A full-term pregnancy lasts 37 weeks, and according to the NHS, babies can typically be expected to survive if born from 24 weeks onwards. Children born so early can have health and development issues as they have not had enough time in the womb to finish developing, so they must be given special care in a neonatal unit.

Although most studies measuring premature-baby outcomes start at 22 and 23 weeks — reporting U.S. survival rates between 10 and 20 percent at that gestation — University of Iowa Health Care is among the few hospital systems that take on babies at 21 weeks.