Evaluation of fetal maturity by amniotic fluid creatinine concentrations and lecithin/sphingomyelin ratio.

In a material of 144 samples of amniotic fluid from the last trimester, creatinine concentration, lecithin/sphingomyelin (L/S) ration and their correlation, have been examined. Amniotic fluid creatinine concentration (a.f.c.) increased gradually through the last trimester up to 39 weeks (273-279 days p.m.) with median values of 2 mg/100 ml at 37 weeks and 2.5 mg/100 ml at 39 weeks gestation. The great range makes a.f.c. of doubtful value in assessment of gestional age in individual samples. The correlation between a.f.c. and L/S ratio was highly significant (Kendall's T=0.56). Even so lung maturity cannot be predicted from a.f.c. A low L/S ratio with a.f.c. larger than or equal to 2 mg/100 ml was found in 8-9%, while a.f.c. 1.1-1.9 mg/100 ml was combined with L/S ratios larger then or equal to 2 in a great number of cases. A.f.c. less than 1.1 mg/100 ml was invariably correlated with low L/S ratios.