Strength and anthropometric measures in identical and fraternal twins: no evidence of masculinization of females with male co-twins.

Sharing of intrauterine environment in twins of opposite sex has been hypothesized to result in masculinization of the female twin. We tested this hypothesis by comparing strength (maximum hand-grip pressure) and various anthropometric measures in a newly established survey panel comprising 4,314 middle-aged twins identified through a Danish population-based twin registry. Sex- and zygosity-specific mean values of handgrip strength, height, weight, body mass index, and waist circumference were highly comparable between fraternal twins of opposite sex and fraternal twins of same sex. Our results provide no support for the hypothesis of masculinization of female twins from opposite sex twin pairs.