Birth defects. If a baby has physical problems, especially with the kidneys, they may not make enough urine, which leads to low amniotic fluid. Health conditions in mom. Maternal complications such as the following can cause low amniotic fluid levels:. Post-term pregnancy.
Amniotic fluid naturally starts decreasing after 36 weeks of pregnancy, and is very likely to get too low after 42 weeks of pregnancy. By that point, though, everyone — and especially you — is probably so eager to meet baby that being induced or otherwise delivering will be more than welcome.
Some medications , especially those used to treat high blood pressure, may cause low amniotic fluid. How can you know for sure if you have low amniotic fluid levels? This will require — you guessed it — a visit to your doctor. They can use an ultrasound to measure if there is enough fluid. The ultrasound technician will scan your uterus to find and measure the single deepest pocket of amniotic fluid they can.
A normal measurement is 2 to 8 centimeters cm. A finding of less than 2 cm indicates low amniotic fluid at this stage. After 24 weeks of pregnancy, the most common way to measure amniotic fluid is called the AFI, or amniotic fluid index.
The AFI is measured exactly like the single deepest pocket method, but the ultrasound technician will measure fluid pockets from four different parts of the uterus. These measurements will be added together to get the AFI. Treatment for low amniotic fluid will depend on the cause and how far along you are.
Some causes of low amniotic fluid have a simple solution, but others may require more intensive intervention. Anytime during your pregnancy, drinking a lot of water can make a huge difference.
According to one study , hydration is very helpful for upping amniotic fluid levels in women between 37 and 41 weeks of pregnancy. While more research is needed, a Cochrane database review also found that simple hydration increased amniotic fluid levels. The nice thing about this remedy? An amnioinfusion is when your doctor squirts a saltwater solution saline through your cervix and into the amniotic sac.
This can at least temporarily increase the level of amniotic fluid. Amniocentesis involves a thin needle being inserted directly into the amniotic sac through your abdomen.
Thank you for updating your details. Log In. Sign Up. Become a Gold Supporter and see no ads. Log in Sign up. Articles Cases Courses Quiz. About Recent Edits Go ad-free. Edit article. View revision history Report problem with Article. Citation, DOI and article data. Weerakkody, Y. During this time, uterine contractions may occur, which can be uncomfortable for the patient.
Typically, these contractions will abate spontaneously within 24 hours after the procedure has been completed. The quantity of amniotic fluid that should be removed has also not been established and may be dependent on gestational age, severity, and rapidity of reaccumulation. Volumes aspirated in various reports have ranged from to ml. Periodic evaluation of maternal electrolytes and serum protein may need to be assessed if frequent amniocenteses are required 18 although no studies have demonstrated the efficacy of such surveillance.
Oligohydramnios is defined as a decrease in the volume of amniotic fluid, relative to the gestational age. The incidence in an unselected population without membrane rupture ranges from 0. Acute onset is most commonly the result of membrane rupture, whereas chronic oligohydramnios may reflect a structural abnormality of the fetal urinary tract or a pathophysiologic response to chronic or intermittent fetal hypoxemia. Risk factors for oligohydramnios are shown in Table 2.
Fetal growth restriction Postterm pregnancy Repetitive cord compression. Fetal anomalies Renal agenesis Renal anomalies e. Non-steroidal anti-inflammatory medications Twin-to-twin transfusion Premature rupture of membranes.
Spontaneous premature rupture of membranes PROM is the most common cause of acute oligohydramnios. Chronic oligohydramnios may be the product of major fetal anomalies or prenatal hypoxia. These anomalies are associated with decreased amniotic fluid formation. Chronic or intermittent fetal hypoxia may also result in reduced amniotic fluid volume. Chronic low-grade fetal hypoxia may be a consequence of long-standing uteroplacental insufficiency or maternal hypoxia, whereas prenatal cord compression may lead to either prolonged or repetitive episodes of acute hypoxia of varying intensity and duration.
Corroborative evidence for this pathophysiologic process leading to oligohydramnios exists in both animal and human models. A redistribution of fetal cardiac output has been noted in pregnant ewes made hypoxic. Under ordinary circumstances, this decreased renal perfusion would ultimately result in reduction of fetal urine production and oligohydramnios. Support for redistribution of cardiac output away from the fetal kidneys as the operative mechanism is also provided by several human observations.
Wladimiroff and Campbell measured hourly human fetal urine production rate HFUPR by measuring bladder volume on two occasions 1 hour apart. A normal curve of HFUPR versus gestational age in 92 normal pregnancies from 30 to 41 weeks was established.
Additionally, all nine subjects that delivered infants whose weights were less than the fifth percentile had HFUPRs below the normal range. However attractive the theory of redistribution of flow is, there may be additional operative mechanisms. In an animal model subjected to hypoxemia, glomerular filtration was maintained despite decreased renal blood flow. A final, hypothesized cause of unexplained oligohydramnios is amniotic rupture with an intact chorion.
Corroborative evidence for this process exists in amniotic band syndrome, in which it is theorized that the fetus is partially extruded into the extra-amniotic space. To date, no experimental confirmation of this pathway for oligohydramnios has been provided. Regardless of the precise mechanism, the presence of oligohydramnios in the absence of structural anomalies or membrane rupture suggests an altered normal physiological process.
Its presence also increases the risk for prenatal cord compression. Unfortunately, it is not known what prognostic significance one should attribute to the observation, particularly in a pre-term fetus. Absence of amniotic fluid at the time of artificial rupture of the membranes is also strongly suggestive of oligohydramnios and, in the absence of a sonographic diagnosis, may be the first indication of its presence.
Although ultrasonography has provided a means of assessing the volume of amniotic fluid, a consensus of criteria for sonographic diagnosis of oligohydramnios has not been achieved. In early reports, amniotic fluid volume was assessed subjectively, allowing for differences according to gestational age.
Subsequent investigators attempted to quantify amniotic fluid volume by various techniques. Data presented in these studies are listed in Table 3 and summarized below. Vertical 2 cm. Crowley used subjective criteria to evaluate amniotic fluid volume in pregnancies after 42 weeks, looking for the presence or absence of anechoic space between fetal limbs and uterine wall, as well as between limbs and the fetal trunk. Bottoms and associates subsequently compared a five-tiered subjective evaluation oligohydramnios, decreased, normal, increased, hydramnios to an objective measurement of maximum vertical pocket diameter, the latter measured with the transducer held at right angles to the sagittal plane of the maternal abdomen.
Similarly, Goldstein and Filly also demonstrated good correlation between subjective and objective evaluations of amniotic fluid volume. In , the concept of the "1 cm rule" was introduced in a selected high-risk patient population.
Volume was arbitrarily classified as decreased if the largest fluid pocket measured less than 1 cm in broadest dimension. However, subsequent studies were less optimistic, showing both a lower prevalence and sensitivity of' oligohydramnios as a predictor of IUGR.
The 1 cm rule was re-evaluated in Vertical diameters less than 1 cm were classified as decreased, 1—2 cm as marginal, and greater than 2 cm to less than 8 cm as normal. It was found that 0. As a result of improved sensitivity in detecting FGR by including the marginal category 5. Subsequently, the amniotic fluid component of the biophysical profile was modified to a 2 cm cutoff in two perpendicular planes.
In addition to the 2 cm rule, other objective techniques of amniotic fluid volume have been evaluated. Patterson and colleagues measured the vertical and two horizontal dimensions of the largest fluid pocket and calculated a mean value of the three dimensions.
By using a receiver operating characteristic curve, a statistical tool that is employed to maximize sensitivity and specificity, a cutoff of 3. The 3. Observed differences in average fluid volume were more likely to be due to true differences between patients and not due to measurement error; measurement of the average dimension of the largest amniotic fluid pocket had an interpatient variability that was fourfold higher than the intraobserver variability.
In contrast, use of maximum vertical diameter had an intraobserver variability that was higher than the interpatient variability. The authors concluded that average amniotic fluid volume was more reproducible than the largest vertical diameter and would be a superior screening test to identify malnourished fetuses.
In , Phelan and colleagues introduced the four-quadrant technique of amniotic fluid volume assessment. For all measurement, the transducer was held in a sagittal plane perpendicular to the floor. This number, in centimeters, was termed the amniotic fluid index AFI. Between 36 and 40 weeks, the average AFI was Whereas two standard deviations below and above the mean would have resulted in statistical cutoffs of 3. Further investigation by these authors demonstrated a significant increase in meconium-stained fluid, cesarean section, and low Apgar scores in subjects with AFI less than 5 cm.
Moore and Cayle subsequently assessed the amniotic fluid index in normal pregnancies between 16 and 42 weeks. This study demonstrated the importance of establishing gestation-specific norms for the AFI, rather than a single cutoff value. Interestingly, the 2. Amniotic fluid index percentile values. To date, no single method to assess amniotic fluid volume has proved to be the most valuable clinically.
Difficulty in comparing fluid assessment methods arises from differences in the population tested, the abnormal end point chosen, and the variety of ultrasonographic criteria. The 2 cm rule traditionally had been most widely used, predominantly as a component of the biophysical profile.
Recently, however, the amniotic fluid index has appeared with increasing frequency in the literature and in clinical practice. The AFI, by measuring all four quadrants, would appear to more accurately assess serial changes in fluid volume over time, compared to a single vertical pocket, which might be subject to greater variation due to fetal positioning. Additionally, by using gestation-specific norms, the AFI may more accurately reflect abnormalities in fluid volume compared to the 2 cm rule.
However, the AFI has not been evaluated as extensively in identifying the fetus at risk for IUGR, cord compression, and abnormal perinatal outcome.
By comparison, the use of subjective criteria, which may be less dependent on fetal positioning in serial testing, relies more on a gestalt of fluid volume than on any one measurement value. As a result, the experience of the examiner may be more critical in determining if the amniotic fluid is appropriate for the gestational age, as the same subjectively normal amniotic fluid volume at 42 weeks might be decreased for 34 weeks. Additionally, subjective criteria may vary from individual to individual, making interobserver communication and statistical comparisons more difficult to express.
At the author's institution, the amniotic fluid volume is initially assessed subjectively. If it is normal, no AFI or largest vertical pocket is measured. However, if the fluid subjectively appears decreased, an AFI is calculated. The variability in definitions of ultrasound-based oligohydramnios was highlighted in a clinical commentary by Magann and colleagues, which included a plea for future studies that correlate amniotic fluid volume assessment to clinically relevant perinatal outcomes.
Indices evaluated included the largest vertical pocket, largest transverse pocket, AFI, largest pocket product vertical x transverse , sum of all pocket measurements, and the sum of the pocket products.
They found that the largest vertical pocket, the AFI, and the sum of all pockets were significantly different between the normal and abnormal perinatal outcome groups. Using receiver operating characteristic curves to establish optimal threshold values, a vertical pocket of 2. Chauhan and colleagues performed a prospective randomized clinical trial comparing the AFI to the largest vertical pocket.
They defined oligohydramnios as either an AFI of 5 cm or less, or the absence of a fluid pocket measuring at least 2 x 1 cm. The authors concluded that using the AFI increases the number of interventions for oligohydramnios without improving perinatal outcome. They also observed that both techniques of amniotic fluid assessment are poor diagnostic tests for predicting adverse perinatal outcome. Difficulties arise when comparing various criteria for oligohydramnios.
One variable not often addressed in studies is the inclusion or exclusion of fluid pockets that contain loops of umbilical cord. With oligohydramnios, the umbilical cord makes up an increased proportion of fluid pockets.
Some studies excluded any pocket that contained cord, while others measured the dimensions of fluid that surrounded cord. A frequently overlooked but critically important issue is that of transducer positioning. In some reports, the transducer was held at right angles to the uterine contour, 54 , 58 whereas in others the plane of the ultrasound was perpendicular to the floor or sagittal plane of the abdomen.
Orientation is critical in evaluating vertical diameter. If the transducer is held perpendicular to the uterine contour, a view from the lateral aspect of the uterus might falsely create a vertical pocket on the ultrasonography screen. For the sake of consistency, it is recommended that the transducer be oriented longitudinally and perpendicular to the plane of the floor the plane in which the fluid has layered , thereby minimizing differences if the subject is laterally displaced.
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