Occupational exposures and risk of female infertility

Exposomics as a tool to investigate differences in health and disease by sex and gender

The health and disease of an individual is mediated by their genetics, a lifetime of environmental exposures, and interactions between the two. Genetic or biological sex, including chromosome composition and hormone expression, may influence both the types and frequency of environmental exposures an individual experiences, as well as the biological responses an individual has to those exposures. Gender identity, which can be associated with social behaviors such as expressions of self, may also mediate the types and frequency of exposures an individual experiences. Recent advances in exposome-level analysis have progressed our understanding of how environmental factors affect health outcomes; however, the relationship between environmental exposures and sex- and gender-specific health remains underexplored. The comprehensive, non-targeted, and unbiased nature of exposomic research provides a unique opportunity to systematically evaluate how environmental exposures interact with biological sex and gender identity to influence health. In this forward-looking narrative review, we provide examples of how biological sex and gender identity influence environmental exposures, discuss how environmental factors may interact with biological processes, and highlight how an intersectional approach to exposomics can provide critical insights for sex- and gender-specific health sciences.

Killing two birds with one stone: Pregnancy is a sensitive window for endocrine effects on both the mother and the fetus

Pregnancy is a complex process requiring tremendous physiological changes in the mother in order to fulfill the needs of the growing fetus, and to give birth, expel the placenta and nurse the newborn. These physiological modifications are accompanied with psychological changes, as well as with variations in habits and behaviors. As a result, this period of life is considered as a sensitive window as impaired functional and physiological changes in the mother can have short- and long-term impacts on her health. In addition, dysregulation of the placenta and of mechanisms governing placentation have been linked to chronic diseases later-on in life for the fetus, in a concept known as the Developmental Origin of Health and Diseases (DOHaD). This concept stipulates that any change in the environment during the pre-conception and perinatal (in utero life and neonatal) period to puberty, can be "imprinted" in the organism, thereby impacting the health and risk of chronic diseases later in life. Pregnancy is a succession of events that is regulated, in large part, by hormones and growth factors. Therefore, small changes in hormonal balance can have important effects on both the mother and the developing fetus. An increasing number of studies demonstrate that exposure to endocrine disrupting compounds (EDCs) affect both the mother and the fetus giving rise to growing concerns surrounding these exposures. This review will give an overview of changes that happen during pregnancy with respect to the mother, the placenta, and the fetus, and of the current literature regarding the effects of EDCs during this specific sensitive window of exposure.

Effects of environmental contaminants on fertility and reproductive health

Recent research indicates that the human infertility rate is increasing. Although various reasons have been hypothesized for the growing infertility rate, environmental contaminants are potentially important causal agents associated with this change. Chemical contaminants are widespread throughout our environment and human exposure is virtually unavoidable. The overall contribution of environmental exposure to infertility is unknown, but studies involving occupational exposure, together with results from animal experiments, suggest that environmental contaminants may adversely affect fertility. We reviewed the adverse effects of environmental exposure on fertility and related reproductive outcomes. Environmental contaminants covered in this review include heavy metals, organic solvents, pesticides and endocrine disrupting chemicals. It is hoped that this review will highlight the need for further research in this area.

Exposure to tetrachloroethylene-contaminated drinking water and time to pregnancy

BACKGROUND

The synthetic solvent tetrachloroethylene (PCE), commonly used in dry cleaning operations, is a human neurotoxicant and carcinogen. However, its effect on reproduction is poorly understood, as prior studies have been limited to small occupational cohorts. We examined the association between PCE exposure from contamination of the public drinking water supply and time-to-pregnancy (TTP) in a cohort of mothers from Cape Cod, Massachusetts.

METHODS

The Cape Cod Family Health Study is a retrospective cohort study designed to examine the reproductive and developmental health effects of exposure to PCE-contaminated drinking water. Our analysis included 1565 women who reported 3826 planned pregnancies from 1949 to 1990. Women completed self-administered questionnaires that ascertained TTP for each of her pregnancies, regardless of the outcome, as well as residential history and demographic information. We utilized EPANET water distribution system modeling software and a leaching and transport model to assess PCE exposure for each pregnancy. We used log-binomial regression models to estimate relative risks (RR) and 95% confidence intervals (CI), adjusting for potential confounders. We performed a probabilistic bias analysis to examine the effect of outcome misclassification on our results.

RESULTS

Any cumulative PCE exposure before pregnancy was associated with a 15% reduction in risk of TTP > 12 months (RR = 0.85, 95% CI: 0.70, 1.03). However, women with the highest average monthly PCE exposure around the time of the pregnancy attempt (≥ 2.5 g) had increased risk of TTP > 12 months (RR = 1.36, 95% CI: 1.06, 1.76).

CONCLUSIONS

We found little evidence for long-term, cumulative adverse effects of PCE exposure on TTP, but high levels of PCE exposure around the time of the pregnancy attempt were associated with longer TTP. These associations may be underestimated due to the exclusion of unsuccessful pregnancy attempts from our study population, and may be biased by outcome and exposure misclassification given the long-term recall of TTP and use of a leaching and transport model to estimate PCE exposure.

Pesticides: an update of human exposure and toxicity

Pesticides are a family of compounds which have brought many benefits to mankind in the agricultural, industrial, and health areas, but their toxicities in both humans and animals have always been a concern. Regardless of acute poisonings which are common for some classes of pesticides like organophosphoruses, the association of chronic and sub-lethal exposure to pesticides with a prevalence of some persistent diseases is going to be a phenomenon to which global attention has been attracted. In this review, incidence of various malignant, neurodegenerative, respiratory, reproductive, developmental, and metabolic diseases in relation to different routes of human exposure to pesticides such as occupational, environmental, residential, parental, maternal, and paternal has been systematically criticized in different categories of pesticide toxicities like carcinogenicity, neurotoxicity, pulmonotoxicity, reproductive toxicity, developmental toxicity, and metabolic toxicity. A huge body of evidence exists on the possible role of pesticide exposures in the elevated incidence of human diseases such as cancers, Alzheimer, Parkinson, amyotrophic lateral sclerosis, asthma, bronchitis, infertility, birth defects, attention deficit hyperactivity disorder, autism, diabetes, and obesity. Most of the disorders are induced by insecticides and herbicides most notably organophosphorus, organochlorines, phenoxyacetic acids, and triazine compounds.

Fallopian damage induced by organophosphate insecticide methyl parathion, and protective effect of vitamins E and C on ultrastructural changes in rats

The aim of the present study was to examine the effects of subchronic methyl parathion (MP) administration on lipid peroxidation and fallopian tube damage, and to evaluate the preventive effects of the use of vitamins E and C against toxicity. The experimental groups were: rats treated with corn oil (control group), with 5 mg/kg MP and with 5 mg/kg body weight MP plus vitamins E and C (MP + Vit). The groups were given MP by oral gavage for five days a week for four weeks at a daily dose of 5 mg/kg (MP and MP + Vit) using corn oil as a vehicle. Vitamins E and C were injected at doses of 50 mg/kg intramuscularly and 20 mg/kg intraperitoneally, respectively, just after the treatment with MP in the MP + Vit group. The levels of malondialdehyde (MDA) were determined in rat plasma. Electron microscopic ultrastuructural and histopathological changes in the fallopian tissue were examined. MDA levels were higher in the MP group than in the control group, and lower in the MP + Vit group than in the MP group. MP led to deletions in microvilli and marked loss in kinocillia of surface epithelium. But these marked histopathological findings decreased in the MP + Vit group. Multiple doses of MP administration caused some damage in the fallopian tube, and treatment with vitamins E and C after MP could reduce this effect. Toxicology and Industrial Health 2007; 23: 429—438.

Association between intrafollicular concentration of benzene and outcome of controlled ovarian stimulation in IVF/ICSI cycles: a pilot study

BACKGROUND

Several studies have shown that exposure to benzene is associated to menstrual disorders, miscarriages and other disorders of the reproductive system. We performed an observational prospective pilot study to evaluate if levels of benzene in follicular fluid were correlated with response to controlled ovarian stimulation.

METHOD

Thirty-four normogonadotrophic women undergoing IVF were enrolled. Intra-follicular benzene levels were evaluated by chromatography/mass spectrometry. Based on median benzene level, we divided the study population in two groups: Group A with a "low" intra-follicular benzene concentration (n=19, benzene <0.54 ng/mL) and Group B with a "high" intra-follicular benzene concentration (n=15, benzene ≥ 0.54 ng/mL). The ovarian response to gonadotrophins and the outcome of IVF were analyzed in the two groups.

RESULTS

The two groups did not differ in terms of demographic or anthropometric characteristics. Group B had significantly higher basal FSH levels, lower estradiol peak concentration, and fewer oocytes retrieved and embryos transferred (p<0.05). Number of gonadotrophin vials, length of controlled ovarian stimulation and ongoing pregnancy rate were similar in the two groups.

CONCLUSION

In conclusion, ovarian response to endogenous and exogenous gonadotrophins appeared to be influenced by intra-follicular benzene levels.

A generation of childless women: lessons from the United States

BACKGROUND

Childlessness is a major public health concern in the United States, particularly among educated adults. Among women who turned 45 in 2006, one fifth had no children. We examine the likelihood that a childless woman wants a baby sometime in the future and its determinants.

METHODS

From 2006 to 2010, 5,410 in-person interview surveys were conducted with childless women as part of the National Survey of Family Growth. Age-specific likelihoods of wanting a baby were compared with likelihoods of having a baby before age 45. Female respondents were 1) born after 1960, 2) age 15 to 44, 3) childless (never given birth to a live infant), and 4) not pregnant at time of interview.

FINDINGS

Most childless women at any age want a baby sometime in the future. By age 32, fewer than half the childless women who want a baby will have one. At age 39, the majority of childless women (73%) still want a baby someday, but only 7% will have one. By age 45, more than 1 in 10 women will be childless, but still want to have a baby.

CONCLUSIONS

Although attitudes toward childlessness have become more positive over time, our findings suggest that the United States is experiencing a high prevalence of childless women who want a baby. Clinicians may consider counseling young women about age-related declines in fertility and the costs and success rates of assisted reproductive technologies often required for women with advanced maternal age to better inform their career, family, and lifestyle decisions.

Organochlorine compound levels in fertile and infertile women from Rio de Janeiro, Brazil

OBJECTIVE: The aim of the study was quantify organochlorine compounds in women seeking for infertility treatment (n = 15) and in spontaneously pregnant ones (n = 21). MATERIALS AND METHODS: A questionnaire was applied regarding lifestyle, occupational and reproductive history. Blood samples were collected from both groups. RESULTS: From the pesticides studied, pp'DDE was detected in 100% of infertile women, at higher mean levels than in pregnant women (3.02 mcg/L vs. 0.88 mcg/L; p = 0.001; power of 69%), without correlation with the etiology of infertility. Levels of the polychlorinated biphenyls (PCBs) were low, with positive samples in 100% in the infertile women for PCBs 138, 153, 180, while in pregnant women, they were 85.7% for congeners 138 and 153. Only PCB180 showed significance, with frequency of 71.4% (p = 0.019). CONCLUSIONS: The risk factors for female infertility were: age, consumption of untreated water and of canned foods. Exposure to the most prevalent organochlorine compounds described in literature was confirmed in the study, indicating that pp'DDE may adversely influence female fertility.

Antiovulatory and abortifacient effects of Areca catechu (betel nut) in female rats

Objectives:

To study the antiovulatory and abortifacient effects of ethanolic extract of Areca catechu in female rats.

Materials and Methods:

For antiovulatory effect, ethanolic extract of A. catechu at 100 and 300 mg/kg doses was administered orally for 15 days. Vaginal smears were examined daily microscopically for estrus cycle. Rats were sacrificed on 16^th day. Ovarian weight, cholesterol estimation, and histopathological studies were done. Abortifacient activity was studied in rats at 100 and 300 mg/kg doses administered orally from 6^th to 15^th day of pregnancy. Rats were laparotomised on 19^th day. The number of implantation sites and live fetuses were observed in both horns of the uterus.

Results:

The extract of A. catechu showed a significant decrease in the duration of estrus at 100 mg/kg (P = 0.015) and 300 mg/kg doses (P = 0.002) as compared with control. Metestrus phase was also significantly reduced at 100 mg/kg (P = 0.024) and 300 mg/kg doses (P = 0.002). There was a significant increase in proestrus (P < 0.001) phase. However, diestrus phase was unchanged. Histopathological study of the ovaries showed mainly primordial, primary, and secondary follicles in the test groups as compared to control. There was also a significant (P = 0.002) decrease in ovarian weight and a significant (P = 0.021) increase in ovarian cholesterol level at 100 mg/kg dose. In the study to evaluate abortifacient effect, the mean percentage of abortion with 100 and 300 mg/kg doses were 75.5% and 72.22%, respectively, which was significantly (P = 0.008 and P = 0.006, respectively) increased when compared with control.

Conclusion:

The ethanolic extract of A. catechu at doses of 100 and 300 mg/kg has antiovulatory and abortifacient effects.

Assessment of time to pregnancy and spontaneous abortion status following occupational exposure to organic solvents mixture

PURPOSE

Due to increasing usage of chemicals in various industries, occupational exposure of women with these materials is unavoidable. Nowadays, some studies indicate adverse effects of exposure to these chemicals, especially organic solvents on the reproductive system of females. This study aimed to assess the relationship between spontaneous abortion and occupational exposure to organic solvents mixture in pharmaceutical industry.

METHODS

This study was carried out in a pharmaceutical factory located in the suburb of Tehran in 2010. During the study, married women who were working in the factory laboratory units and had exposure to mixed organic solvents were compared with married women who were working in the packing units of the factory without occupational exposure to organic solvents in terms of spontaneous abortion frequency and duration of pregnancy using statistical methods.

RESULTS

In this study, the frequency of spontaneous abortion in employees with and without exposure to organic solvents mixture was 10.7 and 2.9% respectively. This study showed that even after adjustment for confounding factors, there was a significant correlation between spontaneous abortion and occupational exposure to organic solvents mixture and this correlation increased with increasing levels of exposure to organic solvents. Also, a significant correlation was observed between occupational exposure to mixed organic solvents and waiting time to become pregnant (TTP). Furthermore, this study showed that even after adjustment for confounding variables, shift workers were significantly more affected by spontaneous abortion compared to daytime workers (P < 0.001). Also, in our study, synergistic effect between shift working and occupational exposure to organic solvents mixture on spontaneous abortion was seen.

CONCLUSIONS

According to the results of this study, since there is probability of spontaneous abortion resulting from occupational exposure to various chemicals including organic solvents, recommendation to review the status of occupational exposure of workers can be helpful in improving fertility consultations and reproductive health.

Lifetime occupational history and risk of endometriosis

OBJECTIVES

Endometriosis is the presence of functioning endometrial glands and stroma outside the uterine cavity, most often in the pelvic peritoneal cavity. Women with endometriosis commonly have dysmenorrhea, dyspareunia, pain, menorrhagia, and/or metrorrhagia. Disease complications can include adhesions, chronic pain, and infertility. In this exploratory case-control study, we investigated the relationship between lifetime occupational history and surgically confirmed endometriosis in a population-based sample.

METHODS

We conducted interviews with participants, all reproductive-aged female members of a large health-maintenance organization who were first diagnosed with surgically confirmed endometriosis between April 1, 1996 and March 31, 2001. Interviews were also conducted with randomly selected controls, reproductive-aged female enrollees of the same organization from the same time period. Each reported job was coded using US Census Occupations and Industries codes, and classified into categories. We used unconditional logistic regression to compare having worked in a given job class with never having done so.

RESULTS

Our study found that an increased risk of endometriosis was associated with having worked as a flight attendant, service station attendant, or health worker, particularly as a nurse or health aide (flight attendant: odds ratio (OR) 9.80, 95% CI 1.08-89.02; service station attendant: OR 5.77, 95% CI 1.03-32.43; health worker: OR 1.49, 95% CI 1.03-2.15). Income and education did not make a difference in the OR estimates for the occupations examined.

CONCLUSIONS

This exploratory study suggested that there might be an associated risk of endometriosis for those women who have worked as a flight attendant, service station attendant, or health worker, particularly a nurse.

Dust and chemical exposures, and miscarriage risk among women textile workers in Shanghai, China

INTRODUCTION

To investigate possible associations between miscarriage and occupational exposures in the Shanghai textile industry.

METHODS

A retrospective cohort study of miscarriages among 1752 women in the Shanghai textile industry was conducted. Reproductive history was self-reported by women and occupational work histories were collected from factory personnel records. Occupational exposures were assigned by linking work history information to an industry-specific job-exposure matrix informed by factory-specific textile process information and industrial hygiene assessments. Estimates of cotton dust and endotoxin exposure were also assigned. Odds ratios (OR) and 95% CI were estimated by multivariate logistic regression, with adjustment for age at pregnancy, educational level, smoking status of the woman and her spouse, use of alcohol, and woman's year of birth.

RESULTS

An elevation in risk of a spontaneously aborted first pregnancy was associated with exposure to synthetic fibres (OR 1.89, 95% CI 1.20 to 3.00) and mixed synthetic and natural fibres (OR 3.31, 95% CI 1.30 to 8.42). No increased risks were observed for women working with solvents, nor were significant associations observed with quantitative cotton dust or endotoxin exposures. Associations were robust and similar when all pregnancies in a woman's reproductive history were considered.

CONCLUSIONS

Occupational exposure to synthetic fibres may cause miscarriages, and this possibility should be the subject of further investigation.

Pesticide exposure: the hormonal function of the female reproductive system disrupted?

Some pesticides may interfere with the female hormonal function, which may lead to negative effects on the reproductive system through disruption of the hormonal balance necessary for proper functioning. Previous studies primarily focused on interference with the estrogen and/or androgen receptor, but the hormonal function may be disrupted in many more ways through pesticide exposure. The aim of this review is to give an overview of the various ways in which pesticides may disrupt the hormonal function of the female reproductive system and in particular the ovarian cycle. Disruption can occur in all stages of hormonal regulation: 1. hormone synthesis; 2. hormone release and storage; 3. hormone transport and clearance; 4. hormone receptor recognition and binding; 5. hormone postreceptor activation; 6. the thyroid function; and 7. the central nervous system. These mechanisms are described for effects of pesticide exposure in vitro and on experimental animals in vivo. For the latter, potential effects of endocrine disrupting pesticides on the female reproductive system, i.e. modulation of hormone concentrations, ovarian cycle irregularities, and impaired fertility, are also reviewed. In epidemiological studies, exposure to pesticides has been associated with menstrual cycle disturbances, reduced fertility, prolonged time-to-pregnancy, spontaneous abortion, stillbirths, and developmental defects, which may or may not be due to disruption of the female hormonal function. Because pesticides comprise a large number of distinct substances with dissimilar structures and diverse toxicity, it is most likely that several of the above-mentioned mechanisms are involved in the pathophysiological pathways explaining the role of pesticide exposure in ovarian cycle disturbances, ultimately leading to fertility problems and other reproductive effects. In future research, information on the ways in which pesticides may disrupt the hormonal function as described in this review, can be used to generate specific hypotheses for studies on the effects of pesticides on the ovarian cycle, both in toxicological and epidemiological settings.

Fertility and exposure to solvents among families in the Agricultural Health Study

BACKGROUND

Several studies have reported associations between solvent exposure and reduced female fertility, but the evidence is inconclusive for male fertility.

OBJECTIVES

To investigate the impact of solvent exposure on subfertility among families of male licensed pesticide applicators in the Agricultural Health Study cohort.

METHODS

The couples enrolled between 1993 and 1997. Cross-sectional questionnaire information on work tasks was used to assess exposure to solvents. The data were limited to couples (wife aged less than 40 years) with an attempt at pregnancy in the last four years (n = 2112).

RESULTS

Twenty eight per cent of the couples were defined as subfertile (not conceiving a pregnancy after at least 12 months of unprotected intercourse, regardless of whether or not a pregnancy ultimately occurred). Adjusted subfertility odds ratios (OR) for exposure to solvents were calculated with logistic regression. Female (OR 1.42, 95% CI 1.15 to 1.75) and male exposure to solvents (OR 1.21 (95% CI 0.93 to 1.57) for monthly exposure and 1.40 (95% CI 0.97 to 2.03) for daily or weekly exposure) were associated with subfertility. In farming, spouses may share or exchange jobs. To account for potential dual exposure, variables for parental exposure (either parent exposed or both parents exposed) were also defined. Both were strongly associated with subfertility (OR 1.62 (95% CI 1.20 to 2.17) and OR 2.10 (95% CI 1.22 to 3.60), respectively).

CONCLUSIONS

Solvents may impair fertility of either gender, though the evidence for female effects is stronger than for male effects.

Genomic alterations in the endometrium may be a proximate cause for endometriosis

OBJECTIVE

To test the hypothesis that endometriosis may originate from genomic alterations in the endometrium by genomic analysis of endometrial tissues in patients with endometriosis and compare them with those from normal controls.

METHODS

Endometrial tissue samples were taken from five women with endometriosis. For controls, we used endometrial tissue samples from four women who underwent elective abortions and one sample from placenta. Using array-based comparative genomic hybridization (CGH), we determined the normal range of variation in CGH signals using normal controls. CGH results were further confirmed by real-time quantitative PCR and loss of heterozygosity analysis.

RESULTS

We identified several regions of genomic alterations in all five patients. Some of these regions were the same regions identified previously in endometriotic lesions. For select markers, the genomic alterations were confirmed by real-time PCR and LOH analyses.

CONCLUSIONS

There is evidence that the endometrium in women with endometriosis has genomic alterations. This is consistent with numerous reports that the endometrium of women with endometriosis differ from those of women without. Our finding suggests that genomic alterations in the endometrium may be a proximate cause for endometriosis.

Risk factors for female infertility in an agricultural region

BACKGROUND

Recent studies have suggested that agricultural occupations or exposure to pesticides may impair female fertility.

METHODS

The Fertility Risk Factor Study retrospectively examined agricultural and residential exposures and the risk of female infertility. Cases and controls (N = 322 each) came from women who sought treatment at a large group medical clinic in Wisconsin. Women and their male partners provided information on health, occupational and lifestyle exposures in response to a telephone interview during 1997-2001.

RESULTS

Mixing and applying herbicides 2 years before attempting conception was more common among infertile women (odds ratio [OR] = 27; 95% confidence interval [CI] = 1.9-380), as was the use of fungicides (OR = 3.3; CI = 0.8-13). Residing on a farm, ranch or in a rural area during this time period was protective of female fertility. Households supplied with central Wisconsin groundwater were at less risk for infertility than households using municipal sources (OR = 0.6; CI = 0.4-0.9). Behavioral risk factors included alcohol consumption (OR = 1.8; 1.2-2.5), smoking (1.6; 0.9-2.9), passive smoke exposure (1.8; 1.2-2.5), steady weight gain in adult life (3.5; 2.0-6.1), and having a male partner over the age of 40 (4.5; 1.2-16.3). Drinking 3 or more glasses of milk per day was protective of female fertility (0.3; 0.1-0.7).

CONCLUSION

These results suggest that certain agricultural, residential and lifestyle choices may modify the risk of female infertility.

Future directions in endometriosis research

Future research in endometriosis must focus on pathogenesis studies in the baboon model, the early interactions between endometrial and peritoneal cells in the pelvic cavity at the time of menstruation, and potential differences between eutopic endometrium and myometrium in women with and without endometriosis. More integration is needed between the areas of epidemiology and genetics. Pelvic inflammation in women with endometriosis could be the target for new diagnostic and therapeutic approaches. Important questions remain regarding the relationship between endometriosis and environmental factors. Systemic and extrapelvic manifestations of endometriosis must be analyzed carefully, and better tools are needed to measure quality of life in women with chronic pain caused by endometriosis. Most current evidence supports a causal relationship between endometriosis and subfertility, and the spontaneous progressive nature of endometriosis has been demonstrated in 30% to 60% of patients. Recurrence of endometriosis after classic medical and surgical therapy is a major and underestimated problem, especially in women with advanced disease. Integrated clinical and research teams are needed that combine expert medical, surgical, and holistic care with state-of-the-art research expertise in immunology, endocrinology, and genetics to discover new diagnostic methods and medical treatments for endometriosis.

On the rumors about the silent spring. Review of the scientific evidence linking occupational and environmental pesticide exposure to endocrine disruption health effects

Occupational exposure to some pesticides, and particularly DBCP and chlordecone, may adversely affect male fertility. However, apart from the therapeutic use of diethylstilbestrol, the threat to human reproduction posed by "endocrine disrupting" environmental contaminants has not been supported by epidemiological evidence thus far. As it concerns other endocrine effects described in experimental animals, only thyroid inhibition following occupational exposure to amitrole and mancozeb has been confirmed in humans. Cancer of the breast, endometrium, ovary, prostate, testis, and thyroid are hormone-dependent, which fostered research on the potential risk associated with occupational and environmental exposure to the so-called endocrine-disrupting pesticides. The most recent studies have ruled out the hypothesis of DDT derivatives as responsible for excess risks of cancer of the reproductive organs. Still, we cannot exclude a role for high level exposure to o,p'-DDE, particularly in post-menopausal ER+ breast cancer. On the other hand, other organochlorine pesticides and triazine herbicides require further investigation for a possible etiologic role in some hormone-dependent cancers.

Environmental factors in infertility

In conclusion, several studies indicate that there is an association between cigarette smoking and adverse reproductive outcomes in women as well as men. Some studies indicate that alcohol consumption impairs the reproductive capacity of women. Exposures to PCE in the dry cleaning industry, toluene in the printing business, ethylene oxide and mixed solvents have been associated with decreased fecundity. Abnormalities in sperm production have been found in men exposed to radiant heat or heavy metals. Environmental exposure to chlorinated hydrocarbons (e.g., DDT, PCB, pentachlorophenol, hexachlorocyclohexane) has been associated with an increase in rates of miscarriage and endometriosis. Clinicians should counsel patients who are trying to achieve a successful pregnancy to stop smoking and limit alcohol intake. Clinicians can additionally counsel patients who are in contact with potentially harmful occupational and environmental toxicants to limit their exposure. It is important to recognize, however, that many of the studies to date are limited by small sample size, poor exposure assessment, poor outcome measurements, recruitment bias, or recall bias. Additional studies will be necessary to clarify the magnitude of risk associated with these factors.

Delayed conception and active and passive smoking. The Avon Longitudinal Study of Pregnancy and Childhood Study Team

OBJECTIVE

To determine whether passive as well as active smoking by women or smoking by men is associated with delayed conception, after adjustment for confounding factors.

DESIGN

Population study of couples expecting a baby. Logistic regression was performed to identify factors associated with delayed conception.

SETTING

The Avon Health Authority area, United Kingdom.

PATIENT(S)

All couples expected to deliver between April 1991 and December 1992.

INTERVENTION(S)

Questionnaires administered early in pregnancy.

MAIN OUTCOME MEASURE(S)

Time taken to conceive, categorized as <6 months, 6-11 months, 1-3 years, and >3 years.

RESULT(S)

After correction for confounding factors, delayed conception was statistically significantly associated with both active smoking by the woman (odds ratio [OR] 1.23 [95% CI 0.98-1.49] for > 6 months and 1.54 [95% CI 1.19-2.01] for >12 months) and her exposure to passive smoking (OR 1.17 [95% CI 1.02-1.37] and 1.14 [95% CI 0.92-1.42]) compared with women with no exposure to tobacco smoke (referent). Heavy smoking by men was independently associated with delayed conception. In active smokers, the effect increased with the number of cigarettes.

CONCLUSION(S)

Smoking by men and passive and active smoking by women are associated with delayed conception.

Reproductive endocrine effects of acute exposure to toluene in men and women

OBJECTIVES

Despite observation of adverse reproductive effects of toluene, including alterations of serum gonadotropins (luteinising hormone (LH) and follicle stimulating hormone (FSH)) in humans, little is known of the mechanism of toxicity. The hypothesis was tested that toluene acutely suppresses pulsatile gonadotropin secretion by measuring LH and FSH at frequent intervals during controlled exposure to toluene.

METHODS

Women in the follicular and luteal phases of the menstrual cycle and men were randomised to inhale filtered air with or without 50 ppm toluene through a mouthpiece for 3 hours (19% of the OSHA permissible exposure limit). Blood was sampled by intravenous catheter at 20 minute intervals for 3 hours before, 3 hours during, and 3 hours after exposure. Plasma LH, FSH, and testosterone were measured. Pulse amplitude, pulse frequency, and mean concentrations of LH and FSH for each of the 3 hour periods before, during and after exposure to toluene versus sham exposure were calculated with the ULTRA pulse detection program and compared by analysis of variance (ANOVA) with repeated measures.

RESULTS

In men mean concentrations of LH showed a significant interaction (p < 0.05) between exposure and sampling period, with a greater LH decline during exposure to toluene than sham exposure. However, there was no concomitant effect on testosterone concentrations. The LH pulse frequency of women in the luteal phase showed a trend towards a significant interaction between exposure and sampling period (p = 0.06), with a greater decline in pulse frequency during exposure to toluene than sham exposure. There were no other significant effects of exposure to toluene.

CONCLUSIONS

Three hour exposure to 50 ppm toluene did not result in abnormal episodic LH or FSH secretion profiles, however, subtle effects on LH secretion in men and women in the luteal phase were found. The clinical relevance of these effects is unclear, indicating the need for further study of reproductive function in exposed workers.

Women's reproductive health: some recent developments in occupational epidemiology

Epidemiological research on occupational hazards and reproductive health is an expanding and strongly developing area. This article focuses on some recent areas of occupational reproductive epidemiology that are or seem to be important for the future. Interest in the research on fertility has increased during the past decade, and time to pregnancy has proved to be a useful measure of fertility. The research on menstrual function or early fetal loss is still limited, and further research is desirable. It is important to chart the advantages and disadvantages of various methods for measuring these outcomes. Recently developed methods of exposure assessment provide new possibilities to improve the validity of exposure data. Biological exposure markers can also provide useful dosimeters for reproductive studies. Research on the reproductive effects of job stress and individual susceptibility to reproductive toxicants is also gaining in importance.

Reduced fertility among female wood workers exposed to formaldehyde

BACKGROUND

The aim of the study was to investigate whether exposure to formaldehyde, organic solvents or other chemicals in the wood-processing industry affects the fertility of women.

METHODS

For this purpose, a retrospective study on time to pregnancy was conducted among female wood workers who had given birth during 1985-1995. Data on pregnancy history, time to pregnancy, occupational exposures, and potential confounders were collected by a questionnaire; 64% (699/1,094) participated. The exposure assessment was conducted by an occupational hygienist. The data on time to pregnancy were analyzed with the discrete proportional hazards regression.

RESULTS

Exposure to formaldehyde was significantly associated with delayed conception: adjusted fecundability density ratio, FDR, was 0.64 (95% CI 0.43-0.92). At high exposure if no gloves were used, the FDR was 0.51 (% CI 0.28-0.92). Exposure to phenols, dusts, wood dusts, or organic solvents was not related to the time to pregnancy. Additionally, an association was observed between exposure to formaldehyde and an increased risk of spontaneous abortion (concerning previous spontaneous abortions, reported by the women). Associations between exposure to formaldehyde or to organic solvents and endometriosis, and between exposure to organic solvents or to dusts and salpingo-oophoritis were also suggested.

CONCLUSIONS

The study suggests that a woman's occupational exposure to formaldehyde has an adverse effect on fertility.

Intrauterine effects of electromagnetic fields--(low frequency, mid-frequency RF, and microwave): review of epidemiologic studies

Electromagnetic radiations are named according to frequency or to wavelength (which is inversely proportional to frequency) and create electromagnetic fields (EMFs). Frequencies widely vary according to sources: high-voltage power lines, electrically heated beds, MRI, VDTs, microwave ovens, satellite, and radio/TV transmissions or cellular phone transmitters/receivers. Public concern has increased about the potential health effects of EMFs. There are arguments in favour of EMFs being biologically active, but no mechanism has been identified that explains the link between EMFs and bioeffects. Human data reviewed concern the potential reproductive effects (mainly spontaneous abortions, low birthweight and congenital malformations) of exposure to sources of EMFs: maternal residence, electrically heated beds, occupational exposure (mainly video display terminals), and medical exposures. The available epidemiologic studies all have limitations that prevent to draw clearcut conclusions on the effects of EMFs on human reproduction. EMFs are ubiquitous and unavoidable exposures. The matter of possible effects cannot be considered closed, but until our understanding of the biologic important parameters of EMFs exposures is stronger,design of new studies will be difficult and small epidemiologic studies are unlikely to provide definitive answers and should not be given high priority. No conclusion can be drawn for radiofrequencies and microwaves because of lack of data. There is no convincing evidence today that EMFs of the sort pregnant women or potential fathers meet in occupational or daily life exposures does any harm to the human reproductive process.

Chemicals and menopause: effects on age at menopause and on health status in the postmenopausal period

Menopause, a natural stage in women's lives, signals the cessation of fertility and causes changes in health status for many women. Chemical exposures may induce early or premature menopause and increase the risks of morbidity and mortality in the postmenopausal period. Chemicals that are toxic to follicles can lower the age of menopause by depleting the ovary of oocytes. Women may be exposed to these chemicals in the workplace, at home, and through exposure to contaminated drinking water near hazardous waste sites, as well as by direct or indirect exposure to cigarette smoke.

Environmental toxicants and female reproduction

OBJECTIVE

To review current knowledge on the potential effects of environmental toxicants on female reproduction in laboratory animals, wildlife, and humans.

DESIGN

Published literature about the effects of endocrine disruptors, heavy metals, solvents, pesticides, plastics, industrial chemicals, and cigarette smoke on female reproduction.

RESULT(S)

Published data indicate that chemical exposures may cause alterations in reproductive behavior and contribute to subfecundity, infertility, pregnancy loss, growth retardation, intrauterine fetal demise, birth defect, and ovarian failure in laboratory animals and wildlife. Data on the association of chemical exposures and adverse reproductive outcomes in humans are equivocal and often controversial. Some studies indicate that chemical exposures are associated with infertility, spontaneous abortion, or reproductive cancer in women. In contrast, other studies indicate that there is no association between chemical exposures and adverse reproductive outcomes. The reasons for ambiguous findings in human studies are unknown but likely include the fact that many studies are limited by multiple confounders, inadequate methodology, inappropriate endpoints, and small sample size. The mechanism by which chemicals alter reproductive function in all species is complex and may involve hormonal and/or immune disruption, DNA adduct formation, altered cellular proliferation, or inappropriate cellular death.

CONCLUSION(S)

Studies are needed to clarify which toxicants affect human reproduction and by which mechanisms of action. Furthermore, methods should be developed to minimize exposure to known reproductive toxicants such as dioxins and cigarette smoke.

Pesticide exposures and fetal death: a review of the epidemiologic literature

Despite considerable concern regarding the effects on reproductive outcome of exposures to pesticides, convincing evidence for the developmental toxicity of occupational and environmental pesticide exposure in humans is lacking. In this comprehensive review of the English language epidemiologic literature, we summarize studies that have examined potential associations between fetal deaths (both spontaneous abortions and stillbirths) and specific pesticides, as well as maternal and paternal employment in occupations with potential for exposure. While many of the epidemiologic studies to date suffer from methodologic problems, the data are suggestive of increased risks of fetal deaths associated with pesticides in general and maternal employment in the agricultural industry. There is a clear need for epidemiologic research that focuses on specific pesticide products or chemical families, with improved exposure assessment. The potential role of solvents in developmental toxicity associated with pesticide use by both males and females should also be considered.