ObjectiveTo investigate the situation of mother to child transmission of HIV after mothers acquired HIV prenatally or before pregnancy and the related factors. Methods Two hundred and seventy-seven mothers who acquired HIV prenatally or before pregnancy and their 322children from Yi-ning city of Xinjiang Uygur autonomous region and some counties of central China were enrolled in this study from January 2000 to December 2009.Subtypes of HIV were determined by detection of Gag sequence,the rate of HIV transmission from mother to child was calculated and its related factors were analyzed by Chi-square test and Logistic regression analysis.ResultsThe HIV subtype of all mothers who were infected through blood (n=174) was B'.The major subtype of mothers who were infected via sexuality (n =58) was recombined subtype CRF01-BC (n=35) and CRF-AE (n=20),accounting for 60.3％ and 34.5％,respectively,and only 3 mothers with B'subtype (5.2％).Twelve infants died before HIV detection,and 108 infants out of the rest 310infants were found to be HIV positive, giving the HIV mother-to-child transmission rate of 34.8％ (95％ CI:29.5％-40.1％).The infection rate of bottle feeding infants was lower than that of breastfeeding infants [12.5％ (6/48) vs 38.9％ (102/262),x2 =12.484,P=0.000].The infection rate of the infants whose mothers' HIV infection ＜7 years was lower than that of the infants whose mothers' HIV infection ≥7 years [28.8％ (46/160) vs 54.2％ (32/59),x2 =12.211,P=0.000].Multi-factor Logistic analysis showed that the duration of maternal HIV infection (OR =1.342,95％ CI:1.189-1.515,P=0.000) and duration of breastfeeding (OR =1.137,95％ CI:1.053-1.227,P=0.001) were risk factors of HIV vertical transmission.ConclusionsThe HIV subtypes might be associated with transmission route.Formula feeding could decrease the vertical transmission rate of HIV,while long duration of maternal HIV infection and breastfeeding might increase the vertical transmission rate of HIV.