A new U.S. study suggests the hormonal environment of late pregnancy may influence when babies cut their first teeth — a finding researchers say could help explain why eruption timelines vary so widely in early childhood.
The prospective cohort study, published in Frontiers in Oral Health, followed 142 mother–child pairs from late pregnancy through the first two years of life. Dentists tracked tooth eruption at regular intervals from six to 24 months.
While most children follow a predictable sequence of primary tooth eruption, the researchers found notable differences. Only 15 per cent of infants had at least one erupted tooth by six months, and one-quarter had all 20 primary teeth by age two.
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Cortisol’s strongest association
Maternal stress-related hormones — including cortisol, estradiol, progesterone, testosterone and triiodothyronine (T3) — were all significantly linked to the number of erupted teeth at various visits. Cortisol showed the strongest association. Infants whose mothers had the highest cortisol levels in pregnancy had, on average, four more erupted teeth at six months compared to those at the lowest end of the scale.
The authors used documented prenatal depression and anxiety diagnoses as a proxy for stress. Although these diagnoses were common — affecting 36 per cent of participants — they were not directly associated with eruption timing. Hormone levels, however, showed strong internal correlations and consistent ties to tooth count.
Researchers say the findings point to late pregnancy as a sensitive window in dental development, with maternal hormones potentially influencing bone metabolism, nutrient pathways and tooth formation. They emphasize that early or delayed eruption can affect enamel quality, alignment and future caries risk.
The team calls for larger studies to confirm the hormonal pathways behind eruption timing and to explore whether prenatal stress reduction could benefit early oral development.
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