Measurement of AFV is helpful for estimating the changes in total amounts of certain substances that circulate in the amniotic fluid, including bilirubin, creatinine, and surface-active agents. Knowledge of AFV is important because marked changes in the amount of amniotic fluid can decrease the predictive value of serial concentration measurements of specific substances. This measurement is most important when test results do not agree with the clinical picture.
Study a sample of amniotic fluid with the use of a solution of para-aminohippuric acid for absorbency and dilution to calculate the probable AFV in milliliters.
Correct AFV by multiplying the measured levels of specific substance by the actual fluid volume divided by average volume (for gestation age).
If either polyhydramnios or oligohydramnios is suspected, the fetus should be screened with ultrasound to detect physical anomalies.
Polyhydramnios (increased amniotic fluid, >2000 mL) is suggested by a total intrauterine volume >2 standard deviations (SD) above the mean for a given gestational age. It is estimated that 18%–20% of fetuses in such pregnancies have congenital anomalies, the two most common being anencephaly and esophageal atresia (fetal swallowing is greatly impaired). The remainder have involvement secondary to Rh disease, diabetes, or other unknown causes. Polyhydramnios is also associated with multiple births (e.g., twins).
Oligohydramnios (reduced volume of amniotic fluid, <300 mL) is suggested by a total intrauterine volume >2 SD below the mean occurring before the 25th week of gestation. A disturbance of kidney function caused by renal agenesis or kidney atresia can result in oligohydramnios (fetal urination is impaired). After 25 weeks, the suspected causes of decreased AFV are premature rupture of membranes, fetal growth restriction, and postterm pregnancy.
Pretest Patient Care
Explain the reason for amniotic fluid testing and the meaning of results.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review AFV test results; report and record findings. Modify the nursing care plan as needed.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.