At your booking appointment with your midwife, your blood will be tested to determine your ‘rhesus status’. If the results are rhesus negative, there’ll be further steps your medical team will take to manage your status; here’s what to expect.
Along with the usual blood groupings—A, B, AB and O, human blood also comes with a rhesus factor: rhesus positive or rhesus negative. How likely is it you’ll be rhesus negative? Only 15% of women hold the status, so chances are low.
But if you do test as rhesus negative, what exactly does it mean? Rhesus negative people do not have a substance called D antigen on the surface of their blood cells; this doesn’t pose a problem during pregnancy if your baby is rhesus negative, too, or if you’re expecting for the first time. But if your baby tests as rhesus positive, a process referred to as ‘sensitisation’ can be triggered, where maternal antibodies are produced to attack the ‘foreign’ rhesus positive blood cells. This can lead to anaemia, and a dangerous condition known as rhesus disease or haemolytic disease of the newborn.
As scary as it sounds, a couple anti-D injections can resolve the situation.
Anti-D – or anti-D immunoglobulin injections neutralise rhesus-positive antigens that may have been produced during your pregnancy, effectively shutting down sensitisation.
Typically, you should receive anti-D injections in 2 doses, at 28 weeks and 34 weeks—the developmental period in gestation when your baby’s blood starts to mingle with your own.
A further injection may be administered within 72 hours of birth.
As far as risk factors go, the injection will not harm your unborn baby—but there’s a minimal chance of you developing an allergic reaction, so your midwife will observe you for 20 minutes post-jab, just to ensure you’re good to go.