The underlying mechanisms of the recent declines in sex ratios at birth may be related to decreased fertilization of XY embryos by reduced motility of Y spermatozoa from a male factor approach and increased cortisol secretion prior to conception, low level of glucose at implantation and/or increased maternal adrenal androgens during pregnancy from a female factor approach. The present data suggest that the recent temperature fluctuation in Japan appears to be linked to a lower male to female ratio of newborn infants partially via increased male fetal deaths. Like sea turtles human male concepti appear to be especially vulnerable to external stress factors including climate changes. In order not to share the same fate as the sea turtles showing 90% females, temperature differences and male to female ratios of fetal deaths and newborn infants are of great importance to human reproductive health and balance between the sexes. We must take every caution to monitor these indicators for future human reproductive health.

Autorentext

Misao Fukuda was born in Hiroshima in 1950. He qualified in 1976 as M.D. from Kagoshima University Faculty of Medicine and then as Ph.D. from Kobe University Graduate School in 1981. He was Chief at the Department of Obstetrics and Gynaecology in Ako Municipal Hospital, Japan. In 1985 he founded M&K Health Institute (formerly Fukuda Ladies Clinic).