Perinatal mortality and sex ratios in Hawaii

Abstract

Retrospective data obtained from a sample of 926 mothers of European ancestry (AEA) and 368 mothers of Japanese ancestry (AJA) living in Hawaii were used to evaluate two hypotheses, the selective male affliction hypothesis and the Trivers-Willard female condition hypothesis, for male-biased perinatal mortality and altered sex ratio at birth. Logit analyses using pregnancy outcome (live-birth versus stillbirth or miscarriage) as the dependent variable and either sex of prior sib, sex of offspring, parity, age of mother, or interval since last pregnacy as independent variables did not support either hypothesis. In contrast to the prediction of the selective male affliction model, sex of previous pregnancy was not related to perinatal mortality. Although each of the other independent variables exerted significant effects on perinatal mortality and, therefore, presumably affected female condition, in no case did natal sex ratios become female-biased. The Trivers-Willard hypothesis predicts that female-biased sex ratios are expected when female condition is reduced. The results are discussed in relation to the possibility that degree of sexual dimorphism may favor male-biased perinatal mortality and explains the observed decline in sex ratio with parity.