CONCEIVING WITHIN A year of stillbirth is common and is not associated with increased risk of stillbirth, preterm birth, or small-for-gestational-age birth in the following pregnancy.

That is according to new research, published in the Lancet, which compared these pregnancies with an interpregnancy interval of at least two years.

The results are from the first large-scale study to investigate the period between stillbirth and a new pregnancy, including almost 14,500 births in women from Australia, Finland and Norway who had a stillbirth in their previous pregnancy. 

The World Health Organisation (WHO) recommends that women wait at least two years after a livebirth and at least six months after a miscarriage or induced abortion before conceiving again, but there is no guidance for the optimal interval after a stillbirth because there is limited evidence in this area.

“Our results consistently showed that an interpregnancy interval of less than one year was not associated with increased risk of adverse birth outcomes in the next pregnancy, compared with an interval of at least two years. Our findings provide valuable evidence for recommended pregnancy spacing after a stillbirth,” says study author Dr Annette Regan of Curtin University, in Australia.

Approximately 3.5 in every 1,000 births in high-income countries are stillborn, and there is limited guidance available for planning future pregnancies. We hope that our findings can provide reassurance to women who wish to become pregnant or unexpectedly become pregnant shortly after a stillbirth.

The study used birth records spanning 37 years (1980-2016) from Finland, Norway, and Australia to investigate intervals between pregnancies and the risk of subsequent stillbirth, preterm birth, and small-for-gestational-age birth.

The authors noted that these countries have access to universal health care and free antenatal care, and the populations are primarily white, so the findings might not be generalisable to low-or middle-income countries, countries without access to universal health care, or ethnic minority groups.

Overall, the study included 14,452 births among mothers who had a stillbirth in their previous pregnancy. Results were compared with 1,654,289 births following a previous livebirth from the three countries – 536,392 in Finland, 854,999 in Norway, and 262,898 in Australia. 

Of the 14,452 births in women whose previous pregnancy ended in stillbirth, 14,224 (98%) were livebirths, 2,532 (18%) were preterm births, and 1,284 (9%) were small-for-gestational-age births. Of the 228 stillbirths (2% of the total births), 201 (88%) were preterm and 27 (12%) were stillborn at term.

For women who had experienced stillbirth in their last pregnancy, intervals shorter than 12 months were not associated with increased risk of subsequent stillbirth, preterm birth, or small-for-gestational-age birth, compared with an interpregnancy interval of 24–59 months. 

This trend remained the same when adjusted for maternal age, number of previous births, and decade of delivery. .

The authors also noted no difference in the association between interpregnancy interval and birth outcomes based on the gestational length of the previous stillbirth.

The authors note the difference in optimal intervals following livebirth and stillbirth.

Dr Regan explains: “Although the mechanism linking interpregnancy interval and perinatal health is unclear, previous research offers several hypotheses, including depleted nutrition from past pregnancy, cervical insufficiency, and breastfeeding–pregnancy overlap in closely spaced pregnancies.

“Without sufficient time to recover from a previous pregnancy, women may be at increased risk of entering a reproductive cycle with poor nutritional status, which has been linked to increased risk of foetal growth restriction and birth defects.

“Such nutritional depletion might not occur to the same extent after a pregnancy loss, and this may affect the optimal interpregnancy interval, explaining why it may be different after stillbirth and livebirth.”

The authors note that other factors that they could not study (such as maternal chronic medical conditions, pregnancy intention, use of assisted reproductive technology, cause of previous stillbirth, or socioeconomic status) may have affected their findings. They also add that women who conceive soon after a previous pregnancy might be healthier and more fertile than women who conceive later and therefore could be less prone to adverse birth outcomes.