HIV-I infection in perinatally exposed siblings and twins. The Italian Register for HIV Infection in Children.

In a multicentre study on perinatal HIV-I infection including 1493 children born from 1471 pregnancies to 1415 infected mothers, 22 twin pairs and 56 sibships (115 children) were recorded. The frequency of twin pregnancies was 1.5 (22/1471) and 3.9% (56/1415) seropositive women had more than one at risk pregnancy. In 18 twin pairs with a known infection status nine of the 36 children (25%) were infected. Discordance in infection status was present in only one (5.5%) dizygous pair. A high relative risk of infection (23.1) in a twin was observed when the other was infected. Infection was unrelated to gestational age, mode of delivery, or birth weight. Infection status was defined in 41 sibships (84 children including one first born twin pair and one third born child). When the first born was infected, 11/26 (42.3%) second born children were also infected, whereas this happened in only 2/16 (12.5%) second or third born children when the first born was uninfected. Two out of nine first born (22.2%) and 5/21 (23.8%) second born children prospectively followed up from birth acquired the infection. Results of this study demonstrate that neither twin nor second pregnancies are at increased risk of mother to child HIV-I transmission. Overall data suggest that non-casual factors in mother and/or child influence perinatal infection.