Summary of evidence for reproductive outcomes associated with noise exposure-experimental and human studies

In recent years there has been growing interest in the effects of physical agents on human reproductive functions both in occupational and environmental settings. Reproductive outcomes such as gestation length, preterm labour, low birth weight, preterm birth, congenital malformations that may be affected by noise exposure, have been extensively studied mostly in animal studies and only to a lesser extent, in human studies. However the strength of evidence for any association in humans is still insufficient. While experimental studies have shown that exposure of rodents to elevated noise levels during pregnancy usually leads to decreased pregnancy maintenance and reduced fetal weight and occasionally to fetotoxicity or teratogenesis, it is unknown whether similar effects occur in humans. Animal studies on stress experienced during pregnancy has shown that the endocrine-immune system is directly affected by noise resulting malfunction in progesterone production and may lead to disorder in fetal development. Occupational studies have shown that noise exposure with other occupational factors can cause adverse reproductive outcomes like preterm birth, low birth weight, even congenital malformations in specific sectors of occupation. The main limitation of occupational studies is the lack of objective noise exposure assessment that can show which noise levels caused adverse reproductive outcomes. Furthermore the noise exposure is generally much higher in a workplace than in an environmental setting. A small number of environmental noise studies have found associations between aircraft noise and low birth weight or shortened gestation length and decreased human placental lactogen in serum of pregnant women. Much less is known about the association between other noise sources and preterm health. There is a need for more, well-designed epidemiological studies with better adjustment for confounding factors, such as life-style factors, characteristics of parents and socioeconomic status.