Objective: To describe the changing demographic profile of diagnosed HIV-infected pregnant women over time and trends in pregnancy outcome, uptake of interventions and mother-to-child transmission.

Design: National surveillance study.

Setting: UK and Ireland.

Population: Diagnosed HIV-infected pregnant women, 1990-2006.

Methods: Active surveillance of obstetric and paediatric HIV conducted through the National Study of HIV in Pregnancy and Childhood.

Main outcome measures: Maternal characteristics, pregnancy outcome, use of antiretroviral therapy, mode of delivery and mother-to-child transmission.

Results: A total of 8327 pregnancies were reported, increasing from 82 in 1990 to 1394 in 2006, with an increasing proportion from areas outside London. Injecting drug use as the reported risk factor for maternal HIV acquisition declined from 49.2% (185/376) in 1990-1993 to 3.1% (125/4009) in 2004-2006 (P < 0.001), while the proportion of women born in sub-Saharan Africa increased from 43.5% (93/214) in 1990-1993 to 78.6% (3076/3912) in 2004-2006 (P < 0.004). Reported pregnancy terminations decreased from 29.6% (111/376) in 1990-1993 to 3.4% (135/4009) in 2004-2006 (P < 0.001). Most (56.4%, 3717/6593) deliveries were by elective caesarean section, with rates highest in 1999 (66.4%, 144/217). Vaginal deliveries increased from 16.6% (36/217) in 1999 to 28.3% (321/1136) in 2006 (P < 0.001). Use of antiretroviral therapy in pregnancy increased over time, reaching 98.4% (1092/1110) in 2006, and the overall mother-to-child transmission rate declined from 18.5% (35/189) in 1990-1993 to 1.0% (29/2832) in 2004-2006.

Conclusions: The annual number of reported pregnancies increased dramatically between 1990 and 2006, with changing demographic and geographic profiles and substantial changes in pregnancy management and outcome.