Neonatal sex-steroid hormones and muscular strength of boys and girls in the first three years.

Five sex-steroid hormones were assayed in umbilical cord blood. Strength was assessed in children in three samples at several ages from birth to 33 months. At different ages, different strength measures were taken, viz., at birth, prone head responses; at 3 months, leg strength; from 6 to 33 months, grip strength. Boys had higher average strength scores than girls but the sex differences were small and did not increase or decrease over the age period studied. Across-age strength scores showed a significant relation to androstenedione and a significant interaction of sex and progesterone. Both boys and girls with higher strength scores had lower androstenedione. Girls with high cord blood progesterone showed low strength while boys with high progesterone showed high strength. There were no sex differences in androstenedione or progesterone level. The androstenedione finding did not replicate across samples but the Progesterone X Sex interaction was replicated in all three samples. No relationship was found between strength and other hormones assayed: testosterone, estradiol, and estrone.