Infertility affects 8–12% of couples in the reproductive age with male factors implicated in 50% of these couples [16]. Male factors often stem from conditions such as obstruction of the reproductive tract, hormonal disorders, testicular failures or abnormal semen function and quality including azoospermia, oligozoospermia, teratozoospermia and asthenozoospermia [2]. In addition, the cause and risk factors that contribute to the increasing incidence of male infertility can be classified as congenital, acquired and idiopathic [17]. Infertility significantly affects the personal, social, and economic life of individuals as well as families, particularly in Africa and has been described as a under-recognized, personal, social, and public health issue [18]. Previous studies have demonstrated that semen parameters may change over time and vary based on different geographic regions [19–21]. Hence, this study aimed to identify the prevalence and trends of male factor infertility in Nigeria and South Africa over a period of ten (10) years between 2010 and 2019.
According to Swan [22] there is a global decline in sperm concentration. Carlsen et al. in a meta-analysis also showed a 50% decline in sperm counts over a 50-year period [23]. By analysing the independent variables utilized in this study we observed a significant declining trend in age, normal morphology, progressive motility, and total progressive motile sperm count (TPMSC) over the 10-year period among the infertile men in South Africa and Nigeria. With a high decline of 91% of TPMSC, and 89% of progressive motile sperm, and 50% decline on normal morphology, This report stands significantly higher than the ~ 11% decline in total motile sperm count observed in the United states of America [24], the 22.5% decline in motility reported in India [25, 26], and the 38.2% decline in China [27].
Furthermore, though we did not observe changes in the total sperm count, the alarming decline in progressive motile sperm cells seems to be the major reason for the increased male infertility observed in these countries. Sperm motility plays a central role in both natural and several forms of assisted fertilization [28–30] Only progressive sperm cells will be able to swim through the vagina, cervical mucous, tortuous endometrium, and ultimately arrive at the ampullary site of the fallopian tube for fertilization [30]. This study showed that progressive sperm motility decreased from 38–5% between 2010 and 2019. In addition, our study also showed that TPMSC declined from 25.5 million to 2.3 million between 2010 and 2019. This is far below the lower limit (40%) recommended by the World Health Organization for progressive motility [31], thus more patients are suffering from asthenozoospermia. It is one of the major causes of male infertility which is associated with a couple of factors including genetic, molecular, and environmental factors [30, 32, 33].
In our study, we also observed a decline of 10–5% in normal sperm morphology between 2015 and 2019. While this is at the WHO 2021 lower limit for semen analysis, it should be closely monitored. In another study that focused on the north of Africa, south of Tunisia to be precise demonstrated a decline in sperm concentration and normal morphology over a 12 year period [34]. In an era of intracytoplasmic sperm injection (ICSI), abnormal sperm morphology does not seem to affect fertilisation and embryo development but it is associated with higher implantation and pregnancy failures [35, 36]. Although the role of sperm morphology in natural and assisted pregnancy is still controversial our findings infer that there is increased alterations on spermiogenesis which may have genetic or epigenetic undertones [37, 38].
A comparison of the data collected from Nigeria and South Africa revealed that the number of days of sexual abstinence by patients, and normal sperm morphology were similar in both countries, while the patients’ age was higher in Nigeria compared to South Africa. The reason for this is not clear but we may allude that the low health insurance coverage in Nigeria which has only 3% of its populace on health insurance as compared to South Africa that has less than 20% of its populace makes it financially burdensome for young couples to seek assisted reproduction care [39–41].
In addition, we had poor sperm concentration, progressive motility, total sperm count, total progressive motile sperm count (TPMSC) and semen volume of samples from Nigeria which were older in age compared to South African samples which came from younger men. This is in concordance with reports that aging plays a major role in decreasing semen quality [42, 43]. This is buttressed by our correlation analysis, which observed a significant inverse proportional relationship between age and all the sperm parameters analysed.
A number of factors could be associated with aging and poor semen quality, but they could be broadly divided into two categories: First, degenerative changes in the reproductive tract due to progressive decline in cellular function aging. An increased misorientation in centrosomes which should ensure asymmetric division of germline stem cells has been observed in aged testis thereby distorting the proportion of self-renewing spermatogonia to differentiating spermatogonia thus, causing a decline in spermatogenesis [44]. Oxidative stress has also been linked to advanced paternal aging causing increased inflammation and endocrine dysfunction ultimately impeding spermatogenesis [45]. In addition, there is marked reduction of Leydig cells with age, increased testicular atrophy and Sertoli cell only testis [46, 47]. Secondly, the older one gets, the more prone they are to exogenous toxicants including diseases, lifestyle, environment, and climate change that could be detrimental to the reproductive tract. For instance, older ones are more likely to have smoked, or consumed alcohol for longer which adversely affects semen quality [48–50]. Some therapies for chronic diseases such as human immunodeficiency virus (HIV) and the disease itself reduces the seminal fluid, sperm motility and increases sperm DNA fragmentation [32], High temperatures also exacerbate the production reactive oxygen species in testis inducing testicular germ cell apoptosis [51, 52]. In addition, benign prostatic hyperplasia is also associated with ageing which may result in decreased low ejaculated semen volume [53, 54].
This study revealed that in South Africa, a decline was noted for sperm concentration, normal sperm morphology, total sperm count, TPMSC and volume with an increasing trend for progressive motility. Whereas a declining trend in progressive motility and TPMSC was observed in Nigeria corroborating a previous study conducted in Nigeria which demonstrated a time-dependent decrease in sperm concentration over a 50 year period (between 1980 and 2015), and accounted for a decline of 72.58% [14], and another study, semen analysis of 1726 suspected patients in South Africa between 1985 and 1991 revealed that 70% of the patients contributed to the male factor for infertility (Bornman et al., 1994). A Chinese and Iranian study also reported a significant decline in sperm concentration and sperm morphology (Liu et al., 2020; Vahidi et al, 2020). Although this study did not report significant changes in sperm concentrations, a recent study reported that Black men had significantly lower sperm concentrations than white men and Hispanics (Auger et al., 2022). Exposure to the pesticide, DDT [1,1,1-trichloro-2,2-bis (chlorodiphenyl)ethane] and its main metabolite, p,p′-dichlorodiphenyl-dichloroethylene (p,p′-DDE) has been associated with the declining trend of semen quality in malaria stricken parts of African countries [55]. In addition, environmental pollutants, such as crude oil spillage, and gas flaring increases the oxidative stress levels thereby causing a decline in semen quality [56, 57].