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Interpregnancy interval and risk of preterm birth and neonatal death: retrospective cohort study

BMJ 2003; 327 doi: (Published 07 August 2003) Cite this as: BMJ 2003;327:313

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  1. Gordon C S Smith, professor1 (gcss2{at},
  2. Jill P Pell, consultant2,
  3. Richard Dobbie, senior statistician3
  1. 1Department of Obstetrics and Gynaecology, Cambridge University, Box The Rosie Hospital, Cambridge CB2 2QQ
  2. 2Department of Public Health, Greater Glasgow NHS Board, Glasgow,
  3. 3Information and Statistics Division, Common Services Agency, Edinburgh
  1. Correspondence to: G C S Smith
  • Accepted 18 June 2003


Objective To determine whether a short interval between pregnancies is an independent risk factor for adverse obstetric outcome.

Design Retrospective cohort study.

Setting Scotland.

Subjects 89 143 women having second births in 1992-8 who conceived within five years of their first birth.

Main outcome measures Intrauterine growth restriction (birth weight less than the 5th centile for gestational age), extremely preterm birth (24-32 weeks), moderately preterm birth (33-36 weeks), and perinatal death.

Results Women whose subsequent interpregnancy interval was less than six months were more likely than other women to have had a first birth complicated by intrauterine growth restriction (odds ratio 1.3, 95% confidence interval 1.1 to 1.5), extremely preterm birth (4.1, 3.2 to 5.3), moderately preterm birth (1.5, 1.3 to 1.7), or perinatal death (24.4, 18.9 to 31.5). They were also shorter, less likely to be married, and more likely to be aged less than 20 years at the time of the second birth, to smoke, and to live in an area of high socioeconomic deprivation. When the outcome of the second birth was analysed in relation to the preceding interpregnancy interval and the analysis confined to women whose first birth was a term live birth (n = 69 055), no significant association occurred (adjusted for age, marital status, height, socioeconomic deprivation, smoking, previous birth weight vigesimal, and previous caesarean delivery) between interpregnancy interval and intrauterine growth restriction or stillbirth. However, a short interpregnancy interval (< 6 months) was an independent risk factor for extremely preterm birth (adjusted odds ratio 2.2, 1.3 to 3.6), moderately preterm birth (1.6, 1.3 to 2.0), and neonatal death unrelated to congenital abnormality (3.6, 1.2 to 10.7). The adjusted attributable fractions for these associations were 6.1%, 3.9%, and 13.8%. The associations were very similar when the analysis was confined to married non-smokers aged 25 and above.

Conclusions A short interpregnancy interval is an independent risk factor for preterm delivery and neonatal death in the second birth.


  • Contributors GCSS had the original concept, reviewed previous publications, undertook the statistical analyses, and wrote the initial draft of the paper. JPP interpreted the results and contributed to the draft of the paper. RD performed the linkage and extracted the data. All authors edited and approved the final version of the paper. GCSS is the guarantor.

  • Funding None.

  • Competing interests None declared.

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