Jain, Anrudh K., T.C. Hsu, Ronald Freedman, and Ming-cheng Chang. "Demographic Aspects of Lactation and Postpartum Amenorrhea." Demography, 7, no. 2 (1970): 255-71.
Interrelations between lactation and post-partum amenorrhea are studied from the reports of about 5,000 married women included in a 1966 Follow-up Survey of Acceptors of an Intrauterine Device (IUD) in Taiwan. The length of post-partum amenorrhea and of breastfeeding are positively associated. On an average, breastfeeding delayed the resumption of menstruation by about 7 months. The association between lactation and amenorrhea is not accounted for by differences in mother's age, parity, education and her place of residence. A multiple regression analysis suggests that (1) age affects amenorrhea both directly and through lactation, (2) parity has no independent effect on either lactation or amenorrhea, and (3) education and place of residence affect amenorrhea mainly through the cultural variations in the practice of breastfeeding.