Immunoassay for the determination of surfactant apoprotein (SP-A) in human amniotic fluid: comparison with other indices of assessing foetal lung maturity

Abstract

The concentration of the major surfactant-associated protein SP-A (28–36 kDa) was determined in 73 amniotic fluid samples obtained from normal (n = 40) and complicated (n = 33) pregnancies. Lecithin/sphingomyelin (L/S) ratio and phosphatidylglycerol (PG) levels were also determined in all the samples by one-dimensional step-wise thin-layer chromatography. An enzyme-linked immunosorbent assay was used to determine human lung surfactant apoprotein SP-A. The amount of SP-A in human amniotic fluid increased as a function of gestational age from 8 mg 1^-1 at 36 weeks to 11.75 mg 1^-1 at 40–41 weeks of gestation. There was a significant difference (p < 0.01) in amniotic fluid SP-A concentration from female (9.93 ± 0.60 μg ml^-1) compared to male (9.10 ± 0.52 μg ml^-1) foetuses. In amniotic fluid samples obtained from a group of complicated pregnancies, SP-A levels were significantly lower than in the normal group when adjusted for gestational age and sex of the foetus (p < 0.05).

Key Words:

• amniotic fluid
• apoprotein
• lecithin/sphingomyelin (L/S) ratio
• lung surfactant
• phosphatidylglycerol
• respiratory distress syndrome