Amniotic fluid index and single deepest pocket: weak indicators of abnormal amniotic volumes

Correlation of perinatal outcomes with amniotic fluid assessment techniques in high-risk pregnancies in a Tertiary Hospital in Southern Nigeria

BACKGROUND

Oligohydramnios is a predictor of fetal compromise and a useful tool in pregnancy management. It has been assessed using various techniques, including two-diameter pocket (2-DP) and amniotic fluid index (AFI).

OBJECTIVES

To determine which of these two techniques best diagnose oligohydramnios and predicts adverse perinatal outcomes.

METHODS

This was a comparative cross-sectional study conducted at Delta State University Teaching Hospital, Oghara in southern region of Nigeria over eight months period. One hundred high-risk pregnant women were recruited and ultrasound determination of amniotic fluid was performed using AFI and 2-DP. The women were followed up till delivery to determine adverse perinatal outcomes.

RESULTS

The indices of validity of AFI and the 2-DP were calculated and compared. The 2-DP had a higher sensitivity than AFI for adverse outcomes in high-risk pregnancies complicated by oligohydramnios.

CONCLUSION

The 2-DP technique should preferably be used for the assessment of oligohydramnios in high-risk pregnancies.

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.

Antenatal staging of congenital lower urinary tract obstruction

OBJECTIVE

To propose a staging system for congenital lower urinary tract obstruction (LUTO) capable of predicting the severity of the condition and its prognosis.

METHODS

This was a national retrospective study carried out at the eight Academic Hospitals in The Netherlands. We collected prenatal and postnatal data of fetuses at high risk of isolated LUTO that were managed conservatively. Postnatal renal function was assessed by the estimated glomerular filtration rate (eGFR), calculated using the Schwartz formula, considering the length of the infant and the creatinine nadir in the first year after birth. Receiver-operating characteristics (ROC) curve analysis, univariate analysis and multivariate logistic regression analysis with stepwise backward elimination were performed in order to identify the best antenatal predictors of perinatal mortality and postnatal renal function.

RESULTS

In total, 261 fetuses suspected of having LUTO and managed conservatively were included in the study. The pregnancy was terminated in 110 cases and perinatal death occurred in 35 cases. Gestational age at appearance of oligohydramnios showed excellent accuracy in predicting the risk of perinatal mortality with an area under the ROC curve of 0.95 (P < 0.001) and an optimal cut-off at 26 weeks' gestation. Fetuses with normal amniotic fluid (AF) volume at 26 weeks' gestation presented with low risk of poor outcome and were therefore defined as cases with mild LUTO. In fetuses referred before the 26^th week of gestation, the urinary bladder volume (BV) was the best unique predictor of perinatal mortality. ROC curve analysis identified a BV of 5.4 cm³ and appearance of oligohydramnios at 20 weeks as the best threshold for predicting an adverse outcome. LUTO cases with a BV ≥ 5.4 cm³ or abnormal AF volume before 20 weeks' gestation were defined as severe and those with BV < 5.4 cm³ and normal AF volume at the 20 weeks' scan were defined as moderate. Risk of perinatal mortality significantly increased according to the stage of severity, from mild to moderate to severe stage, from 9% to 26% to 55%, respectively. Similarly, risk of severely impaired renal function increased from 11% to 31% to 44%, for mild, moderate and severe LUTO, respectively.

CONCLUSIONS

Gestational age at appearance of oligo- or anhydramnios and BV at diagnosis can accurately predict mortality and morbidity in fetuses with LUTO. Our proposed staging system can triage reliably fetuses with LUTO and predict the severity of the condition and its prognosis. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Antenatal placental assessment in the prediction of adverse pregnancy outcome after reduced fetal movement

OBJECTIVE

To assess the value of in utero placental assessment in predicting adverse pregnancy outcome after reported reduced fetal movements (RFM).

METHOD

A non-interventional prospective cohort study of women (N = 300) with subjective RFM at ≥28 weeks' gestation in singleton non-anomalous pregnancies at a UK tertiary maternity hospital. Clinical, sonographic (fetal weight, placental size and maternal, fetal and placental arterial Doppler) and biochemical (maternal serum hCG, hPL, progesterone, PlGF and sFlt-1) assessment was conducted. Multiple logistic regression identified combinations of measurements (models) most predictive of adverse pregnancy outcome (perinatal mortality, birth weight <10th centile, five minute Apgar score <7, umbilical arterial pH <7.1 or base excess <-10, neonatal intensive care admission). Models were compared by test performance characteristics (ROC curve, sensitivity, specificity, positive/negative predictive value, positive/negative likelihood ratios) against baseline care (estimated fetal weight centile, amniotic fluid index and gestation at presentation).

RESULTS

61 (20.6%) pregnancies ended in adverse outcome. Models incorporating PlGF/sFlt-1 ratio and umbilical artery free loop Doppler impedance demonstrated modest improvement in ROC area for adverse outcome (baseline care 0.69 vs. proposed models 0.73-0.76, p<0.05). However, there was little improvement in other test characteristics (baseline vs. best proposed model: sensitivity 21.7% [95% confidence interval 13.1-33.6] vs. 35.8%% [24.4-49.3], specificity 96.6% [93.4-98.3] vs. 94.7% [90.7-97.0], PPV 61.9% [40.9-79.3] vs. 63.3% [45.5-78.1], NPV 82.8% [77.9-86.8] vs. 85.2% [80.0-89.2], positive LR 6.3 [2.8-14.6] vs. 6.7 [3.4-3.3], negative LR 0.81 [0.71-0.93] vs. 0.68 [0.55-0.83]) and wide confidence intervals. Negative post-test probability remained high (16.7% vs. 14.0%).

CONCLUSION

Antenatal placental assessment may improve identification of RFM pregnancies at highest risk of adverse pregnancy outcome but further work is required to understand and refine currently available outcome definitions and diagnostic techniques to improve clinical utility.

A comparison between amniotic fluid index and the single deepest vertical pocket technique in predicting adverse outcome in prolonged pregnancy

OBJECTIVE

to compare perinatal outcome in induced postterm pregnancies with normal amniotic volume and in patients with prolonged pregnancy undergone induction for oligohydramnios, evaluated by two different ultrasonographic methods.

METHODS

amniotic fluid volume was measured, using Single Deepest Vertical Pocket (SDVP) and Amniotic Fluid Index (AFI), in 961 singleton uncomplicated prolonged pregnancies. In 109 of these patients, hospitalization was planned for induction of labor, during or after 42 weeks of gestation, for oligohydramnios, postterm pregnancy and other indications in 47, 51 and 11 cases, respectively. Perinatal outcome included: rate of caesarean section, fetal distress, non reassuring fetal heart tracing, presence of meconium, umbilical artery pH < 7.1, Apgar score at 5 minutes < 7, admission to neonatal intensive care unit (NICU).

RESULTS

oligohydramnios was diagnosed in 4.89% of cases, when at least one of the two methods was used. A reduced AFI and SDVP value identified 4.47% and 3.75% of cases, respectively, even if without statistical difference. No statistical differences were reported in perinatal outcomes in postterm versus prolonged pregnancies with oligohydramnios, also in relation to the two different ultrasonographic methods.

CONCLUSIONS

oligohydramnios is more frequently diagnosed using AFI than SDVP, consequently determining a higher rate of induction of labor. Moreover, perinatal outcome in prolonged induced pregnancies is not affected by oligohydramnios.

Association and prediction of amniotic fluid measurements for adverse pregnancy outcome: systematic review and meta-analysis

BACKGROUND

Measurements of amniotic fluid volume are used for pregnancy surveillance despite a lack of evidence for their predictive ability.

OBJECTIVE

To evaluate the association and predictive value of ultrasound measurements of amniotic fluid volume for adverse pregnancy outcome.

SEARCH STRATEGY

Electronic databases (inception to October 2011), reference lists, hand searching of journals, contact with experts.

SELECTION CRITERIA

Studies comparing measurements of amniotic fluid volume with adverse outcome, excluding pre-labour ruptured membranes or congenital/structural anomalies.

DATA COLLECTION

Data on study characteristics, design, quality. Random effects meta-analysis to estimate summary odds ratios (prognostic association) and summary sensitivity, specificity and likelihood ratios (predictive ability).

MAIN RESULTS

Forty-three studies (244,493 fetuses) were included demonstrating a strong association between oligohydramnios (varying definitions) and birthweight <10th centile (summary odds ratio [OR] 6.31, 95% confidence interval [95% CI] 4.15-9.58; high-risk population [author definition] n = 6 studies, 28,510 fetuses), and mortality (neonatal death any population summary OR 8.72, 95% CI 2.43-31.26; n = 6 studies, 55,735 fetuses; and perinatal mortality high-risk population summary OR 11.54, 95% CI 4.05-32.9; n = 2 studies, 27;891 fetuses). There was a strong association between polyhydramnios (maximum pool depth >8 cm or amniotic fluid index ≥25 cm) and birthweight >90th centile (OR 11.41, 95% CI 7.09-18.36; n = 1 study, 3960 fetuses). Despite strong associations, predictive accuracy for perinatal outcome was poor.

AUTHOR'S CONCLUSION

Current evidence suggests that oligohydramnios is strongly associated with being small for gestational age and mortality, and polyhydramnios with birthweight >90th centile. Despite strong associations with poor outcome, they do not accurately predict outcome risk for individuals.

Polyhydramnios: Causes, Diagnosis and Therapy

Polyhydramnios is defined as a pathological increase of amniotic fluid volume in pregnancy and is associated with increased perinatal morbidity and mortality. Common causes of polyhydramnios include gestational diabetes, fetal anomalies with disturbed fetal swallowing of amniotic fluid, fetal infections and other, rarer causes. The diagnosis is obtained by ultrasound. The prognosis of polyhydramnios depends on its cause and severity. Typical symptoms of polyhydramnios include maternal dyspnea, preterm labor, premature rupture of membranes (PPROM), abnormal fetal presentation, cord prolapse and postpartum hemorrhage. Due to its common etiology with gestational diabetes, polyhydramnios is often associated with fetal macrosomia. To prevent the above complications, there are two methods of prenatal treatment: amnioreduction and pharmacological treatment with non-steroidal anti-inflammatory drugs (NSAIDs). However, prenatal administration of NSAIDs to reduce amniotic fluid volumes has not been approved in Germany. In addition to conventional management, experimental therapies which would alter fetal diuresis are being considered.

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.

Maximal amniotic fluid index as a prognostic factor in pregnancies complicated by polyhydramnios

OBJECTIVES

Polyhydramnios is present in approximately 2% of pregnancies and has been associated with a variety of adverse pregnancy outcomes. Our aim was to evaluate the association between the maximal amniotic fluid index (AFI) and the frequency of specific adverse outcomes.

METHODS

This was a retrospective chart review of 524 singleton pregnancies diagnosed with polyhydramnios and delivered in a single tertiary referral center between 2003 and 2008. Polyhydramnios was defined as either AFI ≥ 25 cm or a maximum vertical pocket (MVP) ≥ 8 cm even in the presence of AFI < 25 cm. The cohort was stratified into four groups based on the maximal AFI noted during the pregnancy: < 25 cm but with MVP ≥ 8 cm; 25-29.9 cm; 30-34.9 cm; and ≥ 35 cm. Data were collected to determine the frequency of the following adverse pregnancy outcomes: prenatally diagnosed congenital anomalies, fetal aneuploidy, preterm delivery, Cesarean delivery, low birth weight, 5-min Apgar score < 7 and perinatal mortality.

RESULTS

Higher AFI was associated with a statistically significant increase in the frequency of adverse pregnancy outcomes. The most severe form of polyhydramnios, as based on the maximal AFI (≥ 35 cm; n = 67), was associated with the highest rates of prenatally diagnosed congenital anomalies (79%), preterm delivery (46%), small-for-gestational-age neonate (16%), aneuploidy (13%) and perinatal mortality (27%). No significant association between degree of polyhydramnios and adverse outcome was demonstrated in cases of idiopathic polyhydramnios (n = 253).

CONCLUSIONS

There is an association between the frequencies of a variety of adverse pregnancy outcomes and the severity of polyhydramnios as reflected by the maximal AFI.

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.

Antenatal testing-a reevaluation: executive summary of a Eunice Kennedy Shriver National Institute of Child Health and Human Development workshop

In August 2007, the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the National Institutes of Health Office of Rare Diseases, the American College of Obstetricians and Gynecologists, and the American Academy of Pediatrics cosponsored a 2-day workshop to reassess the body of evidence supporting antepartum assessment of fetal well-being, identify key gaps in the evidence, and formulate recommendations for further research. Participants included experts in obstetrics and fetal physiology and representatives from relevant stakeholder groups and organizations. This article is a summary of the discussions at the workshop, including synopses of oral presentations on the epidemiology of stillbirth and fetal neurological injury, fetal physiology, techniques for antenatal monitoring, and maternal and fetal indications for monitoring. Finally, a synthesis of recommendations for further research compiled from three breakout workgroups is presented.

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.

Correlation of measured amnionic fluid volume to sonographic and magnetic resonance predictions

OBJECTIVE

The purpose of this study was to compare the relationship between the actual amnionic fluid volume that was measured at delivery and magnetic resonance amnionic fluid volume determination, largest vertical pocket, and amnionic fluid index.

STUDY DESIGN

Three hours before cesarean delivery, 80 women had sonographic measurement of the amnionic fluid index and the largest vertical pocket. Magnetic resonance imaging was then completed, and the magnetic resonance amnionic fluid volume was determined. At surgery, the amnionic fluid was collected. Pearson correlations were determined. Receiver operating characteristic curves were developed for each method as a measure of predictability for oligohydramnios.

RESULTS

The correlations for the magnetic resonance amnionic fluid volume, amnionic fluid index, and largest vertical pocket to amnionic fluid volume was 0.84, 0.77, and 0.71, respectively. Magnetic resonance amnionic fluid volume has a statistically higher correlation than the largest vertical pocket ( P = .046). The 3 methods, however, are statistically comparable for identifying oligohydramnios.

CONCLUSION

Magnetic resonance imaging is comparable with ultrasound evaluation for the prediction of oligohydramnios. Correlations to actual amnionic fluid volume are also comparable.

Pathophysiology of Fetal Growth Restriction: Implications for Diagnosis and Surveillance

Normal fetal growth depends on the genetically predetermined growth potential and is modulated by fetal, placental, maternal, and external factors. Fetuses with intrauterine growth restriction (IUGR) are at high risk for poor short- and long-term outcome. Although there are many underlying etiologies, IUGR resulting from placental insufficiency is most relevant clinically because outcome could be altered by appropriate diagnosis and timely delivery. A diagnostic approach that aims to separate IUGR resulting from placental disease from constitutionally small fetuses and those with other underlying etiologies (e.g., aneuploidy, viral infection, nonaneuploid syndromes) needs to integrate multiple imaging modalities. In placental-based IUGR, cardiovascular and behavioral responses are interrelated with the disease severity. Ultrasound assessment of fetal anatomy, amniotic fluid volume, and growth is complementary to the Doppler investigation of fetoplacental blood flow dynamics. A diagnostic approach to IUGR combining these modalities is presented in this review.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to describe the development of the placental interface, to outline the mechanisms of placental insufficiency, and to list the manifestations of placental insufficiency and the tests that can be used to diagnose fetal growth restriction.

Is there a relationship to dye determined or ultrasound estimated amniotic fluid volume adjusted percentiles and fetal weight adjusted percentiles?

OBJECTIVE

This study was undertaken to determine whether there is a correlation between neonatal birth weight and an estimated or dye-determined amniotic fluid volume.

STUDY DESIGN

A prospective observational study of women undergoing an amniocentesis and subsequent delivery within 72 hours. Amniotic fluid volume was estimated using the amniotic fluid index (AFI) and single deepest pocket technique and calculated by the dye-dilution technique.

RESULTS

One hundred seventy-five women participated in the study. Linear regression modelling showed no significant relationship between birth weight and amniotic fluid volume adjusted for gestational age (P=.062). Similarly, there was no evidence of an association between birth weight and a dye determined amniotic fluid volume (P=.180), fixed cutoffs for the AFI (P=.224), percentiles for the AFI (P=.112), or fixed cutoffs for the single deepest pockets (P=.867).

CONCLUSION

Neonatal birth weight is not correlated with a dye-determined or ultrasound estimated amniotic fluid volume.

Monitoring the IUGR fetus

Monitoring of the intrauterine growth retarded fetus in order to improve fetal outcome and define precisely the timing of delivery, when necessary, is based on the study of changes in vital functions observable in cases of hypoxemia. It is easy to believe that ultrasound equipment with Doppler facilities is present in the majority if not in all gynecological units. Cardiotocography is also widely used and the addition of a computerized evaluation system is not expensive and therefore should be available when facing high risk pregnancies such as intrauterine growth retarded cases. IUGR can be recognized through the use of ultrasound fetal biometry and clinical examination of maternal conditions in order to assess fetal conditions. If the above technologies are available further action, such as fetal Doppler study of fetal vessels and cardiotocography, can then be undertaken. In this paper, we will be discussing the issue of monitoring the fetus for fetal well-being, particularly in cases of intrauterine growth retarded fetuses.

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.

Amniotic fluid index measured with the aid of color flow Doppler

OBJECTIVE

To determine whether using color flow Doppler to identify the umbilical cord affects amniotic fluid index (AFI) measurements.

METHODS

A total of 2236 AFI measurements between 24 and 42 weeks in singleton gestations with no known or suspected fetal anomalies and < 14 days' discrepancy between menstrual and ultrasonographic dating were included. Color flow Doppler was used to identify loops of umbilical cord; these were excluded from the measurement. Polynomial regression was used to generate means and centiles. Data were grouped according to completed weeks of gestation and descriptive statistics were calculated. At each week of gestation, the number and percentage of pregnancies diagnosed as < or = 2.5th, < or = 5th, > or = 95th, and > or = 97.5th centile according to a 'standard' nomogram derived without using color flow Doppler were calculated.

RESULTS

The AFI decreased significantly over gestational age, starting at 31 weeks (p < 0.05 by ANOVA). The relationship between AFI and gestational age was best modeled by a second-degree polynomial (p < 0.001). The median and range of the proportion of AFIs that fell outside the ranges of the standard nomogram at each completed gestational age was: 6.0 (2.3-35.4)% for the < or = 2.5th centile, 9.9 (3.1-37.5)% for the < or = 5th centile, 3.8 (0-30)% for the > or = 95th centile, and 1.8 (0-20)% for the > or = 97.5th centile. The 2.5th and 5th centiles using the current data were lower than those of the 'standard', and the difference increased with advancing gestation. Upper centiles were also different.

CONCLUSION

The AFI measured using color flow Doppler overestimates oligohydramnios and may underestimate polyhydramnios when a standard AFI table obtained without color flow Doppler is used. Normal values specific for measurement method should be used for reference.

Comparability of the amniotic fluid index and single deepest pocket measurements in clinical practice

Two ultrasound techniques, the amniotic fluid index (AFI) and the single deepest pocket (SDP), are currently used to detect oligohydramnios, predict variable decelerations, risk of Caesarean delivery for fetal distress, Apgar scores, umbilical cord artery pH, perinatal mortality, and cerebral palsy. Both techniques poorly identify oligohydramnios. Both techniques identify pregnancies at risk for variable decelerations, low Apgar scores, and Caesarean delivery for fetal distress. Only the SDP is predictive of a compromised fetus-umbilical artery pH, as a stand-alone test, has been correlated with perinatal mortality, and as part of the biophysical profile has been linked to cerebral palsy. This brief communication reviews the comparability of these two techniques and which method, if either, is superior in the identification of oligohydramnios, the predictability of these techniques to identify an adverse pregnancy outcome, and the ability to predict cerebral palsy and perinatal mortality.

Prolonged pregnancy

Prolonged pregnancy is defined as any pregnancy that lasts 294 days or more. It is now well recognized that prolonged pregnancy is associated with an increased risk of perinatal mortality and morbidity. It is these complications of pregnancy that have led obstetricians to adopt a policy of induction of labour before the onset of the post-term period. The induction of labour between 41 and 42 weeks is, however, a very crude strategy for reducing term and post-term stillbirth rates. Although the risk of fetal death is increased after 42 weeks, many more fetuses die in utero between 37 and 42 weeks than die in the post-term period. It appears that smaller term fetuses run a greater risk than their larger counterparts, and that current methods of antepartum assessment of the term fetus are still inadequate. It behoves us as obstetricians to improve our capabilities in identifying the compromised fetus at term. This review puts into perspective the most recent publications and highlights areas requiring further study.

Antenatal assessment of the growth restricted fetus

Babies who are small due to intrauterine growth restriction are at higher risk for poor perinatal and long-term outcome than those who are appropriately grown. Through multiple antenatal testing modalities a sequence of deteriorating fetal status can be documented in such cases. The nature of this compromise is best reflected by the combination of fetal biometry, biophysical profile scoring and arterial and venous Doppler. This combination accurately defines fetal states and therefore risk of stillbirth or poor transition to extrauterine life. In the preterm neonate, fetal factors, gestational age and neonatal course interact significantly to impact on short- and long-term outcomes. The potential for iatrogenic prematurity is great and ongoing appraisal of peripartum management is critical. An integrated management protocol accounting for these factors is examined in this review.