AUBF Amniotic

• Amniotic fluid is present in the amnion, a membranous sac surrounding the fetus, serving as a cushion for the fetus and facilitating the exchange of water and chemicals from mother to fetus.
• Amniotic fluid is collected through amniocentesis.
• For chromosomal and cytogenetic analysis, amniotic fluid is collected at approximately the 16th week of gestation.
• For fetal distress and lung maturity, amniotic fluid is collected at the 3rd trimester of gestation.
• The peak volume of amniotic fluid is approximately 800-1200mL during the 3rd trimester.
• Polyhydramnios is an increased amount of amniotic fluid.
• Oligohydramnios is a decreased amount of amniotic fluid.
• Approximately 35 mL of amniotic fluid is derived from maternal circulation during the 1st trimester.
• Fetal urine is the major contributor to the volume of amniotic fluid after the 1st trimester.
• Amniotic fluid analysis is used for cytogenetic analysis, fetal lung maturity, and HDN assessment.
• Amniocentesis types include transabdominal (most frequently performed procedure) and vaginal, which carries a greater risk of infection.
• A maximum of 30 mL of amniotic fluid is collected in sterile syringes.
• The first 2 or 3 mL of amniotic fluid is discarded as it is contaminated by maternal blood, tissue fluids, and cells.
• Samples of amniotic fluid are transferred to sterile plastic containers and taken to the laboratory immediately.
• Amniotic fluid is used to evaluate premature rupture of the membranes.
• A vaginal fluid specimen is spread on a glass slide and allowed to completely air dry at room temperature, then it is observed microscopically.
• The presence of “fern-like” crystals due to the protein and sodium chloride content is a positive screen for amniotic fluid.
• Fern test laboratory test includes macroscopic examination, laboratory test for HDN assessment, and laboratory test for neural tube defects.
• Macroscopic examination of amniotic fluid is normal if it is colorless and slightly to moderately turbid, while meconium is the newborn’s first bowel movement, causing dark-green color.
• Dark red brown indicates fetal death in amniotic fluid.
• Yellow fluid in amniotic fluid indicates the presence of bilirubin.
• Blood-streaked fluid in amniotic fluid indicates traumatic puncture, abdominal trauma, or intra-amniotic hemorrhage.
• HDN assessment in amniotic fluid detects bilirubin using OD450 and is plotted using Liley graph.
• Neural tube defects in amniotic fluid include Anencephaly & Spina bifida.
• Fetal lung maturity in amniotic fluid includes L/S ratio (NV>2.0), phosphatidyl glycerol, amniostat FLM, foam stability index, microviscosity, and optical density 650nm.