Amniotic fluid beta 2 microglobulin: correlation with L/S ratios and creatinine levels.

Beta 2 microglobulin (beta 2 m) levels were measured in amniotic fluids taken after the 32nd week of gestation. Beta 2 m levels fell continuously from 5.2 microgram/ml at the 32nd week to 3.08 microgram/ml after the 39th week of gestation. Abnormally high levels of beta 2 m were found in 12.6% of samples. There was a significant correlation between beta 2 m levels and lecithin/sphingomyelin ratios at 32 weeks of gestation and with creatinine levels at 37-38 weeks (P less than .05). Although elevated beta 2 m levels may be associated with maternal and/or fetal abnormalities, the precise relationship is not clearly established: in particular, our data do not suggest that estimation of beta 2 m levels could be of value in determining fetal maturity.