Fetal exposure to paracetamol is associated with altered markers of ovarian development and reduced uterine volume in girls: the COPANA study

The COPANA study suggests that prenatal exposure to paracetamol, particularly during early fetal life, is associated with reduced ovarian and uterine volumes and altered markers of ovarian development in female offspring.

The Gist

How Prenatal Paracetamol Exposure Relates to Ovarian Development in Girls

Paracetamol is one of the most common medicines used to treat pain and fever. Because it is available without a prescription, many women use it during pregnancy. However, the researchers behind the COPANA study wanted to investigate whether this widespread use might affect how a female fetus develops.

The study focused on the development of the ovaries and the uterus. In girls, the foundation for future reproductive health is laid before birth. During pregnancy, the female fetus develops a pool of primordial follicles, which are the tiny structures in the ovaries that eventually hold the eggs. The number of these follicles a girl is born with is a critical factor for her reproductive life.

To investigate this, the researchers followed two groups of people. The first group, the COPANA cohort, included 302 infant girls. The researchers measured the size of their ovaries and uteri using ultrasound and checked their blood for specific hormones that indicate how active the ovaries are. To track exposure, the researchers used both maternal reports of medicine use and laboratory tests of urine samples to measure actual paracetamol levels. The second group was an independent cohort of girls followed from infancy through adolescence.

The results from the COPANA cohort suggested that the timing of exposure matters. When mothers used paracetamol during the early stages of pregnancy (before 17 weeks), the infant girls had smaller ovarian volumes and smaller uterine volumes. The researchers also found that girls exposed only during this early period had lower levels of a hormone called anti-Müllerian hormone, which is a marker of the ovarian reserve. When exposure occurred later in pregnancy (from 17 weeks onwards), the researchers observed a reduction in the number of follicles in the ovaries.

The researchers also noted a dose-response trend. As the total amount of paracetamol used by the mother increased, or as the concentration of paracetamol in the urine increased, the volumes of the ovaries and the uterus tended to decrease.

The independent second cohort provided further evidence. In this group, girls who had been exposed to paracetamol or other similar pain relievers during pregnancy showed reduced uterine volume by the time they reached puberty. By adolescence, these girls also showed smaller ovarian volumes.

The researchers suggest several biological reasons why this might happen. They note that paracetamol may interfere with the rapid cell division that occurs in the early fetal ovary, or it may affect the chemical signals that tell these cells to survive and develop.

While these findings are consistent with previous studies in animals, the researchers emphasize that this is an observational study in humans. They note that they cannot completely rule out other factors that might influence the results, such as the reason the mother took the medicine (for example, if she had a fever). They also point out that the study population was mostly of Caucasian origin.

The researchers conclude that even relatively low levels of prenatal paracetamol exposure are associated with changes in ovarian morphology and activity in infant girls. Because these associations were also seen in the second cohort during puberty and adolescence, the authors suggest that these changes might persist as a girl grows.

Technical Summary

Technical Summary: Fetal Exposure to Paracetamol and Female Reproductive Development

Problem Statement

While maternal use of paracetamol (acetaminophen) is widespread due to its over-the-counter availability, animal models have consistently demonstrated that fetal exposure can impair the formation of primordial ovarian follicles, leading to subfertility and premature reproductive aging. However, robust human evidence linking prenatal paracetamol exposure to specific markers of ovarian and uterine development has remained limited. This study seeks to determine if fetal exposure to paracetamol is associated with altered ovarian morphology, follicle counts, and reproductive hormone levels in female offspring during infancy and subsequent developmental stages.

Methodology

The research utilized a dual-cohort approach to ensure robustness:

1. The COPANA Study (Primary Cohort): A prospective, single-center observational cohort study conducted at Rigshospitalet, Denmark (2020–2022).

   • Participants: 685 healthy, singleton pregnant women; 302 infant girls were examined during "minipuberty" (approx. 3 months post-partum).
   • Exposure Assessment: A combination of biweekly maternal self-reports and objective first-trimester urinary paracetamol concentrations (analyzed via LC-MS/MS). Exposure was categorized into two critical windows: Early fetal life (<17 weeks GA) and Mid-late fetal life (≥17 weeks GA).
   • Outcomes: Transabdominal ultrasound was used to measure ovarian volume, uterine volume, and antral follicle counts (>2mm). Serum levels of Anti-Müllerian hormone (AMH), FSH, LH, and inhibin B were measured. Breast tissue diameter was also assessed.

2. The Copenhagen Mother-Child Cohort (Confirmatory Cohort): A longitudinal, population-based cohort followed from birth through adolescence.

   • Participants: 1,210 girls.
   • Assessment: Follow-up examinations at infancy, puberty, and adolescence (age ~16) using MRI and ultrasound to track long-term morphological changes.

Statistical Approach: The researchers employed linear regression models with robust variance estimators to account for potential heteroskedasticity. Models were adjusted for various covariates, including maternal BMI, nicotine/alcohol use, IVF conception, and maternal health (diabetes/thyroid disease).

Key Contributions

• First Human-Specific Design: This is the first prospective human cohort study specifically designed to evaluate the link between prenatal paracetamol exposure and postnatal ovarian function.
• Multi-Modal Exposure Validation: By combining subjective self-reporting with objective urinary biomarkers, the study provides a high-fidelity assessment of exposure.
• Longitudinal Validation: The use of an independent confirmatory cohort allows the study to suggest that early-life alterations may persist into puberty and adolescence.

Results

The study found significant associations between paracetamol exposure and altered reproductive markers:

• Early Fetal Exposure (<17 weeks): Associated with significantly reduced ovarian volume (approx. 41% reduction) and reduced uterine volume. Girls exposed exclusively in this window also showed lower AMH levels, suggesting a diminished ovarian reserve.
• Mid-Late Fetal Exposure (≥17 weeks): Associated with a significantly reduced number of ovarian follicles (approx. 51% reduction).
• Dose-Response Relationship: Both total maternal dose and urinary paracetamol concentrations were inversely associated with ovarian volume, uterine volume, and breast tissue diameter.
• Long-term Findings (Confirmatory Cohort): In the independent cohort, prenatal exposure (including NSAIDs) was associated with reduced uterine volume at puberty and smaller ovarian volume during adolescence.

Significance and Implications

The findings provide strong human evidence that aligns with existing animal data, suggesting that paracetamol may interfere with the critical windows of oogenesis and folliculogenesis.

Clinical Implications:

• Reproductive Health: The observed reductions in follicle counts and ovarian/uterine volumes suggest potential long-term implications for female fertility and reproductive lifespan.
• Public Health Guidance: While paracetamol is necessary for managing maternal fever, the study suggests that current guidelines (recommending minimal dose/duration) may need closer scrutiny, as even "mild to moderate" doses were associated with these changes.
• Precautionary Approach: The authors advocate for enhanced education for pregnant women and the consideration of non-pharmacological alternatives to minimize unnecessary exposure.