Anti-D administration is recommended for most Rhesus Negative women (ie. those with Blood Groups A Neg, B Neg, AB Neg or O Neg) at ~ 28 weeks gestation, ~ 34 weeks gestation and again soon after birth if the baby is Rhesus Positive (in Rhesus Negative women the baby’s Blood Group is usually tested on a cord blood sample collected at birth) – and also if there has been vaginal bleeding or an invasive procedure (such as Amniocentesis or CVS).
Brochure from Australian Red Cross about the use of Anti-D in Pregnancy.