2Reasons for testing- To allow antenatal diagnosis of genetic and congenital disorders (15 to 18 weeks) and later in pregnancy (20 to 42 weeks)- To assess fetal pulmonary maturity- To assess degree of fetal distress- HDN- Anomalies: UTI, neural tube, intestinal, etc.- Fetal Infections: bacterial, viral, etc.
3Physiology and composition - Liquid medium that bathes the fetus throughout its gestation - AMNION/amniotic sac – single layer of cuboidal EC
41 2 3 4 Functions of test :- Disease marker Protects the fetus Enables fetal movement3Plays a role in variousbiochemical processes44
5Formation1- Initially produced by placenta & amnion 2- Composition is similar to dialysate of plasma 3- As gestation progresses, fetus plays more of an active role in its composition
6Formation4. Early in gestation, before skin keratinization5. Through fetal respiration6. Latter stages of pregnancy: major constituents come from fetal swallowing & urination7. Exchange between Amniotic fluid & maternal plasma comes into completion every 2 to 3 hours
7volume - Increases steadily throughout pregnancy - 25 to 50 ml at 12 weeks’ gestationMax vol = 1100 to 1500 ml at 36 wks’ gestation- Abnormally decreased (oligohydramnios):Congenital malformation & other conditions (e.g. premature rupture of the membranes)- Abnormally increased (hydramnios):Associated w/ decreased fetal swallowing in congenital malformations
8Specimen collection - Methods 1- Transabdominally 2- Vaginally Increased risk of infectionRisk of contamination w/ vaginal cells & bacteria
9Specimen collection- TimingAfter 14 wks (depending on purpose)IndicationsGenetic studies (bet 15 & 18)- To assess health status of fetus (later in preg) in cases of Rh isoimmunization, toxemia & DM- Maturity of fetal pulmonary system
10Specimen collection Volume: 10 to 20 ml Containers: plastic, why not glass?Cover with aluminum if not colored, why?Transport & storage:ASAPRefrigerate after centrifugation for 5-15 min (24 hours))Freezing (if storage >24 hrs)
11Physical examinationCOLOR Colorless or very pale yellow Distinct yellow or amber – Bilirubin Green – meconium Pinkish to red – blood (e.g. HDN) Brown – severe hemolysis TURBIDITY Slightly turbid due to (fetal cells, hair and secretions
12Chemical examination- Fern test The Fern Test, used in conjunction with the Nitrazine test, detects the leakage of amniotic fluid from the membranes surrounding the fetus during pregnancy. This phenomenon is in part due to the fluid’s protein and sodium chloride content. A positive test shows the presence of fern-like patterns characteristic of amniotic fluid crystals. The risk may be eliminated by the induction of labor.
15Chemical examination - FETAL LUNG MATURITY TESTS Lecithin–sphingomyelin ratioLecithin: major pulmonary surfactantL/S ratio starts out as 1.0, S eventually decreases and L increases<2.0 = fetal lung immaturity- Phosphatidyl glycerol/PGDetectable only in mature fetus
16- Kleihauer–Betke test Chemical examination- Kleihauer–Betke testStaining technique to identify the presence of maternal or fetal red bloods in amniotic fluid
17Reference Value 7-7.5 PH Colorless to pale yellow Color Clear AppearanceLess than 2.0 *MoM = Multiples of the median.α1-FetoproteinAbsentAcetylcholinesterase1.8–4.0 mg/dL at termCreatinineLess than mg/dL at termBilirubinGreater than 2:1 at termL/S ratioPresent at termPhosphatidylglycerolNormal karyotypeChromosome analysisNone seenWhite blood cell countNegativeLeukocyte esterase