[Behavioral characteristics of the only child vs first-born and children with siblings]

To assess the impact of being an only child on characteristics of parental and peer relationships, school achievement, social and sexual behavior.

In the total, 360 adolescents identified at third year of high school were sampled from a private school from Porto Alegre in 2000 and 2001. Fifteen to nineteen years old male and female were selected in a cross-sectional study. Assessment of demographic data, education of the parents, birth order (only child, first born and non-first born children), cigarette smoking, alcoholic beverages consumption, illicit drug use, school achievement, social and sexual behavior were gathered with a pre-tested self-administered questionnaire, anonymously fulfilled at the classroom.

This study encompassed 8% of only children, 35% first-born, and 57% non-first born adolescents of a socioeconomic homogeneous sample. Social behavior, parents and peer relationships, sports participation, smoking and illicit drug were not associated with birth order. Only children were less likely to report an episode of alcohol intoxication (39%) than first-born (68.9%; p=0.03) and adolescents with siblings (72.3%; p<0.001). Only children had high school achievement than adolescents with siblings (p=0.03). Sexual behavior distinguished only children due to younger age at first sexual intercourse and lower rate of heterosexual self-identification, which persisted even after adjustment for confounding variables in comparison with non first-born adolescents (p=0.038).

Our findings suggest that the status of being only child is not associated with a poor outcome in several areas of the development. The impact of the presence of siblings in the development of sexual identification should be further explored.