Nursing interval and maternal responsivity: effect on early infant crying.

In industrialized societies, the unique pattern of crying in the first three months is "unexplained" but thought to be due to different biobehavioral factors from later crying behavior. To increase the range of the feeding and caretaking behaviors hypothesized to be relevant determinants of early crying, home observations and diary records were analyzed from samples of two subcultures of American middle-class women (La Leche League and "standard care" mothers; each n = 16) differing primarily in such practices. Both during and after the early crying stage, frequently fed infants cried or fretted less often (8.1 v 15.8 episodes per hour at 2 months of age; 10.7 v 16.6 episodes per hour at 4 months of age), and fewer of them exhibited rhythmic crying behavior (four v 11 at 2 months; eight v 13 at 4 months) during observations. However, only during the early crying period at 2 months were interval between feedings and maternal response latency shown to be independent determinants of cry/fret frequency (overall r2 = .35, P = .01), each factor accounting for approximately half of the explained individual variance. Furthermore, feeding interval was the only variable associated with rhythmic crying behavior at 2 months of age (r2 = .20;P = .01). In similar analyses at 4 months, there were no significant relationships with later crying or fretting. The results suggest that, in the presence of variation in feeding practice greater than that which is typical for our society, feeding interval may be a significant factor in early (but not later) crying behavior; furthermore, this effect is independent of and additive to the soothing effect of short response latency.