Outcome measures
According to the World Health Organization, PTB was defined as
gestational length ≤ 37 completed weeks (24). Moderate PTB (MPTB) was
defined as gestational length between 32 and 36 completed weeks. Very
PTB (VPTB) was defined as gestational length < 32 completed
weeks. The VPTB included extremely PTB (gestational length <
28 completed weeks).