Pollution: How Environmental Factors Impact Female Fertility

Facilitated by better access to contraception, this postponement of the age of parenthood beyond 30 poses a real challenge, because female fertility declines drastically after 35. This situation also makes the medical management of infertility disorders more complex. Indeed, the later the diagnosis of infertility is made, the more the plan to become parents is jeopardized, because the treatments can be long.

It must be emphasized that the causes of infertility are not limited only to age; other gynecological problems may be involved. These include uterine abnormalities, polycystic ovary syndrome, anatomical problems, and endometriosis.

However, in France, according to the National Institute of Health and Medical Research (Inserm), 10% to 25% of cases of infertility are today of unexplained origin. Some of these cases could be due to exposure to environmental pollutants, which interfere with the hormonal system and disrupt reproductive mechanisms.

Environmental pollutants, the hidden face of infertility

We now know that infertility problems can result from a certain number of environmental factors, such as smoking, excessive alcohol consumption or obesity, to name only the best known.

For several years, various scientific studies have also accused endocrine disruptors, including certain pesticides, of being the cause of certain cases of unexplained infertility.

According to the WHO, an endocrine disruptor is: “A substance or mixture of substances that alters the functions of the endocrine system and thereby induces adverse effects in an intact organism, in its offspring or within a population”

To put it simply, endocrine disruptors are substances that have the ability to interfere with the hormonal system thereby disrupting the menstrual cycle.

Today, we are all exposed to a wide spectrum of endocrine disruptors, whether bisphenols (notably bisphenol A, but not only), pesticides such as chlorpyrifos, or substances such as polychlorinated biphenyls, phthalates and their metabolites, etc.

These compounds are present in many everyday products, for example plastic bottles, food containers, the linings of metal cans, detergents, microplastics, flame retardants, electronic devices and even cosmetic products…

Our lifestyle, our diet, the places we frequent, and even our profession influence our exposure to these substances, and some are more exposed than others: farmers, people working in hairdressing, aesthetics, florists, etc.

Naturally, living near polluted areas, such as a field cultivated using pesticides, for example, also increases the risk of contamination by endocrine disruptors.

A finely regulated hormonal mechanism

Exposure to endocrine disruptors can have particularly harmful effects in women, because they can disrupt the menstrual cycle.

This natural cycle, which prepares the body for a possible pregnancy, is controlled by a set of organs which communicate with each other thanks to hormones: the brain (the hypothalamus and the pituitary gland), the ovaries and the uterus. It is based on two processes that take place in parallel.

One takes place in the ovaries, which go through several stages during the menstrual cycle: development of follicles containing the oocytes, release of an egg ready to be fertilized (ovulation), then formation of a temporary structure called corpus luteum which will allow the continuity of the pregnancy.

The second process takes place in the uterus, which prepares to welcome a future baby by thickening its wall. If fertilization does not take place, this thickened mucous membrane is eliminated by natural means: these are the rules.

This system is orchestrated by several essential hormones, produced by the ovaries (estradiol and progesterone) as well as by the brain (GnRH, LH and FSH). It is this fine hormonal regulation that allows the menstrual cycle to take place each month.

A disorganization, even if only minimal, of this precise system, under the effect for example of endocrine disruptors, can result in so-called “unexplained” infertility.

Endocrine disruptors and female infertility

Substances such as bisphenol A, phthalates and certain pesticides have been linked to accelerated ovarian aging. By causing oxidative stress in the ovarian follicles, they damage the cells involved in the development of oocytes. Contact with these substances results in an early reduction in the quality and quantity of available eggs.

Endocrine disruptors are also suspected of playing a role in a more serious disorder called premature ovarian failure. This results in a definitive cessation of the functioning of the ovaries before the age of 40. This pathology leads to premature menopause, hormonal disorders and difficulty conceiving.

We know that premature ovarian failure can have genetic causes, but certain endocrine disruptors also seem to be involved. This is for example the case of dioxins as well as perfluoroalkyls and polyfluoroalkyls (also called PFAS).

But that's not all: endocrine disruptors also interfere with pregnancy itself. For pregnancy to occur, an egg must mature and be released during ovulation. However, endocrine disruptors disrupt this process in different ways.

Some of them block the maturation of eggs, preventing the normal development of ovarian follicles

Others cause hormonal imbalance, altering the production of hormones like estrogen and progesterone, which disrupts the menstrual cycle and reduces the chances of ovulation.

Impacts beyond design

Endocrine disruptors can also alter hormone receptors. This is for example the case of substances such as atrazine, a widely used pesticide, which reduce the response of the ovaries to the hormones essential for ovulation.

All of these mechanisms result in disturbances in ovulation which interfere with fertilization. The consequence, in some exposed women, is the occurrence of fertility problems, or even, in certain cases, total infertility.

Finally, endocrine disruptors can also prove problematic during the stages following fertilization. For a pregnancy to occur, fertilization alone is not enough: the egg thus formed must then succeed in implanting itself correctly in the uterus. To do this, the uterine lining (called the endometrium) must be receptive.

However, endocrine disruptors, in particular bisphenol A, also disrupt this step. The consequences can be repeated miscarriages, difficulties with embryo implantation or complications during pregnancy: placental dysfunction (preeclampsia), fetal growth retardation, etc.

Finally, endocrine disruptors also seem to play a role in the development of endometriosis. We can take the case of TCDD, a herbicide acting as an endocrine disruptor, which is associated with the severity of the disease.

What science knows…and what it still doesn't know

Today, we know that certain pollutants present in our environment, such as bisphenol A, phthalates, certain pesticides, dioxins or PFAS, can alter female fertility by disrupting ovarian reserve, ovulation, embryo implantation or by promoting pathologies such as endometriosis.

However, many gray areas remain: the exact proportion of infertility cases linked to these substances remains unknown, in particular because of the difficulty in measuring actual exposure and the “cocktail” effect, in other words the results of interactions between different molecules (we are in fact exposed simultaneously to many different substances).

Among the questions that remain unanswered, what is the exact role of these pollutants in cases of infertility? What are the combined effects of multiple exposures? Which periods of life are the most vulnerable?

Inform, prevent, act

Faced with the magnitude of the silent scourge that infertility represents, it is essential to combine research efforts with prevention and public information. We can thus hope to better understand the effects of endocrine disruptors on female fertility, and limit their impact.

Adopting a few simple actions, such as limiting the use of food plastics or opting for cosmetics free from known disruptors, can help reduce exposure. If possible, it is also better to advance your parenting project as much as possible in time.

It is also important that research and prevention actions are supported by institutions. These must ensure that the environmental dimension is fully integrated into strategies aimed at improving reproductive health. This can involve stricter regulations and better monitoring of the use of these substances, while preserving individual responsibility.

Acting today to protect female fertility, through informed choices and collective mobilization, will help preserve the reproductive health of future generations.