How long does anti-D injection take to work for rhesus incompatibility?

Anti-D is used when a pregnant person who is rhesus-negative may have been exposed to rhesus-positive fetal blood. It helps clear fetal red blood cells before the immune system makes antibodies. It does not change your blood group and does not treat antibodies that are already established. Your maternity team uses blood-group testing and the circumstances of pregnancy to decide whether it is needed.

Tell your maternity team promptly about vaginal bleeding, abdominal injury, an invasive procedure, pregnancy loss, birth or any event they have said could cause blood mixing. Give the date and details, even if the event seemed minor. Keep scheduled antenatal appointments and bring your blood-group information if available. Do not delay contacting the team while waiting for symptoms.

Seek urgent maternity advice after bleeding, significant abdominal trauma, severe abdominal pain, fainting or reduced fetal movement when movements are established. A possible exposure may need assessment even without pain. Tell staff if you have missed a planned injection or are unsure whether one was given.

Ask whether you are rhesus-negative, why anti-D is recommended, when it should be given and whether another dose is needed after a later event. Check how the injection will be recorded and what follow-up blood testing is planned.