Epidemiologic methods for investigating male fecundity

Fertility is a couple concept that has been measured since the beginning of demography, and male fecundity （his biological capacity to reproduce） is a component of the fertility rate. Unfortunately, we have no way of measuring the male component directly, although several indirect markers can be used. Population registers can be used to monitor the proportion of childless couples, couples who receive donor semen, trends in dizygotic twinning, and infertility diagnoses. Studies using time-to-pregnancy （TTP） may identify couple subfecundity, and TTP data will correlate with sperm quality and quantity as well as sexual activity and a number of other conditions. Having exposure data available for couples with a fecund female partner would make TTP studies of interest in identifying exposures that may affect male fecundity. Biological indicators such as sperm quality and quantity isolate the male component of fertility, and semen data therefore remain an important source of information for research. Unfortunately, often over half of those invited to provide a sperm sample will refuse, and the study is then subject to a selection that may introduce bias. Because the most important time windows for exposures that impair semen production could be early fetal life, puberty, and the time of ejaculation; longitudinal data over decades of time are required. The ongoing monitoring of semen quality and quantity should continue, and surveys monitoring fertility and waiting TTP should also be designed.

Cross-sectional study of congenital heart disease among Tibetan children aged from 4 to 18 years at different altitudes in Qinghai Province

Background Congenital heart disease （CHD） is a common heart condition which does considerable harm to the health of children and adolescents. CHD epidemiological characteristics of Tibetan children whose ages ranged from 4 to 18 years were investigated in Qinghai Province. Methods A total of 32 578 Tibetan children, living at altitudes of 2535 m, 3600 m and 4200 m, were examined using a three-stage protocol： prescreening, rechecking and diagnosis using a color Doppler. The distribution of CHD at different altitudes was analyzed together with differences in occurrence according to age and gender. Results A total of 235 CHD cases were discovered. The total prevalence of CHD was 7.21‰. Prevalence of CHD has been shown to increase along with increase in altitude with 5.45‰ at an altitude of 2535 m, 6.80‰ at 3600 m and 9.79‰ at 4200 m. There were no statistically significant differences between the prevalence at 2535 m and 3600 m （Х^2=1.594, P 〉0.05）. However, there was a significant difference between the prevalence at 2535 m and 4200 m （Х^2=7.002, P 〈0.01）. Also, apparent differences existed between the prevalence at 3600 m and at 4200 m （Х^2=5.540, P 〈0.05）. There was no statistically significant difference in prevalence according to age at an altitude of 2535 m, but the rate of CHD increased significantly along with increasing age at 3600 m and 4200 m. The total prevalence ratio of children aged from 16 to 18 years was significantly higher than that of children from 4 to 7, and from 8 to 12 with Х^2 values of 10.79 （P 〈0.005）, and 5.60 （P 〈0.05） respectively. Within the constituent ratio of CHD, the prevalence of atrial septal defect （ASD） was the highest at 39.10%, followed by the prevalence of ventricular septal defect （VSD） at 32.8% and patent ductus arteriosus （PDA） at 24.7%. Furthermore the proportion of the four categories of CHD varied at different altitude levels： at 2535 m, of those diagnosed with CHD, the prevalence rate of VSD was the highest at 43.5%, at 3600 m ASD was the highest at 42.8% and at 4200 m, PDA was the highest at 50.8%. Conclusion The epidemiological characteristics of CHD in Tibetan children may be associated with altitude levels.