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Withdrawal of the 1999 JSOG recommendation of weight gain restriction during pregnancy (Commentary of the JSOG Perinatal Committee)

Dear Editor, An increase in low birthweight rates, concomitant with a decrease in mean birthweights, initially occurred in the early 1980s in Japan. The Japanese trajectory toward smaller newborns has been implicated in the increasing incidence of non-communicable diseases according to the developmental origin hypothesis. In August 2018, Science published a study showing that a decline in birthweights in Japan may be a risk factor for long-term health disorders, thereby drawing attention to the critical situation in Japan. This study reported that the guidelines of the Japan Society of Obstetrics and Gynecology (JSOG) recommended a low calorie diet for ordinary pregnant women to prevent toxemia of pregnancy (hypertensive disorders of pregnancy) in 1981 and that this recommendation was causatively associated with an increase in low birthweight rates from the early 1980s in Japan. However, this description was incorrect. The JSOG Perinatal Committee recommended weight gain restriction during pregnancy to prevent toxemia of pregnancy (hypertensive disorders of pregnancy) in 1999, approximately two decades later than the initial increase in low birthweight rates in Japan, that is, the early 1980s. Toxemia of pregnancy (hypertensive disorders of pregnancy) was the second leading cause of Japanese maternal mortality in 1995. Moreover, the Guidelines for Obstetrical Practice in Japan (edited by the Japan Society of Obstetrics and Gynecology – the Japan Association of Obstetricians and Gynecologists) since 2011 have recommended no strict weight gain restriction for pregnant females due to the lack of supportive evidence for its beneficial outcomes. Nevertheless, the JSOG Perinatal Committee agreed that strict weight gain restriction during pregnancy in 1999 lacked sufficient high-quality evidence to support its beneficial contributions to perinatal outcomes. Moreover, we cannot fully deny the possibility that this may have contributed to the persistently high rate of low birthweights in Japan after 1999. As reported in Science, the increase in the rate of low-birthweight newborns in developed countries is the most serious in Japan. Therefore, in 2019, the JSOG Perinatal Committee decided to officially withdraw the 1999 recommendation for weight gain restriction during pregnancy. The JSOG Perinatal Committee is now preparing new recommendations for weight gain during pregnancy to obtain better perinatal outcomes for pregnant Japanese women. Regarding the high rate of low-birthweight newborns in Japan, it is important to promote multidisciplinary as well as scientific approaches for the purpose of developing effective countermeasures.