One in eight confirmed pregnancies end in miscarriage, and women who have had two previous losses have more than double the risk of another, a study shows.

Researchers have used data from three registries in Norway to provide estimates of the miscarriage risk related to maternal age, previous miscarriages and other pregnancy complications in the BMJ study.

Norway is one of the few countries where miscarriage data has been recorded since 2008, and almost all recognised pregnancies are registered in at least one of the national health registers, write the authors from the Norwegian Institute of Public Health.

They looked at all recorded pregnancies in Norway between 2009 and 2013, examining over 421,200 pregnancies.