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Birth weight and risk of asthma in 3–9-year-old twins: exploring the fetal origins hypothesis
  1. Karin Kindlund1,
  2. Simon Francis Thomsen1,
  3. Lone Graff Stensballe2,
  4. Axel Skytthe3,
  5. Kirsten Ohm Kyvik3,4,
  6. Vibeke Backer1,
  7. Hans Bisgaard5
  1. 1Department of Respiratory Medicine, Bispebjerg Hospital, Copenhagen, Denmark
  2. 2Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen, Denmark
  3. 3The Danish Twin Registry, University of Southern Denmark, Odense, Denmark
  4. 4Institute of Regional Health Services Research, University of Southern Denmark, Odense, Denmark
  5. 5Danish Pediatric Asthma Center, University Hospital of Copenhagen, Gentofte, Denmark
  1. Correspondence to Dr Simon Francis Thomsen, Department of Respiratory Medicine, Bispebjerg Hospital, DK-2400 Copenhagen NV, Denmark; sft{at}


Aim To examine the relationship between birth weight and risk of asthma in a population of twins.

Methods Birth weight of all live twins (8280 pairs) born in Denmark between 1994 and 2000 was linked to information on asthma obtained from parent-completed questionnaires at age 3–9 years. Conditional logistic regression was used to calculate the risk of asthma.

Results Subjects with a history of asthma at age 3–9 years weighed on average 122 g (95% CI 85 to 160) less at birth than subjects who had not developed asthma, p<0.001. There was a linear increase in asthma risk with decreasing birth weight, OR (per 100 g) 1.04 (95% CI 1.03 to 1.05), p<0.001. Within twin pairs, the lower birthweight twin had a significantly increased risk of asthma compared with the heavier co-twin (11.3% vs 9.9%), OR 1.30 (95% CI 1.10 to 1.54), p=0.002. The result remained significant after adjusting for sex, birth length and Apgar score, OR 1.31 (95% CI 1.03 to 1.65), p=0.027. The risk tended to be higher in monozygotic co-twins compared with dizygotic co-twins, especially for high birth weight differences.

Conclusions Low birth weight is a risk factor for asthma independently of gestational age, sex, birth length and Apgar score, but this may be due, in part, to residual non-genetic confounding factors. This finding lends support to the “fetal origins hypothesis” suggesting undisclosed prenatal determinants for the risk of asthma.

  • Asthma
  • birth weight
  • twins
  • fetal origins hypothesis
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  • Competing interests None.

  • Ethics approval This study was approved by the local Scientific Ethical Committee.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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