Amniotic fluid index in normal pregnancy: an assessment of gestation specific reference values among Indian women

Determination of reference values for third trimester amniotic fluid index: a retrospective analysis of a large cohort of pregnancies with comparison to previous nomograms

Purpose: To establish a new set of reference values for third-trimester amniotic fluid index (AFI) and compare them to other previously published normograms.Methods: A retrospective cross-sectional cohort analysis of all singleton sonographic evaluations >22 gestational weeks in one university affiliated medical center between 2013 and 2017. Pregnancies complicated by rupture of membranes, major anomalies/chromosomal abnormalities were excluded. One evaluation per patient per pregnancy was randomly selected. Reference values were constructed using a best-fit regression model for estimation of mean and standard deviation at each gestational age after normalization of variables and compared with previously published norms.Results: A total of 7037 ultrasound evaluations entered the analysis. Correlation between AFI and gestational age was best represented by a first-degree polynomial equation. AFI decreased gradually from 16.4 at 22 weeks to 13.3 at 40 weeks (cm, median). The standard deviation increased with gestational age with AFI ranging from 12.9-20.2 at 22 weeks and 4.7-26.2 at 40 weeks (cm, 2.5-97.5 percentile). Compared to other curves, our reference values demonstrated a higher median AFI throughout all gestation.Conclusions: Reference values for the third trimester AFI were established. Curves should be correlated with perinatal outcome prior to wide clinical implementation.

Relationship of amniotic fluid index (AFI) in third trimester with fetal weight and gender in a southeast Nigerian population

BACKGROUND

Amniotic fluid (AF) is one of the major determinants of fetal biophysical profile and can predict pregnancy outcome. Abnormal value of amniotic fluid index (AFI) may indicate fetal and maternal disorders.

PURPOSE

To establish reference standards for AFI for this population after 28 weeks of pregnancy and evaluate the relationship between AFI, the estimated fetal weight (EFWT), and fetal gender.

MATERIAL AND METHODS

A prospective cross-sectional estimation of AFI and FWT was done in 385 apparently healthy pregnant women in the gestational age range of 28-42 weeks. General scanning in longitudinal, transverse, and oblique directions of the abdomen was done to assess the fetal wellbeing and determine the fetal gender for each participant. AF was measured in each of the quadrants of the abdomen. The four values of the AF were summed to get the AFI. Measurement of the head circumference, biparietal diameter, abdominal circumference, and femoral length of the fetus were obtained. The EFWT was calculated using Hadlock's formula. The data were divided into five groups: 28-30 weeks 6 days; 31-33 weeks 6 days; 34-36 weeks 6 days; 37-39 weeks 6 days; and 40-42 weeks. AFI for the different gestational age group studied and their percentiles were obtained.

RESULTS

AFI normogram for the local population was established. Positive and significant correlations of AF and EFWT were seen in all the gestational age groups of the women. No significant correlations between AF and EFWT was seen in male fetuses. Regression equations of EFWT and AFI were obtained for female fetuses.

CONCLUSION

The normal range for AFI values for the third trimester was established and could be used to evaluate AFI in the studied population. Established fetal weight should be taken into account when interpreting AFI for female fetuses but this need not be applied for male fetuses.

Unconditional reference values for the amniotic fluid index measurement between 26w0d and 41w6d of gestation in low-risk pregnancies

OBJECTIVE

To establish reference values for the amniotic fluid index (AFI) measurement between 26w0d and 41w6d of gestation in a Brazilian population.

METHODS

We performed a cross-sectional study with 1984 low-risk singleton pregnant women between 26w0d and 41w6d of gestation. AFI was measured according to the technique proposed by Phelan et al. Maternal abdomen was divided into four quadrants using the umbilicus and linea nigra as landmarks. Single vertical pocket in each quadrant was measured and the AFI was generated by the sum of these four values without umbilical cord or fetal parts. All ultrasound exams were performed by only two experienced examiners. AFI was expressed as median, interquartile range, mean and ranges in each gestational age (GA) interval. Polynomial regressions were performed to obtain the best fit with adjustment by the determination coefficient (R(2)).

RESULTS

Mean of AFI ranged from 14.0 ± 4.1 cm (range, 9.7-14.0) at 26w0d to 8.3 ± 4.7 cm (range, 1.9-16.5) at 41w6d, respectively. The best polynomial regression fit curve was a first-degree: AFI = 16.29-0.125*GA (R(2) = 0.01). According the scatterplot, AFI values practically did not vary with advancing GA.

CONCLUSION

Reference values for the AFI measurement between 26w0d and 41w6d of gestation in a low-risk Brazilian population were established.

Reference ranges of amniotic fluid index in late third trimester of pregnancy: what should the optimal interval between two ultrasound examinations be?

Background. Amniotic fluid index (AFI) is one of the major and deciding components of fetal biophysical profile and by itself it can predict pregnancy outcome. Very low values are associated with intrauterine growth restriction and renal anomalies of fetus, whereas high values may indicate fetal GI anomalies, maternal diabetes mellitus, and so forth. However, before deciding the cut-off standards for abnormal values for a local population, what constitutes a normal range for specific gestational age and the ideal interval of testing should be defined. Objectives. To establish reference standards for AFI for local population after 34 weeks of pregnancy and to decide an optimal scan interval for AFI estimation in third trimester in low risk antenatal women. Materials and Methods. A prospective estimation of AFI was done in 50 healthy pregnant women from 34 to 40 weeks at weekly intervals. The trend of amniotic fluid volume was studied with advancing gestational age. Only low risk singleton pregnancies with accurately established gestational age who were available for all weekly scan from 34 to 40 weeks were included in the study. Women with gestational or overt diabetes mellitus, hypertensive disorders of the pregnancy, prelabour rupture of membranes, and congenital anomalies in the foetus and those who delivered before 40 completed weeks were excluded from the study. For the purpose of AFI measurement, the uterine cavity was arbitrarily divided into four quadrants by a vertical and horizontal line running through umbilicus. Linear array transabdominal probe was used to measure the largest vertical pocket (in cm) in perpendicular plane to the abdominal skin in each quadrant. Amniotic fluid index was obtained by adding these four measurements. Statistical analysis was done using SPSS software (Version 16, Chicago, IL). Percentile curves (5th, 50th, and 95th centiles) were constructed for comparison with other studies. Cohen's d coefficient was used to examine the magnitude of change at different time intervals. Results. Starting from 34 weeks till 40 weeks, 50 ultrasound measurements were available at each gestational age. The mean (standard deviation) of AFI values (in cms) were 34 W: 14.59 (1.79), 35 W: 14.25 (1.57), 36 W: 13.17 (1.56), 37 W: 12.48 (1.52), 38 W: 12.2 (1.7), and 39 W: 11.37 (1.71). The 5th percentile cut-off was 8.7 cm at 40 weeks. There was a gradual decline of AFI values as the gestational age approached term. Significant drop in AFI was noted at two-week intervals. AFI curve generated from the study varied significantly when compared with already published data, both from India and abroad. Conclusion. Normative range for AFI values for late third trimester was established. Appreciable changes occurred in AFI values as gestation advanced by two weeks. Hence, it is recommended to follow up low risk antenatal women every two weeks after 34 weeks of pregnancy. The percentile curves of AFI obtained from the present study may be used to detect abnormalities of amniotic fluid for our population.

Reference range for amniotic fluid index measurements in a Brazilian population

OBJECTIVE

The aim of this study was to determine the reference range for amniotic fluid index (AFI) measurements in a large sample of the Brazilian population.

METHODS

This was a retrospective cross-sectional study on 3837 normal singleton pregnancies between 18+0 and 38+6 weeks of pregnancy. The AFI was measured from the largest vertical pockets of amniotic fluid in the four quadrants of the uterine cavity. To assess the correlation between AFI and gestational age (GA), polynomial equations were calculated, with adjustments using the determination coefficient (R2).

RESULTS

The mean maternal age and gestational age were 27.01±6.57 years and 30.43±5.29 weeks, respectively. The mean AFI ranged from 12.2±2.6 cm at 18 weeks to 11.6±6.0 cm at 38 weeks of pregnancy. The correlation between AFI and GA was best represented by a linear equation: AFI=17.78-0.153*GA (R2=0.027).

CONCLUSION

We established the reference range for the AFI in a large sample of the Brazilian population. This reference range can be used to monitor deviations in the volume of amniotic fluid in fetuses at high risk for intrauterine growth disturbances.

Peripartum outcomes of high-risk pregnancies complicated by oligo- and polyhydramnios: a prospective longitudinal study

AIM

To determine pregnancy outcomes in high-risk non-anomalous singleton pregnancies with oligo- and polyhydramnios.

METHODS

In high-risk pregnancies undergoing antenatal testing, the last amniotic fluid index (AFI) prior to delivery in pregnancies with polyhydramnios (>97.5th percentile) and oligohydramnios (<2.5th percentile) was correlated with pregnancy outcomes.

RESULTS

There were 2597 pregnancies with a normal AFI (2.5th-97.5th percentile), 73 with hydramnios (AFI > 97.5th percentile) and 72 with oligohydramnios (<2.5th percentile). Polyhydramnios and oligohydramnios adversely influenced different pregnancy outcomes. Pregnancies with polyhydramnios versus normal AFI were more likely to have: an abnormal tracing influencing delivery (29% vs 17%, odds ratio [OR] = 2.03, 95% confidence interval [CI] 1.19-3.45, P = 0.009), cesarean delivery performed due to fetal labor intolerance (21% vs 7%, OR = 3.89, 95%CI 2.10-7.18, P < 0.001), increased birthweight (P = 0.016), Apgar score <7 at 5 min (8% versus 1%, OR = 6.41, 95%CI 1.12-16.22, P = 0.001) and newborn intensive care unit admission (10% versus 5%, OR = 2.24, 95%CI 1.12-4.49, P = 0.023). Pregnancies with oligohydramnios versus normal AFI had a greater risk of labor induction (18% vs 9%, OR = 3.18, 95%CI 1.62-6.25, P = 0.001), intrauterine growth restriction (25% vs 9%, OR = 3.4, 95%CI 1.94-5.97, P < 0.001) and preterm delivery (29% vs 17%, OR = 1.97, 95%CI 1.17-3.31, P = 0.010).

CONCLUSIONS

Fetal heart rates influencing delivery, cesarean deliveries for fetal labor intolerance, low 5-min Apgar scores, increased neonatal birthweight, and newborn intensive care unit admissions were more common with polyhydramnios. The fetuses of pregnancies complicated by oligohydramnios had a greater risk of labor induction, intrauterine growth restriction and preterm delivery.

Reduction of aquaporin-8 on fetal membranes under oligohydramnios in mice lacking prostaglandin F2α receptor

AIM

To investigate the association between aquaporin-8 (AQP-8: a water channel protein) expression in fetal membranes and oligohydramnios during near-term and postdate pregnancy, we set up an oligohydramnios model using prostaglandin F2 alpha receptor (FP)-deficient mice.

METHODS

Pregnant FP-deficient mice from 14 to 21 gestational days (GD) were killed to measure the amniotic fluid volume (AFV), and fetal membranes were collected for the analysis of aquaporin-8 expression.

RESULTS

The AFV was highest at 14 GD, and was significantly decreased to 28% and 0% at 20 GD and 21 GD, respectively, compared with the volume at 14 GD. Immunohistochemistry and immunoblot analysis showed that aquaporin-8 was expressed in the basal component of fetal membranes, and that the protein level was significantly decreased to 60% at 20 GD compared with that at 14 GD.

CONCLUSIONS

We demonstrated that AQP-8 expression in the fetal membrane was decreased at post term in FP-deficient mice. Our findings suggest that aquaporin-8 in fetal membranes may be involved in the regulation of AFV, especially when oligohydramnios occurs.