Association of amniotic fluid index with estimated fetal weight.

OBJECTIVE: The relationship between amniotic fluid volume and gestational age has been described previously. The association of body weight and urine output has been observed in human neonates. Our goal was to assess the correlation of the amniotic fluid index (AFI) with estimated fetal weight (EFW) in the third trimester. METHODS: We conducted a retrospective observational study on 426 pregnant women with singleton gestations who were referred to our unit for sonographic evaluation in the third trimester. The AFI, EFW, and EFW percentile corrected for gestational age were evaluated. The sonographic examinations were stratified into 3 gestational age categories: 28 through 33.9 weeks, 34 through 37.9 weeks, and 38 weeks and later. Maternal and fetal outcome variables were collected from medical records. Linear regression, Mann-Whitney U, and Kruskal-Wallis tests were used for statistical analysis. RESULTS: There was no significant relationship between the AFI and EFW in the entire group of patients (R = 0.08; P = .096). There was a significant relationship between the AFI and EFW after 38 weeks' gestation (R = 0.30; P = .003). In addition, in female fetuses the EFW percentile correlated with higher AFI values at all gestational ages (R = 0.31; P < .001); this, however, was not observed in male fetuses. CONCLUSIONS: There is no relationship between the AFI and EFW during the third trimester, although a positive relationship between the AFI and EFW was noted late in gestation. In pregnancies with female fetuses, the AFI was positively associated with EFW percentile before 38 weeks' gestation.     

羊水量异常的超声诊断与胎儿畸形的关系

目的 探讨羊水量异常与胎儿畸形的关系.方法 回顾分析2004年3月至2006年11月在本院进行二维及三维超声检查34 900例20周以上的胎儿,其检出羊水量异常160例,并研究分析羊水量多少与胎儿畸形的关系.结果 160例羊水量异常中,羊水过多100例,羊水过少60例,二者畸形的发生率分别为37%、31.6%.结论 超声是诊断羊水量异常的首选方法,而且还能发现胎儿畸形,进一步证明羊水量异常与胎儿畸形的发生密切相关.     

Correlation between fetal gastric size and amniotic fluid volume

PURPOSE: Since abnormal conditions of the fetal digestive tract may alter both amniotic fluid volume and fetal gastric volume, we sought to determine whether amniotic fluid volume is correlated with fetal gastric volume in normal pregnancy. METHODS: A total of 280 fetal gastric size measurements were made prospectively from routine sonographic examinations of women with normal singleton pregnancies between 16 and 42 weeks of gestation. The fetal stomach was defined as the largest area including the pyloric site on transverse or oblique real-time sonographic scans. Gastric volume was calculated according to the formula for a prolate ellipsoid. The amniotic fluid index (AFI) was used for the evaluation of amniotic fluid volume. RESULTS: Both fetal gastric volume and AFI were significantly correlated with gestational age (R2= 0.422 and R2= 0.128, respectively). Only a weak correlation was found between gastric volume and AFI (R2= 0.036, p <0.001). On multivariate linear regression analysis adjusting for gestational age and fetal biometric measurements, gastric volume was not an independent and significant predictor of AFI. CONCLUSIONS: Although sonographically determined fetal gastric volume measurements appear to be useful in the assessment of fetal digestive tract anomalies, fetal gastric volume has no clinically significant effect on the amniotic fluid volume in normal pregnancy.     

根据胎儿体积模型超声预测胎儿体重

目的探讨胎儿体积模型推导超声预测胎儿估计体重（ＥＦＷ）的公式,并验证其准确性。方法根据胎儿体积模型,胎头重量与头围（ＨＣ）３成比例,胎儿躯干重量与腹围（ＡＣ）２×股骨长度（ＦＬ）成比例,以１９９５～１９９６年２４５例胎儿的超声结果经多元线性回归分析推导出比例常数和新公式：ＥＦＷ＝０．０２６１×ＨＣ３＋０．３０４０８×ＡＣ２×ＦＬ。１９９６～１９９８年应用新公式预测３４１例胎儿的出生体重以验证其准确性,并与Ｓｈｅｐａｒｄ公式比较。结果新公式和Ｓｈｅｐａｒｄ公式的平均相对误差±标准差分别为（３．９±２．９）％和（５．８±４．１）％（Ｐ＜０．０５）,新公式ＥＦＷ与出生体重间有明显相关性（ｒ＝０．９３３,Ｐ＜０．００１）。结论新公式在一定体重范围内（２０００～４５００ｇ）可准确预测胎儿体重。     

Sonographic estimation of amniotic fluid volume. Subjective assessment versus pocket measurements

Amniotic fluid volume (AFV) estimation is an important part of routine obstetric sonography. Despite the clinical importance placed upon excessive or diminished AFV in pregnancy, there is little uniformity in the way it is estimated sonographically. We compared AFV estimations obtained using two commonly employed sonographic methods "subjective" visual assessment and amniotic fluid pocket measurements. Estimates obtained using both methods correlated closely. In addition, there was excellent intraobserver and interobserver agreement among estimates obtained using subjective criteria. This supports the belief that experienced observers tend to agree on the sonographic appearance of normal, excessive or decreased AFV. Methods for AFV estimation and potential pitfalls are discussed.     

Intraobserver reliability of amniotic fluid volume estimation by two techniques: amniotic fluid index vs. maximum vertical pocket.

We evaluated the intraobserver agreement of two techniques of amniotic fluid assessment: amniotic fluid index and maximum vertical pocket. The intraobserver variation of the two forms of amniotic fluid assessment was obtained by evaluating amniotic fluid prior to fetal biometry (post-biometry value) and after fetal biometry (pre-biometry value). Between January and June 1990, this amniotic fluid assessment was by the maximum vertical pocket technique, and between July and December 1990, by the amniotic fluid index technique.In the Grace Maternity Hospital, Vancouver, 352 subjects were evaluated by the maximum vertical pocket technique, and 184 subjects by the amniotic fluid index technique.Amniotic fluid volumes were categorized into normal, oligohydramnios, and polyhydramnios, and the pre-biometry and post-biometry categories of amniotic fluid index and maximum vertical pocket techniques were compared by kappa statistics. The maximum vertical pocket technique showed poor intraobserver agreement (kappa = 0.33), but the amniotic fluid index technique showed good agreement (kappa = 0.72). With the poor reproducibility of the maximum vertical pocket technique in assessing extremes of amniotic fluid volume, it is difficult to support its use as a component of fetal assessment.     

Is there a relationship between fetal weight and amniotic fluid index?

OBJECTIVE: To establish whether there is a relationship between the amniotic fluid index and estimated fetal weight in the third trimester. The presence of a relationship would require adjustment of amniotic fluid index to take account of estimated fetal weight with potential improvement in its prediction of adverse perinatal outcomes. METHODS: Paired measurements of amniotic fluid index and estimated fetal weight from 274 low-risk pregnancies enrolled in a longitudinal study of fetal growth. Measurements were made at fortnightly intervals from 30 weeks' gestation until delivery. A relationship between amniotic fluid index and estimated fetal weight was sought at gestational age week intervals of 30-32, 33-35, 36-38 and 39-41. RESULTS: One thousand and three pairs of measurements of amniotic fluid index and estimated fetal weight were available for analysis. Mean amniotic fluid index decreased towards term as expected. There was no correlation between amniotic fluid index and estimated fetal weight. Furthermore, there was no correlation between amniotic fluid index and estimated fetal weight at any of the gestational age intervals. CONCLUSIONS: There is no clinically relevant correlation between amniotic fluid index and estimated fetal weight. It should remain clinical practice to take account of gestational age when interpreting amniotic fluid index but it is not necessary to make adjustments for estimated fetal weight.     

羊水量正常时胎儿肾发育不良的超声诊断及临床意义

目的 探讨产前超声检查对于羊水量正常时胎儿肾发育不良的诊断价值和临床意义.方法 于孕中晚期对羊水量正常胎儿中发现的单侧或双侧肾超声表现异常(包括大小、回声、形态异常,出现囊肿等)病例进行系统二维超声检查、孕期及生后随访观察、病理学检查等,并进行总结分析.仅有肾盂增宽的胎儿不包括在本组研究中.结果 发现羊水量正常但单侧或双侧肾发育不良的胎儿11例.其中单侧多囊性肾发育不良5例,4例不合并其他异常,1例合并同侧手缺如;单侧肾缺如2例,其中1例不合并其他畸形,另1例合并多发畸形包括脑积水、骶尾部脊柱裂、同侧桡骨缺失及单脐动脉,符合VACTERL综合征;盆腔.肾1例,马蹄肾1例,生后超声证实;常染色体显性遗传多囊肾1例,胎儿一侧肾可见多发囊肿,合并心脏横纹肌瘤,孕妇为双侧多囊肾;双侧肾发育不良1例,产前超声表现为双侧肾回声增强.结论 单侧多囊性肾发育不良是羊水量正常时产前超声最常检出的胎儿肾发育不良性疾病.根据产前超声表现并结合家族史,能在大多数胎儿肾发育不良病例中进行病因学诊断并帮助判断预后.     

Determination of amniotic fluid palmitic acid concentration for the estimation of fetal lung maturity

Palmitic acid concentrations in amniotic fluid (AF) were determined in 135 patients with normal and pathological pregnancies between the 27th and 42nd week of gestation. There was a sharp rise in the mean palmitic acid concentration after the 34th weeks of gestation from 2.7 μg/ml to 9.9 μg/ml at term. This increase is almost identical with the rise of AF-lecithin. It was found that between 70% and 100% of AF-palmitic acid originates from lecithin. 65 patients were delivered within 24 h after amniotic fluid sampling. 7 infants of these patients developed a respiratory distress syndrome (RDS). In all cases with RDS AF-palmitic acid concentration was far below 5 μg/ml. Assuming an AF-palmitic acid concentration > 5 μg/ml for characterising fetal lung maturity (= no RDS), there were no false negative results, but 16% false positive results. However, the determination of AF-palmitic acid concentration seems to be a most reliable method for the assessment of fetal lung maturity.     

Effect of fetal movement on the amniotic fluid index in diamniotic twin gestations

Fetal movement changes the size and location of amniotic fluid pockets during measurement of the amniotic fluid index. In singleton gestations, the effect of redistributing the fixed intrauterine fluid volume on the amniotic fluid index is clinically insignificant. In this study, we tested the hypothesis that the index in twin pregnancies is unaffected by fetal movement. A single examiner prospectively determined the amniotic fluid index before and after three discrete episodes of movement by both fetuses of 82 diamniotic twin pregnancies referred for obstetric sonograms between 20 and 38 weeks' menstrual age. A reliable blinded examiner provided a second post-movement measurement as a control. Data were analyzed by the paired t-test. The mean change in the amniotic fluid index after fetal movement was 2.1 ± 0.2 cm and 3.7 ± 0.3 cm for post-movement determinations by the same and blinded examiners, respectively (p < .001). Interobserver variation was 3.5 cm. Intraobserver variation was 1.8 cm for the first examiner and 2.2 cm for the second examiner. Therefore, interobserved and intraobserver variation can account for the observed change in the amniotic fluid index following movement of both diamniotic twins. © 1997 John Wiley & Sons, Inc. J Clin Ultrasound 25:255–257, 1997     

The evaluation of fetal lung maturity by amniotic fluid analysis.

The frequent necessity for termination of pregnancy before the spontaneous onset of labor requires that we be able to accurately predict fetal lung maturity. We have used amniotic fluid studies for evaluation of fetal lung maturity and have found that (1) a "fat" cell concentration of 30% or more, or (2) a creatinine concentration of 2.0 mg/100 ml or more, or (3) a lecithin:spingomyelin (L:S) ratio of 2.0 or greater all correlated well with fetal maturity. Since each of these studies is open to a variety of possible errors, the use of several different ones adds reliability to the estimation of fetal lung maturity.     

Influence of fetal growth patterns on sonographic estimation of fetal weight

Six published fetal weight estimating regression models proposed for clinical use were evaluated in 259 pregnant women who delivered within 72 h of an ultrasound evaluation performed with sector scanner. The patient sample included 89 (33.2%) fetal weights that were below the 10th or above the 90th percentile for menstrual age. The actual mean percent error (systematic error), standard deviation (random error), and the number of large errors of prediction for all equations were greatest in fetuses that were small- and large-for-gestational age. Whereas there were no significant differences between equations for the patient sample as a whole, equation AC,BPD (Shepard) had the smallest systematic error in intrauterine growth retarded, premature, and normal-term fetuses less than 4000 g. Conversely, the systematic error of the models that included femur length was smallest at the upper end of the weight scale and in macrosomic fetuses in general. In that regard, the accuracy of fetal weight prediction could be increased by selecting the appropriate model for the proper clinical indications. Although these findings can be explained by the limitations of the current regression models in estimating fetal soft tissue mass, a subtle effect of the use of the sector scanner on the results of this study cannot be completely excluded and requires further investigation.     

The influence of fetal position on amniotic fluid index and single deepest pocket.

OBJECTIVE: To evaluate the effect of fetal position on measurement of amniotic fluid index (AFI) and of the single deepest pocket (SDP). METHODS: This was a prospective observational study, in a university obstetric unit, of women with an uncomplicated singleton pregnancy with longitudinal lie and cephalic presentation at or beyond 28 weeks of gestation. AFI was calculated and SDP measured and the fetal position was characterized in terms of three parameters. These were: the side of the maternal abdomen on which the fetus lay; a numerical representation (laterality score) of the distance that the fetus was from the sagittal midline plane of the maternal abdomen; the orientation of the fetal trunk (ventral anterior, lateral or posterior). RESULTS: Eighty-one women were recruited into the study. There was a significant relationship between the laterality score and the AFI (P = 0.005) but not the SDP (P = 0.23): AFI was on average 4.35 cm higher in fetuses lying centrally compared with those lying laterally inside the uterus. There was no significant difference for either SDP (P = 0.8) or AFI (P = 0.3) between fetuses lying on the right or the left side of the maternal abdomen. Similarly, there was no significant difference in SDP (P = 0.9) or AFI (P = 1.0) for the different orientations of the fetal trunk. CONCLUSION: Fetal position affects the measurement of AFI but not that of SDP. Therefore, SDP may be a more consistent parameter for the estimation of amniotic fluid volume.     

Does measurement of amniotic fluid index detect changes in amniotic fluid volume after second-trimester amniocentesis?

The objective of this study was to establish whether variations of amniotic fluid volume induced by second-trimester amniocentesis could be detected by serial measurements of amniotic fluid index. A total of 130 singleton pregnancies undergoing second-trimester amniocentesis for genetic indications were considered. Amniotic fluid index was measured at three different time intervals: 30-60 min before amniocentesis, immediately after the procedure, and 60 min after the procedure. Serial measurements were obtained either by a single operator (n = 55) or by the three independent operators (n = 75). Significantly lower amniotic fluid index values were demonstrated immediately after amniocentesis when compared with the pre-amniocentesis and subsequent measurements in the study design with both the single and multiple operators. No statistically significant changes were found between the first amniotic fluid index measurements and those obtained 1 h after amniocentesis. These results suggest that second-trimester amniocentesis induces a temporary decrease of amniotic fluid volume detectable by serial amniotic fluid index measurements, no longer evident 1 h after the procedure.