Natural fertility in northeastern Mexico

Background. The aims of this study were as follows: 1) to describe the fert ility of a sample of Mexican women (greater than or equal to 45 years of ag e, married, not using any family planning methods, and residing in the Mexi can state of Nuevo Leon); 2) to determine whether or not the distribution o f completed family size fits the negative binomial distribution, as in othe r populations studied in the world, and 3) to assess the association betwee n fertility and 10 explanatory variables. Methods. A sample of 410 women was interviewed at and selected from seven m edical units of the Institute Mexicano del Seguro Social (IMSS). The women were grouped by their pear of birth (1896-1925 and 1926-1955) and birthplac e [persons whose four grandparents were born in northeastern Mexico (NE) an d outside northeastern Mexico (Not-NE], A binomial negative distribution an alysis was assessed. Multiple linear regression was used to assess associat ion between fertility (transformed by the use of inverse hyperbolic sines) and 10 explanatory variables, including age at marriage, heterozygosity, in dividual admixture, wife's education: husband's education, wife's occupatio n, husband's occupation, and couple's residence zone, birth year, and birth place. Results. Completed fertility was only associated with age at marriage. This population showed a fertility pattern similar to those described in Venezu elan and Brazilian populations in 1950 and 1940, respectively. Conclusions. We conclude that before worldwide family planning programs, fe rtility was determined mainly by natural selection forces. (C) 2001 IMSS. P ublished by Elsevier Science Inc.