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BJOG press release: Women with short or long birth spacing face a greater risk of preterm birth

News 13 July 2016

Women who conceive less than 11 months after giving birth have a higher chance of going into labour or being medically induced before 37 weeks of gestation. In addition, the odds of a premature birth are also increased for those who wait three years to have another baby, suggests a new study published today (13 July) in BJOG: An International Journal of Obstetrics and Gynaecology (BJOG).

The study used data from a million women in California who gave birth between 2007 and 2010, in order to assess whether interpregnancy interval was associated with preterm birth in women who had already given birth and those who had experienced a pregnancy loss (miscarriage, stillbirth or abortion). Of these women, 971,211 had already had a baby and 138,405 had suffered a pregnancy loss. Short interpregnancy interval was defined as conception after less than 18 months and long interpregnancy conception after more than 36 months. An interval of 18 to 23 months is considered the optimal interpregnancy interval, when the risk of preterm birth is 5.7% (1 in 17.1).

Results found that women who conceive less than six months after giving birth have a 70% higher risk of preterm birth than women with an optimal interpregnancy interval (absolute risk is 10% or 1 in 10), while the risk for those with an interpregnancy interval of six to 11 months is 20% higher (6.9% or 1 in 14.5). Women who wait 36 to 48 months however, also face a 7% increased risk of going into labour or being induced early (6.3% or 1 in 15.9).

While those who conceive a child less than six months after a pregnancy loss, have a decreased chance of a preterm birth; the risk of this is 7.7% (1 in 12.9). In fact, researchers found these women, and women of advanced maternal age (over 35 years old) and couples with fertility problems, may benefit from a short interpregnancy interval.

Worldwide each year, an estimated 15 million babies are born prematurely and preterm birth complications are the leading cause of death among children under 5 years of age, responsible for nearly 1 million deaths annually. The estimated rate of preterm birth ranges from 5% to 18% of babies born. In the UK, around 8% of babies are born prematurely. 

Lead author, Dr Bat Zion Shachar from the March of Dimes Prematurity Research Centre at Stanford University in California, said: 

“Reducing the rate of premature births globally is a priority. This study adds to our understanding about the potential causes of preterm birth and highlights the importance of communicating the risks of inadequate birth spacing to women. We recommend that obstetricians and midwifes discuss child spacing plans with postpartum mothers, as well as encouraging the use of contraception to reduce the likelihood of unplanned pregnancy occurring soon after live births.

“Interpregnancy interval guidelines for women who have experienced a pregnancy loss are of special importance because these women often wish to conceive again with minimal delay. However, we did not observe an increased risk for preterm birth among women with a short interpregnancy interval after a pregnancy loss, and our results show that there doesn’t appear to be any advantage of waiting more than six months to conceive again after a pregnancy loss.” 

Professor Lesley Regan, President Elect for the Royal College of Obstetricians and Gynaecologists (RCOG) said:

“On a global perspective, approximately 225 million women in the world have no access to family planning and therefore little control over whether and when they become pregnant. Providing women across the world with the choice to use effective contraception and to space their babies by 24 months or more, would prevent 54 million unintended pregnancies, 79,000 maternal deaths and 1.1 million infant deaths.

“The findings of these results stress the importance of birth spacing plans for optimal child health. Family planning is a key international priority that should not only be regarded as an intervention for improving health, but also as a human right.” 

Dr Bob Silver, Scientific Editor of BJOG added:

“We’ve always known that inadequate birth spacing is associated with obstetric complications. Given the size of this study, it has been possible to explore the underlying mechanisms for the association between interpregnancy intervals and premature birth.

“Around 60,000 babies are born prematurely each year in the UK and many suffer lifelong consequences as a result. These findings will not only help healthcare professionals identify those at risk of preterm birth, but also help couples plan birth spacing.” 


For media enquiries please contact the RCOG press office on 020 7772 6357 or email

Notes to editors:

Bat Zion Shachar, Jonathan A. Mayo, Deirdre J. Lyell, Rebecca J Baer, Laura L. Jeliffe-Pawlowski, David K. Stevenson and Gary M. Shaw. Interpregnancy internal after live birth or pregnancy termination and estimated risk of preterm birth: a retrospective cohort study. BJOG 2015: DOI: 10.1111/1471-0528.14165.

The article can be found here: (full paper) (mini commentary)

Information for the public on premature labour is available from the RCOG and NHS Choices

BJOG: An International Journal of Obstetrics and Gynaecology is owned by the Royal College of Obstetricians and Gynaecologists (RCOG) but is editorially independent and published monthly by Wiley. The journal features original, peer-reviewed, high-quality medical research in all areas of obstetrics and gynaecology worldwide. Please quote ‘BJOG’ or ‘BJOG: An International Journal of Obstetrics and Gynaecology’ when referring to the journal and include the website: as a hidden link online. Sign up for new content alerts from BJOG.

The Royal College of Obstetricians and Gynaecologists is a medical charity that champions the provision of high quality women’s healthcare in the UK and beyond. It is dedicated to encouraging the study and advancing the science and practice of obstetrics and gynaecology. It does this through postgraduate medical education and training and the publication of clinical guidelines and reports on aspects of the specialty and service provision.