Male and female sterility in Zambia.

AbstractBACKGROUNDPopulation measures of sterility are traditionally constructed for women, despite fertility and sterility being conditions of the couple. Estimates of male sterility provide insight into population-level sterility, and complement estimates based solely on women.OBJECTIVEThis study seeks to estimate male sterility for the Gwembe Tonga of Zambia using male birth histories collected by the Gwembe Tonga Research Project from 1957 to 1995, while providing context by estimating female sterility for the Gwembe Tonga, as well as female sterility in all of Zambia, from Zambian DHS data (1992, 1997, 2001-02, and 2007).METHODSSterility is measured using the Larson-Menken subsequently infertile indicator. Estimates are produced using discrete time event history analysis.RESULTSThe odds of sterility were higher for women than men, though women's odds of sterility were only 1.5 times that of men's in the middle reproductive years. The odds of sterility increased steadily with age for both men and women, and across all datasets. However, women's sterility increased much more sharply with age than men's did, and women's odds of sterility were higher than men's at all reproductive ages.1. IntroductionPopulation measures of fertility and sterility are usually constructed from birth histories from women, and thus limited to the population of women, rather than the general population. However, fertility or its absence are conditions experienced by a couple, and the causes of sterility can be related to the male partner, the female partner, or both partners. Medical studies (Folkvord, Odegaard, and Sundby 2005) and anthropological studies (Gerrits 1997, Dryer et al 2004) provide direct evidence of male sterility in multiple locations in Africa. Determining whether sterility is due to male or female disorders is often difficult, and generally less is known about the prevalence of male sterility (McFalls and McFalls 1984). McFalls and McFalls (1984) estimate between 20 and 60% of couple infertility across populations is accounted for in whole or in part by male sterility. As sterility, primary or secondary, is potentially related to either the male or female member of the couple, estimating male sterility can provide a more complete picture of population-level sterility than female estimates alone.This analysis aims to describe the sterility of Gwembe Tonga men by applying Larsen and Menken's (1989, 1991) subsequently infertile measure, using incomplete birth histories. Data for the Gwembe Tonga provide a unique opportunity to estimate male sterility, because male birth histories were recorded. Juxtaposed with measurement of sterility for the women in the same population, this analysis seeks to describe sterility among the entire Gwembe Tonga population. Measures of female sterility from Zambia Demographic and Health Surveys (ZDHS) data from 1992, 1996, 2001-02, and 2007 are also presented to provide national context for the Gwembe Tonga analysis.2. Background2.1 Sterility in AfricaFertility rates vary widely across and within countries in sub-Saharan Africa (for example, Bongaarts, Frank, and Lesthaeghe 1984), and evidence from demographic measurement of sterility has shown wide variation across the continent as well. Earlier studies have tried to measure the inability to produce a living child, and we use the word sterility for any measures of the inability to produce a living child. Larsen (2000) found relatively low rates of primary sterility but high rates of secondary sterility. Rates of secondary sterility ranged from less than 10% to 25% for women age 25-44 (Larsen 2000). Other researchers have found similar variation (Ericksen and Brunette 1996). Frank (1983) found great variance in rates of primary sterility by country and also by ethnic group in Africa. Bongaarts et al (1984) cite substantial variation in measured primary sterility across Africa, varying from 3% to 20% or higher, and noted substantial variation within countries. …