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Objective: To evaluate the association between changes in cervical length (CL) after vaginal progesterone treatment and preterm delivery (PTD). Methods: This was a retrospective cohort study that included 197 singleton pregnancies without (n = 178) and with (n = 19) a history of PTD which were found to have a short cervix (≤ 25 mm) between 18 + 0 and 23 + 6 weeks' gestation with a follow‐up transvaginal CL measurement taken at least 1 week after vaginal progesterone treatment started. Receiver‐operating‐characteristics (ROC)‐curve analysis was performed and three CL shortening patterns were evaluated: (1) ≥ 10% reduction; (2) ≥ 20% reduction; and (3) ≥ 5 mm reduction relative to the first CL measurement. The predictive performance of each CL reduction cut‐off and its association with PTD ≤ 34 weeks and PTD < 37 weeks were evaluated. Results: Overall, the rate of PTD ≤ 34 weeks was 16.8% (33/197) and that of PTD < 37 weeks was 36.5% (72/197). The area under the ROC curve of cervical shortening expressed in % for predicting PTD ≤ 34 weeks and PTD < 37 weeks was 0.703 and 0.608, respectively. Cervical shortening was observed in 60/197 (30.5%) patients, with 49/60 (81.7%) women showing ≥ 10% reduction, 32/60 (53.3%) ≥ 20% reduction and 27/60 (45.0%) ≥ 5 mm reduction in CL. Sensitivity and specificity for PTD ≤ 34 weeks were, respectively, 48.5% and 79.9% for ≥ 10% reduction; 36.4% and 87.8% for ≥ 20% reduction; and 27.3% and 89.0% for ≥ 5 mm reduction in CL. For PTD < 37 weeks, sensitivity and specificity were, respectively, 36.1% and 81.6% for ≥ 10% reduction; 27.8% and 90.4% for ≥ 20% reduction; and 20.8% and 90.4% for ≥ 5 mm reduction in CL. The highest positive likelihood ratios for PTD ≤ 34 and < 37 weeks were for ≥ 20% CL reduction (2.98 (95% CI, 1.62–5.49) and 2.89 (95% CI, 1.52–5.57), respectively). Despite significant differences in sensitivity among the different cut‐offs for cervical shortening, favoring the ≥ 10% reduction cut‐off, a reduction of ≥ 20% in CL showed the strongest association with PTD ≤ 34 weeks (odds ratio (OR), 4.11 (95% CI, 1.75–9.62)) and < 37 weeks (OR, 3.62 (95% CI, 1.65–7.96)), as compared with a less pronounced reduction in CL. Conclusions: In women with a short cervix treated with vaginal progesterone, a reduction in CL on a subsequent ultrasound scan can predict PTD ≤ 34 and < 37 weeks. A ≥ 20% reduction in CL had the highest positive likelihood ratio and strongest association with PTD ≤ 34 and < 37 weeks compared with ≥ 10% or ≥ 5 mm reduction. © 2023 International Society of Ultrasound in Obstetrics and Gynecology. [ABSTRACT FROM AUTHOR]

Objective: To evaluate whether the presence of cervical funneling or intra-amniotic debris identified in the second trimester is associated with a higher rate of preterm birth (PTB) in asymptomatic nulliparous pregnant women with a midtrimester cervical length (CL) less than 30 mm (i.e. below the 10th percentile).Methods: This was a secondary cohort analysis of data from a multicenter trial in nulliparous women between 16 and 22 weeks' gestation with a singleton gestation and CL less than 30 mm on transvaginal ultrasound, randomized to treatment with either 17-alpha-hydroxyprogesterone caproate or placebo. Sonographers were centrally certified in CL measurement, as well as in identification of intra-amniotic debris and cervical funneling. Univariable and multivariable analysis was performed to assess the associations of cervical funneling and intra-amniotic debris with PTB.Results: Of the 657 women randomized, 112 (17%) had cervical funneling only, 33 (5%) had intra-amniotic debris only and 45 (7%) had both on second-trimester ultrasound. Women with either of these findings had a shorter median CL than those without (21.0 mm vs 26.4 mm; P < 0.001). PTB prior to 37 weeks was more likely in women with cervical funneling (37% vs 21%; odds ratio (OR), 2.2 (95% CI, 1.5-3.3)) or intra-amniotic debris (35% vs 23%; OR, 1.7 (95% CI, 1.1-2.9)). Results were similar for PTB before 34 and before 32 weeks' gestation. After multivariable adjustment that included CL, PTB < 34 and < 32 weeks continued to be associated with the presence of intra-amniotic debris (adjusted OR (aOR), 1.85 (95% CI, 1.00-3.44) and aOR, 2.78 (95% CI, 1.42-5.45), respectively), but not cervical funneling (aOR, 1.17 (95% CI, 0.63-2.17) and aOR, 1.45 (95% CI, 0.71-2.96), respectively).Conclusions: Among asymptomatic nulliparous women with midtrimester CL less than 30 mm, the presence of intra-amniotic debris, but not cervical funneling, is associated with an increased risk for PTB before 34 and 32 weeks' gestation, independently of CL. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Objective: Our aim was to compare the clinical characteristics of meconium aspiration syndrome in cases with pH > or =7.20 and in those with pH <7.20.Study Design: Medical records of diagnostic codes from the International Classification of Diseases, Ninth Revision, were used to identify neonates with severe meconium aspiration syndrome who had been delivered at our institution from 1994 through 1998. Severe meconium aspiration syndrome was defined as a mechanical ventilator requirement of >48 hours. Clinical data including neonatal outcomes of cases of meconium aspiration syndrome associated with umbilical pH > or =7.20 at delivery were compared with data on outcomes of cases with pH <7.20.Results: During this 4-year study period, 4985 singleton term neonates were delivered through meconium-stained amniotic fluid. Forty-eight cases met all study criteria, and pH values at delivery were as follows: pH > or =7.20, n = 29, and pH <7.20, n = 19. There were no differences between groups in the incidence of clinical chorioamnionitis, in the presence of meconium below the vocal cords, or in birth weight. Neonates with meconium aspiration syndrome and umbilical pH > or =7.20 at delivery developed seizures as often as those with pH <7.20 (20.1% vs 21.1%; P = 1.0).Conclusion: Normal acid-base status at delivery is present in many cases of severe meconium aspiration syndrome, which suggests that either a preexisting injury or a nonhypoxic mechanism is often involved. [ABSTRACT FROM AUTHOR]

Objective: Elevated levels of inflammatory cytokines in the fetus have been linked to neurologic morbidities in preterm neonates. Magnesium sulfate is currently being studied in clinical trials as a potential fetal neuroprotective agent. The purpose of this study was to determine whether intrapartum magnesium sulfate therapy has an effect on the umbilical venous concentrations of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha at delivery.Study Design: Women with singleton gestations >32 weeks with no clinical indications for magnesium sulfate therapy (preeclampsia or tocolysis) and either clinical chorioamnionitis or prolonged rupture of membranes were recruited for the study. Consenting patients were randomly assigned, in a double-blinded fashion, to receive either magnesium sulfate (6-g load then 2 g/hr) or matched volumes of lactated Ringer's solution until delivery. Fetal blood specimens were obtained by aspiration of the umbilical vein after cord clamping but before placental separation. Umbilical cytokine levels were measured with a sensitive and specific immunoassay.Results: Twenty-two patients were randomly assigned to groups and received either magnesium sulfate (n = 11) or placebo (n = 11). There were no differences in the demographic or clinical characteristics between groups. The umbilical venous ionized magnesium concentration was significantly higher in the magnesium sulfate group (2.32 +/- 0.27 mg/dL vs 1.23 +/- 0.15 mg/dL; P <.001). There were no statistically significant differences between groups with respect to umbilical levels of interleukin-1beta (1.5 pg/mL [1.5-58] vs 1.5 pg/mL [1.5-10]; P =.5); interleukin-6 (8.5 pg/mL [1-1000] vs 11.2 pg/mL [1-113]; P =.9); or tumor necrosis factor-alpha (16 pg/mL [7.6-20.3] vs 16.6 pg/mL [8.3-22.2]; P =.5).Conclusion: In this pilot study the intrapartum administration of magnesium sulfate does not appear to affect the concentration of inflammatory cytokines in fetal blood at delivery. [ABSTRACT FROM AUTHOR]

Objective: Our purpose was to determine whether cerclage placement in women with a short cervix on transvaginal ultrasonography reduces the rate of preterm delivery.Study Design: A retrospective cohort study identified patients with an ultrasonographic short cervix (cervical length < or =15 mm) between 14 and 24 weeks' gestation. Cerclage placement was performed at the discretion of the attending physician. Clinical characteristics and outcome with and without cerclage were compared.Results: Seventy patients met inclusion criteria; 25 (36%) underwent cerclage placement. Patients managed with cerclage had a lower gestational age at diagnosis (19.6 weeks vs 21.3 weeks, P <.01) but had a similar median cervical length, presence of funneling, and a history of cervical surgery, in comparison with those managed without cerclage. The rate of spontaneous preterm delivery was not different between groups. Patients with cerclage had a higher rate of preterm premature rupture of membranes than those without cerclage (65.2% vs 36.4%, P <.05).Conclusion: Cervical cerclage in patients with a short cervix did not reduce the rate of spontaneous preterm delivery and increased the risk of preterm premature rupture of membranes. [ABSTRACT FROM AUTHOR]

The authors comment on concerns regarding the use of antenatal betamethasone in late preterm gestation and the potential harms of antenatal corticosteroids (ACS). The authors argue against misleading citations of trials on repeat doses of ACS. They point out that the Antenatal Steroid for Term Elective Cesarean Trial (ASTECS) was an unplanned follow-up study and caution against extrapolation and over-interpretation of a study of children who underwent assessment of cortisol secretion patterns.

Background: Infants who are born at 34 to 36 weeks of gestation (late preterm) are at greater risk for adverse respiratory and other outcomes than those born at 37 weeks of gestation or later. It is not known whether betamethasone administered to women at risk for late preterm delivery decreases the risks of neonatal morbidities.Methods: We conducted a multicenter, randomized trial involving women with a singleton pregnancy at 34 weeks 0 days to 36 weeks 5 days of gestation who were at high risk for delivery during the late preterm period (up to 36 weeks 6 days). The participants were assigned to receive two injections of betamethasone or matching placebo 24 hours apart. The primary outcome was a neonatal composite of treatment in the first 72 hours (the use of continuous positive airway pressure or high-flow nasal cannula for at least 2 hours, supplemental oxygen with a fraction of inspired oxygen of at least 0.30 for at least 4 hours, extracorporeal membrane oxygenation, or mechanical ventilation) or stillbirth or neonatal death within 72 hours after delivery.Results: The primary outcome occurred in 165 of 1427 infants (11.6%) in the betamethasone group and 202 of 1400 (14.4%) in the placebo group (relative risk in the betamethasone group, 0.80; 95% confidence interval [CI], 0.66 to 0.97; P=0.02). Severe respiratory complications, transient tachypnea of the newborn, surfactant use, and bronchopulmonary dysplasia also occurred significantly less frequently in the betamethasone group. There were no significant between-group differences in the incidence of chorioamnionitis or neonatal sepsis. Neonatal hypoglycemia was more common in the betamethasone group than in the placebo group (24.0% vs. 15.0%; relative risk, 1.60; 95% CI, 1.37 to 1.87; P<0.001).Conclusions: Administration of betamethasone to women at risk for late preterm delivery significantly reduced the rate of neonatal respiratory complications. (Funded by the National Heart, Lung, and Blood Institute and the Eunice Kennedy Shriver National Institute of Child Health and Human Development; ClinicalTrials.gov number, NCT01222247.). [ABSTRACT FROM AUTHOR]

Objective: To determine whether β2 -adrenoceptor (β2 AR) genotype is associated with shortening of the cervix or with preterm birth (PTB) risk among women with a short cervix in the second trimester., Design: A case-control ancillary study to a multicentre randomised controlled trial., Setting: Fourteen participating centres of the Maternal-Fetal Medicine Units Network of the Eunice Kennedy Shriver National Institute of Child Health and Human Development., Population: Four hundred thirty-nine women, including 315 with short cervix and 124 with normal cervical length., Methods: Nulliparous women with cervical length <30 mm upon a 16-22-week transvaginal sonogram and controls frequency-matched for race/ethnicity with cervical lengths ≥40 mm were studied. β2 AR genotype was determined at positions encoding for amino acid residues 16 and 27., Main Outcome Measures: Genotype distributions were compared between case and control groups. Within the short cervix group, pregnancy outcomes were compared by genotype, with a primary outcome of PTB <37 weeks., Results: Genotype data were available at position 16 for 433 women and at position 27 for 437. Using a recessive model testing for association between short cervix and genotype, and adjusted for ethnicity, there was no statistical difference between cases and controls for Arg16 homozygosity (OR 0.7, 95% CI 0.4-1.3) or Gln27 homozygosity (OR 0.9, 95% CI 0.3-2.7). Among cases, Arg16 homozygosity was not associated with protection from PTB or spontaneous PTB. Gln27 homozygosity was not associated with PTB risk, although sample size was limited., Conclusions: β2 AR genotype does not seem to be associated with short cervical length or with PTB following the second-trimester identification of a short cervix. Influences on PTB associated with β2 AR genotype do not appear to involve a short cervix pathway., (© 2015 Royal College of Obstetricians and Gynaecologists.)

The absence of fetal pulmonary maturity in patients with preterm premature rupture of the membranes (PPROM) is often considered an indication for conservative management. The purpose of this study was to examine the value of biochemical pulmonary maturity assessment for the prediction of neonatal outcome in patients with PPROM between 32 and 34 weeks' gestation. Pregnancies complicated by PPROM at 32 to 34 weeks' gestation that delivered from January 1995 to May 2000 and had biochemical pulmonary maturity assessment were reviewed. Patients with medical disorders, multiple gestations, fetal growth restriction or structural anomalies, or evidence of intra-amniotic infection were excluded. Neonatal outcome measures were compared between patients with mature and immature pulmonary indices. During this time period, 244 patients with PPROM at 32-34 weeks' gestation were delivered; 78 patients met inclusion criteria (n = 41 patients with mature indices and n = 37 patients with immature indices). There were no cases of perinatal death or sepsis. There was no difference in major neonatal morbidities including need for mechanical ventilation, grade 2 or 3 necrotizing enterocolitis, grade 3 or 4 intraventricular hemorrhage, or seizures. After controlling for confounding factors including gestational age at PPROM and delivery, latency period, group B streptococcus (GBS) vaginal colonization, corticosteroid therapy, neonatal sex, mode of delivery, fetal indications for delivery, and umbilical cord pH, biochemical pulmonary maturity was not predictive of major neonatal morbidity. In our population, biochemical pulmonary maturity status does not appear to be predictive of neonatal morbidity in pregnancies complicated by PPROM at 32-34 weeks' gestation.

The purpose of this study was to determine whether nucleated red blood cell (NRBC) counts are elevated in term neonates who have severe fetal acidemia at birth. The neonatal NRBC counts of term (gestational age > or = 37 weeks) neonates with pathological acidemia were compared with those from control neonates who met the following criteria: gestational age > or = 37 weeks, birth weight > or = 2800 g, umbilical artery pH > or = 7.25, and a 5-minute APGAR > 7. Pathological acidemia was defined as an umbilical artery pH < or = 7.0 and a base excess > -12 mEq/L. Twenty-six neonates met all inclusion criteria and were compared to 78 controls. The mean NRBC/100 WBC was 11.9 +/- 13.5 (range 0 to 45) for acidemic neonates compared to 3.9 +/- 2.9 NRBC/100 WBC (range 0 to 11) for control neonates [p <0.001]. Our findings suggest that the onset of hypoxia-ischemia in pregnancies complicated by severe fetal acidemia often begins prior to the intrapartum period.

Objective: To compare the delivery outcomes in term diabetic patients without a prior cesarean delivery to those attempting vaginal birth after cesarean (VBAC)., Study Design: A retrospective chart review study was performed of singleton pregnancies complicated by class A-2-R diabetes who delivered at > or = 37 weeks from 1991 to 1997. Exclusion criteria were prior classical or low vertical cesarean, more than one prior cesarean delivery, fetal structural defects or any contraindications to labor. Outcome measures were compared for patients without prior cesarean (group 1) to those with a VBAC attempt (group 2)., Results: One hundred fifty-nine patients, 127 patients without a prior cesarean delivery and 32 patients with a VBAC attempt, met all the study criteria. The cesarean delivery rate was 26.3% (34/127) in group 1 and 56.3% (18/32) in group 2 (VBAC success rate, 43.7%). There were no cases of uterine rupture. There were no differences in the frequency of endometritis rates or neonatal intensive care unit admission, whether vaginal or cesarean delivery occurred., Conclusion: VBAC success rates appeared to be lower for diabetic gravidas as compared to those for nondiabetic women reported in the literature. Although maternal and neonatal complication rates were low, further studies are necessary to determine the safety of VBAC in this population.

Objective: This study was undertaken to identify correlates of abruptio placentae and to develop a mathematic model for the prediction of abruptio placentae., Study Design: A total of 170,258 singleton birth records from 1991 to 1996 contained in the Schleswig-Holstein perinatal database were analyzed. Fifty-two recognized obstetric risk factors were subjected to univariate analysis. Correlates of abruptio placentae then underwent stepwise forward binary logistic regression. A constant value B(0), coefficients B(1) through B(p), an odds ratio, and a 95% confidence interval were calculated for individual correlates., Results: Abruptio placentae occurred in 874 of 170,258 singleton gestations (0.5%). Of the 52 risk factors 31 proved to be correlates of abruptio placentae, with 16 among primiparous women and 25 among multiparous women. Ten correlates for primiparous, women and 13 for multiparous women emerged from the linear regression, with 7 correlates being shared by both primiparous and multiparous women., Conclusion: The probability that abruptio placentae will occur (p) can be calculated according to the following expression: p = e (z)/(1 + e (z)), where z = B(0) + B(1), em leaderB(p). For example, for a primiparous woman who smokes with bleeding at >28 weeks' gestation and a male fetus in the breech position, the following calculation would yield the chance of abruptio placentae:z = -2.25 + 2.51 + 0.41 + 0.24 + 0.60 = 1.51; p = e (1.51)/ (1 + e (1.51)) = 4. 53/5.53 = 0.82, or 82%.

Objective: To investigate the role of subspecialization in maternal-fetal medicine (MFM) on the frequency of a trial of labor in term pregnancies with breech presentation., Methods: We conducted a retrospective study of 332 singleton pregnancies > or =37 weeks with nonfootling breech presentation that delivered over a 6-year period (1994-1998) at a university-based, tertiary care hospital. Patients were divided into two groups based on whether the delivery was attended by an MFM or non-MFM obstetrician-gynecologist. Demographic and clinical data were compared between groups and outcome variables included whether the patient had an attempt at vaginal delivery, cesarean delivery after a labor attempt, or vaginal breech delivery., Results: The frequency of labor attempt (OR 1.4, 95% CI 0.9-2.3), vaginal breech success rate (OR 0.6, 95% CI 0.3-1.5), and overall cesarean rates (OR 0.9, 95% CI 0.5-1.7) were similar between groups. Using discriminant function analysis, only nulliparity (R2 = 1.6%, F = 6.0, P = 0.005) and birthweight (R2 = 2.0% F = 6.4, P = 0.01) were associated with trial of vaginal delivery., Conclusions: Subspecialization in MFM had no impact on the frequency of trial of labor in the term pregnancy with a breech presentation.

Objective: This study was undertaken to better define the timing of neurologic insult in neonates with early-onset seizures through evaluation of neonatal nucleated red blood cell levels., Study Design: Medical records and the International Classification of Diseases, Ninth Revision codes were used to identify all term neonates with neonatal convulsions who were delivered at our institution (January 1, 1990-December 31, 1995). Each neonate with early-onset seizures was matched to the next 3 neonates who met the following criteria: gestational age > or =37 weeks, no early-onset seizures, birth weight > or =800 g, umbilical artery pH > or =7.25, and a 5-minute Apgar score >7. Demographic characteristics, clinical factors, and mean initial nucleated red blood cell counts were compared between groups., Results: During the 6-year study period, there were a total of 36, 490 singleton term deliveries of infants who were alive at birth. Forty-five (0.1%) of these neonates had early-onset seizures. Thirty neonates with early-onset seizures met the inclusion criteria. Mean nucleated red blood cell counts (number of nucleated red blood cells per 100 white blood cells) for neonates with early-onset seizures were significantly increased compared with those of control neonates (18.4 +/- 22.0 vs 4.6 +/- 4.5; P <.0008)., Conclusions: Our findings are suggestive of the hypothesis that neurologic injury leading to early-onset seizures often occurs before the intrapartum period.

Objective: The aim of this study was to determine the value in the prediction of spontaneous preterm delivery of ultrasonographically measured cervical length measured between 14 and 24 weeks' gestation., Study Design: A retrospective cohort study examined cervical length by means of a two-stage procedure, transabdominal ultrasonography followed by transvaginal ultrasonography if cervical length was <30 mm., Results: A total of 6877 patients met inclusion criteria. Mean cervical length was 37.5 mm. Odds ratios for early preterm delivery (< or =32 weeks' gestation) for patients with cervical lengths < or =10, < or =15, < or = 20, < or =25, and < or =30 mm were, respectively, 29.3 (95% confidence interval, 11.3-75.8), 24.3 (95% confidence interval, 12. 9-45.9), 18.3 (95% confidence interval, 10.8-31.0), 13.4 (95% confidence interval, 8.8-20.6), and 3.2 (95% confidence interval, 2. 4-4.4). For early preterm delivery a cervical length of < or =15 mm had a positive predictive value of 47.6%, a negative predictive value of 96.7%, a sensitivity of 8.2%, and a specificity of 99.7%., Conclusions: A short cervix seen on a second-trimester sonogram was a powerful predictor of early spontaneous preterm delivery (< or =32 weeks' gestation). Nearly 50% of patients with a cervical length < or =15 mm had an early spontaneous preterm delivery, which suggests that clinical trials of interventions (eg, cerclage) in this population are urgently needed.

Background: Invasive techniques such as amniocentesis and cordocentesis are used for diagnosis and treatment in fetuses at risk for anemia due to maternal red-cell alloimmunization. The purpose of our study was to determine the value of noninvasive measurements of the velocity of blood flow in the fetal middle cerebral artery for the diagnosis of fetal anemia., Methods: We measured the hemoglobin concentration in blood obtained by cordocentesis and also the peak velocity of systolic blood flow in the middle cerebral artery in 111 fetuses at risk for anemia due to maternal red-cell alloimmunization. Peak systolic velocity was measured by Doppler velocimetry. To identify the fetuses with anemia, the hemoglobin values of those at risk were compared with the values in 265 normal fetuses., Results: Fetal hemoglobin concentrations increased with increasing gestational age in the 265 normal fetuses. Among the 111 fetuses at risk for anemia, 41 fetuses did not have anemia; 35 had mild anemia; 4 had moderate anemia; and 31, including 12 with hydrops, had severe anemia. The sensitivity of an increased peak velocity of systolic blood flow in the middle cerebral artery for the prediction of moderate or severe anemia was 100 percent either in the presence or in the absence of hydrops (95 percent confidence interval, 86 to 100 percent for the 23 fetuses without hydrops), with a false positive rate of 12 percent., Conclusions: In fetuses without hydrops that are at risk because of maternal red-cell alloimmunization, moderate and severe anemia can be detected noninvasively by Doppler ultrasonography on the basis of an increase in the peak velocity of systolic blood flow in the middle cerebral artery.

Aims: The purpose of this study was to examine factors relevant to mode of delivery in term pregnancies complicated by gestational and pre-gestational diabetes., Methods: A retrospective chart review of term (> or = 37 weeks) singleton pregnancies complicated by Class A2 through Class R pregnancies which delivered from 1991-1997 was performed. Exclusion criteria were prior cesarean delivery, non-vertex presentation, fetal structural defects, or any contraindications to vaginal delivery. Maternal and fetal factors relevant to mode of delivery were examined and compared. Stepwise logistic regression analysis was performed to examine factors predictive of delivery mode., Results: A total of 148 patients met study criteria. Induction rates were 60.9% for gestational and 79.8% for pre-gestational diabetics. The overall cesarean delivery rate by Diabetes Class for A2, B, C, D-F pregnancies was 20.3%, 40%, 37%, and 57.1% respectively. In Class A2 pregnancies no factor was associated with cesarean delivery and only nulliparity (p = 0.03) was associated in Class B-F pregnancies., Conclusions: These results suggest that physician factors may play an important role in the risk for cesarean delivery in our diabetic population.

Objective: We sought to determine the effect of magnesium sulfate on fetal heart rate baseline value, variability, and acceleration-deceleration pattern., Study Design: Normal, nonlaboring pregnant patients at >30 weeks' gestation were recruited. Baseline fetal heart rate monitoring for 1 hour was performed. After an 800-kcal meal, patients were randomized to receive either an intravenous loading dose of 6 g of magnesium sulfate in 100 mL of isotonic sodium chloride solution or 100 mL of isotonic sodium chloride solution alone. Subsequently, patients in the magnesium sulfate group received a 2-g/h intravenous infusion for 3 hours at a rate of 125 mL/h. Patients randomized to the sodium chloride solution group received a sodium chloride solution infusion at a similar rate (unlabeled intravenous bags). Maternal blood was drawn at 0, 1, and 3 hours for determination of total and ionized magnesium and calcium, electrolyte, and glucose levels. One hour of fetal heart rate monitoring was repeated at 1 and 3 hours of infusion. Tracings were interpreted without identifiers (of time or group) by using the National Institute of Child Health and Human Development fetal heart rate monitoring guidelines., Results: Magnesium sulfate administration resulted in decreased fetal heart rate baseline values and variability in the third hour. The fetal heart rate baseline value was 134.4 +/- 6.3 versus 136.6 +/- 6.4 beats/min before infusion (P >.05), 134.4 +/- 7.1 versus 135.1 +/- 6. 6 beats/min in the first hour (P >.05), and 134.6 +/- 7.1 versus 132. 3 +/- 7.6 beats/min in the third hour (P <.05) in the sodium chloride solution group versus the magnesium sulfate group, respectively. Fetal heart rate variability (grades 1-5) was 2.75 +/- 0.33 versus 2.82 +/- 0.29 before infusion (P >.05), 2.81 +/- 0.30 versus 2.84 +/- 0.28 in the first hour (P >.05), and 2.71 +/- 0.52 versus 2.67 +/- 0.36 in the third hour in the sodium chloride solution group versus the magnesium sulfate group, respectively (P <. 05). Magnesium sulfate blocked the positive correlation between gestational age and number of accelerations found in control subjects. No significant decelerations were identified., Conclusions: Prolonged administration of magnesium sulfate was associated with decreased fetal heart rate baseline values and variability. Given the small magnitude of these changes, the clinical significance of these findings is questionable. Magnesium sulfate inhibition of the increasing number of accelerations with gestational age needs to be considered when fetal well-being is assessed.