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Peer-reviewedCC BY 4.0Journal of Research in Health Sciences

A Systematic Review and Dose-Response Meta-Analysis of the Association Between the Age of First Pregnancy and Breast Cancer Risk

  • Jalal Poorolajal1,2,3
  • Fatemeh Shahbazi1
  • Nazanin Azmi-Naei4
  • Amin Doosti-Irani1,2,3
  • Bita Azmi-Naei1
4 affiliations
  1. 1Department of Epidemiology, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran
  2. 2Modeling of Noncommunicable Diseases Research Center, Institute of Health Sciences and Technologies, Hamadan University of Medical Sciences, Hamadan, Iran
  3. 3Research Center for Health Sciences, Institute of Health Sciences and Technologies, Hamadan University of Medical Sciences, Hamadan, Iran
  4. 4Department of Epidemiology, School of Public Health, Shahroud University of Medical Sciences, Shahroud, Iran
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Abstract

Introduction:: Despite numerous investigations, variations in breast cancer (BC) risk across different ages at first pregnancy remain inconclusive. Thus, this meta-analysis aimed to clarify this association and provide a comprehensive evaluation of the evidence.

Study Design:: A systematic review.

Methods:: PubMed, Web of Science, and Scopus databases were systematically searched to identify observational studies published up to March 16, 2025, examining BC risk in relation to age at first pregnancy. Statistical analyses were performed using Stata 18 and Review Manager 5.4. Heterogeneity and potential sources were assessed using the I2 statistic and meta-regression, respectively. Publication bias was also evaluated with Begg’s and Egger’s tests. Pooled effect sizes were expressed as risk ratios (RR) or odds ratios (OR) with 95% confidence intervals (CI) using a random-effects model.

Results:: Of 15,586 identified records, 141 studies involving 1,045,983 participants met the inclusion criteria. The pooled RR of BC for age at first pregnancy≥20 years versus<20 years was 1.18 (95% CI: 1.09–1.28), and the pooled OR was 1.31 (95% CI: 1.26–1.37). Moreover, dose-response meta-analysis demonstrated a consistent upward trend, indicating that BC risk increases by 8–12% for every 5-year delay in the first pregnancy.

Conclusion:: Our findings revealed that BC risk increases progressively with older age at first pregnancy. However, the overall evidence was moderate due to study limitations. Accordingly, further research is warranted to clarify underlying mechanisms and population-specific variations.

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Cite

BibTeXRIS
BibTeX
@article{poorolajal2026systematic,
  title = {{A Systematic Review and Dose-Response Meta-Analysis of the Association Between the Age of First Pregnancy and Breast Cancer Risk}},
  author = {Jalal Poorolajal and Fatemeh Shahbazi and Nazanin Azmi-Naei and Amin Doosti-Irani and Bita Azmi-Naei},
  journal = {Journal of Research in Health Sciences},
  year = {2026},
  month = aug,
  doi = {10.34172/jrhs.13923},
  url = {https://doi.org/10.34172/jrhs.13923},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - A Systematic Review and Dose-Response Meta-Analysis of the Association Between the Age of First Pregnancy and Breast Cancer Risk
AU  - Jalal Poorolajal
AU  - Fatemeh Shahbazi
AU  - Nazanin Azmi-Naei
AU  - Amin Doosti-Irani
AU  - Bita Azmi-Naei
PY  - 2026
DA  - 2026/08/15
JO  - Journal of Research in Health Sciences
DO  - 10.34172/jrhs.13923
UR  - https://doi.org/10.34172/jrhs.13923
AB  - Introduction:: Despite numerous investigations, variations in breast cancer (BC) risk across different ages at first pregnancy remain inconclusive. Thus, this meta-analysis aimed to clarify this association and provide a comprehensive evaluation of the evidence.  Study Design:: A systematic review.  Methods:: PubMed, Web of Science, and Scopus databases were systematically searched to identify observational studies published up to March 16, 2025, examining BC risk in relation to age at first pregnancy. Statistical analyses were performed using Stata 18 and Review Manager 5.4. Heterogeneity and potential sources were assessed using the I2 statistic and meta-regression, respectively. Publication bias was also evaluated with Begg’s and Egger’s tests. Pooled effect sizes were expressed as risk ratios (RR) or odds ratios (OR) with 95% confidence intervals (CI) using a random-effects model.  Results:: Of 15,586 identified records, 141 studies involving 1,045,983 participants met the inclusion criteria. The pooled RR of BC for age at first pregnancy≥20 years versus<20 years was 1.18 (95% CI: 1.09–1.28), and the pooled OR was 1.31 (95% CI: 1.26–1.37). Moreover, dose-response meta-analysis demonstrated a consistent upward trend, indicating that BC risk increases by 8–12% for every 5-year delay in the first pregnancy.  Conclusion:: Our findings revealed that BC risk increases progressively with older age at first pregnancy. However, the overall evidence was moderate due to study limitations. Accordingly, further research is warranted to clarify underlying mechanisms and population-specific variations.
SN  - 2228-7795
SN  - 2228-7809
ER  -