Epidemiology of congenital pigmented naevi: II. Risk factors.

Genetic and environmental risks factors were investigated in a sample of 989 non-malformed newborn infants with skin pigmented naevi (PN), and in 989 non-malformed non-PN, control babies. The samples were obtained from a population of 531,831 livebirths, from fifty-nine South-American maternity hospitals. No significant differences were observed between the PN and control groups for the following risk factors: sex, twinning, parental consanguinity, socioeconomic level, parental ages, birth order, fetal presentation, type of delivery, postnatal mortality, and first trimester of pregnancy histories for maternal chronic illnesses or immunizations, radiation exposure, drug intake, and vaginal bleeding. PN infants were associated with high frequencies of Black racial ancestry, positive prenatal history for maternal acute illnesses, and high mean values for length of gestation and birth weight. The observed association of PN with maternal acute illnesses could be a spurious one, due to partial dependence upon Black racial ancestry, and to maternal memory bias. The analysis of the intrauterine growth curves showed that PN infants have a low prematurity rate, and a high mean by the control newborn group. This observation suggest that congenital PN appear in the latest stages of intrauterine development. No evidence was obtained to allow us to consider congenital PN as true developmental anomalies.