Background:  Mother-to-child HIV transmission (MTCT) rates have declined to 1 to 2% in Europe in recent years. With the success of HAART in suppressing HIV RNA viral load, women are increasingly opting for vaginal delivery, instead of elective caesarean section. In the UK, zidovudine monotherapy and elective caesarean section is also offered as an option for some women who do not require HAART for their own health and have low viral loads.

Methods:  Births to women with diagnosed HIV infection in the UK and Ireland are notified to the National Study of HIV in Pregnancy and Childhood through confidential, active surveillance schemes. MTCT rates in infants born between 2000 and 2006 were explored with an emphasis on ART, mode of delivery, and viral load (closest to delivery). Analyses were carried out in Stata 9.0.

Results:  Infection status was available for 86.8% of infants (5136 of 6127). The MTCT rate was 1.1% (61 of 5316, 95%CI 0.9% to 1.5%) overall, and 0.8% (40 of 5027, 95%CI 0.6 to 1.1%) in infants whose mothers received ART for at least 14 days. There was no significant difference in MTCT rates between women on HAART who had an elective caesarean section (17 of 2337, 0.7%, 95%CI 0.4 to 1.2%) or a planned vaginal delivery (4 of 565, 0.7%, 95%CI 0.2 to 1.8%), and those on prophylactic zidovudine (prescribed according to the British HIV Association [BHIVA] Guidelines) who had an elective caesarean section (0 of 467, 0%, upper 95%CI 0.8%; p = 0.094). In these 3 groups, the proportions of women with viral load <50 copies/mL were 59% (1341 of 2276), 80% (508 of 634), and 23% (105 of 447), respectively. Only 3 transmissions were reported among 2202 infants born to women on HAART with viral load <50 copies/mL (0.1%, 95%CI 0 to 0.4%):  2 were born by elective caesarean section (MTCT rate  0.2%, 2 of 1180) and 1 by planned vaginal delivery (MTCT rate 0.2%, 1 of 419). Of the 3 infected infants, 2 had positive polymerase chain reaction (PCR) tests at births, suggesting in utero transmission (the other was negative at birth).

Conclusions:  There was no difference in MTCT rates according to the management strategies outlined in the BHIVA Guidelines: HAART with elective caesarean section or planned vaginal delivery, and zidovudine monotherapy with elective caesarean section. The risk of MTCT in appropriately managed pregnancies in the UK and Ireland is very low.