Predictability of intrapartum and neonatal outcomes with the amniotic fluid volume distribution: a reassessment using the amniotic fluid index, single deepest pocket, and a dye-determined amniotic fluid volume

<p>What is the Impact of Abnormal Amniotic Fluid Volumes on Perinatal Outcomes in Normal Compared with At-Risk Pregnancies?</p>

Objective

Assessing amniotic fluid volume is an integral part of obstetric practice. Data are sparse on at-risk pregnancy and amniotic fluid volumes. The aim of our study was to determine if there is a difference in perinatal outcomes based on complications of pregnancy and amniotic fluid volumes. We hypothesized that at-risk pregnancies with abnormal amniotic fluid volumes would have worse perinatal outcomes than normal pregnancies with abnormal amniotic fluid volumes.

Study Design

This retrospective cohort study evaluated both normal and at-risk singleton pregnancies with intact membranes on admission for delivery. Amniotic fluid volumes were estimated using both the amniotic fluid index (AFI) and single deepest pocket (SDP) techniques. All sonograms were performed by trained ultrasound technicians or obstetrician/gynecologists. We placed 3365 women into 6 separate groups (at-risk versus normal, then further stratified by oligohydramnios by SDP, normal fluid, or polyhydramnios by AFI).

Results

At-risk pregnancies with normal fluid and at-risk pregnancies with polyhydramnios have significantly increased risk of neonatal intensive care unit (NICU) admission [OR 2.06 (95% CI 1.63,2.60), OR 2.74 (95% CI 1.54, 4.87)]. Birthweight is significantly higher in at-risk and normal pregnancies with polyhydramnios than those with normal pregnancies and normal fluid (p<0.0001). Birthweight is significantly lower in at-risk pregnancies with oligohydramnios (p<0.0001). There were no significant differences in need for amnioinfusion in labor, variables or lates influencing delivery, meconium staining, or umbilical artery pH <7.1.

Conclusion

Our study attempted to further define risk of adverse pregnancy outcomes by defining the pregnancy as normal or at-risk and amniotic fluid volumes. Contrary to our hypothesis, we did not find an increased risk of many of the adverse perinatal outcomes we studied amongst at-risk pregnancies with abnormal fluid. There was an increased risk of NICU admission associated with polyhydramnios in normal and at-risk pregnancies.

Red cell distribution width as a potential prognostic biomarker in fetal growth restriction

OBJECTIVE

Red cell distribution width (RDW) is a prognostic marker for adverse outcomes in cardiovascular disease. This association has been attributed to the impaired erythropoiesis and abnormal red blood cell survival originating from chronic hypoxic status or poor nutrition. Considering the pathophysiologic association between fetal growth restriction (FGR) and chronic intrauterine hypoxia, which in turn can result in impaired erythropoiesis, RDW could be a biomarker in FGR. To address this issue, we evaluated the RDW in FGR.

STUDY DESIGN

The study population consisted of singleton preterm neonates (24-34 weeks of gestation) and RDW in cord blood was measured at delivery, and was compared between small-for-gestational age (SGA) neonates (birthweight <10 percentile) and non-SGA neonates (birthweight >10 percentile). Among them, RDW was also examined according to the adverse neonatal outcomes.

RESULTS

Five hundred eighty-four neonates were included, of these, 117 SGA neonates and 467 non-SGA neonates. RDW in the SGA neonates was significantly higher than that in the non-SGA neonates (18.4 versus 16.4, p < .001). This association between SGA and RDW remained significant after adjustment for gestational age at delivery, histologic chorioamnionitis, and hematologic parameters. Among the SGA neonates, RDW was higher in neonates with adverse neonatal outcomes than those without them. The RDW >90 percentile was an independent parameter for the prediction of neonatal outcomes, even after adjustment.

CONCLUSION

The RDW was higher in the SGA neonates and was associated with adverse outcomes. RDW can be a prognostic marker in predicting outcomes among preterm neonates.

Comparison of the Effect of Maternal Rest in Alternative Lateral Decubitus Positions on the Amniotic Fluid Index: A Randomized Controlled Trial

OBJECTIVES

To analyze the effect of maternal rest in the left and right lateral decubitus positions and resting alone on the amniotic fluid index (AFI).

METHOD

Sixty-nine women with singleton pregnancies and an AFI of 6 to 24 cm at 36 to 40 weeks' gestation were included in this randomized controlled trial. The women were randomized into 2 intervention groups. After initial AFI measurements, group 1 (n = 35) rested in the left lateral position for 15 minutes and then rested in the right lateral position for another 15 minutes. Group 2 (n = 34) rested in the right lateral position for 15 minutes and then rested in the left lateral position for another 15 minutes. To compare differences between groups, AFIs were measured at the end of each 15-minute period while the participants were kept on their backs in a semirecumbent position.

RESULTS

The demographic data, gestational ages, and initial AFI values did not differ between groups (P > .05). In group 1, the initial mean AFI ± SD of 12.25 ± 3.81 increased significantly during the first 15 minutes to 15.17 ± 4.27 and decreased significantly during the second 15 minutes to 13.30 ± 4.29 (P< .001); however, the 30-minute AFI was still significantly higher than the initial value (P = .008). In group 2, the initial AFI change during the first 15 minutes, from 12.83 ± 3.99 to 12.72 ± 3.87, was not significant (P> .05); however, it increased significantly to 15.63 ± 4.14 during the second 15 minutes (P< .001). The 30-minute AFI was still significantly higher than the initial value (P< .001).

CONCLUSIONS

Maternal rest in the right lateral decubitus position does not seem to either increase or decrease the AFI, and resting alone does not increase the AFI in the short term.

Usefulness of fetal urine production measurement for prediction of perinatal outcomes in uteroplacental insufficiency

OBJECTIVES

To evaluate whether fetal urine production measurement is useful for predicting adverse outcomes in patients with uteroplacental insufficiency.

METHODS

We enrolled patients with uteroplacental insufficiency at 24 to 40 weeks' gestation and normal pregnancies matched for gestational age and divided them into 3 groups according to perinatal outcomes: group 1 (n = 141), a control group of normal pregnancies; group 2 (n = 29), uteroplacental insufficiency without adverse outcomes; and group 3 (n = 18), uteroplacental insufficiency with adverse outcomes. An adverse outcome was defined as 1 or more of the following: (1) cesarean delivery because of fetal distress; (2) admission to the neonatal intensive care unit; (3) cord arterial pH less than 7.15 at birth; and (4) low 5-minute Apgar score (<7). The fetal urine production rate was obtained by serial bladder volume measurement using virtual organ computer-aided analysis. For bladder volume determination, we scanned the bladder in the 3-dimensional mode and defined the bladder surface contour in the reference plane, repeating the rotation of the reference plane with an angle of 30° and determining the surface contour on each plane. Statistical methods, including the Mann-Whitney U test, Fisher exact test, χ(2) test, and Kruskal-Wallis analysis of variance, were used.

RESULTS

Group 3 had a lower mean fetal urine production rate than groups 1 and 2, whereas the urine production rate was not different between groups 1 and 2 (group 1, 49.0 mL/h; group 2, 59.4 mL/h; group 3, 20.7 mL/h; P < .001 between groups 1 and 3 and between groups 2 and 3). This difference between groups 2 and 3 remained significant after adjusting for the amniotic fluid index, umbilical artery Doppler pulsatility index, and presence of fetal growth restriction.

CONCLUSIONS

Uteroplacental insufficiency cases with adverse perinatal outcomes had a lower fetal urine production rate than those without adverse outcomes. This difference might be used to predict adverse perinatal outcomes in uteroplacental insufficiency.

Clinical application of fetal urine production rate in unexplained polyhydramnios

OBJECTIVE

To evaluate the clinical use of hourly fetal urine production rate (HFUPR) in polyhydramnios.

METHODS

This was a retrospective review of 33 singleton pregnancies with polyhydramnios, 30 of them unexplained and three due to gastrointestinal atresia. HFUPR was estimated using three-dimensional ultrasound and was compared with recently established nomograms. Abnormal midterm outcome, defined as diagnosis or persistence of pathology after the neonatal period until the age of 2 years, was analyzed according to prenatal HFUPR measurements and other polyhydramnios characteristics.

RESULTS

Seventeen of the 30 fetuses with unexplained polyhydramnios had an HFUPR above the 95(th) centile, and five (29.4%) of them developed midterm disorders. None of the 13 with normal HFUPR developed midterm disorders. The HFUPR was 1.9 (SD, 0.7) multiples of the median (MoM) in fetuses with an adverse childhood outcome and 1.4 (SD, 1.2) in fetuses with normal childhood outcome (P = 0.34). In the three fetuses with gastrointestinal atresia, the HFUPR was significantly lower than in those with unexplained polyhydramnios (P = 0.003).

CONCLUSION

HFUPR was associated with the mechanism of polyhydramnios but failed to help in the prognosis of unexplained polyhydramnios because of lack of power. Children with prenatal unexplained polyhydramnios and HFUPR above the 95(th) centile should nevertheless receive detailed pediatric follow-up.

Induction of labor and perinatal outcome: the impact of the amniotic fluid index

OBJECTIVE

The purpose was to determine the impact of the amniotic fluid index on the perinatal outcome of patients admitted for induction of labor at term.

STUDY DESIGN

Patients (n=180) included in the study were those admitted for induction of labor at 37-42 weeks' gestation, with unfavorable cervix and intact membranes. The amniotic fluid index (AFI) was determined in all patients using the four-quadrant technique within 24 h of the induction of labor. Patients were divided into two groups based on their AFI: the oligohydramnios group with AFI < or = 5 cm (n = 66) and a normal group with AFI > 5 cm (n = 114). The perinatal outcomes of the two groups were compared.

RESULTS

The two groups were similar with regard to maternal age, gestational age, and birth weight. Meconium staining of the amniotic fluid was significantly higher in the group with AFI < or = 5 cm (p = 0.040). The number of cesarean deliveries due to fetal distress was significantly higher even after adjusting for other confounding factors in the group with AFI < or = 5 cm (adjusted OR 6.52 [95% CI 1.82, 23.2]; p < or = 0.0001). There was no significant difference between the two groups with regard to Apgar scores or neonatal admission.

CONCLUSION

Induction of labor at term in patients with oligohydramnios is associated with an increased risk of cesarean delivery due to fetal distress.

Comparison of amniotic and intramembranous unidirectional permeabilities in late-gestation sheep

OBJECTIVE

Amniotic fluid volume is regulated by the intrinsic modulation of intramembranous absorption. However, neither the mechanisms nor the rate-limiting barriers of this transport are known. We tested the hypothesis that the amnion is the rate-limiting barrier of intramembranous absorption by comparing unidirectional permeabilities of the amnion in vitro and the intramembranous pathway in vivo.

STUDY DESIGN

Unidirectional permeabilities to 99m technetium pertechnate or [14 C]inulin of fresh ovine amnion were measured in vitro in a Ussing chamber; the permeability-surface area products were calculated by the multiplication of the permeabilities by gestational age-specific amniotic surface areas. Unidirectional permeabilities of the intramembranous pathway of the 2 tracers were calculated from solute fluxes between amniotic fluid and fetal blood in chronically catheterized late-gestation fetal sheep. Statistical comparisons included t -tests, least squares regression, analysis of variance, and analysis of covariance.

RESULTS

In the isolated amnion in vitro, the ratio of permeabilities in the amniotic fluid to chorionic direction and the reverse direction was not significantly different from unity for 99m technetium pertechnate (1.03+/-0.10 [SE]; n=7) or [14 C]inulin (1.10+/-0.17; n=7). In contrast, in the in vivo preparation, the ratio of intramembranous permeabilities outward from the amniotic fluid and the reverse direction was greater than unity for 99m technetium pertechnate (2.10+/-0.34; n=8; P=.014) and [14 C]inulin (4.68+/-1.24; n=7; P=.025). The permeability-surface area product of 99m technetium pertechnate (2.18+/-0.79 mL/min) of the isolated amnion was similar to the in vivo intramembranous permeability (n=8) in the amniotic fluid to fetal blood direction (1.42+/-0.34 mL/min) and greater than that in the reverse direction (0.84+/-0.25 mL/min; P=.046). The permeability-surface area product of [14 C]inulin of the amnion (0.53+/-0.20 mL/min) was similar to intramembranous permeability (n=7) in the amniotic fluid to fetal blood (0.68+/-0.15 mL/min) direction and greater than that in the reverse direction (0.22+/-0.06 mL/min; P=.0097).

CONCLUSION

Solute transport across the ovine amnion depends on solute size and appears to be limited only by the amnion's passive diffusional properties. In vivo intramembranous transport similarly depends on solute size but is not exclusively a passive diffusional process because it is primarily unidirectional outward from the amniotic fluid. Although it is a major barrier, the amnion is not the only barrier and does not appear to be responsible for the unidirectional nature of intramembranous absorption. Thus, unidirectionality appears to be imparted by nonpassive mechanisms in non-amnion tissues, which most likely includes vesicular transport within the endothelial cells of the intramembranous microvessels.

Reevaluation of the relationship between amniotic fluid volume and perinatal outcome

OBJECTIVE

Ultrasound estimation of amniotic fluid volume (AFI) is a critical component of antenatal surveillance. Alterations in AFI have classically been considered an indication of fetal compromise, but recent studies have called this into question. The present study was undertaken to reevaluate the relationship between AFI and perinatal outcome.

STUDY DESIGN

The perinatal data base of the authors' institution was queried for all patients in a 6-year period who had AFI evaluated. Two groups, 1 high-risk and 1 low-risk, were evaluated to determine the relationship between AFI and gestational age. An additional high-risk group that had AFI determined within 48 hours of delivery was also used to correlate AFI with intrapartum and perinatal outcomes. Statistical analysis was performed using linear regression analysis to evaluate the correlation between AFI and gestational age or birth weight. Additional correlations were done using analysis of variance, chi-square, Fisher exact test, or Student t test. Interaction between variables was analyses using logistic regression analysis.

RESULTS

Fourteen thousand seven hundred forty-seven AFI determinations in 4337 high-risk patients, and 1153 AFI determinations in 1153 low-risk patients were evaluated. There were no clinically significant correlations between AFI and gestational age. In the second high-risk group of 454 patients there was a significant correlation between polyhydramnios and large-for-gestational age infants, congenital anomalies, and an increase in cesarean section for delivery. There was an increased risk of nonreassuring fetal heart rate patterns during labor for the oligohydramnios patient, but only in preterm patients. There was no strong relationship between AFI and neonatal complications or length of stay in the neonatal intensive care unit. Logistic regression confirmed that AFI was not significantly correlated with perinatal outcome.

CONCLUSION

The present study suggests that AFI is a weaker predictor of perinatal outcome than has been classically suggested. Although the AFI identification of polyhydramnios was helpful in identifying LGA fetuses and fetuses at risk for congenital abnormalities, oligohydramnios was a rather weak predictor of poor perinatal outcome.