The Billings Ovulation Method Association of T&T (BOMA-TT) found the article below useful in explaining the circumstances in which Natural Family Planning could be used to space births, among other things.
“If, then, there are serious motives to space out births, which derive from the physical or psychological conditions of husband and wife, or from external conditions, the Church teaches that it is then licit to take into account the natural rhythms immanent in the generative functions…” [Pope Paul VI, Humanae Vitae 16].