Obstetrics and Gynecology - A. M. Gromova 2000

Modern methods for assessing fetal condition
Determination of fetal lung maturity

Assessment of fetal lung maturity is indicated when deciding on delivery via Cesarean Section in preterm pregnancies, or when considering Pregnancy prolongation in cases of preterm prelabor rupture of membranes (PPROM) in the third trimester, provided There is a need for fetal respiratory distress syndrome (RDS) prophylaxis.

Amniotic Fluid contains Phospholipids derived from the fetal Lungs, predominantly sphingomyelin and lecithin. Up to 32 weeks of gestation, their ratio is typically 1:1. As the lungs mature, the concentration of lecithin increases. A lecithin-to-sphingomyelin (L:S) ratio greater than 2 indicates fetal lung maturity.

Because Biochemical Methods for phospholipid determination are complex, rapid quantitative assays are used to measure their levels in amniotic fluid during preterm pregnancies:

a) Clements' ethanol foam test (1972);

Class="center">Procedure for the Clements Test

b) Determination of the optical density of amniotic fluid by spectrophotometry at a wavelength of 650 nm. Amniotic fluid (5–6 mL) is first centrifuged at 2000 rpm for 10 min, after which the supernatant is subjected to spectrophotometry. An amniotic fluid optical density of 0.15 or higher combined with an L:S ratio of 2 indicates mature fetal lungs; an optical density of 0.05–0.15 and an L:S ratio of less than 2 indicates moderately immature lungs; and an optical density below 0.05 with an L:S ratio under 1.3 indicates immature fetal lungs. Distilled Water is used as a control for spectrophotometry;

c) amniocrit determination.

Amniotic fluid is drawn into an ESR capillary tube, centrifuged for 3 min at 2000 rpm, and the height of the sediment is measured. If the sediment height exceeds 1.1% of the total fluid Column height, the fetal lungs are considered mature; less than 0.9% indicates immaturity; and 0.9–1.1% is regarded as a borderline state;

d) determination of the thromboplastic activity of amniotic fluid. 1 mL of amniotic fluid is mixed with 1.5 mL of venous Blood from the pregnant woman and placed in a water bath at 37°C. A blood clotting time not exceeding 110 s indicates fetal lung maturity, 110–120 s indicates a borderline lung state, and greater than 120 s indicates immaturity;

e) counting of "orange" (lipid-containing) Cells.

To 1 mL of amniotic fluid, 1 mL of a 0.1% aqueous solution of Nile blue sulfate is added; the mixture is covered with a coverslip and the number of orange cells is counted. A Cell count of less than 10% indicates fetal immaturity, while 10–20% is considered an intermediate zone. To reliably assess fetal lung maturity, 3–4 parallel tests should be performed, accompanied by fetal Ultrasonography (Ultrasound examination).