Delayed motherhood poses thyroid cancer risk

Women who gave birth to their first child at an older age face an increased risk of thyroid cancer development, according to an analysis of Asian cohort studies.

Researchers pooled individual data from nine prospective cohorts in the Asia Cohort Consortium. They estimated the risk of thyroid cancer in relation to 10 female reproductive and hormonal factors. Cox proportional hazards and random-effects models were used, with analyses stratified by country, birth years, smoking status, and body mass index.

The analysis included a total of 259,649 women. Over a mean follow-up of 17.2 years, 1,353 incident thyroid cancer cases were recorded, of which 1,140 (88 percent) were papillary thyroid cancer. The risk of thyroid cancer was elevated among women who had their first delivery at older age (≥26 vs 21–25 years: hazard ratio [HR], 1.16, 95 percent confidence interval [CI], 1.03–1.31; p=0.003). This association was pronounced for thyroid cancers diagnosed later in life (≥55 vs <55 years: HR, 1.19, 95 percent CI, 1.02–1.39; p=0.003).

In younger birth cohorts, a greater number of deliveries was associated with an increased thyroid cancer risk (≥5 vs 1–2 children: HR, 2.40, 95 percent CI, 1.12–5.18; p=0.0001). This association was not observed in older birth cohorts.

The association between childbirth and thyroid cancer risk differed across countries, with a significant positive association for Korea (≥5 vs 1–2 children: HR, 1.89, 95 percent CI, 1.21–2.94; p=0.0008) and nonsignificant inverse associations for China and Japan.

The researchers believed that contextual and macrosocial changes in reproductive factors in Asian countries might have influenced the risk of thyroid cancer. Understanding these trends is crucial for public health strategies addressing reproductive factors influencing thyroid cancer risk as women delay motherhood, they added.