Researchers measured the levels of 31 common industrial chemicals in the blood of 60 women and found women with higher levels of chemicals in their blood sample also had fewer immature eggs left in their ovaries.
Birth rates are decreasing worldwide. In all European countries they’re even dropping below population replacement levels, which refers to the number of children needed per woman to keep a population stable.
While these decreases might be due to many adults intentionally postponing when they have their first child — or actively choosing not to have children — an increasing number of studies suggests these don’t fully explain decreasing birth rates. Some research also indicates that decreasing fertility is a major contributing factor in this decline.
One factor linked to decreased fertility is the presence of industrial chemicals found in our environment. Much is known about the impact of these chemicals on male fertility, but little research has looked into how they affect women. This is what our recent study sought to do.
We found that exposure to common chemical contaminants was associated with reduced egg counts in the ovaries of reproductive-aged women. Though these chemicals have since been banned, they were once used in household products like flame retardants and mosquito sprays, and are still present in the environment and in foods like fatty fish.
We measured the levels of 31 common industrial chemicals, such as HCB (an agricultural fungicide) and DDT (an insecticide), in the blood of 60 women. To gauge their fertility, we measured the number of immature eggs they had in their ovaries by counting them in ovarian tissue samples using a microscope. Because ovaries are located inside the body and would require surgery to access, we chose pregnant women who were having a caesarean section, as this made it possible to access tissue samples without additional surgery.
We found that women with higher levels of chemicals in their blood sample also had fewer immature eggs left in their ovaries. We found significant connections between reduced egg numbers and certain chemicals, including PCB (used in coolants), DDE (a by-product of DDT) and PBDE (a flame retardant). As female fertility is age-dependent, we made sure to adjust our calculations accordingly depending on the age of the woman in question. This showed us that exposure to these chemicals resulted in fewer eggs for women of all ages.
We also found that women with higher chemical levels in their blood had to try for longer to get pregnant. For the women with the highest levels of chemicals in their blood, it took more than a year.
Unlike men, women are only born with a fixed set of immature eggs in their ovaries, and cannot produce new ones after birth. A woman’s “reserve” (the number of eggs in her ovaries) naturally diminishes through monthly ovulations, as well as by normal follicle death. When depleted below a critical level, natural fertility ends and menopause begins. Our findings imply that toxic chemicals may speed up the disappearance of ovarian follicles, which could lead to reduced fertility and earlier menopause.