Glyphosate and AMPA Linked to Pregnancy Hormone Changes

Spray it on, wait for it to dry, and many homeowners assume the task is finished. The prevailing belief is that weed killer remains outdoors rather than entering the body of a pregnant person living in the home.

A research team examined that belief in 752 pregnant women, measuring a widely used herbicide in urine samples taken at several stages of pregnancy.

They also assessed the hormones needed to sustain pregnancy. Their findings revealed something that had not previously been recorded in humans.

Glyphosate is widespread

Glyphosate is the world’s most extensively used herbicide. It is applied to agricultural land and domestic gardens, and can ultimately enter food and water supplies.

Researchers increasingly regard it as a potential endocrine disruptor: a substance capable of interfering with the body’s hormonal systems.

After entering the environment, glyphosate degrades into a more persistent chemical known as AMPA, which can remain in soil and water for longer.

Repeated studies throughout North America have detected both substances in human urine. That broad exposure prompted the team to undertake this new research.

John Meeker, professor of environmental health sciences at the University of Michigan School of Public Health (U-M), led the study.

“This is the most extensively used herbicide in the world, yet there are shockingly few research studies on the potential impacts it may have on human reproductive health, pregnancy, or fetal and child development,” said Meeker.

Most existing evidence has come from laboratory animal studies rather than research involving people.

How the researchers measured exposure

Meeker’s team used data from an ongoing pregnancy study in Puerto Rico, which has monitored maternal health and environmental exposures for many years.

The researchers analysed 752 pregnant women who lived in the northern part of the island.

The participants provided urine samples on as many as three occasions during pregnancy, at approximately 18, 22 and 26 weeks.

At two of those appointments, the team also collected blood samples to assess hormones involved in maintaining a healthy pregnancy.

Most samples contained either one chemical or the other. The women were not employed in agricultural fields.

Instead, the exposure appeared to be part of everyday life, with measured concentrations somewhat above those usually reported in the wider US population.

Glyphosate and lower estriol

The strongest association concerned estriol, an oestrogen hormone that rises consistently throughout pregnancy and helps maintain blood flow to the placenta while the fetus develops.

Women whose urine contained higher levels of glyphosate and AMPA generally had lower amounts of estriol in their blood.

For every increase in exposure, estriol levels were approximately 8 to 11 percent lower. This trend remained evident at different stages of pregnancy and across several analyses.

Before this research, glyphosate had not been assessed in relation to this hormone in pregnant women.

The study could not determine why estriol levels declined. Laboratory findings suggest glyphosate might inhibit an enzyme involved in producing oestrogen, which would be consistent with the observed measurements.

However, the researchers measured the hormonal change rather than its biological mechanism, leaving the cause unresolved.

Changes in thyroid and stress hormones

Estriol was not the only hormone affected. AMPA was associated with increased thyroid hormone levels and, later in pregnancy, with a stronger brain-to-thyroid signalling response.

These hormones normally increase during pregnancy to support fetal growth, meaning disruption could have wider effects.

Late in pregnancy, glyphosate was linked with higher levels of CRH, a hormone associated with stress.

CRH contributes to setting the timing of labour, while a separate study has associated the chemical with preterm birth.

The findings could not establish whether these changes began in the thyroid gland itself or in the signals sent to it by the brain.

Fetal sex could shape the response

A notable pattern emerged when the researchers separated results according to fetal sex.

The association between exposure and lower estriol was more pronounced and more distinct among women carrying girls than among those carrying boys.

Thyroid-related effects pointed in the opposite direction, appearing more often in pregnancies involving a boy.

Neither finding met the threshold for statistical significance, so both should be considered trends rather than definitive conclusions.

Nevertheless, their direction matches a broader pattern in which developing boys and girls do not necessarily react to the same chemical in identical ways.

The result provides another reason to account for fetal sex in endocrine research.

What the findings could mean

The study provides a possible biological link. Previous research associated glyphosate with reduced fetal growth and, in another paper, with differences in early childhood development.

Until now, the route by which the chemical might contribute to these outcomes had been unclear. Hormonal disruption is now one possible explanation.

For clinicians and regulators, the discussion can shift from a general concern towards defined and measurable changes.

This raises a specific question: whether reduced estriol or altered stress hormones contribute to the birth outcomes identified in earlier research.

The study cannot show that glyphosate caused these changes, and urine samples reflect only recent exposure.

Even so, it offers the first evidence in humans connecting these chemicals with several hormone systems simultaneously.

The researchers intend to continue following the mothers and their children.