The role of amniotic fluid assessment in evaluating fetal well-being

Historical Assessment, Practical Management, and Future Recommendations for Abnormal Amniotic Fluid Volumes

Objective: The purpose of this review is to examine the evidence that defines normal and abnormal amniotic fluid volumes (AFVs) and current recommendations on the management of abnormalities of AFV. Methods: The studies establishing normal actual AFVs and the ultrasound estimates used to identify normal and abnormal AFVs were evaluated. Recommendations from national and international organizations were reviewed for guidance on the definitions and management of abnormal AFVs. Results: A timeline of the development of the thresholds that define abnormal AFVs was created. Recommendations from 13 national and international guidelines were identified, but the definitions and management recommendations for abnormal AFVs varied considerably between groups. An algorithm for the management of oligohydramnios and polyhydramnios was developed. Knowledge gaps and the structure of future studies were examined. Conclusions: Assessment of AFV is performed multiple times per day in antenatal clinics and hospitals. Current recommendations on defining and managing abnormal AFVs differ between national and international organizations. We have proposed algorithms to assist in the management of abnormal AFVs until further studies can be undertaken.

Amniotic fluid absorption and growth functions in humans: what can we indirectly learn from congenital digestive atresias?

Background

Amniotic fluid (AF) was thought of just as a mechanical cushioning to the foetus. Nowadays, its role during pregnancy is getting more attention, suggesting hitherto unknown aspects. The aim of the study is to speculate on AF nutritional functions and its clinical repercussions based on what digestive tract (DT) atresias seem to suggest.

Methods

A retrospective analysis of the patients admitted to our department for DT atresias between 2000 and 2020 was conducted. Patients’ birth weight (BW), gestational age (GA) at birth and diagnosis were recorded. The following were excluded from the study: oesophageal atresias (OA) with tracheoesophageal fistula (TOF), colonic and anal atresias and patients with associated major comorbidities. A control group was made of patients admitted to our ward in the same period for congenital pulmonary airway malformations (CPAM). To standardize the BW, it was coupled with birth GA calculating the newborn percentiles. The mean newborn percentiles of OAs, duodenal atresias (DAs), jejunal atresias (JAs), and ileal atresias (IAs) were independently compared with the control group using Student’s t-test. Lastly, the significance of the frequencies’ distribution of newborns born small for gestational age (SGA) between the DT atresias and the control group was evaluated with the χ2 test, and the OR were calculated. A p-value < 0.05 was considered statistically significant.

Results

A total of 231 patients were eligible for the study: 36 OAs without TOF, mean BW 2488.8 ± 491 g (range 1630–3750 g), mean GA 36.8 ± 2.1 weeks (31–40 weeks), mean newborn percentile 18 ± 22 (1–75); 20 DAs, mean BW 2586.8 ± 577.9 g (1250–3462 g), mean GA 36.2 ± 2.5 weeks (31–40 weeks), mean newborn percentile 31 ± 23 (3–79); 17 JAs, mean BW 2483.5 ± 621.7 g (900–3205 g), mean GA 34.8 ± 2.1 weeks (30–38 weeks), mean newborn percentile 44 ± 28 (4–96); 17 IAs, mean BW 2646.1 ± 769.8 g (1162.0–3888 g), mean GA 35.9 ± 3.2 weeks (30–41 weeks), mean newborn percentile 44 ± 26 (1–82); and 141 CPAMs with mean BW 3287.4 ± 492.0 g (980–4580 g), mean GA 38.7 ± 1.8 weeks (26–41 weeks), mean newborn percentile 43 ± 26 (1–99). The number of SGA neonates was 18 between OA patients (50%), 4 between DAs (20%), 1 between JAs (6%), 2 between IAs (12%) and 11 between CPAMs (8%). The mean percentile of the OAs and DAs was lower than the control group with a p of < .01 and .03 while no statistical significance was found in the comparison between DAs, JAs, IAs and CPAMs with a p of .06, .86 and .59. The incidence of SGA in the control group resulted lower than the one in the DT atresias where it becomes higher the more proximal the atresia is (p < .05). The OR of SGA newborn in the OA group was 11.8, in DA 3.0, in JA 0.7 and in IA 1.6.

Conclusion

AF showed to have a great impact on foetal growth, and its preferred site of absorption seemed to be the stomach and duodenum. Its nutritional role could have an important predictive value in diagnosing DT atresia both prenatally and postnatally.

<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.

Amniotic Fluid: Technical Update on Physiology and Measurement

OBJECTIVE

OUTCOMES: EVIDENCE: A MEDLINE and KFINDER search was used to identify relevant articles, with review of bibliography identified article including Cochrane reviews and recent review articles.

VALUES

The evidence collected was reviewed by the Diagnostic Imaging Committee of the Society of Obstetricians and Gynecologists of Canada. The recommendations were made according to the guidelines developed by The Canadian Task Force on Preventative Health Care (Table 1).

BENEFITS, HARMS AND COSTS

Amniotic fluid assessment by ultrasound has become an integral part of fetal assessment in modern obstetrics. Abnormalities of fluid volume result in obstetrical intervention and further investigations. In Canada, there are no standard definitions of fluid volume estimation, nor a standard approach to assessing fluid. Multiple randomized trials have suggested that using a Single Pocket Estimation technique (rather than the multi pocket assessment approach known as the amniotic fluid index), will result in fewer obstetrical interventions without any increase in adverse outcomes. Recent literature suggests that there are detectable, modest changes in amniotic fluid that can occur within an hour or two of normal physiological maneuvers. This may account for the variability and inconsistent results from repeated assessments within a short period of time which can lead to confusion and generate further testing. This article hopes to describe the limitations of amniotic fluid assessment, promote a standard method of amniotic fluid assessment, and propose a common set of definitions to be used to describe amniotic fluid volume.

SUMMARY STATEMENTS

RECOMMENDATION.

A contemporary amniotic fluid volume chart for the United States: The NICHD Fetal Growth Studies-Singletons

BACKGROUND

Amniotic fluid is essential to normal fetal development and is estimated clinically with ultrasound scanning to identify pregnancies that are at risk for poor perinatal outcome.

OBJECTIVE

Our goal was to develop a United States standard for amniotic fluid volume that is estimated by the amniotic fluid index and single deepest pocket.

STUDY DESIGN

We performed a planned secondary analysis of a multicenter observational study of 2334 low-risk women with normal singleton gestations from 1 of 4 self-reported racial/ethnic groups. Eligible women had confirmed first-trimester dating criteria with health status, lifestyles, and medical and obstetric histories that were associated with normal fetal growth. Consenting women underwent serial (up to 5) sonographic evaluations of amniotic fluid between 15 and 40 weeks of gestation after being assigned randomly to 1 of 4 gestational age observation schedules. Twelve United States perinatal centers participated, and all sonograms were performed by credentialed sonographers who used identical, high-resolution equipment; caregivers were unaware of results but were notified for oligohydramnios. Women (n=597) who were subsequently found to have clinically significant antepartum complications were excluded. Racial/ethnic-specific nomograms for amniotic fluid index and single deepest pocket across gestation were developed with the use of linear mixed models with cubic splines; racial/ethnic differences were evaluated both with global and between-group tests. Median, 3rd, 5th, 10th, 90th, 95th and 97th percentile values were also estimated. We further considered the possible confounding effects of selected maternal characteristics and the estimated fetal weight at each sonogram.

RESULTS

A total of 1719 pregnant women met inclusion criteria and had available data. These included 480 non-Hispanic white women, 418 non-Hispanic black women, 485 Hispanic women, and 336 Asian women. Both the amniotic fluid index and the single deepest pocket varied across gestation with maximal values at 26 and 33 weeks of gestation, respectively. Statistically significant differences were observed by maternal race/ethnicity. The between-group differences that were observed at 17-22 and 35-40 weeks of gestation remained statistically significant after adjustment for maternal characteristics and estimated fetal weight. These between-group racial/ethnic differences were most prominent after 35 weeks of gestation and at the extremes of dispersion (3rd and 97th percentiles). All 3rd and 97th percentile amniotic fluid index values were within the range of commonly used cutoffs to define oligohydramnios (≤5 cm) and polyhydramnios (≥25 cm). However, the 3rd percentile values ranged between 5.9 cm at 40 weeks of gestation and 10.1 cm at 25-27 weeks of gestation; the 97th percentile values ranged between 24.8 cm at 38 weeks of gestation and 15.7 cm at 15 weeks of gestation.

CONCLUSION

Sonographic amniotic fluid volume estimates vary by racial/ethnic group, but the absolute differences appear to be small and may not be clinically significant. Selected maternal characteristics and estimated fetal weight did not affect the racial/ethnic differences. Between-group differences are maximal after 35 weeks of gestation and at the extremes of the upper and lower dispersion estimates. Given the observed variability in extreme (3rd and 97th percentile) dispersion values over the gestation, use of single cutoffs to define out-of-range measurements may not be appropriate clinically. These data might form a contemporary United States standard for amniotic fluid estimation that uses the amniotic fluid index and the single deepest pocket.

Is There a Difference in Sonographic Estimation of Amniotic Fluid Volume When Measuring With the Probe Perpendicular to the Floor Compared With Perpendicular to the Uterine Contour?

OBJECTIVE

This study sought to determine whether there is a significant difference in amniotic fluid measurements when measuring perpendicular to the floor compared with perpendicular to the uterine contour using both amniotic fluid index and single deepest pocket.

METHODS

This was a single-centre, prospective study of women with singleton gestation who were undergoing fetal ultrasound examination. A total of 240 women were enrolled, and single deepest pocket and amniotic fluid index were measured with both techniques. Correlation coefficient and intraclass correlation coefficient were used to assess the agreement between the values using the two methods of measurement (Canadian Task Force Classification II-2).

RESULTS

A strong correlation was found between amniotic fluid index measurements (correlation coefficient 0.82; intraclass correlation coefficient 0.7). A strong correlation also was found between single deepest pocket measurements (correlation coefficient 0.7; intraclass correlation coefficient 0.6).

CONCLUSION

The measurement of amniotic fluid index and single deepest pocket can be performed either perpendicular to the floor or perpendicular to the uterine contour. There is no significant difference between these measurements and they correlate well.

Point-of-care ultrasound in obstetrics

Point-of-care ultrasound, or PoCUS, where imaging is undertaken at the bedside, clinic or emergency department (ED) by the clinician overseeing treatment, is a rapid form of assessment that may be undertaken alongside or as an alternative to traditional, formal ultrasound performed by a radiology service. PoCUS reduces the time to diagnosis, thus allowing lifesaving treatment to be initiated. This is particularly relevant in Obstetrics and Gynaecology (OBGYN), where delayed diagnosis of pregnancy complications is often fatal or highly debilitating to the mother or fetus. The literature suggests that PoCUS is particularly useful in areas that are inadequately resourced, as it is relatively cheap and accessible. High-quality training is essential to ensure that the staff performing the scans are adequately qualified to deliver the service. Clinicians who perform PoCUS in their practice should be aware of the appropriate indications, as well as when to refer for formal imaging.

Reconstruction and positional accuracy of 3D ultrasound on vertebral phantoms for adolescent idiopathic scoliosis spinal surgery

PURPOSE

Determine the positional, rotational and reconstruction accuracy of a 3D ultrasound system to be used for image registration in navigation surgery.

METHODS

A custom 3D ultrasound for spinal surgery image registration was developed using Optitrack Prime 13-W motion capture cameras and a SonixTablet Ultrasound System. Temporal and spatial calibration was completed to account for time latencies between the two systems and to ensure accurate motion tracking of the ultrasound transducer. A mock operating room capture volume with a pegboard grid was set up to allow phantoms to be placed at a variety of predetermined positions to validate accuracy measurements. Five custom-designed ultrasound phantoms were 3D printed to allow for a range of linear and angular dimensions to be measured when placed on the pegboard.

RESULTS

Temporal and spatial calibration was completed with measurement repeatabilities of 0.2 mm and 0.5° after calibration. The mean positional accuracy was within 0.4 mm, with all values within 0.5 mm within the critical surgical regions and 96% of values within 1 mm within the full capture volume. All orientation values were within 1.5°. Reconstruction accuracy was within 0.6 mm and 0.9° for geometrically shaped phantoms and 0.5 and 1.9° for vertebrae-mimicking phantoms.

CONCLUSIONS

The accuracy of the developed 3D ultrasound system meets the 1 mm and 5° requirements of spinal surgery from this study. Further repeatability studies and evaluation on vertebrae are needed to validate the system for surgical use.

Antenatal interventions based upon fetal surveillance of the daily opioid-exposed fetus: a descriptive analysis

Objective: Daily opioid dependence for maternal pain management, methadone maintenance, or buprenorphine/naloxone therapy is an increasing trend in modern obstetrics. Opioids may produce depressive effects on fetal neurobehavioral status and thus on fetal heart rate patterns. Our primary objective was to describe the current methods utilized in antenatal monitoring of the daily opioid exposed fetus; and to describe interventions based upon monitoring which precipitated a recommendation for delivery. Our ultimate goal was to determine an optimal, evidence-based recommendation for fetal assessment of the daily opioid exposed pregnancy.Study design: A retrospective review of patients undergoing antenatal assessment from January 2016 through April 2017 at two maternal-fetal medicine testing centers identified singleton, fetuses without a known major genetic abnormality with daily opioid exposure. Nonstress tests, amniotic fluid indexes, biophysical profiles, umbilical artery Doppler measurements, and serial biometry were analyzed. Test characteristics and frequency of interventions for abnormal monitoring were quantified.Results: Criteria for daily opioid exposure was identified in 27 patients (77.8% on methadone (n = 21), 14.8% on prescription opioid for chronic pain (n = 4), and 7.4% on buprenorphine/naloxone (n = 2)). Mean maternal age was 30.3 years ±5.5 (range 21-42 years). Parity zero was 6/27 (22.2%). Identified race was 52% Caucasian, 26% African American, 19% Hispanic, and 4% Pacific Islander. There were 112 growth scans, 102 biophysical profiles, 10 isolated nonstress tests, and 81 umbilical artery Doppler studies reviewed. Delivery precipitated by abnormal testing occurred in 6/27 patients (22.2%). Gestational ages of delivery were all between 36 and 38 weeks. Indications for delivery were isolated oligohydramnios 2/6 (one at 37 weeks, one at 38 weeks), oligohydramnios with associated intrauterine growth restriction 2/6 (both at 36 weeks), isolated nonreactive nonstress test 1/6 (occurring at 38 weeks), and low biophysical profile score 1/6 (occurring at 36 weeks). The average nonstress test baseline was 131 (±11) beats per minute (range of 120-150), with no episodes of significant fetal bradycardia or tachycardia. Overall, 94.6% (106/112) of the nonstress tests were reactive, all nonstress tests had variability, 96.4% (108/112) had moderate variability, and 99.1% (111/112) had no decelerations. Time to nonstress test reactivity was <20 min in 93% (104/112), with a mean time to first acceleration of 5.3 (±7.7) min (range of 1-44). Umbilical artery Doppler measurements had an elevated systolic to diastolic ratio >95% for gestational age in 9/83 cases, with no measurements demonstrating absent or reversed end diastolic flow. Umbilical artery Doppler studies did not initiate changes in management.Conclusion: In our population, antepartum assessment with a biophysical profile at no later than 36-week gestation identified all fetuses with testing abnormalities necessitating delivery in the daily opioid exposed fetus (6/27, 22.2%). Oligohydramnios was the most frequent indication for delivery. Serial growth ultrasounds by 32 weeks were necessary to identify the 11.1% of growth restricted, opioid exposed fetuses. A depressive effect of daily opioids on nonstress test reactivity or variability was not evident in our cohort. Future studies should attempt to define optimal monitoring based upon category of opioid dependence, type and dose of opioid consumed, and timing of opioid administration.

Amniotic Fluid Assessment: Amniotic Fluid Index Versus Maximum Vertical Pocket

Amniotic fluid assessment is vital to fetal well-being. Accurately diagnosing an amniotic fluid abnormality can aid in the proper management of a pregnancy at risk for an adverse outcome. Sonography is the most common way to assess amniotic fluid volume throughout a pregnancy; however, the most accurate technique, amniotic fluid index or maximum vertical pocket, is yet to be determined. Dye-dilution techniques are the most accurate way to measure amniotic fluid volume, but they are invasive and can be performed only at the time of a cesarean delivery. Multiple studies have been performed to determine the accuracy of the amniotic fluid index and maximum vertical pocket methods when diagnosing amniotic fluid volume abnormalities. Based on the studies reviewed in this article, neither method stands out as superior to the other when it comes to diagnosing amniotic fluid abnormalities during pregnancy. However, the maximum vertical pocket should also always be considered when an amniotic fluid abnormality is suspected because the amniotic fluid index overdiagnoses amniotic fluid abnormalities, leading to increased rates of pregnancy intervention and the potential for adverse pregnancy outcomes.

Mise à jour technique sur la physiologie et l'évaluation du liquide amniotique

OBJECTIF

RéSULTATS: SOURCES DES DONNéES PROBANTES: Nous avons effectué une recherche sur MEDLINE et Kfinder pour trouver des articles pertinents, puis avons examiné les bibliographies des articles retenus, notamment des revues Cochrane et des articles de revue récents.

VALEURS

Les données recueillies ont été analysées par le Comité d'imagerie diagnostique de la Société des obstétriciens et gynécologues du Canada. Les recommandations ont été classées selon les critères établis par le Groupe d'étude canadien sur les soins de santé préventifs (Tableau 1). AVANTAGES, DéSAVANTAGES ET COûTS: En obstétrique moderne, l'évaluation du volume de liquide amniotique par échographie fait partie intégrante de l'évaluation fœtale. Toute anomalie donne lieu à une intervention obstétricale et à des examens approfondis. Au Canada, il n'existe aucune définition normalisée associée à l'estimation du volume de liquide amniotique ni aucune approche d'évaluation uniforme. Plusieurs essais randomisés semblent indiquer que l'évaluation de poche unique, plutôt que de plusieurs poches (indice de liquide amniotique), diminue les interventions obstétricales sans augmenter l'incidence de résultats indésirables. La littérature récente laisse croire que des changements légers, mais détectables du liquide amniotique peuvent survenir une heure ou deux suivant des manœuvres physiologiques normales, ce qui pourrait expliquer la variabilité et le manque de cohérence des résultats d'évaluations répétées en peu de temps et ainsi créer de la confusion et donner lieu à d'autres examens. Le présent article vise à décrire les limites de l'évaluation du volume de liquide amniotique, à promouvoir une méthode d'évaluation normalisée et à proposer un ensemble commun de définitions. DéCLARATIONS SOMMAIRES: RECOMMANDATION.

Using frogs faces to dissect the mechanisms underlying human orofacial defects

In this review I discuss how Xenopus laevis is an effective model to dissect the mechanisms underlying orofacial defects. This species has been particularly useful in studying the understudied structures of the developing face including the embryonic mouth and primary palate. The embryonic mouth is the first opening between the foregut and the environment and is critical for adult mouth development. The final step in embryonic mouth formation is the perforation of a thin layer of tissue covering the digestive tube called the buccopharyngeal membrane. When this tissue does not perforate in humans it can pose serious health risks for the fetus and child. The primary palate forms just dorsal to the embryonic mouth and in non-amniotes it functions as the roof of the adult mouth. Defects in the primary palate result in a median oral cleft that appears similar across the vertebrates. In humans, these median clefts are often severe and surgically difficult to repair. Xenopus has several qualities that make it advantageous for craniofacial research. The free living embryo has an easily accessible face and we have also developed several new tools to analyze the development of the region. Further, Xenopus is readily amenable to chemical screens allowing us to uncover novel gene-environment interactions during orofacial development, as well as to define underlying mechanisms governing such interactions. In conclusion, we are utilizing Xenopus in new and innovative ways to contribute to craniofacial research.

Borderline amniotic fluid index and its relation to fetal intolerance of labor: a 2-center retrospective cohort study

OBJECTIVES

To determine whether a borderline amniotic fluid index (AFI) in the third trimester is associated with an increased rate of cesarean delivery for fetal intolerance of labor, meconium-stained amniotic fluid, and intrauterine growth restriction, among other adverse perinatal outcomes.

METHODS

Patients with a diagnosis of a borderline AFI between January 2008 and August 2012 were identified. Antepartum, delivery, and neonatal data were collected and compared to a cohort with a normal AFI.

RESULTS

We enrolled 739 patients, including 177 with a borderline AFI (>5 and <10 cm) and 562 with a normal AFI (≥ 10-24 cm); 360 patients delivered at University of Arizona Medical Center, and 379 delivered at St Joseph's Hospital. Combined and individual analyses of each center revealed no significant difference in fetal intolerance of labor (P = .19) or cesarean delivery for fetal intolerance (P = .074) between cohorts. In both settings, patients with a borderline AFI were more likely than those with a normal AFI to undergo antepartum testing (P < .001). A statistically significant increase in intrauterine growth restriction in the borderline AFI group was noted, with a calculated risk ratio of 13.76 (P < .001). There was no difference between groups for meconium-stained amniotic fluid (P = .23), neonatal intensive care unit admission (P = .054), preterm delivery (P = .31), or operative vaginal delivery (P = .45).

CONCLUSIONS

The findings of this study suggest that there is no difference in the rate of fetal intolerance of labor in pregnancies with a borderline AFI and those with a normal AFI. Pregnancies complicated by a borderline AFI are more likely to undergo antepartum testing, yet the benefit is unclear. Significantly more patients with a borderline AFI had underlying growth restriction, which may provide a useful tool for risk stratification in the management of a borderline AFI.

The origin of fetal sterols in second-trimester amniotic fluid: endogenous synthesis or maternal-fetal transport?

OBJECTIVE

Cholesterol is crucial for fetal development. To gain more insight into the origin of the fetal cholesterol pool in early human pregnancy, we determined cholesterol and its precursors in the amniotic fluid of uncomplicated, singleton human pregnancies.

STUDY DESIGN

Total sterols were characterized by gas chromatography-mass spectrometry in the second-trimester amniotic fluid of 126 healthy fetuses from week 15 until week 22.

RESULTS

The markers of cholesterol biosynthesis, lanosterol, dihydrolanosterol, and lathosterol, were present in low levels until the 19th week of gestation, after which their levels increased strongly. β-sitosterol, a marker for maternal-fetal cholesterol transport, was detectable in the amniotic fluid. The total cholesterol levels increased slightly between weeks 15 and 22.

CONCLUSION

Our results support the hypothesis that during early life the fetus depends on maternal cholesterol supply because endogenous synthesis is relatively low. Therefore, maternal cholesterol can play a crucial role in fetal development.