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Study question Is it necessary to collect more than one semen sample from each individual in epidemiological studies? Summary answer Single semen samples can be used in model construction as long as the model adjusts for major relevant covariates. What is known already If a series of semen samples are taken from one individual at different times, significant intra-individual variation may exist. Study design, size, duration A population-based cross-sectional study was conducted from 1 December 2000 to 20 November 2002. A total of 1010 volunteers, aged between 20 and 60 years old, were recruited. Participants/materials, setting, methods A total of 998 subjects were included for statistical analysis. Of these, 332 men provided single semen samples (group 1) and 666 men provided two samples (group 2). Semen parameters, including semen volume, sperm concentration, total sperm number, progressive motility, vitality, and sperm morphology, were analyzed with standardized methods according to the World Health Organization (WHO) laboratory manual for the examination of human semen and sperm-cervical mucus interaction (3rd edition). Main results and the role of chance Rapidly progressive motility of semen from group 1 was lower than that of group 2, but other parameters were not significantly different. The differences in mean values between the double samples were small on all semen parameters. The correlations between the two ejaculates were high, but the agreements were poor except for sperm vitality and normal morphology. Model selection and validation analysis supported the premise that the regression model from the first samples was applicable for the second samples. The large sample size with extensive quality control provides robust parameter estimation and promises good applicability for model selection and validation. Limitations, reasons for caution The results are valid for healthy men in China, not for subfertile or infertile men. Wider implications of the findings The overall semen quality of a given group of healthy men will not vary significantly in the short term. Single semen samples can be used in model building as long as major relevant covariates are considered. Utilizing multiple semen donations may actually cause the samples to be less representative. Study funding/competing interests This research was supported by a grant from Shanghai Science and Technical Committee (02DJ14053) and a grant from Ministry of Science and Technology, China (9902). All authors have no competing interests.

Aim: To determine whether induced abortion (IA) increases breast cancer (BC) risk. Materials and Methods: A population-based case-control study was performed from Dec, 2000 to November, 2004 in Shanghai, China, where IA could be verified through the family planning network and client medical records. Structured questionnaires were completed by 1,517 cases with primary invasive epithelial breast cancer and 1,573 controls frequency- matched to cases for age group. The information was supplemented and verified by the family planning records. Statistical analysis was conducted with SAS 9.0. Results: After adjusting for potential confounders, induced abortions were not found to be associated with breast cancer with OR=0.94 (95%CI= 0.79-1.11). Compared to parous women without induced abortion, parous women with 3 or more times induced abortion (OR=0.66, 95%CI=0.46 to 0.95) and women with 3 or more times induced abortion after the first live birth (OR=0.66, 95%CI =0.45 to 0.97) showed a lower risk of breast cancer, after adjustment for age, level of education, annual income per capita, age at menarche, menopause, parity times, spontaneous abortion, age at first live birth, breast-feeding, oral contraceptives, hormones drug, breast disease, BMI, drinking alcohol, drinking tea, taking vitamin/calcium tablet, physical activity, vocation, history of breast cancer, eating the bean. Conclusions: The results suggest that a history of induced abortions may not increase the risk of breast cancer.

Objective To explore the male condom use and the using problems as well as the influencing factors among Shanghai women. Methods A prospective follow-up was conducted among 1 562 subjects who used either the condom or the combined regimen as their method for fertility regulation in nine districts in Shanghai. The study began in the October, 2003 with a baseline survey, and finished in the December, 2007. There were two groups, group I with condom use combined regimen (condom + ECP) and group II with condom use only. Totally 812 eligible subjects were assigned to group I, and 750 to group II. Data was collected with a daily diary card, on which menses, acts of intercourse, information on condom and ECP use, and condom using problems were recorded. Data were analyzed with binary logistic regression models adjusting the potential confounding factors. Results During the whole study years, in group I the mean condom using frequency was (59.5±17.9) times and the whole course condom using frequency was (58.1±18.5). In group II, the mean condom using frequency and the whole course condom using frequency are (57.4±19.0) and (56.4±19.7), respectively. The condom using problem rate (CUPR) in group I and group II in the first month were 5.05 and 9.64 per 100 condoms. With the progress of the study, the CUPR in both groups were decreasing. The total year's CUPR in group I and group II were 0.82% and 1.45% ( P =0.002). The study showed that the common condom using problems during the 1st year were too loose (41.9% in group I and 27.1% in group II), too long (15.6% in group I and 25.6% in group II), and too slippery (21.2% in group I and 20.2% in group II) among those reported condom using problems. Condom problems were more common in the inexperienced and in those who had not experienced problems previously. Subject's age, education and occupation might influence condom using problem rate. Conclusions The condom using problems indicated that condom manufacturers should continue to refine the products so as to increase the condom acceptability. Experience was significant associated with condom using problem.

Objective To explore the relationship between age and semen quality in Chinese men. Design Population-based cross-sectional study. Setting The Department of Reproductive Epidemiology and Social Science, Shanghai Institute of Planned Parenthood Research, People's Republic of China. Patient(s) Healthy 20- to 60-year-old men. Intervention(s) Standard World Health Organization procedures (3rd ed.) for semen analysis. Main Outcome Measure(s) Semen volume, sperm concentration, total sperm number, progressive motility, vitality, and sperm morphology. Result(s) Statistical analysis results of 998 subjects showed that age was negatively correlated with progressive motility, vitality, and percentage of normal sperm. No declining trend was found between age and parameters semen volume, sperm concentration, or total sperm number. Rapidly progressive motility and percentage of normal sperm began to decrease slowly at age 30 years, and progressive motility began to decrease at age 40 years. Compared with the 20- to 29-year age group, the values of the latter three parameters showed significant differences in men aged ≥35, ≥45, and ≥40 years. Conclusion(s) Increasing age mainly influences sperm motility, vitality, and normal morphology, but these parameters have turning points at different ages. Because of the large sample size, this information can be used to provide standard values for Chinese men, particularly in the age range 30–50 years. Further research would enroll a large sample of healthy 40- to 70-year olds to examine declining semen parameters in these age groups.

Aim: To examine whether reproductive hormones play a role in the association between body mass index (BMI) and semen quality. Methods: Semen quality and testosterone (T), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and estradiol (E2) were evaluated in 990 fertile males with age 38.9 ± 9.7 (mean ± SD) years recruited from the Chinese general population in 2001 and 2002. Results: Semen quality was reduced among underweight (BMI < 18.5) compared with normal (BMI 18.5–24.9) and overweight (BMI 25.0–29.9), but the associations were independent of reproductive hormones. After adjustment for the potential confounders, underweight men had reductions in sperm concentration (22.4 × 10 6 /mL), total sperm count (52.9 × 10 6 ) and percentage of normal sperm forms (6.9%) compared with men with normal BMI. Being underweight may be a risk factor for low sperm concentration (OR: 4.68, 95% confidence intervals [CI]: 2.01–10.91). Otherwise, being overweight may be a protected factor for low sperm concentration (OR: 0.25; 95% CI: 0.08–0.83) and low total sperm count (OR: 0.37, 95% CI: 0.15–0.87). Conclusion: Low BMI was associated with reduced semen quality. The associations between BMI and semen quality were found statistically significant even after adjustment for reproductive hormones. Reproductive hormones cannot explain the association between BMI and semen quality. (Asian J Androl 2007 Nov; 9: 827–834)

Aim: To investigate the relationship between Ureaplasma urealyticum (UU) infection and semen quality. Methods: From 2001 to 2003, 346 eligible patients aged 20–45 years were invited from two hospitals in Shanghai, China, to participate in an investigation which included questionnaires about general and reproductive health, an external genital tract examination, UU culture and semen analysis. Multiple linear regression models were used to examine whether UU had a significant effect on semen quality after adjustment for confounding factors. Results: Findings suggested that UU infection was associated with higher semen viscosity and lower semen pH value. Sperm concentration was lower in UU positive subjects than that in UU negative subjects (54.04 × 10 6 /mL vs.70.58 × 10 6 /mL). However, UU did not significantly affect other semen quality indexes. Conclusion: UU infection of the male genital tract could negatively influence semen quality. (Asian J Androl 2006 Sep; 8: 562–568)

Aim: To assess whether exposure to computers harms the semen quality of healthy young men. Methods: A total of 178 subjects were recruited from two maternity and children healthcare centers in Shanghai, 91 with a history of exposure to computers (i.e., exposure for 20 h or more per week in the last 2 years) and 87 persons to act as control (no or little exposure to computers). Data on the history of exposure to computers and other characteristics were obtained by means of a structured questionnaire interview. Semen samples were collected by masturbation in the place where the semen samples were analyzed. Results: No differences in the distribution of the semen parameters (semen volume, sperm density, percentage of progressive sperm, sperm viability and percentage of normal form sperm) were found between the exposed group and the control group. Exposure to computers was not found to be a risk factor for inferior semen quality after adjusting for potential confounders, including abstinence days, testicle size, occupation, history of exposure to toxic substances. Conclusion: The present study did not find that healthy men exposed to computers had inferior semen quality. (Asian J Androl 2005 Sep; 7: 263–266)

Objective This study aimed to determine the contribution of individual and contextual socioeconomic status (SES) to the prevalence of diabetes mellitus and glucose intolerance in the adult population in rural southwest China. Methods A population-based cross-sectional study of diabetes was performed in 4801(2152 men) Chinese adults (≥ 25 years old). Multilevel logistic regression model was used to examine the association between individuals' and townships' variables and the prevalence of diabetes mellitus and glucose intolerance. Results The age-and gender-standardized prevalence of diabetes mellitus and glucose intolerance were 7.1% (3.6% for undiagnosed) and 8.8% in adults aged ≥ 25 years, respectively, and increasing with age. Females were more likely to develop diabetes than males. The probability of developing diabetes increased with BMI. Both contextual and individual educational level and yearly household income were found to be negatively associated with the prevalence of diabetes. Residence in communities with a higher percentage of ethnic minorities was associated with higher prevalence of diabetes. Smoking had a protective effect for diabetes, drinking had a positive association with diabetes mellitus and glucose intolerance. Conclusions Diabetes mellitus and glucose intolerance are common in rural adults of southwest China by international standards. These results indicate that diabetes mellitus has become a major public health problem in rural areas in southwest China, and strategies aimed at the prevention and treatment of diabetes mellitus and glucose intolerance are needed.