A quantitative and cytological study of germ cells in human ovaries

Diminished ovarian reserve in the United States assisted reproductive technology population: diagnostic trends among 181,536 cycles from the Society for Assisted Reproductive Technology Clinic Outcomes Reporting System

OBJECTIVE

To evaluate trends in diminished ovarian reserve (DOR) assignment in the Society for Assisted Reproductive Technology (SART) Clinic Outcomes Reporting System database and to evaluate its accuracy in predicting poor ovarian response (POR) as defined in European Society of Human Reproduction and Embryology's Bologna criteria (2011).

DESIGN

Retrospective cohort study.

SETTING

Not applicable.

PATIENT(S)

A total of 181,536 fresh, autologous ART cycles reported to SART by U.S. clinics in 2004 and 2011 (earliest and most recent available reporting years).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

DOR assignment was the primary exposure. POR, defined as cycle cancellation for poor response or less than 4 oocytes retrieved after conventional gonadotropin stimulation (>149 IU FSH daily), was the primary outcome. Secondary outcomes were live birth and number of oocytes retrieved. DOR prevalence, power of DOR and FSH (</≥12 mIU/mL) to predict POR, and live birth in POR cycles were also calculated.

RESULT(S)

DOR prevalence increased from 19% to 26% from 2004 to 2011. Among cycles clinically assigned as DOR, incidence of POR decreased from 32% to 30%, and live birth improved from 15% to 17%. Comparing basal FSH ≥12 versus clinical assignment of DOR, basal FSH had a higher specificity (92.2% vs. 81.6%) and positive predictive value (38.3% vs. 30.9%) for predicting POR. Live birth among POR cycles was 4%.

CONCLUSION(S)

DOR diagnosis is increasing, and accuracy remains poor, despite the availability of additional diagnostic parameters such as antral follicle count and antimüllerian hormone. POR entailed poor outcomes, but the majority of patients clinically assigned as DOR did not experience POR. Development and use of more accurate predictors of POR are needed to minimize patient distress resulting from overdiagnosis.

Birth month affects lifetime disease risk: a phenome-wide method

OBJECTIVE

An individual's birth month has a significant impact on the diseases they develop during their lifetime. Previous studies reveal relationships between birth month and several diseases including atherothrombosis, asthma, attention deficit hyperactivity disorder, and myopia, leaving most diseases completely unexplored. This retrospective population study systematically explores the relationship between seasonal affects at birth and lifetime disease risk for 1688 conditions.

METHODS

We developed a hypothesis-free method that minimizes publication and disease selection biases by systematically investigating disease-birth month patterns across all conditions. Our dataset includes 1 749 400 individuals with records at New York-Presbyterian/Columbia University Medical Center born between 1900 and 2000 inclusive. We modeled associations between birth month and 1688 diseases using logistic regression. Significance was tested using a chi-squared test with multiplicity correction.

RESULTS

We found 55 diseases that were significantly dependent on birth month. Of these 19 were previously reported in the literature (P < .001), 20 were for conditions with close relationships to those reported, and 16 were previously unreported. We found distinct incidence patterns across disease categories.

CONCLUSIONS

Lifetime disease risk is affected by birth month. Seasonally dependent early developmental mechanisms may play a role in increasing lifetime risk of disease.

Parenthood in adult female survivors treated for Hodgkin's lymphoma during childhood and adolescence: a prospective, longitudinal study

BACKGROUND

Little is known about parenthood in women who were treated for Hodgkin's lymphoma during childhood and adolescence. We aimed to assess the frequency of parenthood in female survivors of Hodgkin's lymphoma younger than 18 years at diagnosis, and to compare it with that in a female population control group.

METHODS

In this prospective, longitudinal study, our cohort consisted of 590 female patients younger than 18 years at diagnosis who participated in one of five Hodgkin's lymphoma treatment studies between June 19, 1978, and July 12, 1995. Women who had been followed up for 5 years or longer, were in continuous complete remission, and had no second malignancy or Hodgkin's lymphoma relapse before parenthood were included in our parenthood analysis. Parenthood was defined as the delivery of a liveborn child. Frequency of parenthood was compared with that in the German female population aged 16-49 years, using data from the 2012 Mikrozensus population survey. We assessed parenthood by estimating cumulative incidences and hazard ratios (HRs) with associated variables.

FINDINGS

467 of 590 patients in our cohort had long-term follow-up (median 20·4 years [IQR 16·3-24·8]) and were in continuous complete remission. 228 (49%) of 467 patients had 406 children (median of 1·78 children per mother, range 1-7). Cumulative incidences of parenthood were 67% (95% CI 64-75) at 27·7 years of follow-up (the longest number of years that a patient was followed up before she had her first child) and 69% (61-74) at 39·8 years of age (the oldest age of a patient before she had her first child). The incidence of parenthood did not differ between our cohort and the female German population for any age group up to 49 years, except for the 66 women aged 40-44 years at the time of last information, who had a significantly lower frequency of parenthood compared with the general population (40 [61%] of 66 vs 2,208,000 [78%] of 2,847,000; p=0·001). Procarbazine in cumulative doses up to 11,400 mg/m(2), cyclophosphamide in cumulative doses up to 6000 mg/m(2), alkylating agent dose scores of 1-5, therapy group based on disease stage at diagnosis, abdominal and supradiaphragmatic radiation, and age at treatment had no significant or only minor effects on parenthood. Parenthood was significantly reduced in survivors receiving pelvic radiation compared with those who received abdominal and supradiaphragmatic radiation (HR 0·76, 95% CI 0·61-0·95; p=0·01).

INTERPRETATION

The results of this study document an overall favourable prognosis for parenthood in female survivors of Hodgkin's lymphoma. They will assist counselling of female survivors about their positive potential for future parenthood.

FUNDING

Deutsche Kinderkrebsstiftung, Jens-Brunken-Stiftung für Leukämie und Lymphomforschung, and Kinderkrebshilfe Münster.

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

The narrow standard age range of menopause, ∼50 yr, belies the complex balance of forces that govern the underlying formation and progressive loss of ovarian follicles (the "ovarian reserve" whose size determines the age of menopause). We show here the first quantitative graph of follicle numbers, distinguished from oocyte counts, across the reproductive lifespan, and review the current state of information about genetic and epidemiological risk factors in relation to possible preservation of reproductive capacity. In addition to structural X-chromosome changes, several genes involved in the process of follicle formation and/or maintenance are implicated in Mendelian inherited primary ovarian insufficiency (POI), with menopause before age 40. Furthermore, variants in a largely distinct cohort of reported genes-notably involved in pathways relevant to atresia, including DNA repair and cell death-have shown smaller but additive effects on the variation in timing of menopause in the normal range, early menopause (age <45), and POI. Epidemiological factors show effect sizes comparable to those of genetic factors, with smoking accounting for about 5% of the risk of early menopause, equivalent to the summed effect of the top 17 genetic variants. The identified genetic and epidemiological factors underline the importance of early detection of reproductive problems to enhance possible interventions.

Follicle Online: an integrated database of follicle assembly, development and ovulation

Folliculogenesis is an important part of ovarian function as it provides the oocytes for female reproductive life. Characterizing genes/proteins involved in folliculogenesis is fundamental for understanding the mechanisms associated with this biological function and to cure the diseases associated with folliculogenesis. A large number of genes/proteins associated with folliculogenesis have been identified from different species. However, no dedicated public resource is currently available for folliculogenesis-related genes/proteins that are validated by experiments. Here, we are reporting a database ‘Follicle Online’ that provides the experimentally validated gene/protein map of the folliculogenesis in a number of species. Follicle Online is a web-based database system for storing and retrieving folliculogenesis-related experimental data. It provides detailed information for 580 genes/proteins (from 23 model organisms, including Homo sapiens, Mus musculus, Rattus norvegicus, Mesocricetus auratus, Bos Taurus, Drosophila and Xenopus laevis) that have been reported to be involved in folliculogenesis, POF (premature ovarian failure) and PCOS (polycystic ovary syndrome). The literature was manually curated from more than 43 000 published articles (till 1 March 2014). The Follicle Online database is implemented in PHP + MySQL + JavaScript and this user-friendly web application provides access to the stored data. In summary, we have developed a centralized database that provides users with comprehensive information about genes/proteins involved in folliculogenesis. This database can be accessed freely and all the stored data can be viewed without any registration.

Database URL:http://mcg.ustc.edu.cn/sdap1/follicle/index.php

Postnatal oogenesis in humans: a review of recent findings

In spite of generally accepted dogma that the total number of follicles and oocytes is established in human ovaries during the fetal period of life rather than forming de novo in adult ovaries, some new evidence in the field challenges this understanding. Several studies have shown that different populations of stem cells, such as germinal stem cells and small round stem cells with diameters of 2 to 4 μm, that resembled very small embryonic-like stem cells and expressed several genes related to primordial germ cells, pluripotency, and germinal lineage are present in adult human ovaries and originate in ovarian surface epithelium. These small stem cells were pushed into the germinal direction of development and formed primitive oocyte-like cells in vitro. Moreover, oocyte-like cells were also formed in vitro from embryonic stem cells and induced pluripotent stem cells. This indicates that postnatal oogenesis is not excluded. It is further supported by the occurrence of mesenchymal stem cells that can restore the function of sterilized ovaries and lead to the formation of new follicles and oocytes in animal models. Both oogenesis in vitro and transplantation of stem cell-derived "oocytes" into the ovarian niche to direct their natural maturation represent a big challenge for reproductive biomedicine in the treatment of female infertility in the future and needs to be explored and interpreted with caution, but it is still very important for clinical practice in the field of reproductive medicine.

Circulating AMH reflects ovarian morphology by magnetic resonance imaging and 3D ultrasound in 121 healthy girls

CONTEXT

In adult women, Anti-Müllerian hormone (AMH) is produced by small growing follicles, and circulating levels of AMH reflect the number of antral follicles as well as primordial follicles. Whether AMH reflects follicle numbers in healthy girls remains to be elucidated.

OBJECTIVE

This study aimed to evaluate whether serum levels of AMH reflects ovarian morphology in healthy girls.

DESIGN AND SETTING

This was a population-based cohort study involving the general community.

PARTICIPANTS

Included in the study were 121 healthy girls 9.8-14.7 years of age.

MAIN OUTCOME MEASURES

Clinical examination, including pubertal breast stage (Tanner's classification B1-5), ovarian volume, as well as the number and size of antral follicles were assessed by two independent modalities: magnetic resonance imaging (MRI), Ellipsoid volume, follicles ≥2 mm; and Transabdominal ultrasound, Ellipsoid and 3D volume, follicles ≥1 mm. Circulating levels of AMH, inhibin B, estradiol, FSH, and LH were assessed by immunoassays; T and androstenedione were assessed by liquid chromatography-tandem mass spectrometry.

RESULTS

AMH reflected the number of small (MRI 2-3 mm) and medium (4-6 mm) follicles (Pearson's Rho [r] = 0.531 and r = 0.512, P < .001) but not large follicles (≥7 mm) (r = 0.109, P = .323). In multiple regression analysis, small and medium follicles (MRI ≤ 6 mm) remained the main contributors to circulating AMH (β, 0.501; P < .001) whereas the correlation between AMH and estradiol was negative (β, -0.318; P = .005). In early puberty (B1-B3), the number of AMH-producing follicles (2-6 mm) correlated positively with pubertal stages (r = 0.453, P = .001), whereas AMH levels were unaffected (-0.183, P = .118).

CONCLUSIONS

Similarly to adult women, small and medium antral follicles (≤6 mm) were the main contributors to circulating levels of AMH in girls.

Age-related decline in ovarian follicle stocks differ between chimpanzees (Pan troglodytes) and humans

Similarity in oldest parturitions in humans and great apes suggests that we maintain ancestral rates of ovarian aging. Consistent with that hypothesis, previous counts of primordial follicles in postmortem ovarian sections from chimpanzees (Pan troglodytes) showed follicle stock decline at the same rate that human stocks decline across the same ages. Here, we correct that finding with a chimpanzee sample more than three times larger than the previous one, which also allows comparison into older ages. Analyses show depletion rates similar until about age 35, but after 35, the human counts continue to fall with age, while the change is much less steep in chimpanzees. This difference implicates likely effects on ovarian dynamics from other physiological systems that are senescing at different rates, and, potentially, different perimenopausal experience for chimpanzees and humans.

Follicle pool, ovarian surgery and the risk for a subsequent trisomic pregnancy

STUDY QUESTION

Is there an association between trisomic pregnancy, a marker for decreased oocyte quality, and the reduced oocyte quantity that follows ovarian surgery?

SUMMARY ANSWER

Previous ovarian surgery is not associated with an increased risk for a subsequent trisomic pregnancy.

WHAT IS KNOWN ALREADY

Ovarian surgery diminishes the number of oocytes. The risk for a trisomic pregnancy is suggested to be higher in women with fewer oocytes, independent of their chronological age.

STUDY DESIGN, SIZE, DURATION

This is a matched case-control study. Cases are women with a confirmed trisomic pregnancy occurring between 1 January 2000 and 31 December 2010 regardless of pregnancy outcome and controls are women that had a live born child without a trisomy. In total, there were 8573 participants in the study; 1723 cases and 6850 controls.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Data were obtained from Danish medical registries. Matching criteria were maternal age and year of conception. Number of controls matched per case ranged from one to four. Among cases and controls with a trisomic pregnancy, 2.7% (46/1723) versus 2.5% (172/6850) had undergone ovarian surgery before pregnancy.

MAIN RESULTS AND ROLE OF CHANCE

History of ovarian surgery is not associated with a higher risk for a subsequent trisomic pregnancy (odds ratio = 1.00, 95% confidence interval 0.99-1.01). Subgroup analyses by indication of surgery and interval between ovarian surgery and pregnancy do not show an effect on trisomic pregnancy risk.

LIMITATIONS, REASONS FOR CAUTION

The medical registries used to select cases and controls did not contain information on surgical technique nor volume of ovarian tissue resected, previous trisomic pregnancy prior to the ovarian surgery or long-term use of oral contraceptives. Therefore, correction for these factors was not performed.

WIDER IMPLICATIONS OF THE FINDINGS

We did not confirm the hypothesis that ovarian surgery, a marker for decreased oocyte quantity, is related to trisomic pregnancy, a marker for decreased oocyte quality. This suggests that ovarian surgery, which has a direct reductive effect on the size of the follicle pool, may affect oocyte quality differently when compared with the reduction in follicle pool size due to ageing.

STUDY FUNDING/COMPETING INTERESTS

The study was supported by grants from the Gratama Stichting, University of Groningen and the University Medical Center Groningen, The Netherlands. Ø.L. has within the last 3 years received honoraria for speeches in pharmacoepidemiological issues, not related to this study. The Department of Obstetrics and Gynaecology receives unrestricted educational grants from Ferring Pharmaceuticals. A.H. received a grant from ZonMW (i.e. National Dutch Scientific funding) for a RCT not related to this publication. Dr A.H. received speakers fee from MSD for an educational presentation. All other authors have no conflict of interest.

Ovarian stimulation for IVF: mild approaches

In contrast to current approaches, the aim of mild stimulation is to develop safer and more patient-friendly protocols in which the risks of the treatment as a whole are minimized. Mild stimulation is defined as the method when exogenous gonadotropins are administered at lower doses, and/or for a shorter duration in GnRH antagonist co-treated cycles, or when oral compounds (antiestrogens, aromatase inhibitors) are used for ovarian stimulation for IVF, with the aim of limiting the number of oocytes obtained to fewer than eight. In this chapter we discuss the relevant physiology of follicle development, the development of milder stimulation protocols, the implications of mild stimulation, the current state of affairs, and future developments.

Age-related infertility

Oocyte number and quality decrease with advancing age. Thus, fecundity decreases as age increases, with a more rapid decline after the mid-30s. Patients more than 35 years old should receive prompt evaluation for causes of infertility after no more than 6 months of attempted conception. Patients with abnormal tests of ovarian reserve have a poorer prognosis and may need more expedited and aggressive treatment. Although oocyte donation is the best method to overcome age-related infertility, other treatment options may help women proceed quicker toward pregnancy. Patients at an advanced age should be counseled and evaluated before undergoing infertility treatments.

Ultrastructural changes in oocytes during folliculogenesis in domestic mammals

The ultrastructural analysis of oocytes and ovarian follicles has been used to evaluate the effects of assisted reproductive techniques, such as cryopreservation or in vitro oocyte maturation. It also benefits the understanding of such complex mechanisms that occur during folliculogenesis. From the beginning of primordial follicles growth until oocyte maturation in preovulatory follicles oocyte cytoplasmic organelles undergo dynamic alterations that reflect physiological changes and development. This review aims to make a retrospective survey of the relevant features of follicles and oocytes ultrastructure, highlighting the differences between mammalian species, specially the domestic ones.

Through the smoke: use of in vivo and in vitro cigarette smoking models to elucidate its effect on female fertility

A finite number of oocytes are established within the mammalian ovary prior to birth to form a precious ovarian reserve. Damage to this limited pool of gametes by environmental factors such as cigarette smoke and its constituents therefore represents a significant risk to a woman's reproductive capacity. Although evidence from human studies to date implicates a detrimental effect of cigarette smoking on female fertility, these retrospective studies are limited and present conflicting results. In an effort to more clearly understand the effect of cigarette smoke, and its chemical constituents, on female fertility, a variety of in vivo and in vitro animal models have been developed. This article represents a systematic review of the literature regarding four of experimental model types: 1) direct exposure of ovarian cells and follicles to smoking constituents' in vitro, 2) direct exposure of whole ovarian tissue with smoking constituents in vitro, 3) whole body exposure of animals to smoking constituents and 4) whole body exposure of animals to cigarette smoke. We summarise key findings and highlight the strengths and weaknesses of each model system, and link these to the molecular mechanisms identified in smoke-induced fertility changes.

Involvement of FoxO1 in the effects of follicle-stimulating hormone on inhibition of apoptosis in mouse granulosa cells

In mammalian ovaries, follicular atresia occurs periodically and destroys almost all the follicles in the ovary. Follicle-stimulating hormone (FSH) acts as the primary survival factor during follicular atresia by preventing apoptosis in granulosa cells. FoxO1 is a critical factor in promoting follicular atresia and granulosa cell apoptosis. FSH inhibits the induction of FoxO1. In this report, we investigated the role of FSH-FoxO1 pathway in mouse follicular atresia. FSH dampened stress-induced apoptosis and the expression of FoxO1 and pro-apoptosis genes in mouse granulosa cells (MGCs). In contrast, overexpression of FoxO1 inhibited the viability of MGCs and induced the expression of endogenous FoxO1. The signaling cascades involved in regulating FoxO1 activity upon FSH treatment were identified using FSH signaling antagonists. Blocking protein kinase A (PKA), phosphatidylinositol-3 kinase (PI3K) or protein kinase B (AKT) restored the upregulation of FoxO1 and apoptotic signals, which was suppressed by FSH. Moreover, inhibition of PKA or PI3K impaired FSH-induced AKT activity, but inactivation of PI3K or AKT had little effect on PKA activity in the presence of FSH. Correspondingly, constitutive activation of FoxO1 (all three AKT sites were replaced by alanines) also promoted MGC apoptosis despite FSH administration. Furthermore, both luciferase reporter assays and chromatin immunoprecipitation assays showed that FoxO1 directly bound to a FoxO-recognized element site within the FoxO1 promoter and contributed to the regulation of FoxO1 expression in response to FSH. Taken together, we propose a novel model in which FSH downregulates FoxO1-dependent apoptosis in MGCs by coordinating the PKA-PI3K-AKT-FoxO1 axis and FoxO1-FoxO1 positive feedback.

Maternal cigarette smoking during pregnancy and reproductive health in children: a review of epidemiological studies

Maternal cigarette smoking may affect the intrauterine hormonal environment during pregnancy and this early fetal exposure may have detrimental effects on the future trajectory of reproductive health. In this review, we discuss the epidemiological literature on the association between prenatal exposure to maternal cigarette smoking and several aspects of reproductive health. The literature points towards an increased risk of the urogenital malformation cryptorchidism, but a potential protective effect on the risk of hypospadias in sons following prenatal cigarette smoking exposure. Studies on sexual maturation find a tendency towards accelerated pubertal development in exposed boys and girls. In adult life, prenatally exposed men have impaired semen quality compared with unexposed individuals, but an influence on fecundability, that is, the biological ability to reproduce, is less evident. We found no evidence to support an association between prenatal cigarette smoking exposure and testicular cancer. Among adult daughters, research is sparse and inconsistent, but exposure to cigarette smoking in utero may decrease fecundability. In conclusion, prenatal exposure to cigarette smoking may cause some long-term adverse effects on the reproductive health.

Bisphenol A, oocyte maturation, implantation, and IVF outcome: review of animal and human data

Recent data have raised concerns about the detrimental effect of chronic exposure to environmental chemicals. Some chemicals affect the endocrine system (endocrine disruptors) and have been linked to several diseases, including infertility. One such endocrine disruptor is bisphenol A (BPA), a monomer widely used in the plastic industry, with nearly ubiquitous exposure. In this review, data on the effects of BPA on female fertility are summarized. Specifically, its effect is considered on folliculogenesis, oocyte maturation, embryo quality, and implantation, both in animal and human models. Animal studies have shown that BPA might impair prophase I, follicular growth, and implantation, and may be associated with spindle abnormalities. In humans, while in-vitro studies have suggested an association between BPA exposure and impaired oocyte meiosis, clinical evidence indicate possible adverse effects of BPA exposure on IVF outcomes. As human clinical data are still scarce, larger studies are required to further elucidate the effects of BPA exposure on female fertility.

microRNA 376a regulates follicle assembly by targeting Pcna in fetal and neonatal mouse ovaries

In mammals, the primordial follicle pool, providing all oocytes available to a female throughout her reproductive life, is established perinatally. Dysregulation of primordial follicle assembly results in female reproductive diseases, such as premature ovarian insufficiency and infertility. Female mice lackingDicer1(Dicer), a gene required for biogenesis of microRNAs, show abnormal morphology of follicles and infertility. However, the contribution of individual microRNAs to primordial follicle assembly remains largely unknown. Here, we report that microRNA 376a (miR-376a) regulates primordial follicle assembly by modulating the expression of proliferating cell nuclear antigen (Pcna), a gene we previously reported to regulate primordial follicle assembly by regulating oocyte apoptosis in mouse ovaries. miR-376a was shown to be negatively correlated withPcnamRNA expression in fetal and neonatal mouse ovaries and to directly bind toPcnamRNA 3′ untranslated region. Cultured 18.5 days postcoitum mouse ovaries transfected with miR-376a exhibited decreasedPcnaexpression both in protein and mRNA levels. Moreover, miR-376a overexpression significantly increased primordial follicles and reduced apoptosis of oocytes, which was very similar to those in ovaries co-transfected with miR-376a and siRNAs targetingPcna. Taken together, our results demonstrate that miR-376a regulates primordial follicle assembly by modulating the expression ofPcna. To our knowledge, this is the first microRNA–target mRNA pair that has been reported to regulate mammalian primordial follicle assembly and further our understanding of the regulation of primordial follicle assembly.

A role for retrotransposon LINE-1 in fetal oocyte attrition in mice

Fetal oocyte attrition (FOA) is a conserved but poorly understood process of elimination of more than two-thirds of meiotic prophase I (MPI) oocytes before birth. We now implicate retrotransposons LINE-1 (L1), activated during epigenetic reprogramming of the embryonic germline, in FOA in mice. We show that wild-type fetal oocytes possess differential nuclear levels of L1ORF1p, an L1-encoded protein essential for L1 ribonucleoprotein particle (L1RNP) formation and L1 retrotransposition. We demonstrate that experimental elevation of L1 expression correlates with increased MPI defects, FOA, oocyte aneuploidy, and embryonic lethality. Conversely, reverse transcriptase (RT) inhibitor AZT has a profound effect on the FOA dynamics and meiotic recombination, and it implicates an RT-dependent trigger in oocyte elimination in early MPI. We propose that FOA serves to select oocytes with limited L1 activity that are therefore best suited for the next generation.

Female age-related fertility decline. Committee Opinion No. 589

The fecundity of women decreases gradually but significantly beginning approximately at age 32 years and decreases more rapidly after age 37 years. Education and enhanced awareness of the effect of age on fertility are essential in counseling the patient who desires pregnancy. Given the anticipated age-related decline in fertility, the increased incidence of disorders that impair fertility, and the higher risk of pregnancy loss, women older than 35 years should receive an expedited evaluation and undergo treatment after 6 months of failed attempts to conceive or earlier, if clinically indicated. In women older than 40 years, more immediate evaluation and treatment are warranted.

Female reproductive aging is master-planned at the level of ovary

The ovary receives a finite pool of follicles during fetal life. Atresia remains the major form of follicular expenditure at all stages since development of ovary. The follicular reserve, however, declines at an exponential rate leading to accelerated rate of decay during the years preceding menopause. We examined if diminished follicle reserve that characterizes ovarian aging impacts the attrition rate. Premature ovarian aging was induced in rats by intra-embryonic injection of galactosyltransferase-antibody on embryonic day 10. On post-natal day 35 of the female litters, either a wedge of fat (sham control) or a wild type ovary collected from 25-day old control rats, was transplanted under the ovarian bursa in both sides. Follicular growth and atresia, and ovarian microenvironment were evaluated in the follicle-deficient host ovary and transplanted ovary by real time RT-PCR analysis of growth differentiation factor-9, bone morphogenetic protein 15, and kit ligand, biochemical evaluation of ovarian lipid peroxidation, superoxide dismutase (SOD) and catalase activity, and western blot analysis of ovarian pro- and anti-apoptotic factors including p53, bax, bcl2, and caspase 3. Results demonstrated that the rate of follicular atresia, which was highly preponderant in the follicle-deficient ovary of the sham-operated group, was significantly prevented in the presence of the transplanted ovary. As against the follicle-deficient ovary of the sham-operated group, the follicle-deficient host ovary as well as the transplanted ovary in the ovary-transplanted group exhibited stimulated follicle growth with increased expression of anti-apoptotic factors and down regulation of pro-apoptotic factors. Both the host and transplanted ovaries also had significantly lower rate of lipid peroxidation with increased SOD and catalase activity. We conclude that the declining follicular reserve is perhaps the immediate thrust that increases the rate of follicle depletion during the final phase of ovarian life when the follicle reserve wanes below certain threshold size.

The ovarian reserve of primordial follicles and the dynamic reserve of antral growing follicles: what is the link?

The growing follicles develop from a reserve of primordial follicles constituted early in life. From this pre-established reserve, a second ovarian reserve is formed, which consists of gonadotropin-responsive small antral growing follicles and is a dynamic reserve for ovulation. Its size, evaluated by direct antral follicular count or endocrine markers, determines the success of assisted reproductive technologies in humans and embryo production biotechnologies in animals. Strong evidence indicates that these two reserves are functionally related. The size of both reserves appears to be highly variable between individuals of similar age, but the equilibrium size of the dynamic reserve in adults seems to be specific to each individual. The dynamics of both follicular reserves appears to result from the fine tuning of regulations involving two main pathways, the phosphatase and tensin homolog (PTEN)/phosphatidylinositol-3 kinase (PI3K)/3-phosphoinositide-dependent protein kinase-1 (PDPK1)/v-akt murine thymoma viral oncogene homolog 1 (AKT1) and the bone morphogenetic protein (BMP)/anti-Müllerian hormone (AMH)/SMAD signaling pathways. Mutations in genes encoding the ligands, receptors, or signaling effectors of these pathways can accelerate or modulate the exhaustion rate of the ovarian reserves, causing premature ovarian insufficiency (POI) or increase in reproductive longevity, respectively. With female aging, the decline in primordial follicle numbers parallels the decrease in the size of the dynamic reserve of small antral follicles and the deterioration of oocyte quality. Recent progress in our knowledge of signaling pathways and their environmental and hormonal control during adult and fetal life opens new perspectives to improve the management of the ovarian reserves.

Female age-related fertility decline. Committee Opinion No. 589

The fecundity of women decreases gradually but significantly beginning approximately at age 32 years and decreases more rapidly after age 37 years. Education and enhanced awareness of the effect of age on fertility are essential in counseling the patient who desires pregnancy. Given the anticipated age-related decline in fertility, the increased incidence of disorders that impair fertility, and the higher risk of pregnancy loss, women older than 35 years should receive an expedited evaluation and undergo treatment after 6 months of failed attempts to conceive or earlier, if clinically indicated. In women older than 40 years, more immediate evaluation and treatment are warranted.

Loss of the proapoptotic BH3-only protein BCL-2 modifying factor prolongs the fertile life span in female mice

The duration of the female fertile life span is influenced by the number of oocytes stored in the ovary as primordial follicles. Cell death, both during ovarian development in the embryo and in the postnatal ovary, plays a critical role in determining how many primordial follicles are established and maintained within the ovary. However, the roles of individual apoptotic regulators in mediating cell death within the ovary have not yet been characterized. In this study, gene targeted mice were used to investigate the role of BCL-2-modifying factor (BMF), a proapoptotic protein belonging to the BH3-only subgroup of the BCL-2 family, in determining the number of primordial follicles maintained in the adult ovary and the length of the fertile life span. Stereological analysis of ovaries showed that Bmf(-/-) mice had significantly more primordial follicles than wild-type (WT) control animals at Postnatal Days 100, 200, 300, and 400 but not at Day 20. No differences were observed between WT and Bmf(-/-) mice in the number of ova shed following ovulatory stimulation with exogenous gonadotropins. Bmf(-/-) females were fertile and produced the same number pups/litter as WT females, but Bmf(-/-) females produced litters more frequently and consequently more offspring than WT females over a 6-mo period. Furthermore, the fertile life span of Bmf(-/-) females was significantly extended compared to WT females. Our findings support an important role for BMF in determining the number of primordial follicles maintained in the ovary throughout adult reproductive life and thus indicate that the length of female fertility may be extended by increasing the number of primordial follicles maintained within the ovary through inhibition of BMF.

Quantification of healthy and atretic germ cells and follicles in the developing and post-natal ovary of the South American plains vizcacha, Lagostomus maximus: evidence of continuous rise of the germinal reserve

The female germ line in mammals is subjected to massive cell death that eliminates 60-85% of the germinal reserve by birth and continues from birth to adulthood until the exhaustion of the germinal pool. Germ cell demise occurs mainly through apoptosis by means of a biased expression in favour of pro-apoptotic members of the BCL2 gene family. By contrast, the South American plains vizcacha, Lagostomus maximus, exhibits sustained expression of the anti-apoptotic BCL2 gene throughout gestation and a low incidence of germ cell apoptosis. This led to the proposal that, in the absence of death mechanisms other than apoptosis, the female germ line should increase continuously from foetal life until after birth. In this study, we quantified all healthy germ cells and follicles in the ovaries of L. maximus from early foetal life to day 60 after birth using unbiased stereological methods and detected apoptosis by labelling with TUNEL assay. The healthy germ cell population increased continuously from early-developing ovary reaching a 50 times higher population number by the end of gestation. TUNEL-positive germ cells were <0.5% of the germ cell number, except at mid-gestation (3.62%). Mitotic proliferation, entrance into prophase I stage and primordial follicle formation occurred as overlapping processes from early pregnancy to birth. Germ cell number remained constant in early post-natal life, but a remnant population of non-follicular VASA- and PCNA-positive germ cells still persisted at post-natal day 60. L. maximus is the first mammal so far described in which female germ line develops in the absence of constitutive massive germ cell elimination.

The dynamics of the primordial follicle reserve

The female germline comprises a reserve population of primordial (non-growing) follicles containing diplotene oocytes arrested in the first meiotic prophase. By convention, the reserve is established when all individual oocytes are enclosed by granulosa cells. This commonly occurs prior to or around birth, according to species. Histologically, the ‘reserve’ is the number of primordial follicles in the ovary at any given age and is ultimately depleted by degeneration and progression through folliculogenesis until exhausted. How and when the reserve reaches its peak number of follicles is determined by ovarian morphogenesis and germ cell dynamics involving i) oogonial proliferation and entry into meiosis producing an oversupply of oocytes and ii) large-scale germ cell death resulting in markedly reduced numbers surviving as the primordial follicle reserve. Our understanding of the processes maintaining the reserve comes primarily from genetically engineered mouse models, experimental activation or destruction of oocytes, and quantitative histological analysis. As the source of ovulated oocytes in postnatal life, the primordial follicle reserve requires regulation of i) its survival or maintenance, ii) suppression of development (dormancy), and iii) activation for growth and entry into folliculogenesis. The mechanisms influencing these alternate and complex inter-related phenomena remain to be fully elucidated. Drawing upon direct and indirect evidence, we discuss the controversial concept of postnatal oogenesis. This posits a rare population of oogonial stem cells that contribute new oocytes to partially compensate for the age-related decline in the primordial follicle reserve.

The immature human ovary shows loss of abnormal follicles and increasing follicle developmental competence through childhood and adolescence

STUDY QUESTION

Do the ovarian follicles of children and adolescents differ in their morphology and in vitro growth potential from those of adults?

SUMMARY ANSWER

Pre-pubertal ovaries contained a high proportion of morphologically abnormal non-growing follicles, and follicles showed reduced capacity for in vitro growth.

WHAT IS KNOWN ALREADY

The pre-pubertal ovary is known to contain follicles at the early growing stages. How this changes over childhood and through puberty is unknown, and there are no previous data on the in vitro growth potential of follicles from pre-pubertal and pubertal girls.

STUDY DESIGN, SIZE, DURATION

Ovarian biopsies from five pre-pubertal and seven pubertal girls and 19 adult women were analysed histologically, cultured in vitro for 6 days, with growing follicles then isolated and cultured for a further 6 days.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Ovarian biopsies were obtained from girls undergoing ovarian tissue cryopreservation for fertility preservation, and compared with biopsies from adult women. Follicle stage and morphology were classified. After 6 days in culture, follicle growth initiation was assessed. The growth of isolated secondary follicles was assessed over a further 6 days, including analysis of oocyte growth.

MAIN RESULTS AND THE ROLE OF CHANCE

Pre-pubertal ovaries contained a high proportion of abnormal non-growing follicles (19.4 versus 4.85% in pubertal ovaries; 4004 follicles analysed; P = 0.02) characterized by indistinct germinal vesicle membrane and absent nucleolus. Follicles with this abnormal morphology were not seen in the adult ovary. During 6 days culture, follicle growth initiation was observed at all ages; in pre-pubertal samples there was very little development to secondary stages, while pubertal samples showed similar growth activation to that seen in adult tissue (pubertal group: P = 0.02 versus pre-pubertal, ns versus adult). Isolated secondary follicles were cultured for a further 6 days. Those from pre-pubertal ovary showed limited growth (P < 0.05 versus both pubertal and adult follicles) and no change in oocyte diameter over that period. Follicles from pubertal ovaries showed increased growth; this was still reduced compared with follicles from adult women (P < 0.05) but oocyte growth was proportionate to follicle size.

LIMITATIONS, REASONS FOR CAUTION

These data derive from only a small number of ovarian biopsies, although large numbers of follicles were analysed. It is unclear whether the differences between groups are related to puberty, or just age.

WIDER IMPLICATIONS OF THE FINDINGS

These findings show that follicles from girls of all ages can be induced to grow in vitro, which has important implications for some patients who are at high risk of malignant contamination of their ovarian tissue. The reduced growth of isolated follicles indicates that there are true intrafollicular differences in addition to potential differences in their local environment, and that there are maturational processes occurring in the ovary through childhood and adolescence, which involve the loss of abnormal follicles, and increasing follicle developmental competence.

Study funding/competing interest(s)

Funded by MRC grants G0901839 and G1100357. No competing interests.

Activation of the aryl hydrocarbon receptor by a component of cigarette smoke reduces germ cell proliferation in the human fetal ovary

Fetal life is a critical time for female fertility, when germ cells complete proliferation, initiate meiosis and ultimately form the lifetime stock of primordial follicles. Female fertility may be reduced by in utero exposure to cigarette smoke, which contains ligands for the aryl hydrocarbon receptor (AhR). The AhR is a critical regulator of ovarian germ cell survival in mice; thus activation of this receptor in the ovaries of fetuses exposed to maternal cigarette smoke in utero may provide a mechanism by which female fertility is reduced in later life. We have therefore investigated AhR expression in the human fetal ovary, and examined the effects of an AhR ligand present in cigarette smoke, on germ cells in human fetal ovaries cultured in vitro. The results showed that AHR mRNA expression increased 2-fold between first and late second trimester (P = 0.008). AhR protein was confined to germ cells at all gestations, but varied from expression in most germ cells during the first trimester, to only patchy expression by clusters of germ cells at later gestations. Culture of human fetal ovaries with the AhR ligand 9,10-dimethyl-1,2-benzanthracene-3,4-dihydrodiol (DMBA-DHD; a component of cigarette smoke) did not affect germ cell number in vitro, but significantly reduced the proportion of proliferating germ cells by 29% (as assessed by phospho-histone H3 staining (P = 0.04)). Germ cell apoptosis was not significantly affected. These results reveal that germ cells in the human fetal ovary express AhR from the proliferative stage of development through entry into meiosis and beyond, and demonstrate that AhR ligands found in cigarette smoke have the capacity to impair human fetal ovarian germ cell proliferation.

The root of reduced fertility in aged women and possible therapentic options: current status and future perspects

It is well known that maternal ageing not only causes increased spontaneous abortion and reduced fertility, but it is also a high genetic disease risk. Although assisted reproductive technologies (ARTs) have been widely used to treat infertility, the overall success is still low. The main reasons for age-related changes include reduced follicle number, compromised oocyte quality especially aneuploidy, altered reproductive endocrinology, and increased reproductive tract defect. Various approaches for improving or treating infertility in aged women including controlled ovarian hyperstimulation with intrauterine insemination (IUI), IVF/ICSI-ET, ovarian reserve testing, preimplantation genetic diagnosis and screening (PGD/PGS), oocyte selection and donation, oocyte and ovary tissue cryopreservation before ageing, miscarriage prevention, and caloric restriction are summarized in this review. Future potential reproductive techniques for infertile older women including oocyte and zygote micromanipulations, derivation of oocytes from germ stem cells, ES cells, and iPS cells, as well as through bone marrow transplantation are discussed.

A stockpile of ova in the grass frog Rana temporaria is established once for the life span. Do ovaries in amphibians and in mammals follow the same evolutionary strategy?

Most anuran amphibians produce high numbers of eggs during several consecutive breeding seasons. The question is still open whether oocytes are formed anew as a result of oogonial proliferation after each spawning or the definitive pool of oocytes is established during the juvenile period and is sufficient for the whole reproductive life span of a female. Our quantitative studies show that primary oogonia in adult female frogs can proliferate, but they fail to differentiate further and do not enter meiosis, and thereby there is no supplementation of new generations of oocytes after each spawning. Ovaries of one-year-old grass frogs contain (median) 53,447 diplotene oocytes, in two-years-old frogs this number decreased to 33,583 and eventually reached 25,679 in virgin mature females. More than 50% decrease in the total oocyte number was accompanied by massive degeneration (atresia) of oocytes. The final number of oocytes in a female forms a stock for 11-12 breeding seasons and exceeds the number of eggs produced during the potential reproductive life span of this species. The phylogenetic context of oocyte recruitment modes in the major clades of vertebrates is discussed in respect to their ability to replenish the stock (a renewable stock in ovaries named "open" vs. a non-renewable stock in ovaries named "closed").

Intrauterine exposure to diesel exhaust diminishes adult ovarian reserve

OBJECTIVE

To analyze ovarian and uterine morphologic changes resulting from intrauterine and postnatal exposure to diesel exhaust.

DESIGN

Crossover study. Experimental groups: intrauterine and postnatal clean air exposure; intrauterine exposure to diesel only; postnatal exposure to diesel only; and intrauterine and postnatal exposure to diesel.

SETTING

Laboratory of Experimental Air Pollution.

ANIMAL(S)

Swiss mice.

INTERVENTION(S)

Mice exposed to diesel exhaust with doses that correspond to the daily average PM₂.₅ levels (fine particles in the ambient air 2.5 μm or less in size) reported by the World Health Organization.

MAIN OUTCOME MEASURE(S)

Morphometric analyses of the ovaries and uterus were performed to define the relative area occupied by follicles, corpus luteum, and stroma and the proportionate area of glands, epithelial layer, and stroma within the uterine endometrium.

RESULT(S)

A significant reduction in the proportion of primordial follicles was observed in intrauterine-exposed animals, those exposed during the postnatal period, and in animals exposed during both phases. Primary follicle proportion was reduced in animals exposed during pregnancy. No significant changes were detected in uterine morphology.

CONCLUSION(S)

Intrauterine exposure to acceptable levels of diesel exhaust compromises the reproductive potential of female mice, diminishing ovarian reserve when sexual maturity is achieved. This effect could increase the risk of premature menopause. The findings raise concern about current environmental guidelines for diesel exposure, warranting more careful examination of this issue in humans by regulatory authorities.

Caspase 9 is constitutively activated in mouse oocytes and plays a key role in oocyte elimination during meiotic prophase progression

In many mammalian species, more than half of the initial oocyte population is eliminated by neonatal life, thus limiting the oocyte reserve for reproduction. The cause or mechanism of this major oocyte loss remains poorly understood. We examined the apoptotic pathway involved in oocyte elimination in wild-type mouse ovaries as well as in Msh5 -/- ovaries, in which all oocytes were eliminated due to a lack of double strand break repair. Immunoblot and immunofluorescence staining showed that an initiator caspase 9 and an effector caspase 7 were constitutively activated in almost all oocytes in fetal ovaries regardless of their genotypes. In caspase 9 -/- ovaries, the total number of oocytes remained high while that in wild-type ovaries steadily declined during ovarian development. Therefore, the activation of caspase 9 was required for but did not immediately lead to oocyte demise. We found that XIAP, an endogenous inhibitor of apoptosis, was also abundant in oocytes during meiotic prophase progression. On the other hand, a cleaved form of PARP1, a target of effector caspases, was localized to the nuclei of a limited number of oocytes, and the frequency of cleaved PARP1-positive oocyte nuclei increased significantly higher before all oocytes disappeared in Msh5 -/- ovaries. We conclude that the mitochondrial apoptotic pathway mediated by caspase 9 is constitutively activated in oocytes and renders the elimination of oocytes with meiotic errors, which can be captured by the cleavage of PARP1.

The infant and pubertal human ovary: Balbiani's body-associated VASA expression, immunohistochemical detection of apoptosis-related BCL2 and BAX proteins, and DNA fragmentation

STUDY QUESTION

How do apoptosis-related BCL2 and BAX genes, known to regulate death or survival of germ cells in fetal and adult life, and germ-cell-specific VASA protein behave from birth to puberty in the human ovary?

SUMMARY ANSWER

In resting primordial follicles in both infant and pubertal ovaries, BCL2 family members and germ-cell-specific VASA behave as in fetal life. After birth, once follicles leave the resting reserve to enter the growing follicular pool, detection of apoptosis-related genes moves from the germ cell to granulosa cells and VASA expression is lost.

WHAT IS KNOWN ALREADY

In the human ovary, around 85% of the 7 × 10⁶ potential oocytes produced at mid-gestation are lost before birth, an extra 10% before puberty, and loss continues throughout reproductive life until germinal exhaustion of the ovary. Oocyte loss is mainly driven through a balanced expression of BCL2 gene family members. Apoptosis-inducing BAX gene shows a sustained expression throughout fetal and adult life, whereas apoptosis-inhibiting BCL2 is detectable during the proliferative stage of primordial germ cells and oogonia in the fetal ovary and proliferation of granulosa cells in growing follicles in the adult ovary. The germ-cell marker VASA is detectable in the fetal ovary from early oogenesis and is conspicuously expressed in primordial follicles, where in late pregnancy it is associated with the Balbiani's vitelline space. VASA expression is not detectable in the adult ovary.

STUDY DESIGN, SIZE, DURATION

This is a qualitative analysis involving infant/pubertal paraffin-embedded human ovaries screened for apoptosis-related proteins, DNA fragmentation and germ-cell identity.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Ovaries from 13 patients ranging in age from 4 to 16 years, undergoing gynaecological surgical procedures due to benign pathology, were studied. Tissues were fixed in 10% formalin, paraffin-embedded and processed for immunohistochemistry to screen the temporal and cellular localization of germ-cell-specific VASA protein and BCL2 and BAX apoptosis-related proteins. In addition, a terminal deoxynucleotidyl transferase-mediated deoxiuridinetriphosphate nick-end labelling (TUNEL) assay was performed to detect DNA fragmentation. General histology and tissue integrity were assessed by haematoxylin-eosin staining.

MAIN RESULTS AND THE ROLE OF CHANCE

VASA showed a differential pattern of expression; in the resting primordial follicle reserve in infant and pubertal ovaries, it was associated with the Balbiani's body space in the germ cell. VASA remained detectable in primary follicles leaving the resting reserve, but once follicles entered the growing pool it became undetectable. This pattern of VASA expression is the same as in the fetal ovary. BAX was expressed both in the resting primordial reserve and in the pool of growing follicles, whereas BCL2 was detected only in granulosa cells in antral follicles in the growing pool. Apoptosis-related protein expression moved from the germ cell to the somatic stratum when primordial follicles left the resting reserve to enter the pool of growing follicles, irrespective of female age. Most TUNEL-positive cells were detected in the granulosa cells of antral follicles. No TUNEL-positive cells were found in resting primordial follicles.

LIMITATIONS, REASONS FOR CAUTION

The study was limited by the qualitative nature of the immuno-histochemical analysis and the TUNEL assay. The results neither quantify the levels of germ-cell death nor exclude other concurrent cell death mechanisms that could act in the regulation of female germ-cell number.

WIDER IMPLICATIONS OF THE FINDING

This study provides missing knowledge about apoptosis and germ-cell-specific VASA expression in the human ovary between birth and puberty and the participation of BCL2 and BAX genes in the balance between death and survival throughout female germ-line development. Intracellular localization of VASA in resting follicles emerges as a possible marker with prognostic value that needs further investigation, especially in infant patients entering ovarian cryo-preservation programmes. This knowledge will be valuable in optimizing the rescue and clinical use of germ cells to restore fertility in women.

STUDY FUNDING/COMPETING INTEREST(S)

No external funding was obtained for this study. The authors have no conflicts of interest to declare.

Transcription factors in the maintenance and survival of primordial follicles

Primordial follicles are formed prenatally in mammalian ovaries, and at birth they are fated to be activated to primary follicles, to be dormant, or to die. During the early stage of folliclulogenesis, the oocyte undergoes dynamic alterations in expression of numerous genes, which are regulated by transcription factors. Several germ-cell specific transcriptional regulators are critical for formation and maintenance of follicles. These transcriptional regulators include: Figla, Lhx8, Nobox, Sohlh1, and Sohlh2. A subset of these transcriptional regulators is mutated in women with ovarian insufficiency and infertility. Establishment of this oocyte pool is essential for fertility. This review focuses on these transcriptional regulators of female primordial follicles.

Cryopreservation of ovarian tissue for fertility preservation in young female oncological patients

Girls and women suffering from a cancer that requires treatment with gonadotoxic drugs may experience cessation of reproductive function as a side effect due to obliteration of the ovarian pool of follicles. Techniques are now available for fertility preservation, such as cryopreservation of mature oocytes, embryos or ovarian cortical tissue. Whereas collection of mature oocytes and embryos requires at least a 2-week period, ovarian tissue may on short notice be frozen prior to treatment and can be transplanted back into women with ovarian failure. Transplanted frozen/thawed tissue supports survival and growth of follicles, giving rise to menstrual cycles and hormone production for several years. Worldwide, the procedure has resulted in the birth of 15 healthy children. Many cancer patients including girls and young women want fertility preservation, and the techniques are now being further developed and implemented in several centers.

Regulation of the ovarian reserve by members of the transforming growth factor beta family

Genetic or environmental factors that affect the endowment of oocytes, their assembly into primordial follicles, or their subsequent entry into the growing follicle pool can disrupt reproductive function and may underlie disorders such as primary ovarian insufficiency. Mouse models have been instrumental in identifying genes important in ovarian development, and a number of genes now associated with ovarian dysfunction in women were first identified as causing reproductive defects in knockout mice. The transforming growth factor beta (TGFB) family consists of developmentally important growth factors that include the TGFBs, anti-Müllerian hormone (AMH), activins, bone morphogenetic proteins (BMPs), and growth and differentiation factor 9 (GDF9). The ovarian primordial follicle pool is the source of oocytes in adults. Development of this pool can be grossly divided into three key processes: (1) establishment of oocytes during embryogenesis followed by (2) assembly and (3) activation of the primordial follicle. Disruptions in any of these processes may cause reproductive dysfunction. Most members of the TGFB family show pivotal roles in each of these areas. Understanding the phenotypes of various mouse models for this protein family will be directly relevant to understanding how disruptions in TGFB family signaling result in reproductive diseases in women and will present new areas for development of tailored diagnostics and interventions for infertility.

Variation in ovarian follicle density during human fetal development

PURPOSE

To obtain a precise estimate of ovarian follicle density and variation in the number of follicles at several gestational ages during human fetal development.

METHODS

Twelve necropsied ovaries from 9 fetuses (gestational age: 24 to 36 weeks) and 3 neonates (who died within the first hours of life) were studied. Ovaries were fixed with 4 % formaldehyde and embedded in paraffin. Serial, 7 mm thick sections of the ovaries were cut and evaluated at every 50 cuts. Follicles were counted in 10 regions (each measuring 625 μm(2)) of the ovarian cortex and the number of follicles per mm³ was calculated.

RESULTS

The number of follicles per 0.25 mm² ranged from 10.9 (± 4.8) in a neonate to 34.7 (± 10.6) also in a neonate. Among fetuses, follicle density was lowest at 36 weeks of gestation (11.1 ± 6.2) and highest at 26 weeks (32 ± 8.9). The total number of follicles ranged from 500,000 at the age of 22 weeks to > 1,000,000 at the age of 39 weeks.

CONCLUSION

Our results show a peak in the number of follicles during intrauterine life at approximately 26 weeks, followed by a rapid reduction in this number before birth, providing a step forward towards the understanding of primordial follicular assembly in humans and, ultimately, the identification of the determinants of reproductive capacity.

Biology and biotechnology of follicle development

Growth and development of ovarian follicles require a series of coordinated events that induce morphological and functional changes within the follicle, leading to cell differentiation and oocyte development. The preantral early antral follicle transition is the stage of follicular development during which gonadotropin dependence is obtained and the progression into growing or atresia of the follicle is made. Follicular growth during this period is tightly regulated by oocyte-granulosatheca cell interactions. A cluster of early expressed genes is required for normal folliculogenesis. Granulosa cell factors stimulate the recruitment of theca cells from cortical stromal cells. Thecal factors promote granulosa cell proliferation and suppress granulosa cell apoptosis. Cell-cell and cell-extracellular matrix interactions influence the production of growth factors in the different follicular compartments (oocyte, granulosa, and theca cells). Several autocrine and paracrine factors are involved in follicular growth and differentiation; their activity is present even at the time of ovulation, decreasing the gap junction communication, and stimulating the theca cell proliferation. In addition, the identification of the factors that promote follicular growth from the preantral stage to the small antral stage may provide important information for the identification for assisted reproduction techniques.

Immunohistochemical and ultrastructural visualization of different routes of oocyte elimination in adult rats

Cell death is a process for maintaining homeostasis in tissues and organs. In the ovary, apoptotic cell death has been implicated in follicular atresia; in the elimination of the follicles that are not ovulated during adult life. Recent studies indicate that apoptosis and autophagy are two programmed processes of cell death. Apoptosis is performed by proteases called caspases and leads to such morphological traits as DNA fragmentation. Autophagy, in turn, is characterized by the exacerbated formation of autophagosomes; a process in which the amount of the LC3 and Lamp 1 proteins increases. In this study, oocytes from all stages of the estrous cycle of Wistar rats were analyzed. The apoptosis process was identified by immunodetecting active Caspase-3 and locating DNA fragmentation using the TUNEL technique. Autophagy was evaluated through immunodetection of the LC3 and Lamp 1 proteins, and by ultrastructural localization of autophagic vesicle formation. All techniques were conducted using the same oocytes. Results show that all phases of the estrous cycle contain dying oocytes that test positive simultaneously for apoptosis and autophagy markers. The highest level of apoptosis was found during estrus; while the proestrous stage had the highest level of autophagy. The diestrous and metestrous phases were characterized by a high frequency of the presence of markers of apoptosis and autophagy in the same oocyte. Our results demonstrate that during oocyte elimination in adult rats the proteins involved in both processes, apoptosis and autophagy, are present in the same cell at the same time.

Analysis of LIN28A in early human ovary development and as a candidate gene for primary ovarian insufficiency

Lin28 proteins are emerging as important regulators of microRNAs in endocrine systems. Lin28a regulates primordial germ cell development and puberty timing in mice, whereas the related protein LIN28B is associated with age at menarche in genome-wide association studies in humans. Here, we studied expression of LIN28A and LIN28B in early human gonad development. LIN28A increased in the developing ovary between 6 and 9weeks post conception, but not in the developing testis. Immunohistochemistry demonstrated LIN28A in peripheral germ cells. LIN28B was expressed at lower levels in both tissues and did not increase with time. As disruption of Lin28a affects germ cell development in mice, LIN28A was considered a candidate gene for primary ovarian insufficiency (POI) in humans. However, no significant changes were found in 50 women studied. These findings show LIN28A is strongly expressed in germ cells during early human ovary development, but disruption of LIN28A is not a common cause of POI.

The ovarian follicular pool and reproductive outcome in women

Both quantitative and qualitative aspects of the ovarian reserve are inversely related to age, hence the relationship existing between low quantity and low quality may be only indirect and depending on their strong relationship with the third variable, namely women's age. However the possibility exists that they may also be directly related. The objective of this study was to investigate the relationship between ovarian reserve and female reproductive outcome. Eight published studies reporting histological data on the human ovaries have been carefully reviewed. Only studies where the reproductive history of women was reported have been included for the analysis. The non-growing follicle count was plotted versus age and the best fit line through the data was calculated. All patients were assigned as to be above or below the calculated median hence differentiating women with high or low ovarian reserve for their age. A similar number of pregnancies ended in miscarriage in women with low and high ovarian reserve. The number of deliveries per woman in both the groups was not statistically different. The results of the study do not support the hypothesis that quality and quantity of the follicular pool are directly related.

Reproductive hormones and the menopause transition

The hormonal correlates of reproductive aging and the menopause transition reflect an initial loss of the follicle cohort, while a responsive ovary remains, and an eventual complete loss of follicle response, with persistent hypergonadotropic amenorrhea. The physiology of the process is described, along with key findings of relevant studies, with an emphasis on the Study of Women's Health Across the Nation. A clinical framework is provided to help clinicians to forecast the major milestones of the menopausal transition and to predict potential symptoms or disease.