Climate change is associated with male:female ratios of fetal deaths and newborn infants in Japan.

OBJECTIVE: To evaluate whether climate change is associated with male:female ratios (sex ratios) of fetal deaths and births in Japan. DESIGN: A population-based cohort study. SETTING: Not applicable. PATIENT(S): Newborn infants and fetuses spontaneously aborted after 12 weeks of gestation. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Yearly sex ratios of fetal deaths and newborn infants and monthly fetal death rates and sex ratios of newborn infants. RESULT(S): A statistically significant positive association was found between yearly temperature differences and sex ratios of fetal deaths; a statistically significant negative association was found between temperature differences and sex ratios of newborn infants from 1968 to 2012, and between sex ratios of births and of fetal deaths. The sex ratios of fetal deaths have been increasing steadily along with temperature differences, whereas the sex ratios of newborn infants have been decreasing since the 1970s. Two climate extremes, a very hot summer in 2010 and a very cold winter in January 2011, showed not only statistically significant declines in sex ratios of newborn infants 9 months later in June 2011 and October 2011 but also statistically significant increases of fetal death rates immediately, in September 2010 and January 2011. CONCLUSION(S): The recent temperature fluctuations in Japan seem to be linked to a lower male:female sex ratio of newborn infants, partly via increased male fetal deaths. Male concepti seem to be especially vulnerable to external stress factors, including climate changes.

Paternal smoking habits affect the reproductive life span of daughters.

The present study assessed whether the smoking habits of fathers around the time of conception affected the period in which daughters experienced menstrual cycles (i.e., the reproductive life span). The study revealed that the smoking habits of the farther shortened the daughters' reproductive life span compared with daughters whose fathers did not smoke.

The sex ratio of offspring is associated with the mothers' age at menarche.

BACKGROUND: Early menarcheal age is a risk factor for breast and ovarian cancers and is also associated with an increased spontaneous abortion rate. The aim of this study was to investigate whether there is a link between early menarcheal age and the offspring sex ratio. METHODS: We recorded the sex of 21208 live born infants, all singletons, born to 10 847 premenopausal women (mean attending age: 37.5 ± 7.2 years, range 22-54) who attended our clinics for obstetrical and gynaecological assessment. We calculated the sex ratio of newborn infants in relation to the mothers' age of menarche (from 9 to 18 years) and to the number of infants per woman (i.e. fertility index). RESULTS: A low offspring sex ratio (males/females) of 0.800 was observed in mothers who entered menarche at the age of 9 years; the odds ratio (OR) (95% confidence intervals) compared with those of control group with menarche at age 14 was 0.72 (0.29-1.79). The sex ratio remained low, until the group of mothers who entered menarche at 12 years of age [1.009; OR: 0.90 (0.85-0.95)]. The highest sex ratio was observed in mothers with a menarcheal age of 14 years (1.118; OR: 1.00 control) and it gradually decreased until the menarcheal age of 17 years [1.000; OR: 0.89 (0.15-5.26)]. The fertility index was also low in women with menarche at the age of 9 to 11 years. CONCLUSIONS: Women entering menarche outside the normal range, especially those with earlier menarche, may have an increased chance of producing female offspring.

The ovulation pattern during three consecutive menstrual cycles has a significant impact on pregnancy rate and sex of the offspring.

Identification of the ovary at the time of ovulation during three consecutive menstrual cycles results in one of eight ovulation patterns, left-left-right, right-left-right, left-right-right, and right-right-right of right-sided ovulation and right-right-left, left-right-left, right-left-left, and left-left-left of left-sided ovulation. Our data suggest that IVF and IUI treatment in cycles in which development of the preovulatory follicle(s) occurs in the right-sided ovary-and ovulations took place from the left-sided ovary in the preceding two cycles (left-left-right)-is likely to show the best pregnancy potential and high offspring sex ratio.