Dynamics of the ovarian reserve and impact of genetic and epidemiological factors on age of menopause

Environmental pollutants, a possible etiology for premature ovarian insufficiency: a narrative review of animal and human data

BACKGROUND

Because only 25% of cases of premature ovarian insufficiency (POI) have a known etiology, the aim of this review was to summarize the associations and mechanisms of the impact of the environment on this pathology. Eligible studies were selected from an electronic literature search from the PUBMED database from January 2000 to February 2016 and associated references in published studies. Search terms included ovary, follicle, oocyte, endocrine disruptor, environmental exposure, occupational exposure, environmental contaminant, pesticide, polyaromatic hydrocarbon, polychlorinated biphenyl PCB, phenol, bisphenol, flame retardant, phthalate, dioxin, phytoestrogen, tobacco, smoke, cigarette, cosmetic, xenobiotic. The literature search was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We have included the human and animal studies corresponding to the terms and published in English. We have excluded articles that included results that did not concern ovarian pathology and those focused on ovarian cancer, polycystic ovary syndrome, endometriosis or precocious puberty. We have also excluded genetic, auto-immune or iatrogenic causes from our analysis. Finally, we have excluded animal data that does not concern mammals and studies based on results from in vitro culture. Data have been grouped according to the studied pollutants in order to synthetize their impact on follicular development and follicular atresia and the molecular pathways involved. Ninety-seven studies appeared to be eligible and were included in the present study, even though few directly address POI. Phthalates, bisphenol A, pesticides and tobacco were the most reported substances having a negative impact on ovarian function with an increased follicular depletion leading to an earlier age of menopause onset. These effects were found when exposure occured at different times throughout the lifetime from the prenatal to the adult period, possibly due to different mechanisms. The main mechanism seemed to be an increase in atresia of pre-antral follicles.

CONCLUSION

Environmental pollutants are probably a cause of POI. Health officials and the general public must be aware of this environmental effect in order to implement individual and global preventive actions.

Correlation of age at natural menopause with occupational status and other epidemiologic factors in women from Prefecture of Kavala, Greece

AIM

Aim of this study was to explore possible associations between the timing of natural menopause and occupational status and other determinant epidemiologic factors among women living in the Prefecture of Kavala, a region of North-East Greece.

METHODS

The sample of the study comprised of 827 naturally menopausal women, who consented to participate in this questionnaire-based interview study between 2011 and 2016. The study population was recruited from women who were hospitalized or visited the outpatient clinics of the General Hospital of Kavala and women working in the public sector services and private companies in the Prefecture of Kavala.

RESULTS

The mean age of the sample at natural menopause was 49.1 years; 12.2 % had early menopause, and 4.5 % were diagnosed with premature ovarian failure. For the majority of enrolled women (80.5 %) menopause occurred between 45-54 years, and for the rest (2.8 %) after 54 years of age. In univariate analysis, a statistically significant correlation was found between age at menopause and occupational status, year of birth, mother's age at menopause, age at menarche, and high levels of chronic stress. Multiple regression analysis revealed that occupational status, year of birth and mother's natural menopausal age could predict age at menopause.

CONCLUSION

Socioeconomic, demographic and familial variables appear to be associated with age at natural menopause in a representative sample of women in the Prefecture of Kavala, Greece. HIPPOKRATIA 2017, 21(1): 32-37.

Fertility Preservation in Women with Turner Syndrome: A Comprehensive Review and Practical Guidelines

In this article we review the existing fertility preservation options for women diagnosed with Turner syndrome and provide practical guidelines for the practitioner. Turner syndrome is the most common sex chromosome abnormality in women, occurring in approximately 1 in 2500 live births. Women with Turner syndrome are at extremely high risk for primary ovarian insufficiency and infertility. Although approximately 70%-80% have no spontaneous pubertal development and 90% experience primary amenorrhea, the remainder might possess a small residual of ovarian follicles at birth or early childhood. The present challenge is to identify these women as early in life as is possible, to allow them to benefit from a variety of existing fertility preservation options. To maximize the benefits of fertility preservation, all women with Turner syndrome should be evaluated by an expert as soon as possible in childhood because the vast majority will have their ovarian reserve depleted before adulthood. Cryopreservation of mature oocytes and embryos is a proven fertility preservation approach, and cryopreservation of ovarian tissue is a promising technique with a growing number of live births, but remains investigational. Oocyte cryopreservation has been performed in children with Turner syndrome as young as 13 years of age and ovarian tissue cryopreservation in affected prepubertal children. However, current efficacy of these approaches is unknown in this cohort. For those who have already lost their ovarian reserve, oocyte or embryo donation and adoption are strategies that allow fulfillment of the desire for parenting. For those with Turner syndrome-related cardiac contraindications to pregnancy, use of gestational surrogacy allows the possibility of biological parenting using their own oocytes. Alternatively, gestational surrogacy can serve to carry pregnancy resulting from the use of donor oocytes or embryos, if needed.

The Bologna criteria for poor ovarian response: a contemporary critical appraisal

Postponement of child bearing and maternal age at first pregnancy are on the rise, contributing considerably to an increase in age-related infertility and the demand for assisted reproductive technologies (ART) treatment. This brings to the infertility clinics many women with low ovarian reserve and poor ovarian response (POR) to conventional stimulation. The Bologna criteria were released to standardize the definition of POR and pave the way for the formulation of evidence-based, efficient modalities of treatment for women undergoing IVF-ET. More than four years have passed since the introduction of these criteria and the debate is still ongoing whether a revision is due. Women with POR comprise several sub-groups with diverse baseline distinctiveness, a major issue that has fueled the discussion. Although antral follicle count (AFC) and anti-Müllerian hormone (AMH), are considered good predictors of ovarian reserve, their threshold values are still not universally standardized. Different definitions for sonographic AFC and diverse assays for AMH are held responsible for this delay in standardization. Adding established risk factors to the criteria will lead to more reliable and reproducible definition of a POR, especially in young women. The original criteria did not address the issue of oocyte quality, and the addition of risk factors may yield specific associations with quality vs. quantity. Patient’s age is the best available criterion, although limited, to predict live-birth and presumably oocyte quality. High scale studies to validate these criteria are still missing while recent evidence raises concern regarding over diagnosis.

Genetics of the ovarian reserve

Primordial follicles or non-growing follicles (NGFs) are the functional unit of reproduction, each comprising a single germ cell surrounded by supporting somatic cells. NGFs constitute the ovarian reserve (OR), prerequisite for germ cell ovulation and the continuation of the species. The dynamics of the reserve is determined by the number of NGFs formed and their complex subsequent fates. During the reproductive lifespan, the OR progressively diminishes due to follicle atresia as well as recruitment, maturation, and ovulation. The depletion of the OR is the major determining driver of menopause, which ensues when the number of primordial follicles falls below a threshold of ∼1,000. Therefore, genes and processes involved in follicle dynamics are particularly important to understand the process of menopause, both in the typical reproductive lifespan and in conditions like primary ovarian insufficiency, defined as menopause before age 40. Genes and their variants that affect the timing of menopause thereby provide candidates for diagnosis of and intervention in problems of reproductive lifespan. We review the current knowledge of processes and genes involved in the development of the OR and in the dynamics of ovarian follicles.

How Is the Number of Primordial Follicles in the Ovarian Reserve Established?

The number of primordial follicles in the ovarian reserve is an important determinant of the length of the ovarian lifespan, and therefore the fertility of an individual. This reserve contains all of the oocytes potentially available for fertilization throughout the fertile lifespan. The maximum number is set during pregnancy or just after birth in most mammalian species; current evidence does not support neofolliculogenesis after the ovarian reserve is established, although this is increasingly being reexamined. Under physiological circumstances, this number will be influenced by the number of primordial germ cells initially specified in the epiblast of the developing embryo, their proliferation during and after migration to the developing gonads, and their death during oogenesis and formation of primordial follicles at nest breakdown. Death of germ cells during the establishment of the ovarian reserve occurs principally by autophagy or apoptosis, although the triggers that initiate these remain elusive. This review outlines the regulatory steps that determine the number of primordial follicles and thus the number of oocytes in the ovarian reserve at birth, using the mouse as the model, interspersed with human data where available. This information has application for understanding the variability in duration of fertility that occurs between normal individuals and with age, in premature ovarian insufficiency, and after chemotherapy or radiotherapy.