Age at first birth and the length of the second birth interval: is a positive relationship universal in modern populations?

"Age at first birth has been found to be positively associated with the length of the second birth interval in several studies. One researcher has hypothesized that such a relationship would be found in any population in which contraception is widespread and women are exposed to non-maternal roles. However, in this study a positive relationship is not found for caucasian women in Hawaii, a population in which contraception is wide-spread and women are exposed to non-maternal roles. The findings suggest a revision of the hypothesis to accommodate more complex relationships."