1 URINALYSIS AND BODY FLUIDS (AMNIOTIC FLUID) LECTURE Dr. Essam H. Jiffri

2 Amniotic fluid is found in the membranous sac that surrounds the fetus and provides a cushion to protect the fetus

3 Amniotic Fluid - The Fluid formed from the metabolism of fetal cells, transfer of water across the placental membrane, and, in later stage of development, by fetal urine. - By the time production of fetal urine occurs, the fetus begins swallowing the amniotic fluid in an amount approximately equal to the urine output.

4 Amniotic Fluid - The buildup of amniotic fluid to a total volume of 500 to 2500 ml at term is produced primarily by increased cell metabolism and placental water exchanges. - In ability of the fetus to swallow is a critical sign and is indicated by an abnormal increase in amniotic fluid.

5 Amniotic Fluid - Fluid for analysis obtained by needle aspiration into the amniotic sac, a procedure called amniocentesis. - The procedure is relatively safe and can be performed on an out­patient basis.

6 Amniotic Fluid - Specimens should be protected from light. - Special precautions must be taken with specimens for cytogenetic analysis because cells in the fluid must be kept alive for culturing by the laboratory.

7 Amniotic Fluid - Cytogenetic analysis has become an important predictor of birth defects.

8 FETAL DISTRESS - Clinical analysis of amniotic fluid assesses both fetal well being and maturation. - Because amniotic fluid is a product of fetal metabolism, the constituents that are present in the fluid provide information about the metabolic processes taking place and the progress of fetal maturation.

9 FETAL DISTRESS - The oldest routinely performed laboratory test on amniotic fluid evaluates the severity of the fetal anemia produced by hemolytic disease of the newborn. - Those infants are referred to as (R h babies).

10 FETAL DISTRESS - The incidence of this disease has been decreasing rapidly since the development of methods to prevent anti-R h antibody production. - The destruction of fetal red blood cells by antibodies that are present in the maternal circulation results in the appearance of the red blood cell degradation product, bilirubin, in the amniotic fluid.

11 FETAL DISTRESS - By measuring the amount of bilirubin present in the fluid, it is possible to determine the degree of hemolysis taking place and to assess the danger of this anemia presents to the fetus. ­In cases of premature or prolonged rupture of the amniotic membranes there is concern over possible infection of the mother and fetus.

12 FETAL DISTRESS - Testing of the fluid with the leukocyte esterase reagent strip for the presence of white blood cells is shown to be a good indicator of infection and is more rapid and cost effective than Gram stains and cultures.

13 FETAL MATURITY - Fetal distress, whether caused by hemolytic disease of the newborn or other conditions, forces the obstetrician to consider a preterm delivery, therefore, it becomes necessary to assess fetal maturity. - Respiratory distress is the most frequent complication of early delivery.

14 FETAL MATURITY - Laboratory tests are performed to determine the overall fetal maturity. - The laboratory procedure routinely used to measure fetal lung maturity is the lecithin ratio (L/S ratio). - Lecithin is the primary component of the phospholipids that make up the majority of the alveolar lining and a count for alveolar stability.

15 FETAL MATURITY - Lecithin is produced at a relatively low and constant rate until the 35th week of gestation, at which time a noticeable increase in its production occurs, resulting in the stabilization of the fetal lung alveoli. - Sphingomyelin is a lipid that is produced at a constant rate throughout fetal gestation; therefore, it can serve as a control on which to base the rise in lecithin.

16 FETAL MATURITY - Prior to 35 weeks of gestation, the L/S ratio is usually less than 1.6 and it will rise to 2.0 or higher when lecithin production increases. - When the L/S ratio reaches 2.0 a preterm delivery is usually considered to be a relatively safe procedure.

17 FETAL MATURITY - Measurement of lecithin and sphingomyelin is performed using thin-layer chromatography. - Absence of phosphatidylglycerol in the presence of a normal L/S ratio is seen in children of diabetic mothers

18 FETAL MATURITY - At about 36 weeks of gestation, urine from the fetal kidney begins appearing in the amniotic fluid; therefore, creatinine concentration above 2.0 mg per dl indicates a fetal age of approximately 36 weeks.

19 FETAL MATURITY - The measurement of alpha fetal protein levels and acetylcholinesterase activity is being used to provide early detection of neural tube disorders, such as spina bifida.

20 Summary of the routine chemical tests performed on amniotic fluid Tests for the Well-being and Maturity __________________________________________________________ Test Normal values at term Significance __________________________________________________________ Bilirubin scan0.025 mg/dlHemolytic disease of the newborn L/S ratio2.0Fetal lung maturity Phosphatidyl-PresentFetal lung maturity Glycerol Creatinine1.3 – 4.0 mg/dlFetal age Alpha fetal protein4.0 mg/dlNeural tube disorders __________________________________________________________