A Case Study of Birth Interval Dynamics.

The article focuses on birth interval dynamics. A birth interval free from pregnancy wastage may be viewed as the sum of three sub-intervals namely the period of post-partum amenorrhoea following a birth, the menstruating interval extending from the end of post-partum amenorrhoea to the next conception and the months of pregnancy leading to the next live birth. When the birth interval includes a pregnancy loss, then in addition to the above three components there is a fourth component, which will be termed time added by pregnancy wastage. This latter consists of the pregnancy leading to wastage, a month or more of post-abortion or post-stillbirth amenorrhoea, and a second menstruating interval. In a small minority of birth intervals the length of this fourth component is increased by the occurrence of two or more foetal losses. A basic understanding of birth intervals requires the ability to relate the central tendencies and variability of birth intervals to the means and variances of these four components.