Why should Anti D be given only at 28 weeks POG (antenatal period)? Why not before or after that?

why should Anti D be given only at 28 weeks POG (antenatal period)? Why not before or after that?

Routine antenatal antiD prophylaxis is usually not administered until 28 weeks gestation, since transplacental hemorrhages large enough to cause sensitisation do not usually occur until the third trimester and thus Rhesus antibodies usually develop after the 28th week of gestation.

Thank you.

Because risk of antepartum hemorrhage is more after 28weeks so Risk of fetomaternal blood mixing is more during this time period and single Prophylactic dose is enough to combat it untill delivery. During delivery of baby there’s again chance of mixing of blood if baby is Rh+ then we again give postpartum Prophylactic dose . So 1 antepartum and 1 postpartum dose is enough