (2.0/2.6) across groups. In the diabetic group at 33 weeks GA, the nature of the FHR change over time, showed more varied patterns of response, a shorter latency to peak acceleration, was less organized, and less mature; as average maternal blood glucose levels increased, elicited body movements decreased. These findings suggest immaturity and differential functional development of sensory-motor response systems in fetuses of diabetic mothers.

Differential maturation of fetal responses to vibroacoustic stimulation in a high risk population

Maturation of human fetal response to vibroacoustic stimulation was examined in 163 high risk fetuses from 23 to 36 weeks gestational age (GA). Each fetus received three vibroacoustic trials and three no‐stimulus control trials (randomly assigned) while fetal heart rate (FHR) was recorded and body movement was observed on ultrasound scan. For data analyses, fetuses were categorized into preterm compromised (n = 57), preterm healthy (n = 42) and term healthy (n = 64) based on evidence of compromise at birth. Differential maturation was observed among the outcome groups. The term healthy group exhibited a body movement and, on the first stimulus trial, an FHR deceleration response at 27 weeks GA with a shift to an FHR acceleration response at 30 weeks GA. By 33 weeks GA, responding was indistinguishable from that reported for low risk fetuses with response rates of 92% for both movements and FHR accelerations. The preterm healthy outcome group showed a body movement and an FHR acceleration response at 27 weeks GA. Over gestation, there was no maturation of either response. The preterm compromised outcome group showed a body movement response at 24 weeks GA which did not mature. An FHR acceleration response was elicited at 27 weeks GA with the magnitude of the acceleration increasing over gestation; at 33 weeks GA the magnitude was below that observed in the term healthy group. With advancing gestation, the rate of cardiac–movement coupling increased only in the two healthy outcome groups. It was concluded that differential fetal behaviour as a function of fetal/newborn outcome may reflect differential functional development of the fetal nervous system.

Analysis of Umbilical Artery Flow Parameters during Fetal Variable Decelerations Using Computerized Doppler Waveforms

Umbilical artery velocity waves were obtained by Doppler ultrasonography before, during, and after 20 episodes of fetal heart rate (FHR) variable decelerations (VD) during the active stage of labor in 8 women. During 50% of the VD periods, the umbilical artery resistance flow parameters increased significantly (p < 0.01). The increase in resistance preceded the decrease in FHR in six episodes (30%) of VD (AR-VD group; arterial resistance VD) and did not precede the change in FHR in another ten episodes (50%) of VD (VR-VD group; venous resistance VD). In the AR-VD group the FHR accelerations occurred before the decelerations in only 1 case (17%), while in the VR-VD group FHR accelerations preceded the decelerations in 8 out of the 10 episodes (80%). Using these Doppler studies, it may be possible to differentiate between two groups of VD: AR-VD – which are caused by umbilical artery occlusion and thus preceded by a measurable increase in umbilical artery resistance – and VR-VD – which are not preceded by a measurable increase in umbilical artery resistance and may be caused by fetal hypoxia.

The effect of maternal position on fetal heart rate during epidural or intrathecal labor analgesia

OBJECTIVE: This study was designed to determine the relationship between maternal position and the incidence of prolonged decelerations after epidural bupivacaine or intrathecal sufentanil analgesia for labor. STUDY DESIGN: Laboring, healthy, term parturient women, with reassuring fetal heart rate tracings, requesting either epidural ( n = 145) or intrathecal ( n = 160) analgesia were randomly assigned to lie either supine with measured 30-degree left uterine displacement ( n = 136) or in the left lateral decubitus position ( n = 145). Patients received either intrathecal sufentanil, 10 μg, or epidural 0.25% bupivacaine, 13 mL. An obstetrician, unaware of patient position or type of anesthesia, examined the fetal heart rate tracings. RESULTS: No demographic differences were noted among the groups. Prolonged decelerations occurred with equal frequency after epidural bupivacaine and intrathecal sufentanil (3.9%). Prolonged decelerations were not related to maternal position. No emergency cesarean deliveries were performed as a result of prolonged decelerations. Prolonged decelerations correlated with the frequency of contractions before induction of analgesia ( P < .05). Fewer fetal heart rate accelerations were noted after intrathecal sufentanil than after epidural bupivacaine ( P < .005). More ephedrine was used after epidural bupivacaine ( P < .001). Patients who received epidural analgesia in the left lateral position were more likely to have an asymmetric block ( P < .05). CONCLUSIONS: The risk of prolonged deceleration after epidural bupivacaine or intrathecal sufentanil labor analgesia is unrelated to maternal position or analgesic technique. (Am J Obstet Gynecol 1998;179:150-5.)

The fetal admission test and intrapartum fetal death.

Our objective was to describe the admission and subsequent intrapartum fetal heart rate (FHR) patterns in 21 singleton term pregnancies with an intrapartum fetal death. Through a retrospective chart review, 21 pregnancies with a term intrapartum fetal death were divided into 2 groups based on the fetal admission test (FAT): Group I-reactive (one or more FHR accelerations of 15 bpm x 15 sec in the first 30 min of monitoring); and Group II-nonreactive (NR [the absence of accelerations]). The FAT was compared with the subsequent intrapartum FHR pattern. Of the 21 deaths, the FAT was reactive in 7 fetuses (33%) or NR in 14 fetuses (67%). While the demographic features of these groups were statistically similar, Group II had higher rates of meconium (12 out of 14 (86%) vs. 2 out of 7 [29%] p = 0.017) and admission FHR decelerations (9 out of 14 (64%) vs. 1 out of 7 [14%] p = 0.06). In Group I, a sudden catastrophic event such as a uterine rupture produced a prolonged FHR deceleration in six fetuses (86%). One (14%) fetus died after a Hon pattern. In Group II, four patients had a stair steps to death pattern. Intrapartum fetal death can occur after a reactive or NR FAT. With a reactive FAT, a catastrophic event appears necessary to cause fetal death. The higher rates of meconium, FHR decelerations, and stair steps to death patterns in the NR group suggest the underlying basis for the fetal demise was related to preadmission fetal compromise.

Fetuses differentiate vibroacoustic stimuli

In three studies, human fetal sensory sensitivity was examined using three different vibroacoustic transducers including an artificial larynx (AL), a plastic-(M1) and a rubber-headed (M2) body massager. Forty-four term fetuses received blocks of stimulus/control trials intermixed and randomly presented. AL and M1 provoked generalized activation and elicited fetal heart rate accelerations (averaging 26 and 22 BPM, respectively) on the first stimulus trial. The magnitude of the FHR response elicited by AL was sustained over three trials while that to M1 declined. Contrary to expectations, M2 failed to elicit heart rate accelerations and body movements. However, lowering the power of M2 resulted in a small decrease in both heart rate and movement. Thus, vibroacoustic transducers may elicit either generalized activition or quieting in the term fetus. The direction of the response appears to depend upon subtle differences in stimulus intensity and spectral characteristics.

Role of antepartum computerized fetal heart rate analysis in the prediction of fetal distress during labor

Objective: To ascertain the diagnostic ability of a computerized fetal heart rate (FHR) analysis system in the identification of patients at risk of fetal distress in labor. Study design: Five-hundred and seventy-seven healthy term pregnancies were enrolled in a prospective, cross-sectional study and subdivided into two groups, with ( n = 90) or without ( n = 487) fetal distress in labor. Computerized FHR recordings were performed periodically and regression analysis was performed in a univariate and multivariate way to assess the ability of the last FHR recording in the prediction of subsequent fetal distress. Results: The two groups showed a significant difference in almost all of the FHR parameters studied. The multivariate analysis showed that only the FHR baseline and the percentage of small accelerations were independently and significantly related to the labor outcome. The combination of these two parameters reaches a sensitivity of 45%, specificity of 91%, positive predictive value of 48% and negative predictive value of 90%, with an overall accuracy of 84%. Conclusions: The increase in FHR baseline and in small FHR accelerations can be major factors in the prediction of subsequent fetal distress in healthy term fetuses.

Fetal heart rate patterns in growth-restricted fetal sheep induced by chronic fetal placental embolization

OBJECTIVE: Our purpose was to test the hypothesis that chronic placental insufficiency and intrauterine growth restriction in fetal sheep causes a decrease in the number of fetal heart rate accelerations and fetal heart rate variability. STUDY DESIGN: Chronically catheterized fetal sheep were embolized ( n = 6) daily with 15 to 50 μm latex microspheres for 21 days between 0.74 and 0.88 of gestation into the abdominal aorta, until fetal arterial oxygen content was decreased by 40% to 50% of the preembolization value. Control animals ( n = 6) received saline solution only. Signals from chest electrodes were analyzed on-line with the Sonicaid System 8000 in 2-hour epochs every 6 hours starting at 8 am over the first 48 hours of hypoxemia and for 2 hours between 8 and 10 am every other day from day 3 to day 21 of hypoxemia. Umbilical artery Doppler-derived resistance index and fetal plasma catecholamine concentrations were also measured. RESULTS: Embolized fetuses had asymmetric intrauterine growth restriction and became chronically hypoxemic ( p < 0.001) with a progressive increase in the umbilical artery resistance index ( p < 0.001). During the first 48 hours of hypoxemia the number of accelerations and decelerations and both short- and long-term fetal heart rate variability increased initially, followed by a return to control levels by 20 hours after the onset of embolization. After 21 days of hypoxemia the number of accelerations was significantly reduced by 30% compared with controls ( p < 0.05). Both short- and long-term fetal heart rate variability in control fetuses gradually increased with advancing gestational age ( p < 0.001 and p < 0.01, respectively), whereas in embolized fetuses the fetal heart rate variability remained unchanged and was 20% lower than that of controls on day 21 (both p < 0.01). CONCLUSION: Intrauterine growth restriction and long-term hypoxemia in fetal sheep are associated with a decrease in short- and long-term fetal heart rate variability, possibly because of a delay in the normal maturational changes of the autonomic control of fetal heart rate. (Am J Obstet Gynecol 1997;176:282-90.)

The intrapartum CTG prior to neonatal encephalopathy at term: a case-control study.

To compare cardiotocograph (CTG) records during labour in cases of neonatal encephalopathy and matched controls. Case-control study. Metropolitan area of Perth, Western Australia. Term deliveries complicated by neonatal encephalopathy and controls matched for sex, hospital, time of birth, day of week of birth and maternal health insurance. Low fetal heart rate (FHR) variability, FHR accelerations, late decelerations, total Kreb's score and FIGO classification of CTG records. The neonatal encephalopathy group had significantly more abnormal CTG records (89%) classified according to FIGO, although 52% of control CTG records were also abnormal. CTG records from cases developed significant differences in terms of absence of FHR accelerations and low FHR variability, but not late decelerations, prior to delivery. Given the low incidence of neonatal encephalopathy in this study (7 per 1000) the predictive value of an abnormal CTG record is clinically unhelpful. However, the changes in the FHR in such cases suggest a greater disturbance of fetal (rest-activity) behaviour during labour.

Fetal heart rate patterns in pregnancies complicated by maternal diabetes

Objective: To compare the fetal heart rate (FHR) pattern between fetuses of well controlled diabetic and non diabetic mothers using a computerized analysis of FHR. Study design: Weekly fetal surveillance was performed in 99 fetuses of mothers with diabetes class A, 21 fetuses of mothers with diabetes class B-R, and 55 fetuses of non-diabetic women, starting at 30 weeks' gestation. All diabetic patients were well controlled. Fetal surveillance included a computerized analysis of the FHR, umbilical and uterine Doppler velocimetry, and a biophysical profile. Changes of FHR variation, frequency of FHR accelerations, and umbilical and uterine Doppler velocimetry were calculated using a regression analysis for each patient. The average slopes and the intercept at 30, 34, and 38 weeks' gestation of these variables were compared among the three groups. Results: The slope of FHR variation and the frequency of accelerations had a lower rate of increase during the third trimester in fetuses of mothers with diabetes class A (0.84 ± 0.25 ms/week and 0.06 ± 0.02/20 min/week, respectively) compared with fetuses of non-diabetic mothers (1.34 ± 0.55 ms/week and 0.5 ± 0.1/20 min/week, respectively). In fetuses of mothers with diabetes class B-R, FHR variation did not change with gestation (−0.011 ± 0.2 ms/week) with a small increase in the frequency of accelerations (0.02 ± 0.004/20 min/week. While no differences were observed at 30 weeks' gestation, FHR variation and the frequency of accelerations were significantly reduced at 34 weeks' gestation in fetuses of mothers with diabetes class B-R compared with fetuses of non-diabetic mothers ( P < 0.01). At 38 weeks' gestation, fetuses of mothers with diabetes class B-R and diabetes class A had both significantly reduced FHR variation as well as frequency of accelerations compared with fetuses of non-diabetic mothers ( P < 0.01). The rate of decrease of the umbilical and uterine artery S/D ratios were similar among the three groups. Conclusions: The FHR pattern appears to be different in fetuses of well controlled diabetic mothers when related to fetuses of non-diabetic mothers. Disease specific standards should be considered for interpretation of FHR patterns in diabetic pregnancies.

Assessment of fetal health should be based on maternal perception of clusters rather than episodes of fetal movements.

To determine the level of correlation between mother and machine detected episodes and clusters of fetal movements and their association with fetal heart rate acceleration. An observational study conducted on health pregnant women between 29-40 weeks gestation who were admitted in spurious labour to the Department of Obstetrics and Gynaecology, National University Hospital, Republic of Singapore. A continuous record of fetal heart rate and fetal movement was obtained using the fetal actocardiograph. Fetal movements felt by mother were also noted. If a continuous series of fetal movements were perceived over a period of 15 secs or more it was termed clusters of fetal movement. The presence or absence of acceleration in relation to these movements were noted. There was a highly significant correlation between mother and machine in detection of clusters of fetal movements (r = 0.77, p < 0.001); for episodes of fetal movements, the correlation was weaker (r = 0.23, p < 0.05). All clusters of fetal movements perceived by the mother were recorded by the machine and were associated with fetal heart rate accelerations. Two or more accelerations within 3 minutes of the fetal movements were seen with 87.8% of clusters felt by mother compared with 66.7% detected by the machine (p = 0.01). In the 2,263 minutes of recording in 42 women, a cluster of fetal movements was felt at least every 25 minutes by the mother. Maternal perception of 1 or 2 clusters of fetal movements in 30 to 60 minutes may be as reliable as a non-stress test in reassuring good health. It would be less time consuming than the traditional count to 10 fetal movement chart and a more reliable indicator of fetal health than counting episodes of fetal movements. Thus, our study suggests that clusters rather than episodes of fetal movements should be considered for evaluating fetal health based on fetal movements.

The efficacy of individual computer heart rate indices in detecting acidemia at birth in growth-restricted fetuses

To determine the efficacy of individual fetal heart rate (FHR) indices, as determined by computer analysis of the FHR tracing, in detecting fetal acidemia at birth in growth-restricted fetuses. The study population consisted of 38 growth-restricted fetuses at 26-37 weeks' gestation from pregnancies with abnormal uterine and/or umbilical artery Doppler velocimetry. The 1-hour FHR tracing was analyzed by computer within 4 hours of cesarean birth before the onset of labor. Umbilical artery cord blood was collected at birth, and pH was determined within 5 minutes of collection. On linear regression, the duration of episodes of low variation in minutes (r = -0.77, r2 = 0.59) and short-term (r = 0.72, r2 = 0.52) and long-term (r = 0.69, r2 = 0.47) variation in milliseconds were significantly related to umbilical artery pH at birth, and more so than the number of accelerations of ten (r = 0.57, r2 = 0.32) and 15 (r = 0.38, r2 = 0.14) beats per minute. There were significant differences in computer measurements of FHR accelerations and variation between the umbilical artery pH categories of acidemia (pH less than 7.20), preacidemia (7.20-7.25), and nonacidemia (greater than 7.25). Stepwise regression revealed that episodes of low variation best described the model for predicting umbilical artery pH at birth (P < .001), with no improvement provided by the addition of other computer-analyzed FHR characteristics. In this population of growth-restricted fetuses delivered by elective cesarean, the computer indices of duration of episodes of low variation and short-term and long-term variation were significantly associated with umbilical artery pH and predicted umbilical artery acidemia at birth.

Effects of hypoglycaemia on fetal heart activity and umbilical artery Doppler velocity waveforms in pregnant women with insulin-dependent diabetes mellitus.

To study the effect of induced hypoglycaemia on fetal wellbeing as indicated by fetal heart rate and umbilical artery flow velocity waveforms. A prospective experimental investigation. High risk pregnancy unit and diabetes research unit at Karolinska Institutet, Danderyd Hospital, a university affiliated hospital. Ten women with insulin-dependent diabetes mellitus in the third trimester of pregnancy. The fetal heart rate, the blood flow velocity waveforms in the umbilical artery and the maternal catecholamine levels were investigated during a 150-minute hyperinsulinaemic hypoglycaemic clamp with induction and maintenance of an arterial blood glucose level of about 2.2 mmol/l. 1. Fetal: changes of fetal heart rate pattern and pulsatility index of the umbilical artery flow velocity waveforms. 2. Maternal: levels of plasma adrenaline and plasma noradrenaline. Maternal hypoglycaemia was associated with an increase in frequency and amplitude of fetal heart rate accelerations, a slight decrease in the pulsatility index of the umbilical artery and a rise in the maternal catecholamine levels. We speculate that the increased number of fetal heart rate accelerations reflects an increased sympathico-adrenal activity during the hypoglycaemia clamp. No potentially harmful effects on the fetus were observed in the fetal heart rate or in the umbilical artery Doppler waveform analysis during hypoglycaemia.

Effect of fetal placental embolization-induced hypoxemia for up to 48 hours on fetal heart rate accelerations, decelerations and variability in sheep.

Effect of fetal placental embolization-induced hypoxemia for up to 48 hours on fetal heart rate accelerations, decelerations and variability in sheep.

Neural network prediction of nonstress test results: How often should we perform nonstress tests?

OBJECTIVE: Our purpose was to predict outcomes and optimal intervals for nonstress tests of term gravid women with neural networks. STUDY DESIGN: We studied 100 normal term patients whose 30-minute nonstress tests, performed on 5 consecutive days, were computer analyzed for the following elements: fetal heart rate baseline, variability, signal loss, accelerations (>15 beats/min), and decelerations. The training set used 65 patients; the testing, 35 patients. Nonstress test data (days 1 to 4) were inputs; day 5 data were training patterns. Networks for each nonstress tet element used Brainmaker Macintosh 1.0 (California Scientific Software, Nevada City, Calif.) trained to 0.12 tolerance. Actual fetal heart rate elements and their daily differences were compared with predictions by the networks and multiple regressions. RESULTS: There was little difference between networks using daily or alternate-day inputs for predicting test performance on day 5; networks using test intervals >2 days could not be trained to tolerance. Long-term fetal heart rate variation was the nonstress test element best predicted. Daily differences networks provided better prediction of all day 5 data than did actual daily values networks or multiple regression formulas. CONCLUSIONS: Baseline long-term fetal heart rate variability seems to be the most predictable fetal heart rate element over time and should merit more consideration in overall fetal testing. Fetal heart rate elements are not easily predicted by any method for intervals longer than 2 days. Using longer test intervals might run a greater risk for unanticipated changes in nonstress test outcomes, even when fetal condition is normal.

Effect of Magnesium on Fetal Heart Rate Variability Using Computer Analysis

We studied 16 women, at 32 weeks' or more gestation who required magnesium sulfate (MgSO4) therapy for preterm labor or preeclampsia. A 60-minute Doppler fetal heart rate (FHR) tracing, analyzed by the Oxford Sonicaid System 8000, was obtained for 1 hour before and 2 hours after each patient received intravenous MgSO4 therapy. Maternal serum Mg2+ levels were obtained at the second monitoring session. Matched paired measures of FHR parameters were compared with the Student's t test. After MgSO4 administration, we noted significant falls in long-term variability, short-term variability, and total acceleration (more than 10 beats/min) counts. Reduced short-term and overall variability occurred in all cases with maternal serum Mg2+ levels more than 4.6 mg/dL. Therapeutic maternal serum Mg2+ levels are linked with decreases in long-term and short-term FHR variability and acceleration counts. These findings should be considered when evaluating resting FHR baseline of patients thus treated.

Utilization of Fetal Heart Rate Acceleration Following Vibroacoustic Stimulation in Labor to Predict Fetal Acidemia and Base Deficit Levels

The absence of a fetal response to vibroacoustic stimulation (VAS) performed during labor may be an indicator of fetal acidemia. A lack of fetal heart rate (FHR) acceleration following VAS has been correlated with fetal scalp blood pH 7 mEq/L but was more sensitive to detect levels >10 mEq/L. All patients with pH 10 mEq/L. This stud...

Antenatal bleeding and fetal heart rate.

Objective of the paper was to determine the fetal heart rate (FHR) changes that occur in preterm fetuses whose mothers have suffered antepartum bleeding, versus uncomplicated controls. Over a 12-year span, 91 patients with significant antenatal bleeding (bleeding requiring inhospital observation) were examined and compared to 75 controls with uncomplicated normal pregnancies. None of the women were in labor and all were evaluated at 25-37 weeks' gestation. Excluded were: patients with any other complication (i.e., premature rupture of membranes, intrauterine growth retardation, diabetes, hypertension, collagen vascular disease, postuterine surgery, substance abuse and twins). Analysis of the FHR tracings included baseline heart rate, long-term FHR variability, and number and amplitude of FHR accelerations in 20-min segments. There was no difference in baseline heart rate in the preterm fetuses of pregnancies complicated by antepartum bleeding versus controls. However, the parameters associated with FHR reactivity (number of accelerations in 20 min, and amplitude of accelerations) were higher to a statistically significant degree in fetuses of pregnancies complicated by antenatal bleeding than in controls. Fetuses of mothers suffering antenatal bleeding exhibited significant higher rates of reactive FHR patterns at earlier gestational ages than did controls. In conclusion, there is a significant increase in FHR reactivity in pregnancies in which significant antenatal bleeding occurs, suggesting a probable acceleration in fetal central nervous system maturation in these fetuses.