Mother-to-child transmission of human immunodeficiency virus type 1: influence of parity and mode of delivery. Paediatric AIDS Group of Switzerland.

UNLABELLED: In a national prospective study of risk factors for mother-to-child transmission of human immunodeficiency virus (HIV), 316 children of HIV-positive mothers were followed up for at least 6 months. Infection status was determined in 254 of them and 46 were found to be infected giving a transmission rate of 18.1%. Univariate analysis of potential risk factors for mother-to-child transmission showed an association between primiparity and increased transmission rate: odds ratio 2.2, 95% confidence interval (CI) 1.1-4.6, P < 0.05. Analysis by logistic regression confirmed this association (adjusted odds ratio 2.4) and showed, in addition, a negative association between transmission rate and elective Caesarean section (adjusted odds ratio 0.36, 95% CI 0.13-0.97, P < 0.05). The effect of primiparity was less pronounced in combination with elective Caesarean section (odds ratio 1.7) than with other delivery modes (odds ratio 2.5, difference not significant). HIV-infected children were less likely to experience the birth of a younger sibling during the observation period than their uninfected counterparts (2 of 46 vs 27 of 208, P < 0.05 by logrank test).
CONCLUSION: Primiparous women appear to transmit HIV to their children at a higher rate. This could be explained by increased intrapartum transmission because of longer and more complicated labour in primiparas and/or by a self-selection of women with lower risk of transmission among those deciding to have additional children.