Previous researchers have observed more rapid placental maturation and earlier fetal pulmonary maturity. An earlier development may benefit a newborn if it is delivered pre-term. Placental function may set a growth limit in twins after 37 weeks of gestation. Twins may also experience more physical constraint in utero during late pregnancy. Hence the cross-over of mortality curves for twins and singletons.

Twins and singletons have different causes of short gestational duration. The mortality cross-over can be confounded by those causes if they are not sufficiently adjusted for. For instance, do twins with a short GA receive better care than twins with longer GA and singletons? More research is required to ascertain such possibility of residual confounding.