http://www.sciencemag.org/news/2018/08/staying-slim-during-pregnancy-carries-price

“The image Japanese mothers-to-be are striving for is the look of having a basketball in front of them while the rest of the body is slim,” says Naho Morisaki of Japan’s National Center for Child Health and Development in Tokyo.

Japan's obsession with slender women may harm unborn children and create long-term health problems for the Japanese population. Already, one in five Japanese women is starting pregnancy underweight, and many scientists have criticized the country's official guidelines for weight gain during pregnancy as too strict. Now, a survey shows many pregnant women strive to keep their weight gain below even those targets. This combination of factors has led to an unusually high percentage of low-weight births, which is likely the reason that the height of the average Japanese adult has declined every year for those born after 1980.