Growth in the first year of life: effects of sex and weight for gestational age at birth.

Fifty-five small-for-dates (SFD), 56 average-for-dates (AFD) and 55 large-for-dates (LFD) babies were weighed and measured at regular intervals from birth to 12 months. Within the SFD and AFD groups weight gain was greater for boys than for girls so that by one year there were highly significant differences between the two sexes. Within the LFD group the sex difference was slight at all ages. Gain in length was similar to that for weight within each group; but head circumference showed a different pattern. Absolute increase in head circumference respectively for boys and girls between birth and one year was greatest in the SFD group and least in the LFD group. Within all three groups it was greater for boys than girls. By the age of six months AFD boys had larger heads than LFD girls and SFD boys had larger heads than AFD girls. At 12 months the head-circumference values for LFD girls and SFD boys did not significantly differ.