The amniotic fluid index in normal twin pregnancies

A systematic review of amniotic fluid assessments in twin pregnancies

The objectives of this systematic review were to examine the reproducibility of sonographic estimates of amniotic fluid volume (AFV) in twin pregnancies, compare the association of sonographic estimates of AFV with dye-determined AFV, and correlate AFV with antepartum, intrapartum, and perinatal outcomes in twin pregnancies. Studies were included if they were adequately powered and investigated antepartum, intrapartum, and/or perinatal adverse outcome parameters in twin gestations. Studies with comparable populations and exclusion criteria were merged into forest plots. Data comparing the accuracy of AFV assessment, correlation of AFV with gestational age, and adverse outcomes were tabulated. Five of the 6 studies investigating AFV by the amniotic fluid index as a function of gestational age reported data fitting a quadratic equation, with fluid volumes peaking at mid gestation and then declining. This trend was less pronounced when AFV was assessed by the single deepest pocket (2 of 4 studies reporting a quadratic fit). Polyhydramnios was associated with prematurity in 2 of 4 studies (1 amniotic fluid index and 1 single deepest pocket), and oligohydramnios was associated with prematurity in 1 single deepest pocket study. Stillbirth was the only intrapartum outcome reported in more than 1 study. Perinatal outcomes associated with polyhydramnios included neonatal death (P < .05 in 1 of 2 studies), low Apgar scores (1 of 2 studies), neonatal intensive care unit admission (1 of 2 studies), and low birth weight (2 of 3 studies).

Polyhydramnios: Causes, Diagnosis and Therapy

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.

Toward consistent terminology: assessment and reporting of amniotic fluid volume

Amniotic fluid is typically measured by ultrasound using the amniotic fluid index (AFI) or the maximum vertical pocket (MVP). Although both parameters correlate poorly with the actual amniotic fluid volume measured with dye-dilution methods, cross-sectional studies have been used to establish gestational norms. The current acceptable definition of polyhydramnios in the late second and the third trimester in both singleton and multiple gestations is a MVP > 8 cm, while the definition of oligohydramnios is a MVP < 2 cm. The pocket to be measured should exclude the umbilical cord or fetal parts. Randomized clinical trials have indicated that defining oligohydramnios as a MVP < 2 cm will result in fewer obstetrical interventions and similar perinatal outcomes when compared to an AFI < 5 cm.

The role of amniotic fluid assessment in evaluating fetal well-being

Owing to the frequent use of bedside ultrasound, much is known about the regulation of and normative values for amniotic fluid volume and the mechanisms by which this fluid is regulated. The management protocols for conditions with extremes of amniotic fluid volume have become more exact, resulting in interventions more likely to improve outcome. Much is still unclear; there are no tools to measure amniotic fluid volume with precision, and measurement of fetal urinary output is cumbersome and error-prone.