Amniotic fluid volume in normal singleton pregnancies

Evaluating the correlation between amniotic fluid volume and estimated fetal weight in healthy pregnant women

OBJECTIVES

The establishment of cut-offs for normal amniotic fluid volume (AFV) is valuable to predict perinatal outcomes. However, the most common methods to measure AFV are not accurate enough. It is important to understand factors that may be able to increase the accuracy of the calculation of AFV cut-off values. The objective of this study was to verify the correlation between AFV and estimated fetal weight (EFW).

METHODS

Records from almost 7,000 patients between 2012 and 2017 were accessed through hospital databases. The AFV measurements included in our analysis were obtained using the maximum vertical pocket technique.

RESULTS

AFV was positively correlated with EFW in the overall, male and female samples; however, the magnitude of the association was small (0.1

CONCLUSIONS

The incorporation of EFW together with other factors (e.g., gestational age, fetus sex) may increase the accuracy of the AFV cut-offs calculation and, ultimately, reduce morbidity.

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Key Words

• amniotic fluid
• estimated fetal weight
• maximum vertical pocket
• pregnancy complications

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MESH Headings

• Amniotic Fluid/diagnostic imaging
• Female
• Fetal Weight
• Gestational Age
• Humans
• Male
• Pregnancy
• Pregnant Women
• Prenatal Care
• Ultrasonography, Prenatal

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Affiliation(s)

Sara C S Souza OMNI Research Group, Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Canada
Katherine Kim OMNI Research Group, Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Canada
Alysha L J Dingwall-Harvey OMNI Research Group, Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Canada
Romina Fakhraei OMNI Research Group, Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Canada School of Epidemiology and Public Health, University of Ottawa, Ottawa, Canada
Yan Liao OMNI Research Group, Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Canada
Laura M Gaudet OMNI Research Group, Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Canada School of Epidemiology and Public Health, University of Ottawa, Ottawa, Canada Department of Obstetrics and Gynecology, Kingston Health Sciences Center, Kingston, Canada Department of Obstetrics and Gynecology, Queen's University, Kingston, Canada

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Amniotic fluid index measurements in the second and third trimester and correlation to fetal biometric parameters - new reference based on a big retrospective data

INTRODUCTION

Estimation of amniotic fluid volume (AFV) is part of routine obstetric sonography which reflects maternal-fetal circulation efficiency, fetal hemodynamic status, and a parameter for predicting adverse neonatal outcome. Fetal weight is positively correlated with AFV. Therefore, our objective is to provide a new nomogram of AFV indices and to evaluate the relation between AFV and fetal biometric parameters.

MATERIALS AND METHODS

Retrospective cohort study between 2011 and 2018, at a large tertiary medical center. Data were collected from medical charts of prenatal sonographic evaluation of normal pregnancies, including routine estimation of AFV by using amniotic fluid index (AFI). Generalized estimating equations model was used to study the association between AFI, gestational age and fetal biometric parameters. Centiles were calculated using the Generalized Additive Models for Location, Scale, and Shape model. Box-Cox-t distribution and smoothing splines were used.

RESULTS

Analysis included 28,650 pregnancies. From 25 to 41 weeks gestation, the median and fifth percentile AFI gradually decreased from 174 (IQR 157-193) to 138 mm (IQR 107-173) and from 125 to 68 mm, respectively. The change in the 95th percentile was less significant, ranging around 230 mm throughout pregnancy. Multivariate regression analysis demonstrated a significant correlation between AFI and maternal body mass index (B = -0.147; CI = -0.27 to -0.02), gestational age (B = -11.8; CI = -12.5 to -11.4), estimated fetal weight (EFW) (B = 0.05; CI = 0.049-0.053) and abdominal circumference (AC) (B = 0.94; CI = 0.95-1). There was no correlation between AFI and other fetal biometric parameters.

CONCLUSIONS

We suggest new AFI indices of singleton pregnancies. We found a positive correlation between AFI and EFW and AC.

Amniotic Fluid Volume Assessment: Eight Lessons Learned

Actual AFV can be determined by a dye-dilution technique or be directly measured at cesarean. This allows investigators to correlate estimated and actual AFVs. Lessons learned by assessing the relationship of estimated to actual AFVs. 1) Ultrasound estimates normal actual AFVs well, but abnormal AFVs poorly. 2) Quantile regression is a better statistical methodology to create a normal AFV curve across pregnancy. 3) There is no difference in the accuracy of the subjective (visualization without measurements) compared with the objective (visualization with measurements) technique in identifying normal and abnormal AFVs. 4) Color Doppler use leads to the over-diagnosis of oligohydramnios. 5) Intravenous hydration increases actual AFVs. 6) The estimation of AFV can be done with the transducer held perpendicular to the floor or perpendicular to the uterine contour. 7) The single deepest pocket should be used for identifying low AFVs. 8) The AFI should be used for identifying high AFVs.

Accuracy of the Ultrasound Estimate of the Amniotic Fluid Volume (Amniotic Fluid Index and Single Deepest Pocket) to Identify Actual Low, Normal, and High Amniotic Fluid Volumes as Determined by Quantile Regression

OBJECTIVES

To identify abnormal amniotic fluid volumes (AFVs), normal volumes must be determined. Multiple statistical methods are used to define normal amniotic fluid curves; however, quantile regression (QR) is gaining favor. We reanalyzed ultrasound estimates in identifying oligohydramnios, normal fluid, and polyhydramnios using normal volumes calculated by QR.

METHODS

Data from 506 dye-determined or directly measured AFVs along with ultrasound estimates were analyzed. Each was classified as low, normal, or high for both the single deepest pocket (SDP) and amniotic fluid index (AFI). A weighted κ statistic was used to assess the level of agreement between the AFI and SDP compared to actual AFVs by QR.

RESULTS

The overall level of agreement for the AFI was fair (κ = 0.26), and that for the SDP was slight (κ = 0.19). Although not statistically significant (P = .792), the positive predictive value to classify a low volume using the AFI was lower compared to the SDP (35% vs 43%). The positive predictive value for a high volume was higher using the AFI compared to the SDP (55% versus 31%) but not statistically significant. The missed-call rate for high-volume identification by the SDP versus AFI was statistically significant (odds ratio, 5.5; 95% confidence interval, 2.04-14.97). The missed-call rate for low-volume identification by the AFI versus SDP was not statistically significant (odds ratio, 3.3; 95% confidence interval, 0.96-11.53).

CONCLUSIONS

Both the AFI and SDP identify actual normal AFVs by QR, with sensitivity higher than 90%. The SDP is superior for identification of oligohydramnios, and the AFI superior for identification of polyhydramnios.

Efficiency of leukocyte depletion filters and micro-aggregate filters following intra-operative cell salvage during cesarean delivery

BACKGROUND

Intra-operative cell salvage is not routinely used during cesarean delivery because it is not cost-effective for patients at low risk of hemorrhage and there are theoretical concerns about amniotic fluid embolism. Some guidelines recommend using leukocyte depletion filters to decrease the risk of amniotic fluid embolism before re-infusing salvaged blood, but these filters are not available in Japan. We compared the efficacy and safety of leukocyte depletion and micro-aggregate filters in combination with intra-operative cell salvage during cesarean delivery.

METHODS

Blood was collected in a Cell Saver 5 reservoir during cesarean delivery. Four samples were collected: pre-wash, post-wash, post-filtration with a leukocyte depletion filter and post-filtration with a micro-aggregate filter. Each sample was analyzed for amniotic fluid markers of zinc coproporphyrin-1 and sialyl-Tn, for fetal hemoglobin, and the sample underwent pathological examination for white blood cells and squamous cells. Post-filtration samples were compared using paired t-tests with P <0.05 indicating statistical significance.

RESULTS

Zinc coproporphyrin-1 and sialyl-Tn were negative at almost all sample points. Squamous cells decreased by 59.1% post-wash and 91.2% post-filtration using a leukocyte depletion filter. Leukocyte depletion filters removed 99.7% of white blood cells and were more effective in removing white blood cells than micro-aggregate filters (P=0.02).

CONCLUSION

Leucocyte depletion filters are more effective in removing white blood cells and squamous cells than micro-aggregate filters, and their introduction for intra-operative cell salvage during cesarean delivery should be considered in Japanese clinical practice.

Antenatal fetal surveillance "Assessment of the AFV"

The evaluation of amniotic fluid volume (AFV) is an established part of the antenatal surveillance of pregnancies at risk for an adverse pregnancy outcome. The two most commonly used ultrasound techniques to estimate AFV are the amniotic fluid index (AFI) and the single deepest pocket (SDP). Four studies have defined normal AFVs, and although their normal volumes have similarities, there are also differences primarily due to the statistical methodology used in each study. Dye-determined AFV correlates with ultrasound estimates for normal fluid volumes but correlates poorly for oligohydramnios and polyhydramnios. The addition of color Doppler in estimating AFV leads to the overdiagnosis of oligohydramnios. Neither the AFI nor the SDP is superior in identifying oligohydramnios, but the SDP is a better measurement choice as the use of AFI increases the diagnosis rate of oligohydramnios and labor inductions without an improvement in pregnancy outcomes.

Pregnancy, Labor, and Delivery after Ebola Virus Disease and Implications for Infection Control in Obstetric Services, United States

Many of the survivors of the 2014-2015 epidemic of Ebola virus disease (EVD) in western Africa were women of childbearing age. Limited clinical and laboratory data exist that describe these women's pregnancies and outcomes. We report the case of an EVD survivor who became pregnant and delivered her child in the United States, and we discuss implications of this case for infection control practices in obstetric services. Hospitals in the United States must be prepared to care for EVD survivors.

Twin-to-Twin Transfusion Syndrome: Definition, Staging, and Ultrasound Assessment

Objective: The purpose of this article is to review the definition of twin-to-twin transfusion syndrome (TTTS) and the sonographic diagnostic assessment of these cases prior to therapy.

Materials and Methods: The article addresses the terminology used to refer to the condition and describes the systematic ultrasound assessment of the condition, including the ultrasound diagnosis, the staging of the disease, cervical assessment and pre-operative mapping.

Results: From an etymologic and medical point of view, the term ‘fetofetal transfusion’ is more appropriate than ‘TTTS’. However, as the latter, and its attendant acronym TTTS, have been widely adopted in the English language, it is impractical to change at this point. TTTS is defined sonographically in the combined presence of a maximum vertical pocket (MVP) of 8 cm or greater in one sac and 2 cm or less in the other sac, regardless of the gestational age at diagnosis. Staging of the condition using the Quintero staging system is practical, reproducible, and accepted. Transvaginal cervical length assessment should be an integral part of the ultrasound evaluation. Pre-operative mapping to anticipate the location of the placental vascular anastomoses and avoid injuring the dividing membrane is also discussed.

Conclusions: The term ‘TTTS’ can continue to be used in the English medical literature. The condition can be diagnosed and assessed following a systematic ultrasound methodology. The use of such ultrasound methodology breaks the examination into a distinct set of components, assuring a comprehensive examination and proper communication among caregivers.

Effects of Passive Hydrotherapy WATSU (WaterShiatsu) in the Third Trimester of Pregnancy: Results of a Controlled Pilot Study

Background. WATSU (WaterShiatsu) is a complementary therapeutic treatment method comprising passive stretches and massage techniques administered in 35°C warm water. Pregnant women claim safe methods to reduce pain, stress, and fatigue. Therefore, we conducted a pilot study evaluating the effects of WATSU on pregnancy-related complaints in third trimester pregnant women. Methods. Nine healthy pregnant women at gestational week ≥34 were included in an intervention group (receiving WATSU) and compared to eight women in a passive control group (receiving no treatment). WATSU was performed on days 1 and 4 of the study, accompanied by ultrasound examinations. Outcomes include physiological and psychometric as well as qualitative data. Participants in the control group completed questionnaires only. Results. WATSU was found to significantly lower participants' levels of stress and pain and to improve their mental health-related quality of life and mood. In comparison to the passive control group, participants in the intervention group reported reduction in perceived stress from day 1 to day 8 (P = 0.036, Cohen's f = 0.57). Qualitative data indicate that WATSU was appreciated as enjoyable and deeply relaxing. No negative side effects were reported. Conclusion. Our findings support the notion that WATSU yields therapeutic benefits for pregnant women and warrant further research. This study has been registered at ClinicalTrials.gov: NCT01708018.

Correlation of ultrasound estimated with dye-determined or directly measured amniotic fluid volume revisited

BACKGROUND/AIMS

To examine the relationship of the amniotic fluid index (AFI) and single deepest pocket (SDP) with an AFV as modelled by Brace or Magann.

METHODS

AFI and SDP were evaluated for their correlation with an actual AFV using the Spearman correlation coefficient.

RESULTS

482 AFI and 468 SDP pregnancies were evaluated. There was a significant association between the AFI and SDP and an actual AFV (p < 0.0001). The AFI range of 5.1-20 was better correlated than 5.1-24 for normal AFVs Brace (κ = 0.175) and Magann (κ = 0.356) versus 5.1-24 (κ = 0.150 and κ = 0.319), respectively. The agreement level t for the AFI (κ = 0.175) and SDP (κ = 0.126) using Brace was slight and for the AFI (κ = 0.356) and SDP (κ = 0.295) using Magann was fair.

CONCLUSIONS

Both the AFI and SDP were correlated with actual AFV using both models. AFI of 5.1-20 better categorizes normal volumes. Although the Magann model correlates AFI/SDP and AFV better, the superiority is minimal.

Accuracy of the lamellar body count in amniotic fluid contaminated by meconium

OBJECTIVE

To determine whether meconium-contaminated amniotic fluid falsely elevates the lamellar body count in fetal lung maturity testing.

METHODS

Thirty mothers undergoing amniocentesis for fetal lung maturity testing were prospectively consented. A 2 mL portion of the patient's sample was mixed with a 10% meconium solution and the meconium-stained sample was then run in tandem with the patient's sample used in clinical management. Pure meconium samples without amniotic fluid were also run through the cell counter for analysis.

RESULTS

Following meconium contamination, the lamellar body count value increased in 67% of the cases, decreased in 23% and remained the same in 10%. There were 13 test results that had "immature" values in the uncontaminated patient management sample group and nine of these (69%) became elevated to a "mature" level (a false elevation) following the addition of meconium. All of the 10 pure liquid meconium samples devoid of amniotic fluid processed by the cell counter identified and quantified some particle the size of platelets.

CONCLUSIONS

The lamellar body count test result is not reliable in meconium-stained amniotic fluid specimens. There is some unknown particle found in meconium that is the size of platelets/lamellar bodies that can falsely elevate the test result. Currently, the only reliable fetal lung maturity test in meconium-stained amniotic fluid is the presence of phosphatidylglycerol.

Toward consistent terminology: assessment and reporting of amniotic fluid volume

Amniotic fluid is typically measured by ultrasound using the amniotic fluid index (AFI) or the maximum vertical pocket (MVP). Although both parameters correlate poorly with the actual amniotic fluid volume measured with dye-dilution methods, cross-sectional studies have been used to establish gestational norms. The current acceptable definition of polyhydramnios in the late second and the third trimester in both singleton and multiple gestations is a MVP > 8 cm, while the definition of oligohydramnios is a MVP < 2 cm. The pocket to be measured should exclude the umbilical cord or fetal parts. Randomized clinical trials have indicated that defining oligohydramnios as a MVP < 2 cm will result in fewer obstetrical interventions and similar perinatal outcomes when compared to an AFI < 5 cm.

Amniotic fluid as a vital sign for fetal wellbeing

Introduction: Amniotic fluid, once thought to merely provide protection and room for necessary movement and growth for the fetus, is now understood to be a highly complex and dynamic system that is studied as a data point to interpret fetal wellbeing. Methods: Assessment of amniotic fluid volume is now routine when performing a sonographic evaluation of fetal status and is an important consideration in the assessment and management of perinatal morbidity and mortality.1,2 In this review, we will cover the dynamics that affect amniotic fluid volume, review methods for measurement and quantification of volume, review definitions for normative data as related to neonatal outcomes, and provide evidence based guidance on the workup and management options for oligoydramnios and polyhydramnios in singleton and twin pregnancies. Conclusions: When abnormalities of fluid exist, appropriate workup to uncover the underlying etiology should be initiated as adverse fetal outcomes are sometimes associated with these variations from normalcy.

Amniotic fluid and the clinical relevance of the sonographically estimated amniotic fluid volume: oligohydramnios

The amniotic fluid volume (AFV) is regulated by several systems, including the in-tramembranous pathway, fetal production (fetal urine and lung fluid) and uptake (fetal swallowing), and the balance of fluid movement via osmotic gradients. The normal AFV across gestation has not been clearly defined; consequently, abnormal volumes are also poorly defined. Actual AFVs can be measured by dye dilution techniques and directly measured at cesarean delivery; however, these techniques are time-consuming, are invasive, and require laboratory support, and direct measurement can only be done at cesarean delivery. As a result of these limitations, the AFV is estimated by the amniotic fluid index (AFI), the single deepest pocket, and subjective assessment of the AFV. Unfortunately, sonographic estimates of the AFV correlate poorly with dye-determined or directly measured amniotic fluid. The recent use of color Doppler sonography has not improved the diagnostic accuracy of sonographic estimates of the AFV but instead has led to overdiagnosis of oligohydramnios. The relationship between the fixed cutoffs of an AFI of 5 cm or less and a single deepest pocket of 2 cm or less for identifying adverse pregnancy outcomes is uncertain. The use of the single deepest pocket compared to the AFI to identify oligohydramnios in at-risk pregnancies seems to be a better choice because the use of the AFI leads to an increase in the diagnosis of oligohydramnios, resulting in more labor inductions and cesarean deliveries without any improvement in peripartum outcomes.

Management of oligohydramnios in pregnancy

The finding of oligohydramnios in pregnancy is problematic. The various mechanisms that control amniotic fluid, the inability to precisely measure and quantify the amount, and the relevance of a "decreased" amount of fluid make the management of this finding unclear. Given the limited amount of data, the single deepest vertical pocket may be a better method than the amniotic fluid index to define oligohydramnios. A large prospective study is needed to develop the most optimal management recommendations, especially for idiopathic oligohydramnios at or near term.

A Review of Fetal ECG Signal Processing; Issues and Promising Directions

The field of electrocardiography has been in existence for over a century, yet despite significant advances in adult clinical electrocardiography, signal processing techniques and fast digital processors, the analysis of fetal ECGs is still in its infancy. This is, partly due to a lack of availability of gold standard databases, partly due to the relatively low signal-to-noise ratio of the fetal ECG compared to the maternal ECG (caused by the various media between the fetal heart and the measuring electrodes, and the fact that the fetal heart is simply smaller), and in part, due to the less complete clinical knowledge concerning fetal cardiac function and development. In this paper we review a range of promising recording and signal processing techniques for fetal ECG analysis that have been developed over the last forty years, and discuss both their shortcomings and advantages. Before doing so, however, we review fetal cardiac development, and the etiology of the fetal ECG. A selection of relevant models for the fetal/maternal ECG mixture is also discussed. In light of current understanding of the fetal ECG, we then attempt to justify recommendations for promising future directions in signal processing, and database creation.

Dye-determined amniotic fluid volume and intrapartum/neonatal outcome

OBJECTIVE

To ascertain if a dye-determined amniotic fluid volume was predictive of intrapartum and perinatal outcome.

MATERIALS AND METHODS

The low and normal amniotic fluid volumes (< 5th percentile and > or =5th percentile for gestational age) and the raw dye-determined amniotic fluid distributions were correlated with 10 clinical outcome measures in 74 pregnancies.

RESULTS

In this observational study, median gestational age at delivery was 36 weeks (range 26 to 41) and 16 deliveries were for fetal distress (14 Cesarean and two forceps). There were no differences between the outcomes of pregnancies with low and normal amniotic fluid volumes for any of the clinical outcomes (variable decelerations influencing delivery, p=0.381; late decelerations, p=0.875; Cesarean births for fetal intolerance of labor, p=0.259; intrauterine growth restriction, p=0.998; or umbilical cord arterial pH< 7.2, p=0.259). Analogous results were obtained when the gestational age-adjusted amniotic fluid volumes were compared directly between the pregnancies with normal and abnormal outcomes. There was no difference between the mean amniotic fluid volumes in those pregnancies with variable decelerations influencing delivery (p=0.287), late decelerations (p=0.555), Cesarean births for fetal intolerance of labor (p=0.310), intrauterine growth restriction (p=0.267) or umbilical cord arterial pH< 7.2, and the pregnancies without these intrapartum events. Reduced variability was more commonly observed in pregnancies with higher amniotic fluid volumes (p=0.038, 771 ml, 95% CI 468 to 1269, compared to those without normal variability 444 ml, 95% CI 374 to 526).

CONCLUSIONS

Dye-determined amniotic fluid volume does not appear to be predictive of adverse intrapartum and neonatal outcome.

How well do the amniotic fluid index and single deepest pocket indices (below the 3rd and 5th and above the 95th and 97th percentiles) predict oligohydramnios and hydramnios?

OBJECTIVE

This study was undertaken to determine whether the amniotic fluid index (AFI) and single deepest pocket percentiles can reliably identify a dye-determined amniotic fluid volume.

STUDY DESIGN

Ultrasound measurements and dye-determined volumes were prospectively collected. Oligohydramnios predictors included AFI and single deepest pocket below the 3rd and 5th percentiles, and hydramnios predictors were based on AFI and single deepest pocket above the 95th and 97th percentiles.

RESULTS

Two hundred ninety-one women with singleton pregnancies participated, including 75 pregnancies (26%) with oligohydramnios and 31 pregnancies (10%) with hydramnios. The predictive ability of the AFI and single deepest pocket indices (<3rd and 5th percentiles) to identify oligohydramnios was between 11% and 27% and to identify hydramnios (>95th and 97th percentiles) ranged between 33% and 46%. The best prediction was for normal fluid volume with an accuracy of 83% to 94%.

CONCLUSION

Amniotic fluid indices perform best for the identifying normal AF volumes, whereas the identification of oligohydramnios or hydramnios is poor.

Mode of delivery in pregnancies with suspected fetal growth restriction following induction of labor with vaginal prostaglandin E2

BACKGROUND

Many fetuses below the 10th percentile for gestational age are uncompromised. We aimed to evaluate the mode of delivery and immediate neonatal outcome in pregnancies with suspected fetal growth restriction (FGR) and normal antenatal assessment following induction of labor with vaginal application of prostaglandin E2 (PGE2).

METHODS

Ninety women with suspected FGR (sonographic estimated fetal weight < 10th percentile) with normal oxytocin contraction test (OCT), biophysical profile (BPP) and reassuring fetal heart rate underwent induction of labor with vaginal application of PGE2 tablets. The findings were compared with 115 women admitted for induction of labor because of decreased fetal movement (group 2) and with 510 women with normal spontaneous onset of labor (group 3).

RESULTS

There were no between-group differences in mean maternal age, gravidity, parity, nulliparity rate, number of tablets used or rate of patients receiving more than one PGE2 application. The rate of cesarean section (CS) in the study group (8.9%) was similar to the rate in groups 2 and 3 (14.8% and 9.0%, respectively). The incidence of nonreassuring fetal heart rate pattern leading to cesarean delivery was higher in the study group, but the rate of low 5-min Apgar scores (< 7) was similar in all groups. A logistic regression model and forward likelihood analysis yielded no single significant variable associated with increased risk of cesarean delivery.

CONCLUSIONS

In selected cases of suspected FGR with reassuring fetal heart rate and normal OCT and BPP, induction of labor with vaginal PGE2 may yield a similar immediate fetal outcome and CS rate as in uncomplicated, induced or spontaneous deliveries.

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

OBJECTIVE

The purpose of this study was to establish whether ultrasound-estimated or dye-determined amniotic fluid distribution (upper compared with lower quadrant) is predictive of perinatal outcome.

STUDY DESIGN

Amniotic fluid distribution as measured by the amniotic fluid index, single deepest pocket, and dye-determined volumes was ascertained and correlated with intrapartum and neonatal outcomes.

RESULTS

Between January 1997 and January 2001, 135 women (70 upper-greater and 65 lower-greater) participated in this prospective observational study. The sum of the amniotic fluid index (P =.309), single deepest pocket (P =.168), and dye-determined amniotic fluid volume (P =.368) for the upper-greater compared with the lower-greater groups were similar. Decelerations in labor (P =.597), late decelerations (P =.999), cesarean deliveries for fetal distress (P =.413), and umbilical cord pH < 7.2 were similar (P =.647)

CONCLUSION

Ultrasound-estimated and dye-determined amniotic fluid volumes are similar between upper-greater and lower-greater groups, and intrapartum/neonatal outcomes are not affected by the amniotic fluid distribution.

Is amniotic fluid volume status predictive of fetal acidosis at delivery?

OBJECTIVE

To ascertain if dye-determined amniotic fluid volume just prior to delivery correlates with fetal acidosis at delivery.

DESIGN

The present was a prospective observational study.

SETTING

The study took place at the University of Mississippi Medical Center, Jackson MS, USA.

POPULATION

The population included 100 unlaboured women undergoing an amniocentesis for the assessment of fetal lung maturity before an elective Caesarean delivery between January 1997 and December 2000.

MAIN OUTCOMES MEASURED

The amniotic fluid volume was estimated by ultrasound measurement and quantified by dye-determined methodology immediately prior to Caesarean delivery. Umbilical cord artery pH was collected at the time of Caesarean delivery.

RESULTS

The predictive accuracy of an amniotic fluid index < or = versus > 5 to identify an umbilical artery pH of < 7.20 had a sensitivity of 0%, a specificity of 84%, and a likelihood ratio of zero. None of the dye-determined low amniotic fluid volumes were identified using the single deepest pocket technique. Dye-determined low, normal, and high amniotic fluid volume groups contained a similar number of fetuses with umbilical cord arterial pH < 7.20 (P = 0.371), < 7.10 (P = 0.460), and < 7.00 (P = 0.614). Receiver-operating characteristic curves could not identify any amniotic fluid index from 0 to 18, single deepest pocket from 0 to 12, or dye-determined amniotic fluid volume 100-1900 mL to differentiate between the two newborns with an umbilical cord artery pH < 7 from 98 babies with cord pH > or = 7.0.

CONCLUSIONS

Neither ultrasound estimates nor dye-determined amniotic fluid volumes are predictive of a low umbilical artery pH at delivery.

Ultrasound estimation of amniotic fluid volume using the largest vertical pocket containing umbilical cord: measure to or through the cord?

OBJECTIVES

The purpose of this investigation was to determine the preferable method, either measuring to the umbilical cord or through the umbilical cord to the base of the pocket, of ultrasonically estimating amniotic fluid volume.

SUBJECT AND METHODS

This was a prospective study carried out in singleton pregnancies undergoing a third-trimester amniocentesis. The amniotic fluid index (AFI) and single deepest pocket (SDP) were measured prior to amniocentesis. If measured spaces contained umbilical cord, measurements were made to and through the cord. Actual amniotic fluid volume was determined by the dye-dilution technique.

RESULTS

One-hundred pregnancies were evaluated. Low dye-determined volume was identified in a significantly greater number of pregnancies using the AFI to the cord (7/28, 25%) compared to through the cord (2/28, 7%) (P = 0.025). The SDP technique to the cord was superior in low volumes (2/28, 7%) vs. (0/28, 0%) through the cord (although statistical significance could not be determined because there were no low through-the-cord measurements).

CONCLUSIONS

For the detection of low amniotic fluid volumes, the AFI to the cord is better than through the cord. Measurement to the cord and through the cord had similar accuracy for both the AFI and SDP techniques in normal and high dye-determined amniotic fluid volumes.

The influence of fetoabdominal tissues on fetal ECGs and MCGs

Both fetal electrocardiography and fetal magnetocardiography are influenced by the volume conduction within the abdomen of the pregnant woman. In this paper, various models are used to simulate this influence. Such models are helpful to determine where to attach electrodes at the maternal abdomen in case fetal ECGs are measured and where to position the magnetocardiograph in case fetal MCGs are measured. Another goal is to assess the influence of individual differences, such as the amount of amniotic fluid. Seven models based on MR-images have been created, four for the third trimester of gestation, with the fetus in left occiput position, and three for the second trimester. The models consist of four compartments; the fetus, the vernix caseosa, the amniotic fluid, and the remainder of the maternal abdomen. It turns out that individual differences have a large impact on the fetal MCG and that the best measurement positions are expected over the centre of the abdomen near the fetal heart. The fetal ECG is dependent on the vernix caseosa and when this layer is present, the fetal ECG is best measured by two electrodes, one over the fetal mouth and the other over the bottom of the fetus.

Amniotic fluid volume assessment in singleton and twin pregnancies

The best method of ultrasonic mensuration to identify abnormal AFV reliably in singletons and the individual sacs of diamniotic twins remains elusive. With respect to twins, localization of the dividing membrane seems to be necessary for AFV assessments of each amniotic cavity. The relationship of ultrasonic estimates, actual AFV, and pregnancy outcome remains undetermined. In the authors' opinion, the subjective assessment in twin gestation may be as accurate as semiquantitative ultrasonic estimates of AFV, similar to the situation in singleton pregnancies. The authors propose that further prospective research address the following questions: (1) What is the appropriate threshold for intervention when AFI decreases to lower ranges? (2) What other factors (e.g., cervical examination, fetal heart rate patterns, underlying obstetric conditions, fetal growth pattern) are important when the AFI falls to low values in making clinical decisions?