| Premature birth rate and low birth weight rate are increasing in industrialized countries including USA and Japan. The Infant mortality rate (IMR) is three times and 50-75 times greater for infants born at 32-36 weeks and <32 weeks respectively than term-born counterparts. In the U.S., the IMR is greater than in Japan particularly among black infants and simply the "lower socioeconomic class" is not the answer. Premature birth is heterogeneous in origin and idiopathic in 70% of the cases. Increased utilization of assisted reproductive technology only accounts for a part of the recent trend. Evidence suggests environmental factors play a significant role, and genetic-environmental interaction is plausible. A chronic psychosocial stress of pregnant women has been postulated to be modifying the endocrine milieu thereby influencing pregnancy outcomes. In a preliminary observation in St. Louis, homeless pregnant women with high behavioral and social risks, when accommodated in a shelter home designed for these women, produced significantly less numbers of premature and low birth weight infants as compared with the general population. Furthermore, in a randomized controlled study in Washington DC, psychobehavioral intervention specifically targeting smoking (primary and secondary), intimate partner violence (IPV), and depression among black pregnant women significantly decreased the rate of miscarriage and low birth weight. These reports may have significant implication to the Japanese situation. Increasing number of Japanese women at reproductive age are exposed to smoking, may have underling psychosocial stress and may suffer from subclinical depression and/or from IPV. Detailed epidemiological studies of women before and during the reproductive age with regard to risk factors can lead to an effective intervention strategy against premature birth in Japan.
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