Eric D. Clegg

Estimates of human fertility and pregnancy loss

OBJECTIVE To examine the fertility and pregnancy wastage rates in a group of presumably fertile couples. DESIGN Prospective observational study of 200 couples desiring to achieve pregnancy over 12 menstrual cycles coupled with pregnancy outcome follow-up. SETTING A university-based obstetrics and gynecological center. PATIENTS Personal interviews and questionnaires were used to screen couples for entry into the study. Couples were counseled to have intercourse centered on predicted day of ovulation. Phase 1 included the first three cycles in which women collected daily morning urine samples, underwent midcycle postcoital tests, and, if late for their menses, presented for serum hCG testing. Phase 2 encompassed the next nine cycles in which women were contacted monthly by phone and underwent serum hCG testing if menses was delayed. Urine samples from cycles in which clinical (serum hCG) pregnancy did not occur underwent sensitive hCG testing to detect occult pregnancies. Pregnancies were followed until delivery to ascertain outcome. RESULTS Eighty-two percent of the 200 couples followed for the entire study period conceived. The maximal fertility rate was approximately 30% per cycle in the first two cycles. This rate quickly tapered over the remainder of the study. Pregnancy wastage during phase 1 accounted for 31% of the pregnancies detected. Forty-one percent (15/36) of these losses were seen only by urine hCG testing and were categorized as occult. Eleven of these same patients later achieved clinically recognized conceptions during the study. CONCLUSIONS These results support the concept that the efficiency of human reproduction is maximum at approximately 30% per cycle. A very significant number of these pregnancies end in spontaneous abortion. In addition, pregnancy loss before missed menses occurs in a significant proportion of women.

Methods for assessing sperm motility, morphology, and counts in the rat, rabbit, and dog: A consensus report☆

Reproductive toxicity studies are increasingly including assessments of sperm parameters including motility, morphology, and counts. While these assessments can provide valuable information for the determination of potential reproductive toxicity, the methods for conducting the assessments have not been well developed in all laboratories and are continually evolving. The use of different methods in different laboratories makes comparison of data among laboratories difficult. To address the differences in methods, a working group was convened to discuss methods currently in use, share data, and try to reach consensus about optimal methods for assessing sperm parameters in rats, rabbits, and dogs. This article presents the consensus report, as well as future research needs, with the hope that optimized common methods will aid in the detection of reproductive effects and enhance interlaboratory comparisons.

Leydig cell hyperplasia and adenoma formation: Mechanisms and relevance to humans

Leydig cell adenomas are observed frequently in studies evaluating the chronic toxicity of chemical agents in laboratory animals. Doubts have been raised about the relevance of such responses for human risk assessment, but the question of relevance has not been evaluated and presented in a comprehensive manner by a broad group of experts. This article reports the consensus conclusions from a workshop on rodent Leydig cell adenomas and human relevance. Five aspects of Leydig cell biology and toxicology were discussed: 1) control of Leydig cell proliferation; 2) mechanisms of toxicant-induced Leydig cell hyperplasia and tumorigenesis; 3) pathology of Leydig cell adenomas; 4) epidemiology of Leydig cell adenomas; and 5) risk assessment for Leydig cell tumorigens. Important research needs also were identified. Uncertainty exists about the true incidence of Leydig cell adenomas in men, although apparent incidence is rare and restricted primarily to white males. Also, surveillance databases for specific therapeutic agents as well as nicotine and lactose that have induced Leydig cell hyperplasia or adenoma in test species have detected no increased incidence in humans. Because uncertainties exist about the true incidence in humans, induction of Leydig cell adenomas in test species may be of concern under some conditions. Occurrence of Leydig cell hyperplasia alone in test species after lifetime exposure to a chemical does not constitute a cause for concern in a risk assessment for carcinogenic potential, but early occurrence may indicate a need for additional testing. Occurrence of Leydig cell adenomas in test species is of potential concern as both a carcinogenic and reproductive effect if the mode of induction and potential exposures cannot be ruled out as relevant for humans. The workgroup focused on seven hormonal modes of induction of which two, GnRH agonism and dopamine agonism, were considered not relevant to humans. Androgen receptor antagonism, 5 alpha-reductase inhibition, testosterone biosynthesis inhibition, aromatase inhibition, and estrogen agonism were considered to be relevant or potentially relevant, but quantitative differences may exist across species, with rodents being more sensitive. A margin of exposure (MOE; the ratio of the lowest exposure associated with toxicity to the human exposure level) approach should be used for compounds causing Leydig cell adenoma by a hormonal mode that is relevant to humans. For agents that are positive for mutagenicity, the decision regarding a MOE or linear extrapolation approach should be made on a case-by-case basis. In the absence of information about mode of induction, it is necessary to utilize default assumptions, including linear behavior below the observable range. All of the evidence should be weighed in the decision-making process.

LABORATORY METHODS FOR ASSESSING HUMAN SEMEN IN EPIDEMIOLOGIC STUDIES: A CONSENSUS REPORT

It is clear that additional methodologic work needs to be performed. Some data gaps described above are being actively investigated. Other standards were not addressed at this meeting; statistical handling of the data, differences among CASA machines, and factors to consider as potential confounders in analysis are just a few. These may be the subject of future workshops, which will also review progress made in the existing knowledge base. For now, this effort represents a first attempt to share information and to use it to encourage investigators in different laboratories to employ similar methods. In this way more direct comparisons among studies can be made, and our collective data base can be strengthened.

Relationship between sperm characteristics and hormonal parameters in normal couples

OBJECTIVE To examine the relationships between hormone profiles and semen analysis measures and fertility in the male partners of presumed normal couples. DESIGN Prospective clinical study. SETTINGS Healthy volunteers in an academic research environment. PATIENT(S) One hundred forty-five reproductive age couples without known risk factors for infertility and who had discontinued contraception to achieve pregnancy completed this component of this study. Each couple was followed for < or =12 menstrual cycles while they attempted to conceive. INTERVENTION(S) Semen quality measures for the first ejaculates were obtained at the start of the study along with a single blood sample. Levels of FSH, bioactive FSH, inhibin B, LH, and T were measured for each man. MAIN OUTCOME MEASURE(S) Semen analysis, FSH, inhibin B, LH, T, and clinical pregnancy. RESULTS Significant positive relationships were observed between the two measures of FSH as well as between both of the FSH measures and LH. Follicle-stimulating hormone as measured by RIA was significantly negatively correlated with inhibin B. Inhibin B showed a marginally significant negative correlation with LH, and LH and T had a marginally significant positive correlation. Inhibin B increased significantly, and both measures of FSH activity showed significant decreases, with increasing levels in several semen quality measures. There was no significant relationship between the measured hormones and the pregnant and nonpregnant groups or time to pregnancy. CONCLUSION(S) These results contribute additional information on the utility of reproductive hormone measurements for predicting semen quality in couples without known reduced fertility.

A novel amphibian tier 2 testing protocol: A 30-week exposure of Xenopus tropicalis to the antiandrogen flutamide

In 1996, the U.S. Congress mandated the development of a screening program for endocrine-disrupting chemicals (EDCs) using validated test systems. Subsequently, the Endocrine Disruptor Screening and Testing Advisory Committee recommended the development of a standardized amphibian assay for tier 2 testing of EDCs. For that reason, a tier 2 testing protocol using Xenopus (Silurana) tropicalis and a 30-week, flow-through exposure to the antiandrogen flutamide from stage 46 tadpoles through sexually mature adult frogs were developed and evaluated in this pilot study. The endpoints for this study included measurements of frog body lengths and weights, liver weights, ovary/egg mass weights, testicular and ovarian histopathology, plasma vitellogenin levels, and notes on any abnormalities observed at necropsy. Increasing exposure concentrations to flutamide caused significant increases in frogs with no recognizable gonadal tissue and increased body and liver weights in male frogs, whereas the body lengths and weights decreased significantly in female frogs. Important issues must be resolved before a tier 2 amphibian assay can be further developed and validated, including the establishment of baseline values in the controls for the parameters under study; the maintenance, measurement, and timing of exposure concentrations; and the development of additional biomolecular markers of effect. This study demonstrated the feasibility of conducting long-term EDC exposure studies using X. tropicalis.

Reversibility of Effects: Overview and Reproductive Systems

AbstractRecovery from adverse noncancer health effects may occur in some circumstances after cessation of exposure or after adaptation to continuing low-dose exposure. In this overview, factors that influence the reversibility of toxic effects of environmental chemicals are presented, using examples derived from toxicity to the reproductive system. Aspects that must be considered include exposure scenario, stage of the life cycle at which exposure occurs, and the nature of the toxicity. Selected categories of reproductive effects are considered briefly with respect to potential for recovery. Finally, the incorporation of reversibility into risk assessments is discussed