Amniotic Fluid
Definition:
· Amniotic fluid is a liquid that surrounds the unborn baby (fetus) during pregnancy. It is contained in the amniotic sac.
· The fetus floats in the amniotic fluid. During pregnancy the amniotic fluid increases in volume as the fetus grows. Approximately 1000 ml of amniotic fluid surround the baby at full term (40 weeks gestation).
Function:
· Acts as a cushion to protect embryo from mechanical injuries.
· Allows for freedom of fetal movement.
· Permits musculoskeletal Development.
· Helps baby’s lungs grow and develop because baby breathes in the fluid.
· Maintains a relatively constant temperature for the environment surrounding the fetus.
· Allows for symmetrical growth and development of the fetus.
· It contains bacteriostatic properties which can protect the intrauterine environment from infection.
Formation:
Amniotic fluid is composed of a mixture of different substances that reach or are removed from the amniotic cavity by various routes:
1. Fetal urine appears in the amniotic cavity as soon as the metaneprhos
develops and increases gradually.
2. Pulmonary secretions increase gradually.
3. Oro-nasal secretions may contribute a small and indeterminate amount.
4. The fetal skin.
5. Intramembranous secretions.
6. Transmembranous passage.
Volume:
Volume of amniotic fluid is varied according to the period of pregnancy.
o First trimester 30 ml.
o Second trimester 350 ml.
o Third trimester 1500 ml.
· Polyhydramnios is generally defined as amniotic fluid volume greater than 2,000 ml. This condition often accompanies multiple pregnancy (twins or triplets), or some congenital defect such as hydrocephalus.
· An abnormally small amount of amniotic fluid is known as oligohydramnios. This condition can cause deformities in the fetus. And may be due to congenital anomalies such as renal agenesis or bladder outlet obstruction.
Amniocentesis:
· Removal of a sample of the fluid is called amniocentesis.
· Amniocentesis is a prenatal diagnostic test performed at around (14 -22) weeks during second trimester of pregnancy.
· Amniotic fluid test or AFT may be done to:
· To check on the well-being of your baby if you have a blood sensitization, such as Rh sensitization.
· To discover genetic fetal disorders with chromosomal abnormalities (Down’s syndrome) or congenital metabolic disorders.
· Determine if the amniotic fluid is infected.
· To assess pulmonary maturity.
· Early in the pregnancy to determine if the fetus has certain types of birth defects.
· The test can also determine the baby’s sex.
Specimen:
· Container: Amber plastic transfer tube and amber stopper. Identify specimen with patient name directly on the container and on the outside of the aluminum foil.
· Storage Instructions: Freeze within 4 hours to transport to laboratory; stable refrigerated up to 1 week. Protect from light. Avoid repeated freezing and thawing of the specimen, which may cause the sample to precipitate, resulting in a lower than expected value. If cell culture is requested the specimen should be kept at 37oC.
Physical Examination
Color
Normal: Colorless or pale straw
Abnormal:
1. Yellow-orange is indicative of the presence of bile pigment released from red blood cell hemolysis.
2. Brown due to severe hemolysis
3. Green due to contamination with meconium
4. Yellow – brown opaque fluid may indicate intrauterine death ,although not necessarily from erythroblastosis.
Turbidity: Turbid due to presence of variant cell types.
TESTS:
1. Alpha-fetoprotein (AFP):
This test can help determine principle protein in weeks and if there is an opening in the fetal skin. The most common place is the spine. This would be a neural tube defect (NTD), such as spina bifida.
2. Creatinine:
Normal value: 1.5-2.0mg\dl or greater indicates fetal maturity, we measure creatinine because fetal urine is component of amniotic fluid.
3. Lipids(Lecithin / Sphingomyelin ratio):
Used to evaluate fetal pulmonary maturation.
An L/S ratio of 2 or more indicates fetal lung maturity and a relatively low risk of infant respiratory distress syndrome.
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