Key Takeaways From This Article:
- fertility levels are on a downward trend all across the globe
- researchers are noticing that infertility may be an inheritable trait
- a person’s lifetime fertility levels is created mostly during the fetal stages
- seasons, stress, and changing societal norms are contributing to potential intergenerational infertility
For a long time now, we have known that lifestyle and environment can affect the fertility of men and women. But did you know that those effects can also impact the fertility of their children? Researchers are now slowly beginning to find the evidence of what they are calling ‘intergenerational infertility’—infertility that is genetically passed down. Through lifestyle, environment, and physical biology, we might be creating the road to a massive population crisis on a global level.
The idea of genetically passing down infertility can seem far fetched. There are so many factors to infertility, how can it be passed down? And while it is true that infertility can stem from any number of reasons, researchers and scientists are beginning to see certain lifestyle and environmental trends that affect adults of reproductive age, which can in turn affect a fetus.
Men’s fertility is measured by the number of healthy sperm produced per day. And this number is determined by the number of Sertoli cells within the testes. And the numbers of Sertoli cells are determined largely by their rate of growth during fetal and neonatal (1-9 months post-natal) periods and again later to some extent during pre-pubertal life. But this fetal period sets the crucial groundwork for Sertoli cell count and therefore, the baby’s future sperm count. The growth of Sertoli cells is controlled by a variety of hormones, namely follicle-stimulating hormone (FSH), thyroid hormones, and growth hormones. Having testes correctly descended into the scrotum is also a hormone-dependent process which normally occurs by birth. Incomplete descent of one or both testes (cryptorchidism) is associated with lower sperm count and infertility in adulthood. It also increases the chances of testicular cancer. During the fetal period, the timing and amount of these crucial hormones are tied to the mother’s health and well-being. Any negative lifestyle or environmental changes towards the mother will affect the baby, thus potentially ensuring a likelier future of infertility issues.
Women’s fertility is measured by the monthly ovulation of a mature egg (oocyte). The human ovary acquires its full arsenal of germ cells (oocytes) during fetal life. Most of these cells will die by birth, dropping the number from approximately 7 million to 1-2 million. That might sound like more than enough eggs for one lifetime but only less than 500 oocytes will be ovulated in adulthood. The ‘primary oocytes’ in the fetal ovary are created and done by the first meiotic prophase of the fetus, possibly in the earliest stages of baby’s life. Then those oocytes remain in place until some 15-50 years later when triggered by a surge of luteinizing hormone (LH), which stimulates ovulation. This is what most of us experience as puberty. All of the eggs a woman will carry in her adult life for procreation are made in utero as a baby. Any negative lifestyle or environmental changes towards the expecting mother will most definitely affect the baby, altering her future of fertility.
So what are these possible negative lifestyle and environmental effects that can alter a person’s fertility so early on? Researchers are still studying the scope of causes and narrowing in on what may be more likely than others but many things from the seasons to lifestyle and diet to stress to even social and cultural norm changes can create this intergenerational infertility.
When we hear seasons may affect our fertility, it may sound a little ludicrous. But there has been scientific research to show that the seasons do indeed affect fertility. For example, in summer, sperm counts in men are consistently 30% lower during the summer than in winter. The higher temperatures in summer can impair sperm production and conception. Heat is a big factor especially for men’s fertility. A study of Indian iron workers showed that they had disproportionately lower sperm count than Indian men not working in such high temperature conditions. Sperm production requires the testes to be 3-4 degrees Celsius cooler than the core body temperature. This has led some researchers to extrapolate that increasingly warmer temperatures due to climate change can possibly have a negative impact on birth rates/fertility. Sedentary lifestyles (such as sitting in front of a computer or driving for long periods) are also guilty of increasing scrotal temperatures by 1.7-2.2 degrees Celsius.
Lifestyle and diet choices are the most commonly known factors for fertility issues. And reading about the fetal effects from negative lifestyle and diet choices, it can be easy to assume it is more incumbent on the woman to maintain a healthy lifestyle but men can also tip the fetal scales negatively with poor choices. Smoking is incredibly unhealthy and for women, smoking unequivocally impacts fertility in all aspects from ovulation, egg pick-up and transportation down the fallopian tubes, fertilization, to early embryo development. But smoking also impacts a man’s fertility as well. Smoking has been associated with lowered sperm count for a long time now but recently, there have been some research indicating that smoking induces DNA damage in sperm, which can lead to possible health problems (future fertility issues being one) for the fetus.
Diet and bodyweight play a huge role for reproductive women. Underweight women rarely ovulate and menstruate. Reproduction is a highly caloric mechanism. It requires a ton of energy from the body and when the body is so underweight, the body shuts down the ovarian function to protect itself.
Being overweight also has its own set of issues. Not only do overweight women also experience inconsistent menstruation but they also are more likely to miscarry. And recently, researchers are beginning to link weight and PCOS within fetal development. Polycystic ovary syndrome (PCOS) is when ovaries contain many small follicles. It is one of the most common causes of infertility and is associated with a failure of ovulation. A new hypothesis that is now being studied is that polycystic ovaries and associated hormone abnormalities are genetically programmed during ovarian development in the fetus if the mother herself is overweight, laying the groundwork for the fetus to be more likely to develop PCOS later in life, the consequences of which mean increased chances of infertility and greater risk of developing type 2 diabetes.
Stress seems too simple a cause to point a finger at for infertility. Who doesn’t have stress? But stress shouldn’t be shrugged off so lightly. Women who tested with higher levels of alpha amylase, an enzyme correlated with stress, had a harder time becoming pregnant. And stress can also affect a fetus’s future fertility as well. In a 1998 research study, nineteen girls adopted from developing countries were studied when after improved nutritional and psychological conditions, these girls experienced precocious (early) puberty. One definitive answer couldn’t be given for the cause and cases are still being studied today but one popular hypothesis is that the girls in utero were adapting to the stress of the mother and the environment, with their bodies learning to conserve energy. Only once they were adopted out into homes with improved nutrition and lower stress, the girl’s bodies were ‘kick started’ changing their metabolism and hormonal cycles earlier than expected. Stress is serious and can affect us from day one of conception.
And finally, social and cultural norms can affect fertility and contribute to intergenerational infertility. Recently, Japan announced a record low birth rate for 2019. The estimated number of babies born that year fell to 864,000—the lowest since records began in 1899. This figure is 54,000 less babies than 2018, another clear indicator of a dangerously downward trend. The biggest cause for this decreasing trend in births are the changing social and cultural norms of the country. In Japan, it is now becoming more commonplace for women to strive for higher levels of education. More women are prioritizing their careers over family planning and are experiencing less social criticism for that desire. And economically, it is expensive to raise children—much too expensive to raise a child on one income. So partners who cannot afford a child are forgoing them.
This kind of change in cultural attitudes can be found across the globe. Women are making great strides in the workforce and education. They are delaying or sometimes completely forgoing the desire for children. Men as well seem more likely to want to delay the start of a family. One income households are rare and if two incomes are necessary, costs for daycare or nursery schools can be exorbitant. Many partners are finding satisfaction in having smaller families and having children later in life, if at all.
But this can also have an affect on intergenerational infertility. Our social and cultural norms change and adapt faster than our biological processes do. While it is becoming more the norm for women to have children in their mid to late 30s, a woman’s eggs are still on the biological clock of generations past. As women age, the health and viability of their eggs deteriorate. Men as well decrease the health and quality of their sperm as they age. There are greater risks of birth abnormalities the older the expectant mother is. These abnormalities can manifest in many different ways, for example Down Syndrome being a commonly known one. But they can also manifest in subtler ways that won’t be known until the child is an adult, such as having lower Sertoli cell counts or less oocytes. And with a generation of the population born with higher chances of infertility in a world seemingly growing less interested or supportive of having children, a potential fertility crisis seems to be looming at the end of the road.
Intergenerational infertility is a culmination of a broad spectrum of issues that affect the global population. It can feel as we journey into our own personal experiences with fertility and family planning that perhaps we alone are experiencing problems or obstacles. But no one is alone. Fertility issues are quite common but in today’s climate, they are extremely common and for a number of reasons. But if family planning and pregnancy are your goals, you shouldn’t be discouraged. The more common and widespread fertility issues are being discussed, the more resources and knowledgeable professionals there are to help and assist you on your journey.