Noradrenaline to adrenaline ratio in amniotic fluid as an index of fetal maturity.

Amniotic fluid lecithin to sphingomyelin ratio (L/S) and adrenaline concentration, noradrenaline concentration, and noradrenaline to adrenaline ratio (NA/A) were measured in 50 normal women late in pregnancy. Between gestation weeks 37 and 43 the maturity-linked increase in L/S ratio was accompanied by similar increases in NA/A ratio and noradrenaline but by decreases in adrenaline concentration. Although the amniotic fluid NA/A ratio reflects fetal sympathetic nervous system development rather than pulmonary development as mirrored by the L/S ratio, a high correlation existed between log NA/A and L/S, indicating that the NA/A ratio could provide a further index of fetal maturity.