Research in obstetrics is notoriously challenging. Obstetrics deals with mothers and babies, two patients who are both vulnerable at the same time but who sometimes have conflicting interests. Fortunately, at least in highly resourced set-tings, the incidence of poor outcomes is low. This creates a challenge for researchers, however, as to show differences, studies require large sample sizes that are often unachievable for a single centre. Asa result, collaboration between researchers is essential.