Amniotic Fluid Physiology PDF

# Amniotic Fluid Physiology * Amniotic fluid is present in the amnion. * A membranous sac that surrounds the fetus. * Is involved in the exchange of water and chemicals between the fluid, fetus, and maternal circulation ## Functions of Amniotic Fluids * Provide a protective cushion for...

# Amniotic Fluid Physiology * Amniotic fluid is present in the amnion. * A membranous sac that surrounds the fetus. * Is involved in the exchange of water and chemicals between the fluid, fetus, and maternal circulation ## Functions of Amniotic Fluids * Provide a protective cushion for the fetus * Allow fetal movement * Stabilize the temperature to protect the fetus from extreme temperature changes. * Permit proper lung development. ## Amniotic Fluid Volume ### Sources * During 1st trimester: 35mL of amniotic fluid is derived from maternal circulation * After the 1st trimester: fetal urine becomes the major contributor to the amniotic fluid volume. * When fetal urine production occurs, fetal swallowing of amniotic fluid begins. * The amount of amniotic fluid increases in quantity throughout pregnancy. * Peaks to 800-1200 ml during the 3rd trimester, and then gradually decreases prior to delivery. ### Variation In Amniotic Fluid Volume | | | | | | :-------------------- | :-------------------------------------------------------------- | :-------------------- | :----------------------------------------------------------------- | | **Polyhydramnios** | ↑ amniotic fluid volume (>1200 ml) | **Oligohydramnios** | ↓ amniotic fluid volume (<800 ml) | | **Causes:** | | **Causes:** | | | ✓ Decrease fetal swallowing of urine | | ✓ Increase fetal swallowing of urine | | | * Neural Tube Defect | | ✓ Membrane leakage | | | | | | ✓ Urinary Tract deformities | ## Specimen Collection and Handling ### Method of Collection: Amniocentesis * Up to 30 ml is collected in a sterile syringe. * The first 2 or 3 mL collected can be contaminated by maternal blood, tissue fluid, and are discarded. * 2nd trimester collection * To assess genetic defects (Trisomy 21 or Down Syndrome) * 3rd trimester collection * Fetal Lung Maturity (FML), Fetal Hemolytic Disease (HDN) ### Table 13-2 **Indications for Performing Amniocentesis** Amniocentesis may be indicated at 15 to 18 weeks' gestation for the following conditions to determine early treatment or intervention: * Mother's age of 35 or older at delivery * Family history of chromosome abnormalities, such as trisomy 21 (Down syndrome) * Parents carry an abnormal chromosome rearrangement * Earlier pregnancy or child with birth defect * Parent is a carrier of a metabolic disorder * Family history of genetic diseases such a sickle cell disease, Tay-Sachs disease, hemophilia, muscular dystrophy, sickle cell anemia, Huntington chorea, and cystic fibrosis * Elevated maternal serum alpha-fetoprotein * Abnormal triple marker screening test * Previous child with a neural tube disorder such as spina bifida, or ventral wall defects (gastroschisis) * Three or more miscarriages **Amniocentesis is indicated later in the pregnancy (20 to 42 weeks) to evaluate:** * Fetal lung maturity * Fetal distress * HDN caused by Rh blood type incompatibility * Infection ## Amniotic Fluid Vs. Maternal Urine * Necessary to determine possible premature membrane rupture or accidental puncture of the bladder during specimen collection. | Test | Amniotic Fluid | Maternal Urine | | :---------- | :------------- | :-------------- | | Creatinine | <3.5 mg/dl | up to 10 mg/dl | | Urea | <30 mg/dl | up to 300 mg/dl | **\*Less reliable tes: Glucose and Protein: Higher in amniotic fluid than maternal urine** ## Fern Test * Use to evaluate premature rupture of membrane * Specimen: Vaginal Fluid → Slide (Air Dry) → (+) Fern-like crystals * Detect early pregnancy ## Specimen Handling and Storage: * **Fetal Lung Maturity Test:** placed in ice for delivery and kept refrigerated. * Filtration is recommended to prevent the lost of phospholipids. * **Bilirubin Test:** protected from light at all times * **Cytogenetics and Microbial studies:** Kept at room temperature or body temperature (37°C) prior to analysis to prolong the life of the cells needed for analysis. # Laboratory Examination of Amniotic Fluids ## Color and Appearance | Amniotic Fluid Color | Clinical Significance | | :--------------------- | :--------------------------------------------------------------------------------------------------- | | Colorless | Normal | | Blood-streaked | Traumatic tap, abdominal trauma, and intra-amniotic hemorrhage | | Yellow | Hemolytic disease of the newborn ( ↑ Bilirubin ) | | Dark green * | Meconium - Newborn's first bowel movement | | Dark red-brown | Fetal death | ## I. Test for Hemolytic Disease of the Newborn * Measured by spectrophotometric analysis * Bilirubin causes a rise in OD at 450 nm. * Oxyhemoglobin will peak at 410 nm and may interfere thus specimen contaminated with blood are not accepted. * Specimen with meconium will cause false low value and are not accepted. * O.D. 450 nm - Normal Absorbance * Reported with Liley graph. * Zone 1 = non-affected/mildly affected fetus * Zone 2 = moderately affected (requires close monitoring) * Zone 3 = Severely affected (requires intervention) ## II. Test for Neural Tube Defect * Neural tube defects (NTD) are one of the most common birth defects in the United States. It can be detected by maternal serum alpha-fetoprotein (MSAFP) blood test, high-resolution ultrasound, and amniocentesis. * Common Neural Tube Defects: * Spina bifida, slit-spine (incomplete closing of spine and backbone) * Anencephaly (absence of major part of the brain) * Screening Test: Alpha-fetoprotein * ↑ in NTD * ↓ in Down Syndrome * Confirmatory Test: Acetylcholinesterase ## III. Test for Fetal Lung Maturity * Respiratory Distress Syndrome (RDS) * Most frequent complication of early delivery * 7th most common cause of morbidity and mortality in premature infant * Caused by insufficiency of lung surfactant production and structural immaturity of fetal lungs. * **a.** Lecithin-Sphingomyelin (L/S ratio) (REFERENCE METHOD) * **Lecithin** = Primary surfactant; for alveolar stability * **Sphingomyelin** = Serves as a control (contrast production) * ✓ L/S RATIO of >2.0 = Mature Lungs * Reject specimens contaminated with blood and meconium * **b.** Amniostat-FLM – immunologic test for Phosphatidylglycerol (PG) -surfactant * Replaces L/S Ratio; Not affected by blood and meconium * Production of PG is delayed in diabetic mother * Low or High Positive: Mature Lungs * Negative: Immature lungs * **c.** Foam Stability (Foam Shake Test) * Amniotic fluid + 95% ethanol → Vigorous shaking for 15 seconds * Stand for 15 minutes * (+) Continuous line of bubble/ foam = Mature Lungs * **d.** Microviscosity – presence of phospholipids decrease microviscosity * **e.** Lamellar Body Count (LBC) – Lamellar Bodies * Type II Pneumocytes - Responsible for the production of alveolar surfactants. * 32,000/ UL lamellar body count = Adequate FLM * **f.** OD 0.150 at 650 nm - Presence of Lamellar Bodies = ↑ Optical Density * OD of ≥ 0.15 = L/S ratio >2.0 * (+) Phosphatidylglycerol ## IV. Test for Fetal Age * **a.** Creatinine * 1.5 to 2.0 mg/dl = prior to 36 weeks of gestation * >2.0 mg/dl = Fetal age is over 36 weeks of gestation