Amniotic Fluid and hCG Pregnancy Testing

Produced by syncytiotrophoblast cells of the placenta; Peaks during the first trimester; Increased in blood, urine, and amniotic fluid.

Alpha subunit: Identical in hCG, LH, FSH, and TSH; Beta subunit: Confers specificity for hCG.

Principle: Enzyme immunoassay; Specimen: First morning urine; Cutoff: 25 mIU/mL; Anti-hCG source: Rabbit.

Present in the amnion, a membranous sac surrounding the fetus; Placenta is the ultimate source of amniotic fluid water and solutes.

Cushions the fetus; Stabilizes temperature; Allows fetal movement; Supports proper lung development.

Derived from fetal urine and lung fluid; Normal third-trimester volume: 800–1,200 mL; During the first trimester, approximately 35 mL is derived primarily from maternal circulation; Fetal urine becomes the major contributor after the first trimester.

Increased amniotic fluid volume; Causes: Decreased fetal swallowing, neural tube defects (e.g., spina bifida), fetal structural anomalies, cardiac arrhythmias, congenital infections, and chromosomal abnormalities.

Decreased amniotic fluid volume; Causes: Increased fetal swallowing, membrane leakage, urinary tract deformities, congenital malformations, premature rupture of amniotic membranes, and umbilical cord compression.

Amniocentesis; Up to 30 mL collected using a sterile syringe.

Second trimester: Assessment of genetic defects (e.g., Trisomy 21/Down syndrome); Third trimester: Assessment of fetal lung maturity (FLM) and fetal hemolytic disease (HDN).

Alpha-fetoprotein (AFP); Human chorionic gonadotropin (hCG); Unconjugated estriol (uE3); Inhibin A.

Place on ice upon delivery; Keep refrigerated or frozen; Filtration prevents loss of phospholipids.

Cytogenetic studies: Keep at room temperature or 37°C; HDN testing: Protect from light.

Colorless: Normal; Blood-streaked: Traumatic tap, abdominal trauma, or intra-amniotic hemorrhage; Yellow: HDN due to bilirubin; Dark-green: Meconium (first fetal bowel movement), a sign of fetal distress; Dark red-brown: Fetal death.

Most frequent complication of early delivery; Seventh most common cause of morbidity and mortality in premature infants; Caused by insufficient lung surfactant (phospholipid) production and fetal lung immaturity.

Allows alveoli to remain open throughout inhalation and exhalation; Decreases surface tension to prevent alveolar collapse; Allows alveoli to inflate with air more easily.

1.5–2.0 mg/dL: Before 36 weeks' gestation; >2.0 mg/dL: 36 weeks (9 months).

Optical Density (Absorbance) at 450 nm; Evaluates the severity of fetal anemia due to HDN; Oldest routinely performed laboratory test on amniotic fluid.

Normal: Increased absorbance at 365 nm and decreased absorbance at 550 nm; HDN: Increased absorbance at 450 nm due to bilirubin.

Zone I: Non-affected or mildly affected fetus; Zone II: Moderately affected fetus, requiring close monitoring; Zone III: Severely affected fetus, requiring intervention.

Cells, meconium, debris, and hemoglobin; Hemoglobin has a peak absorbance at 410 nm.

Spina bifida: Incomplete closure of the backbone and membranes surrounding the spinal cord; Anencephaly: Absence of a major portion of the brain, skull, and scalp during embryonic development.

Screening: Alpha-fetoprotein (AFP); Confirmatory: Acetylcholinesterase.

Increased in neural tube defects; Decreased in Down syndrome; Major protein produced by the fetal liver during early gestation, before 18 weeks

Supplies nutrients to the nervous system; Removes metabolic waste; Provides a mechanical barrier that cushions the brain and spinal cord against trauma.

Dura mater: Outermost layer lining the skull and vertebral canal; Arachnoid mater: Spiderweb-like filamentous inner membrane; Pia mater: Innermost layer lining the surface of the brain and spinal cord.

Subarachnoid space, located below the arachnoid mater.

Choroid plexus: Produces CSF through selective filtration at approximately 20 mL/hour; Arachnoid villiranulations: Reabsorb CSF.

Protects the brain from harmful chemicals and substances circulating in the blood; Disruption allows WBCs, proteins, and other chemicals to enter the CSF; Examples include meningitis and multiple sclerosis.