Early first period, more pregnancy blood-pressure problems. Childhood size may explain it.

People say: “Does an early first period raise pregnancy risks?” We read the study.

What they did

Cohort study. 9,441 pregnancies. ALSPAC pregnancies with due dates 1991-1992; MR outcome data from 77,683-707,797 pregnancies across 5 cohorts (ALSPAC, Born in Bradford, FinnGen, MoBa, UK Biobank).

People were watched for years. Nobody was told what to do. A clue, not proof.

Who: ALSPAC: 9,441 singleton pregnancies in Avon, UK (mean age at first period 12.9, mean age at delivery 28.5); MR: predominantly European-ancestry cohorts from the UK, Finland and Norway

What they found
  • Later period: high BPlowerodds, both methods
  • After childhood sizeunclearlink shrank
  • Depression near birthnoneno clear link
The catch

More to know, from our read of the paper:

  • Observational cohort + Mendelian randomization: linked, not proven. MR relies on assumptions (no pleiotropy); between-SNP heterogeneity was high for blood-pressure outcomes
  • Attenuation is partial, not complete: preeclampsia stayed lower in multivariable MR (OR 0.92, 95% CI 0.86-0.98). So say 'shrank and was no longer clear' only for the overall hypertensive-disorders outcome, and 'may be explained by' (authors' wording), never 'fully explained'
  • In the cohort, pre-pregnancy BMI was used as a proxy for childhood adiposity and may over-adjust (adult BMI may be a mediator)
  • Age at first period was self-reported in adulthood (recall error); data mostly European ancestry, so may not generalise
  • goals: 'mood' only because perinatal depression was measured (null)
The verdict

Little solid evidence period timing itself causes problems.

In short

Researchers tested whether the age of a woman's first period affects 13 pregnancy outcomes, using 9,441 pregnancies in a British cohort plus genetic data from up to 707,797 pregnancies. A later first period went with lower odds of blood pressure problems in pregnancy in both methods. After accounting for body size, that link shrank and was no longer clear. There was no clear link with low birthweight, small babies, late births or depression around birth. Mostly European-ancestry data: linked, not proven.

The video
The paper

Aiton E, Borges MC, Gonçalves Soares A, Clayton GL, Bond TA, Yang Q, Magnus MC, Lawlor DA, Fraser A, Taylor AE (2026). Age at menarche and adverse pregnancy and perinatal outcomes: triangulating evidence from multivariable and Mendelian randomization analyses. International Journal of Epidemiology.

Design: Cohort study · triangulation: observational multivariable regression in one UK pregnancy cohort (ALSPAC) plus two-sample Mendelian randomization (genetic variants for age at first period) and multivariable MR accounting for childhood body size; 13 pre-specified outcomes (linked, not proven)

DOI: 10.1093/ije/dyag094

Goals:

Better mood
How we checked

We read the abstract and the full text of this paper and checked every number on this page against it (15 facts, checked on 2026-10-29). The study design is named above. Cohort and other observational studies are described as linked, not proven. Found an error? Email theis@onestudyaday.com.

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