A case study of birth interval dynamics

A birth interval free from pregnancy wastage may be viewed as the sum of three sub-intervals: (1) the period ofpost-partum amenorrhoea following a birth; (2) the menstruating interval extending from end of post-partum amenorrhoea to next conception; and (3) the months of pregnancy losses, then in addition to the above three components there is a fourth component, which may be termed 'time added by pregnancy wastage'. 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. The present analysis draws upon uniquely detailed materials from the India-HarvardLudhiana Population Study that took place in eleven villages of the Punjab, India, during the years 1953–59. Means and variances of post-partum amenorrhoea, menstruating intervals, and time added by pregnancy wastage are estimated for two broad age classes and the results related to corresponding statistics for total birth intervals.