Pesticide exposure in male farmers and survival of in vitro fertilized pregnancies

Mapping the past, present and future research landscape of paternal effects

BACKGROUND

Although in all sexually reproducing organisms an individual has a mother and a father, non-genetic inheritance has been predominantly studied in mothers. Paternal effects have been far less frequently studied, until recently. In the last 5 years, research on environmentally induced paternal effects has grown rapidly in the number of publications and diversity of topics. Here, we provide an overview of this field using synthesis of evidence (systematic map) and influence (bibliometric analyses).

RESULTS

We find that motivations for studies into paternal effects are diverse. For example, from the ecological and evolutionary perspective, paternal effects are of interest as facilitators of response to environmental change and mediators of extended heredity. Medical researchers track how paternal pre-fertilization exposures to factors, such as diet or trauma, influence offspring health. Toxicologists look at the effects of toxins. We compare how these three research guilds design experiments in relation to objects of their studies: fathers, mothers and offspring. We highlight examples of research gaps, which, in turn, lead to future avenues of research.

CONCLUSIONS

The literature on paternal effects is large and disparate. Our study helps in fostering connections between areas of knowledge that develop in parallel, but which could benefit from the lateral transfer of concepts and methods.

Review: Toxicants in reproductive fluid and in vitro fertilization (IVF) outcome

Some of the physical, chemical, dietary, occupational and environmental factors are having adverse effect on human reproduction. Increasing trend in reproductive disorders in recent years at least in part might be associated with these factors. The data available suggests less success rate of in vitro fertilization (IVF) outcome of parents exposed to some of the reproductive toxic chemicals as compared to parents who were not exposed to such chemicals. However, data are very meager and require more studies as some debatable data also exists. But existing positive findings encourage in advising that sub-fertile subjects, who are planning to go for the IVF, should reduce toxic exposure well in advance by adopting positive life style and work environment. Further, clinician ought to be aware of occupational and environmental exposure history of the participating couple.

The influence of the environment and other exogenous agents on spontaneous abortion risk

It is estimated that close to 30% of all pregnancies end in spontaneous abortion. Although about 60% of spontaneous abortions are thought to be due to genetic, infectious, hormonal, and immunological factors, the role of the environment remains poorly understood. Pregnancy involves a delicate balance of hormonal and immunological functions, which may be affected by environmental substances. Many toxic substances that are persistent in the environment and accumulate in the fatty tissues may disrupt this equilibrium. This overview addresses known risk factors for spontaneous abortions and examines the role, if any, that environmental factors (chemical and physical) may play in the etiology of this adverse health outcome.

Pesticide exposures and developmental outcomes: the epidemiological evidence

Since the advent of DDT as an insecticide in the late 1930s, billions of kilograms of pesticide active ingredient have been sold in North America and around the world. In recent years, there has been a heightened public awareness of pesticides and child health and a number of epidemiologic studies linked pre- and postnatal exposures to pesticides to a number of adverse developmental outcomes, including fetal death, intrauterine growth restriction, preterm birth, and birth defects. Given this, it was felt prudent to critically appraise the evidence for periconceptual pesticide exposures and developmental outcomes. The epidemiological evidence for specific pesticide classes, families, and active ingredients were examined and summarized and recommendations were made for how to improve future studies in order to address the current pitfalls and gaps in the studies in this area. Many of the studies suffered from poor exposure estimation, relying on job title only and/or the exposure category "any pesticide" as a measure of exposure, and there was limited or inadequate evidence to support causality for all associations examined.

Spontaneous abortion in IVF couples—a role of male welding exposure

BACKGROUND

Fume from welding of stainless steel contains hexavalent chromium, which in animal studies can induce paternally mediated spontaneous abortion. Human studies have shown conflicting results. The best studies include early pregnancy experience, but these are expensive to conduct. In vitro fertilization (IVF) provides new design opportunities. Our aim was to study pregnancy survival in IVF treated women with respect to paternal welding exposure.

METHODS

We mailed a questionnaire to 5879 couples from the Danish IVF register that covers all IVF treatments after 1993 (response ratio 68.2%). A subgroup of male metal workers received a second questionnaire on exposure to welding (n = 319 men, response ratio 77%). Information on outcome was collected from national health registers. Survival of the first hCG-positive pregnancy was analysed using Cox regression.

RESULTS

The proportion of pregnancies terminated by spontaneous abortion before 28 gestational weeks was 18% (n = 91 pregnancies) and 25% (n = 128) in pregnancies with paternal exposure to stainless steel welding and mild steel welding, respectively. In the reference group of 2925 pregnancies the abortion ratio was 28%. The risk ratio for pregnancies with paternal exposure to stainless steel was 0.6 (95% CI 0.4-1.0).

CONCLUSIONS

We found no increased risk of spontaneous abortion in IVF treated women, who became pregnant by a man exposed to welding of any sort. Since the process of fertilization and selection of IVF pregnancies differs from natural pregnancies the negative results need not apply to other pregnancies.

Environmental and occupational factors affecting fertility and IVF success

Reproductive function has been shown to be sensitive to changes in the physical, psychosocial and chemical environments. Although reproductive effects of occupational exposure to hazardous chemicals have been well documented in the literature, the potential effects of chemical contaminants at levels representative of contemporary exposures in the general population are much less certain. Evidence for adverse effects of exposure to environmental contaminants is more conclusive among the lower animals than for humans where considerable controversy remains. In addition to potential reproductive hazards of exposure to environmental contaminants, there is also evidence for adverse reproductive effects of the physical and psychosocial environments. In this review we focus on the difficulties involved in linking exposure to putative hazardous substances in environmental and occupational settings to adverse reproductive outcomes, especially success of IVF procedures. We highlight the plausibility of adverse events through animal and cell studies and the application of these results to the interpretation of human data. We consider both the male and female partners since it is essentially their combined contributions of gametes which may be affected by chemicals, which lead to successful outcomes.