Reproductive Health and Environmental Toxins: Fertility, Miscarriage, and Birth Defects

In 2017, endocrinologist Shanna Swan published the finding that sperm counts among men in Western countries had declined by more than 50% between 1973 and 2011 — a drop of approximately 1.4% per year, every year, for nearly four decades. The study, a meta-analysis of 185 studies covering nearly 43,000 men, was methodologically careful and peer-reviewed. Its implications were, as Swan later wrote in her book, "nothing less than a threat to human survival."

The proposed explanation centres substantially on endocrine-disrupting chemicals — particularly phthalates and BPA, which are anti-androgenic and oestrogenic respectively — that are nearly universal in the environments of men in high-income countries, and at lower but rising concentrations in lower-income countries as they industrialise. The same chemicals that disrupt thyroid function and metabolic regulation also disrupt the hormonal environment that governs sperm production, oocyte development, placental function, and the extraordinarily precise hormonal choreography of pregnancy.

Reproductive health is where the environmental chemical burden comes closest to being a civilisational question. The effects are not at the margins of biology — they are at its centre.

The male reproductive system is exquisitely sensitive to anti-androgenic chemicals — compounds that block testosterone signalling or reduce testosterone synthesis — during critical developmental windows and throughout reproductive life.

Phthalates and testicular dysgenesis The "testicular dysgenesis syndrome" hypothesis proposes that a range of male reproductive disorders — cryptorchidism (undescended testes), hypospadias, reduced sperm counts, and testicular cancer — share a common aetiology in disrupted androgen signalling during foetal development. Phthalates are the primary chemical candidates.

Swan's work established that maternal urinary phthalate concentrations during pregnancy predict anogenital distance (AGD) in male infants — a marker of androgen exposure in the womb. Shorter AGD in males is associated with reduced sperm count, lower testosterone, and higher rates of reproductive disorders in adult life. This is not a subtle statistical association; it's a measurable anatomical outcome of prenatal chemical exposure.

BPA and male fertility BPA is oestrogenic — it activates oestrogen receptors. In the male reproductive system, excess oestrogen signalling impairs Sertoli cell function (the cells that support sperm development) and suppresses testosterone production. Cross-sectional studies in men attending fertility clinics consistently find associations between urinary BPA concentrations and reduced sperm quality — lower counts, poorer motility, more abnormal morphology.

Female fertility and EDC exposure For women, phthalate and BPA exposure has been associated with polycystic ovary syndrome (PCOS), reduced ovarian reserve, and altered oestrogen metabolism. The evidence for female fertility effects is less studied than male effects but points in a consistent direction across multiple chemical categories.

Air pollution has emerged as a significant risk factor for adverse pregnancy outcomes — a finding with implications for every pregnant woman living in an urban environment, which is most pregnant women.

The miscarriage and preterm birth evidence A 2019 systematic review published in Environmental Health Perspectives found that PM2.5 and NO₂ exposure during early pregnancy was associated with increased risk of miscarriage, with effects most pronounced during the first trimester. Proposed mechanisms include oxidative stress impairing placental development and inflammatory pathways disrupting immune tolerance of the pregnancy.

Preterm birth — birth before 37 weeks — has been associated with air pollution in multiple large cohort studies. The PEACH cohort study of over 1,000 women in Atlanta found significant associations between third-trimester NO₂ exposure and preterm delivery. Preterm birth is the leading cause of infant mortality and morbidity in the US; even modest population-level risk factors become important given its frequency.

Birth weight and pollution Reduced birth weight — a predictor of infant health and long-term developmental outcomes — is one of the most consistent findings in air pollution and pregnancy research. The ESCAPE study found that each 5 µg/m³ increment in PM2.5 exposure during pregnancy was associated with a 13 gram reduction in birth weight. The effect is small per unit, but the exposure is near-universal.

Traffic proximity and birth outcomes Living within 200 metres of a major road during pregnancy has been associated with preterm birth, low birth weight, and neural tube defects in multiple studies. The combination of traffic-related NO₂, ultrafine particles, and PAHs at near-road concentrations produces a multi-pollutant exposure that affects multiple aspects of foetal development.

For people trying to conceive or in the early stages of pregnancy, the evidence from reproductive environmental health points to specific, actionable exposure reductions.

The pre-conception window: 3–6 months before pregnancy Sperm takes approximately 70–90 days to develop from stem cell to ejaculated sperm. Egg quality is determined over a similar time period before ovulation. Reducing chemical exposures during the pre-conception window — when germ cells are developing that will form the embryo — may improve fertility outcomes and reduce developmental chemical load.

Priority reductions for people trying to conceive: • Eliminate or greatly reduce fragranced personal care products and laundry products (phthalate exposure) • Switch plastic food storage and beverage containers to glass and stainless (BPA/BPS exposure) • Choose fragrance-free, paraben-free personal care products • Reduce processed food consumption, which is the primary phthalate dietary exposure route • Use PollutionProfile's Home Toxin Audit to identify the highest EDC exposure items in your home

During pregnancy specifically: • Air quality monitoring becomes a clinical tool — PollutionProfile's Air Quality feature should be checked daily, and outdoor physical activity adjusted accordingly • Avoid high-mercury fish (swordfish, king mackerel, bigeye tuna, tilefish); continue low-mercury fish consumption for omega-3 benefit • Never microwave in plastic • Delay major home renovations involving paints, adhesives, or flooring — the off-gassing window is not the time to be sleeping in a freshly painted bedroom

For couples undergoing IVF: Multiple studies have found associations between urinary phthalate and BPA concentrations in women undergoing IVF and reduced fertilisation rates, reduced blastocyst development, and lower clinical pregnancy rates. The evidence base is sufficient to warrant EDC reduction as a complementary strategy alongside standard IVF protocol.