Has Human Fertility Declined Over Time?

ArticleinEpidemiology 16(4):494-9 · August 2005with30 Reads
Impact Factor: 6.20 · DOI: 10.1097/01.ede.0000165391.65690.e1 · Source: PubMed

Reports of decreased semen quality over time have raised concerns about possible reductions in human fertility. Studies of couple fertility have produced conflicting results. We evaluate how changes in the availability and use of effective contraception and induced abortion might bias the direct study of time trends in couple fertility. We assess the potential for bias in the context of 2 common study designs: (1) a study of time-to-pregnancy that estimates fecundability (excluding unintended pregnancies) and (2) a study of infertility rates that categorizes couples as fertile or infertile (including couples with unintended pregnancies as fertile). In time-to-pregnancy studies, bias alone could produce more than a 2-fold apparent increase in fecundability over recent decades. In studies of infertility rates, the bias works in the opposite direction: a 30% underestimation of infertility during earlier decades could produce an apparent decrease in fertility over time. Over the past 5 decades, changes in social factors that affect the rate and fate of unintended pregnancies could substantially bias time trends in fertility. These biases may explain the conflicting reports in the literature. Except in rare settings in which the factors affecting reproductive choices have not changed, it is probably impossible to identify biologic changes in fertility over recent decades.

    • "Female fecundity is defined as the biologic capacity for reproduction irrespective of pregnancy intentions (Buck Louis, 2011), and is speculated to be on the global decline though with limited empirical evidence (Lutz et al., 2003; te Velde et al., 2010). Some authors have suggested a role for endocrine disrupting chemicals such as persistent organochlorine pollutants (POPs) while other authors point to changes in lifestyle for recent birth cohorts (Sallmen et al., 2005). While firm answers remain lacking, an evolving body of evidence suggests an adverse relation between environmental chemicals and a spectrum of fecundity and fertility endpoints as recently summarized (Toft et al., 2004; Buck Louis et al., 2006; Mendola and Buck Louis, 2010). "
    [Show abstract] [Hide abstract] ABSTRACT: An evolving body of evidence suggests an adverse relation between persistent organochlorine pollutants (POPs) and menstruation, though prospective longitudinal measurement of menses is limited and served as the impetus for study. We prospectively assessed the relation between a mixture of persistent organochlorine compounds and menstrual cycle length and duration of bleeding in a cohort of women attempting to become pregnant. Eighty-three (83%) women contributing 447 cycles for analysis provided a blood specimen for the quantification of 76 polychlorinated biphenyls and seven organochlorine pesticides, and completed daily diaries on menstruation until a human chorionic gonadotropin confirmed pregnancy or 12 menstrual cycles without conception. Gas chromatography with electron capture detection was used to quantify concentrations (ng g(-1)serum); enzymatic methods were used to quantify serum lipids (mg dL(-1)). A linear regression model with a mixture distribution was used to identify chemicals grouped by purported biologic activity that significantly affected menstrual cycle length and duration of bleeding adjusting for age at menarche and enrollment, body mass index, and cigarette smoking. A significant 3-d increase in cycle length was observed for women in the highest tertile of estrogenic PCB congeners relative to the lowest tertile (β=3.20; 95% CI 0.36, 6.04). A significant reduction in bleeding (<1 d) was observed among women in the highest versus lowest tertile of aromatic fungicide exposure (γ=-0.15; 95% CI -0.29, -0.00). Select POPs were associated with changes in menstruation underscoring the importance of assessing chemical mixtures for female fecundity.
    Full-text · Article · Dec 2011 · Chemosphere
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    • "In the last decade or so, concern has aroused about decreasing fecundity and infertility in men [1, 2]. The reasons for this are often linked to various types of environmental and occupational exposure, leading to possible causes of reduced sperm quality345 and present study has been carried out on antioxidant enzymes, malondialdehyde (MDA), histone kinase, micronuclei, cell cycle, and ROS to investigate the possible adverse effect of mobile phone radiations. "
    [Show abstract] [Hide abstract] ABSTRACT: The present study investigates the effect of free radical formation due to mobile phone exposure and effect on fertility pattern in 70-day-old male Wistar rats (sham exposed and exposed). Exposure took place in Plexiglas cages for 2 h a day for 35 days to mobile phone frequency. The specific absorption rate was estimated to be 0.9 W/kg. An analysis of antioxidant enzymes glutathione peroxidase (P < 0.001) and superoxide dismutase (P < 0.007) showed a decrease, while an increase in catalase (P < 0.005) was observed. Malondialdehyde (P < 0.003) showed an increase and histone kinase (P = 0.006) showed a significant decrease in the exposed group. Micronuclei also show a significant decrease (P < 0.002) in the exposed group. A significant change in sperm cell cycle of G(0)-G(1) (P = 0.042) and G(2)/M (P = 0.022) were recorded. Generation of free radicals was recorded to be significantly increased (P = 0.035). Our findings on antioxidant, malondialdehyde, histone kinase, micronuclei, and sperm cell cycle are clear indications of an infertility pattern, initiated due to an overproduction of reactive oxygen species. It is concluded that radiofrequency electromagnetic wave from commercially available cell phones might affect the fertilizing potential of spermatozoa.
    Full-text · Article · Jun 2011 · Applied biochemistry and biotechnology
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    • "Whether nicotine results in impaired male fertility is controversial; however, because of its negative effect on erectile function, nicotine use is discouraged in men attempting to impregnate their partners. A male who does not have biological offspring and who presents for reproductive evaluation is labeled as having "primary infertility," whereas one who is unable to impregnate his partner but who already has biological children is referred to as having "secondary infertility" (Sallmen et al., 2005; MacLeod, 1951; Guzick et al., 2001; Greenberg et al., 1978). A physical examination of the scrotum, including the testes, is essential for any male fertility work-up. "
    [Show abstract] [Hide abstract] ABSTRACT: Infertility is one of the most tragic of all marital problems. Despite recent advances in the treatment of male infertility, the problem has not been satisfactorily tackled. The infertility may be due to an inadequate number of spermatozoa in the semen, the failure of the spermatozoa to move with sufficient vigor towards their goal or that they are deficient in other respects. Aims of the study is to investigate the safety and efficacy of Xperm (Herbal Medicine) in test group in comparison with Sulfonylureas plus (Allopathic) in control group. A Causi experimental randomized controlled, two-arm parallel group clinical trial conducted at Shifa-ul-Mulk Memorial Hospital for Eastern Medicine, Hamdard University Karachi. Hundred patients in the age group of 20-50 years with idiopathic infertility with a total sperm count less than 20 million/ml. Comparison of data recorded by participants relating to these variables showed significant differences between test and control groups (p<0.05) despite the fact that no side effects were at all recorded in test group. Overall clinical success was observed in both treatment groups however the efficacy of the test treated medication (Xperm) was superior as p = 0.03. Xperm is more effective than the Sulfonylureas plus in the treatment of Oligospermia and male infertility.
    Full-text · Article · Mar 2011 · Pakistan Journal of Nutrition
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