Ultrasound evaluation of amniotic fluid: outcome of pregnancies with severe oligohydramnios

Severe oligohydramnios, defined as a condition in which the largest pocket of amniotic fluid measures less than 1 cm in its vertical axis as determined by an ultrasound method, was observed in 113 patients in a population of 15,431 referred high-risk patients (0.7%). In all cases, intervention took place unless there was a recognized structural anomaly or extreme prematurity. Overall gross perinatal mortality was 132.7/1000, and the incidence of major anomaly was 13.3%. With intervention the corrected perinatal mortality rate was 17.7/1000, a rate not significantly different from that observed in the entire population. All end points of perinatal mortality were significantly increased in patients with severe oligohydramnios, in comparison with randomly selected control subjects with normal amniotic fluid. These findings are interpreted to indicate that severe oligohydramnios in a structurally normal fetus is an indication for delivery.     

Ultrasound estimate of amniotic fluid volume: color Doppler overdiagnosis of oligohydramnios.

OBJECTIVE: To determine if concurrent use of color Doppler affects ultrasound estimates of amniotic fluid (AF) volume. METHODS: Study gravidas underwent ultrasound estimations of AF volume subjectively (visualization without measurements) and objectively (using amniotic fluid index [AFI]) and single-deepest pocket techniques, without and with concurrent color Doppler. Amniocentesis with the dye-dilution technique to measure actual AF volume was utilized for comparison. RESULTS: Sixty-seven women at a mean gestational age of 37.1 +/- 2.5 weeks were entered into this investigation between June 1999 and March 2000. Dye-determined AF volume was classified as low in 18 patients and as high in seven, with the remaining 42 within normal range. Using either ultrasound technique with color Doppler produced significantly lower estimates of AF volume (9.3 +/- 4.9) compared to those without color ([11.6 +/- 5], P <.001) for the AFI and (3.7 +/- 1.5) with color compared to those without color ([4.5 +/- 1.5], P <.003) for the single-deepest pocket. Using AFI without color identified two of 67 (3%) of the pregnancies as having low fluid compared to 14 of 67 ([21%] P =.002) using color. The increased classification of oligohydramnios with color did not accurately identify a greater number of dye-determined low volumes; instead, the AFI with color mislabeled nine pregnancies with normal fluid as low. The diagnosis of dye-determined low and high fluid volumes was not significantly different with or without color. CONCLUSION: Concurrent use of color Doppler with AFI measurements leads to the overdiagnosis of oligohydramnios.     

Ultrasound needle guidance for amniocentesis in pregnancies with low amniotic fluid

In six pregnancies accompanied by oligohydramnios (three cases) or decreased amniotic fluid and maternal obesity (three cases), needles specifically designed for use with ultrasound were successfully utilized in combination with real-time ultrasound guidance for amniocentesis. There was successful fluid retrieval in all six, with two requiring more than one needle pass. All three cases accompanied by oligohydramnios later resulted in fetal death. In the three cases accompanied by decreased amniotic fluid and maternal obesity, the amniocentesis results were helpful in ensuring the existence of a normal pregnancy. A specially designed ultrasound needle used in combination with a real-time guidance system is helpful in the performance of difficult amniocentesis.     

Ultrasound evaluation of amniotic fluid volume. II. The relationship of increased amniotic fluid volume to perinatal outcome

Qualitative amniotic fluid volume determination is a routine part of fetal biophysical profile score testing. The relationship between polyhydramnios and poor perinatal outcome has been previously documented. We have undertaken a retrospective chart review which relates qualitative amniotic fluid volume as determined at the time of last biophysical profile score assessment to perinatal outcome in 7562 referred high-risk obstetric patients. Gross and corrected perinatal mortality in association with normal qualitative amniotic fluid volume ranged from 4.65/1000 and 1.97/1000, respectively, to 32.9/1000 and 4.12/1000 in association with increased qualitative amniotic fluid volume, respectively. The incidences of major congenital anomaly and fetal macrosomia were significantly related to qualitative amniotic fluid volume.     

Ultrasound evaluation of amniotic fluid volume. I. The relationship of marginal and decreased amniotic fluid volumes to perinatal outcome

Qualitative amniotic fluid volume determination is a routine part of fetal biophysical profile score testing. The relationship between oligohydramnios and poor perinatal outcome has been previously documented. We have undertaken a retrospective chart review relating qualitative amniotic fluid volume as determined at the time of last biophysical profile score assessment to perinatal outcome in 7582 referred high-risk obstetric patients. Gross and corrected perinatal mortality in association with normal qualitative amniotic fluid volume ranged from 4.65/1000 and 1.97/1000, respectively, to 187.5/1000 and 109.4/1000 in association with decreased qualitative amniotic fluid volume, respectively. The incidences of major congenital anomaly and intrauterine growth retardation were significantly related to qualitative amniotic fluid volume.     

Perinatal outcome associated with oligohydramnios in uncomplicated term pregnancies

Purpose In high-risk pregnancies, oligohydramnios is frequently used to identify fetuses at risk of an adverse outcome. The purpose of this study was to evaluate the effect of oligohydramnios on perinatal outcome in uncomplicated pregnancies between 40.0 and 41.6 weeks.Methods From January 1997 to December 2000 all uncomplicated pregnancies reaching 40.0 weeks' gestation with a singleton non-malformed fetus and reliable dating underwent monitoring with serial determination of amniotic fluid index (AFI) and biophysical profile. Labor was induced for AFI 5 cm, biophysical profile score of 6 or less, rise in maternal blood pressure >140/90 mm Hg, or gestational age of 42.0 weeks. Perinatal outcome was compared between cases with AFI 5 cm and those with AFI >5 cm using Chi-square or Fisher's exact test for categorical variables, Student's t-test for continuous variables, and logistic regression analysis. A two-tailed p value <0.05 or an odds ratio (OR) with 95% confidence interval (CI) not inclusive of the unity was considered significant.Results Three thousand and forty-nine women met the inclusion criteria, 341 of which (11%) had an AFI 5 cm. Gestational age at delivery, rates of nulliparity and induction of labor were significantly different between cases with oligohydramnios and those with normal AFI (all p<0.001). Rates of cesarean delivery for non-reassuring fetal testing (8.2% vs. 3.9%, p<0.001) and of neonates with birth weight <10th percentile (13.2% vs. 5.5%, p<0.001) were significantly higher in the AFI 5 cm group compared with the AFI >5 cm. No significant differences were identified between the two groups in rates of meconium-stained amniotic fluid, 5-min Apgar score <7, or umbilical artery pH <7. Logistic regression analysis demonstrated that the association between oligohydramnios and rate of cesarean delivery for non-reassuring fetal testing lost significance after controlling for gestational age at delivery, nulliparity and induction of labor, whereas the association between AFI 5 cm and low birth weight centiles remained statistically significant (OR=2.2, 95% CI 1.5, 3.2).Conclusion In conclusion, in uncomplicated pregnancies at 40.0 to 41.6 weeks, oligohydramnios is independently associated with a higher risk of low birth weight centile.     

Obstetric and perinatal outcome of pregnancies with term labour and meconium-stained amniotic fluid

The purpose of this study was to evaluate the meconium staining of amniotic fluid (AF) in term of fetal distress, meconium aspiration syndrome, and perinatal morbidity and mortality. In a prospective study at Princess Badeea Teaching Hospital from April to November 1999, women with a singleton cephalic pregnancy of completed 37–42 weeks and with no pre-defined risk factor were recruited into the study. Study patients comprised 390 (10%) patients with meconium and 400 patients as controls but with clear amniotic fluid. Virtually meconium staining of the amniotic fluid was significantly associated with poor neonatal outcome in all outcomes measures assessed. Perinatal mortality increased from 2 per 1000 births with clear AF to 10 per 1000 with meconium (P<0.001). Other adverse outcomes also increased; e. g. , severe fetal acidemia, Apgar score ≤3 at 1 min and 5 min, and meconium aspiration syndrome. Delivery by cesarean section also increased with meconium from 7–14% (P<0.001). We concluded that meconium in the amniotic fluids associated with an obstetric hazard and significantly increase risks of adverse neonatal outcomes. Women with thin meconium in the presence of normal fetal heart rate can be safely managed at the clinical level. Mod-thick meconium alone should alert the obstetrician to a high risk fetal condition. Continuos fetal heart rate monitoring during labour and reassurance of fetal well-being by acid-base assessment were most significant factors in the reduction of meconium aspiration syndrome. Received: 15 November 1999 / Accepted: 12 April 2000     

Pathological pregnancies. Results of amniotic fluid studies and fetal outcome

Late amniocenteses (greater than 20 weeks' gestation) were performed in 114 pregnancies with no a priori genetic risk, but referred because of abnormal clinical and/or ultrasound findings suggesting fetal malformations. Reasons for referral included polyhydramnios (51 cases), oligohydramnios (15 cases), fetal growth retardation (FGR) (16 cases) and abnormal fetal ultrasound findings excluding anencephaly (32 cases). In 42 of these cases, referral was motivated by a combination of the above abnormal findings. When polyhydramnios was the sole anomaly (25 cases), 5 fetuses were malformed (20%), abnormal fetal karyotype and/or elevated amniotic fluid alphafetoprotein (AFP) were demonstrated in 2 cases. Oligohydramnios was the sole anomaly in one case; the infant died of prematurity. Fetal growth retardation was the sole anomaly in 14 cases, 11 otherwise normal newborns were small for date, 2 died at birth and 1 was malformed (1/14, 7%). In this group all fetal karyotypes were normal and in 2 cases amniotic fluid AFP were increased. In the 32 pregnancies without abnormal amniotic fluid volume and/or FGR and with fetal malformation(s) suggested by ultrasound, all malformations except one (ovarian cyst possibly ruptured during birth) were confirmed at birth, amniotic fluid AFP was elevated, and/or karyotype was abnormal in 6 cases. In 42 pregnancies where more than one alarm sign was present, abnormal karyotype and/or elevated amniotic fluid AFP level were recorded in 21 of the 39 cases where amniocentesis was performed, 33 fetuses were malformed (79%) and 13 died in the perinatal period (31%). The high incidence of abnormal results of amniocentesis found in this survey of pathological pregnancies, particularly in those with multiple alarm signs, emphasizes the need for amniocentesis in these situations.     

The fetal outcome in pregnancies with isolated reduced amniotic fluid volume in the third trimester

Our aim was to assess the outcome of pregnancies where oligohydramnios, defined by a published gestational reference range for amniotic fluid index, was the only abnormal finding at third trimester scan, and all other ultrasound parameters including biometry were within normal limits at initial scan. A retrospective case-control study was performed at The Liverpool Maternity Hospital. 103 pregnancies with reduced amniotic fluid index in the third trimester and apparently normal fetal growth profile ultrasonographically were identified from ultrasound reports throughout 1993. Pregnancies in the third trimester with normal amniotic fluid index on index scan were also identified from these reports and 103 were matched for parity, gestational age at delivery, mode of onset of labour, presentation at labour and medical conditions. Exclusion criteria were ruptured membranes, fetal abnormalities, estimated fetal weight below the fifth centile at index scan and multiple pregnancies. The outcome criteria were birthweight, Apgar scores at delivery, induction and emergency delivery for fetal reasons and admission to Neonatal Intensive Care Unit. Statistical analysis was performed by Fisher's exact test and Gart's odds ratio. Compared with controls, pregnancies in the reduced liquor group had a higher number of babies below the 5th centile (odds ratio 5.2, 95% confidence interval 1.6 to 22), a higher risk of induction for fetal reasons (odds ratio 34.4, 95% confidence interval 5.35 to 1425.5) and admission to Neonatal Intensive Care Unit (odds ratio 9.77, 95% confidence interval 1.3 to 432). Any observed difference in the need for emergency delivery due to fetal reasons was not clinically significant (odds ratio 2.16, 95% confidence interval 0.77 to 6.6) The definition used for oligohydramnios used in this study appears to identify a group of babies with a fourfold risk of low birthweight and a high risk of admission to the Neonatal Intensive Care Unit and induction of labour for fetal reasons. This would suggest that pregnancies with isolated oligohydramnios require some form of fetal monitoring and further prospective studies are required to determine the most appropriate method.     

Determination of amniotic fluid volume in twin pregnancies: ultrasonographic evaluation versus operator estimation

OBJECTIVE: We sought to determine the accuracy of amniotic fluid volume estimation (visually) in diamniotic twin pregnancy versus ultrasonography techniques. STUDY DESIGN: In this prospective study the volume of each sac in 23 sets of diamniotic twin pregnancies was subjectively and objectively estimated by a second-year obstetric resident, nurse sonographer, maternal-fetal medicine fellow, and maternal-fetal medicine staff. The actual volume was confirmed by amniocentesis and a dye-dilution technique. RESULTS: There was no difference in the total number of correct estimates of volume by level of operator experience (P =.98), ultrasonography technique (P =.87), or combined subjective versus objective correct estimates (P =.87). Identification of low volume was not different among the four evaluators (P =.48), but the percentage of correct estimates was poor (7%-29%). The 2-diameter pocket was a better predictor of oligohydramnios (57%) than the amniotic fluid index or the largest vertical pocket (12.5%; P =.002). CONCLUSION: The extremes of volume (low or high) are poorly identified by the subjective or objective assessment of volume.     

Alpha-fetoprotein concentration in amniotic fluid during the last trimester in normal pregnancies and in pregnancies with severe fetal abnormalities.

The concentration of alpha-fetoprotein (AFP) in the amniotic fluid was studied during the last trimester of pregnancy. 129 samples of amniotic fluid were collected by transabdominal amniocentesis in 94 pregnant women. Only women with uncomplicated pregnancies giving birth to normal infants at term were included. The 90% reference interval was calculated and a distinct decrease in the amniotic fluid AFP concentration was found during the last trimester. An AFP concentration above the 90% reference interval was found in 8 out of 10 cases of anencephaly. Normal AFP concentration was found in a case of congenital heart disease with severe oedema, and a low concentration was found in a case of Down's syndrome (Trisomy 21).     

High-risk pregnancies and amniotic fluid isoamylase activity

A kinetic test (Phadebas) was employed to determine the isoamylase activity in 77 amniotic fluid samples taken from a total of 60 high-risk pregnancies at different gestational ages. It was ascertained that in high-risk pregnancies the s-type isoamylase level frequently deviates from the common scatter range of the respective week of gestation. The measured activity of the s-type isoamylase is subsequently set in relation to the pre- and postnatal state of the newborn. The findings support the assumption that in addition to ultrasound, hormone determination and cardiotocography, the estimation of s-type amylase activity in amniotic fluid may serve as an index for fetal well-being. A reduced secretion of the parotid gland as a result of fetal stress is discussed as a possible cause of the ascertained enzymatic changes in the amniotic fluid.     

Falling amniotic fluid palmitates in diabetic pregnancies

Palmitic acid levels were measured in samples of amniotic fluid obtained from 15 patients with diabetes. Seven patients had palmitate values which decreased at some time in pregnancy but only one of the infants developed respiratory distress. Eight of the 15 patients had final amniotic fluid palmitate values which were greater than 0.07 mmol/l and one infant developed respiratory distress. The other seven patients had final amniotic fluid palmitate values of 0.07 mmol/l or less and one of the infants developed respiratory distress. The significance of falling amniotic fluid palmitate values is discussed.     

Serial assessment of amniotic fluid index in uncomplicated term pregnancies: prognostic value of amniotic fluid reduction

Objective: Assessment of amniotic fluid volume in association with a non-stress test is a commonly used method to monitor fetal well-being in high-risk pregnancies. The aims of our study were to determine whether oligohydramnios and the trend in amniotic fluid volume have prognostic significance in low-risk pregnancies between 40.0 and 41.6 weeks' gestation.

Methods: Between January 1997 and December 2000, all uncomplicated gestations with a singleton non-anomalous fetus reaching 40.0 weeks' gestation underwent semi-weekly monitoring of amniotic fluid index (AFI) until delivery. Oligohydramnios was defined as an AFI of ??5?cm. Changes in AFI were expressed as centimeters per day, and were calculated as: [(last AFI before delivery minus first AFI at 40.0 weeks) / interval in days between the two scans]. Adverse outcome was considered the occurrence of 5-min Apgar score <?7; umbilical artery pH <?7.0; Cesarean section for fetal distress; or fetal death. Comparisons between the groups with favorable and adverse outcomes was performed with χ² or Fisher's exact test for categorical variables, and Student's t test for continuous variables. A two-tailed p value <?0.05 was considered significant.

Results: A total of 3050 women met the study criteria, and underwent a median number of two (range 1–7) sonographic assessments of AFI after 40.0 weeks, with oligohydramnios detected in 341 women. In 1466 women at least two serial AFI determinations were obtained, allowing computation of an AFI trend. Gestations resulting in adverse perinatal outcome (n?=?167, 5.5%) had a significantly higher rate of oligohydramnios (33/167, 19.8% vs. 308/2883, 10.7%, p?=?0.001), but a similar rate of reduction in AFI (???0.65?±?0.64 vs. –?0.66?±?0.66?cm/day; p?=?0.85) than those with favorable outcome. The difference in rate of reduction of AFI between the two groups was not significant, even in the subset of gestations that developed oligohydramnios (???1.08?±?0.87 vs. –?1.26?±?0.89?cm/day; p?=?0.27).

Conclusion: A sonographic diagnosis of oligohydramnios carries an increased risk of adverse perinatal outcome, even in low-risk pregnancies after 40 weeks. The trend in amniotic fluid volume reduction does not seem to have prognostic significance.     

Artificial instillation of amniotic fluid as a new technique for the diagnostic evaluation of cases of oligohydramnios

In cases of severe oligohydramnios, sonographic diagnosis is hampered by poor visibility and by increased fetal flexion. Therefore, 74 artificial instillations of amniotic fluid were performed in 50 pregnancies by sonographic guidance. Fetal diseases included Potter's syndrome, obstructive uropathy, cystic kidneys (20 cases); Meckel's syndrome, C. de Lange syndrome, cytomegaly fetopathy (1 case each); VATER association (2 cases); triploidy (5 cases); severe intrauterine growth retardation (8 cases); and premature rupture of membranes (12 cases). By improved sonographic visibility and the observation of fetal behaviour (drinking, filling of stomach and bladder, voiding of bladder after artificial instillation of amniotic fluid), the fetal anatomy could be studied more accurately, malformations could be identified or excluded, and bladder function could be examined. Thus, differentiation between fetuses without functioning kidneys and those with severe intrauterine growth retardation becomes possible. Further, re-aspiration on the day following instillation permitted determination of the karyotype. Finally, the artificial instillation of amniotic fluid is a hazardous intervention (rupture of membranes, labour) and should be reserved only for a small number of selected cases with diagnostically unclear oligohydramnios. For these cases, it seems to be the method of choice permitting a variety of diagnostic information to be obtained.