Management of isolated abnormal amniotic fluid volume in pregnancy

This investigation was undertaken to determine if the accuracy of the ultrasound assessment of abnormal amniotic fluid volume (oligohydramnios or polyhydramnios) is improved by employing multiple sonographic amniotic fluid measurements. Four ultrasound techniques consisting of the subjective assessment (ultrasonic visualization without measurement), largest vertical pocket, amniotic fluid index and 2-diameter pocket technique were performed followed by amniocentesis and dye-dilution confirmation of amniotic fluid volume in 66 singleton pregnancies. The ultrasound accuracy to detect abnormal amniotic fluid volume ranged from 61% with the largest vertical pocket to 70% with the 2-diameter pocket procedure used separately. Receiver operator characteristic curves demonstrated that combining the 4 ultrasonic measurements did not improve the accuracy of identifying amniotic fluid volumes.

Correlation between amniotic fluid glucose concentration and amniotic fluid volume in pregnancy complicated by diabetes

Although there are fairly wide variations AFV normally undergoes characteristic changes across gestation in which it increases from 10-20 ml at 10 weeks gestation to average 800 ml at 24 weeks. Little change occurs from then until near term when AFV begins to decrease, and large decreases can occur in postterm pregnancies. Across gestation, 95% of AFVs are within the range of 1/2.57-2.57 times the gestational mean volume and 99% are within the range of 1/3.40-3.40 times the gestational mean. Although there are six pathways in which fluid and solutes can enter and/or leave the amniotic sac, there are only four primary pathways that contribute to AFV during late gestation. These include fetal urine and lung fluid secretion as the two primary sources of fluid, with fetal swallowing and intramembranous absorption as the two primary routes of amniotic water clearance. The intramembranous pathway also appears to be a primary source of amniotic solutes (e.g., sodium and chloride). Although fetal hypoxia has been widely believed to cause oligohydramnios, fetal hypoxic hypoxia and anemic hypoxia both appear to be associated with an increased AFV and polyhydramnios rather than oligohydramnios. It is speculated that the oligohydramnios associated with fetal hypoxia is caused by placental dysfunction in addition to the hypoxia.

To compare sildenafil plus hydration with hydration alone in improving the amniotic fluid index and neonatal outcomes in pregnancies complicated by idiopathic oligohydramnios ( amniotic fluid index less than 5 cm without underlying maternal or fetal causes and with normal fetal growth). This was an open-label randomized trial for women carrying singleton pregnancies at 30 weeks of gestation or more with idiopathic oligohydramnios detected during routine ultrasonogram. Women received either oral sildenafil citrate (25 mg every 8 hours) plus intravenous infusion of 2 L isotonic solution or fluids only until delivery. The primary study outcome was the amniotic fluid volume at 6 weeks of follow-up or the final volume before delivery, whichever occurred first. Secondary outcomes were duration of pregnancy prolongation, mode of delivery, and select neonatal outcomes. The study was powered to detect a 45% difference between groups, so, at an α level of 0.05 and 80% power, a sample size of 167 women was required. From February 24, 2015, through April 2016, 196 women were screened and 184 were randomized. Follow-up was completed in 166 (90%): 82 in the sildenafil group and 84 in the hydration group. Baseline characteristics were similar between groups. The amniotic fluid volume was higher in the sildenafil group at the final assessment (11.5 compared with 5.4 cm, P=.02). The sildenafil group delivered later (38.3 compared with 36.0 weeks of gestation, P=.001), had a lower rate of cesarean delivery (28% compared with 73%), and their neonates were less likely to be admitted to the neonatal intensive care unit (11% compared with 41%, P=.001). Sildenafil citrate increases amniotic fluid volume in pregnancies complicated by oligohydramnios. ClinicalTrials.gov, www.clinicaltrials.gov, NCT02372487.

Do semiquantitative amniotic fluid indexes reflect actual volume?

To determine the changes in amniotic fluid (AF) volume and solute concentrations during the last 3 weeks of gestation in fetal sheep with a ligated urachus. AF volume as well as solute concentrations of AF, fetal urine, fetal blood, and maternal blood were measured serially over the last 24 days of gestation in chronically catheterized fetal sheep. Statistical analyses included regression analysis and analysis of variance (ANOVA). Delivery occurred at 145.5 +/- 1.1 (SE) days (n = 11 animals). AF volume averaged 913 +/- 46 mL (n = 119 determinations total from 11 animals) and was unchanged with time when analyzed against either gestational age (P = .9) or time prior to delivery (P = .81). Amniotic osmolality, sodium, chloride, glucose, and calcium concentrations decreased as gestation progressed, while potassium and lactate concentrations increased. Only amniotic lactate underwent a pre-delivery increase in concentration. From multivariate regression, AF solute concentrations correlated positively with fetal blood and urine concentrations and negatively with gestational age. In fetal sheep with a ligated urachus, AF volume does not decrease prior to labor and delivery. This differs from the sharp pre-delivery decrease in AF volume that occurs in rats, mice, and pigs and is similar to the relatively constant AF volume in humans, baboons, and monkeys. Further, pre-delivery changes in AF lactate concentration may reflect the consequences of a low AF volume. Regression analysis suggests that fetal blood and urine independently contribute to AF solute concentrations and that gestational age-specific changes in intramembranous transport also may contribute.

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.

Amniotic fluid volume of third-trimester diamniotic twin pregnancies

2 Developments in CTG analysis

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.

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.

Outcome of a pregnancy is dependent on high-quality ovulation, successful fertilization, normal embryonic and fetal development, and homeostasis of amniotic fluid. Throughout pregnancy, aquaporins are expressed in the placenta, uterus, adnexa, brain, urinary system, and the lacrimal gland. The regional and temporal regulation of aquaporins play important roles in normal pregnancy, fetal growth, and homeostasis of amniotic fluid volume, and water handling in other organs. The pregnant phenotypes of aquaporin-knockout mice provide direct evidence that aquaporins deficiency results in adverse outcome of pregnancy. Therefore, screening for modulation of aquaporin in abnormal pregnancy becomes desirable. Alteration of aquaporins is seen in preeclampsia, abnormal amniotic fluid volume, chorioamnionitis, and maternal under-nourished pregnancy. Although the functional importance of aquaporins remains to be elucidated, its expression and regulation in abnormal pregnancy suggests potential therapeutic strategies for the treatment of abnormal pregnancy.

A contemporary amniotic fluid volume chart for the United States: The NICHD Fetal Growth Studies–Singletons

The purpose of this study was to assess the effects of maternal smoking on amniotic fluid volume and fetal urine output. Seventeen women (10 smokers and 7 non-smokers) were serially assessed through pregnancy. Smoking status was determined by self-report and carbon monoxide manometry. Amniotic fluid volume was assessed by sonographically measuring the maximum vertical pocket, the amniotic fluid index, and the two dimensions of the largest pockets. The coronal area formula was used to calculate bladder volume at 5-minute intervals for 20 minutes. Urine output was calculated from serial measurements of bladder volume. The mean gestational age of the first session was 26.8 (2.7) weeks, of the second session 32.4 (1.6) weeks, and of the last session 36.9 (2.1) weeks. In the univariate analysis there were no differences between smokers and non-smokers at any of the three visits for gestational age, fetal weight, maximum vertical pocket, amniotic fluid index, two-dimensional maximum pocket, and urine output. In the regression model, while controlling for gestational age, smoking status could not predict significant differences in any parameter. Maternal smoking does not appear to affect either amniotic fluid volume or fetal urine output.

To determine whether color Doppler sonography increases the detection of pregnancies at risk for adverse outcomes. Participants admitted to labor and delivery with the anticipation of a vaginal delivery underwent measurements of amniotic fluid volume (AFV) using amniotic fluid index (AFI) and single deepest pocket (SDP) techniques by grayscale followed by color Doppler sonography. Oligohydramnios was defined as an AFI of less than 5 cm or an SDP of less than 2 cm. Intrapartum and perinatal outcomes were compared between participants with a diagnosis of a low AFV by grayscale and color Doppler sonography. Over 42 months, 428 women were enrolled in the study. Color Doppler sonography resulted in lower AFV estimates (mean ± SD by the AFI, 10.7 ± 3.7 cm by grayscale sonography and 8.6 ± 3.6cm by color Doppler sonography; P < .0001). For the SDP, the mean AFVs were 4.6 ± 2.0 cm by grayscale sonography and 3.4 ± 1.4 cm by color Doppler sonography (P < .0001). The level of agreement between grayscale and color Doppler sonography in estimating the AFV was fair, with κ = 0.32 for the AFI and 0.28 for the SDP. Outcome measures of AFVs classified as low based on color Doppler sonography (normal by grayscale sonography) and those classified as low by grayscale sonography (low by color Doppler sonography) were compared. There was no difference in composite perinatal complications, mode of delivery, or composite neonatal complications. The use of color Doppler sonography leads to the overdiagnosis of low AFVs and does not appear to increase the detection of pregnancies destined for adverse intrapartum or perinatal outcomes.