Final answer:
Lactational amenorrhea can lead to a prolonged interbirth interval by providing a natural form of contraception while a mother breastfeeds. The effectiveness varies greatly among individuals, and this variability affects the average interbirth interval.
Step-by-step explanation:
Lactational amenorrhea, which is the postnatal infertility that occurs when a woman is breastfeeding, can lead to an extended period between births, also known as the interbirth interval. It is a natural form of contraception that can be quite effective during the first six months postpartum, provided the mother breastfeeds exclusively. However, this method's effectiveness and the duration of amenorrhea can vary greatly between individuals.
The term that quantifies the number of births per 1,000 people per year is typically referred to as the birth rate, or fertility rate, and numbers for this rate tend to fall within the 5-30 range. Nonetheless, the specific number you are looking for regarding the average interbirth interval due to lactational amenorrhea is not commonly represented by a single figure, like '38' or '426', because it is heavily dependent on cultural, biological, and individual lifestyle factors.