Effects of noise on human placental lactogen (HPL) levels in maternal plasma.

The levels of human placental lactogen (HPL) in the serum of expectant mothers both subjected to and not subjected to aircraft noise were measured. The HPL levels in the quiet reference area and in the noise area were similar before the 29th week of pregnancy. However, the HPL levels of subjects in the noise area tended to be lower than those in the reference area after the 30th week of pregnancy and the difference became significant after the 36th week of pregnancy. The lower HPL levels were associated with lower birth weight for infants of mothers who lived in the noise area.