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Pregnancy Health A-Z: Rhesus Factor And Disease

Being told your blood type is an issue in pregnancy can be worrying, but is can be easily managed

What is rhesus status?

Your blood type is determined by the genes you inherit from your parents and is either A, B, AB or O. But on top of that, within each group, you can be either rhesus (RhD) positive or rhesus negative. And this is important in pregnancy.

Around 25% of the population will have a blood type that is rhesus negative, but the issues can occur if your blood type differs to the blood type of the baby you’re carrying.

Your rhesus status is discovered during routine blood tests at your booking in appointment at the beginning of your pregnancy by your midwife. But your baby’s blood type won’t be known until he’s born.

What causes rhesus disease?

‘If you are rhesus negative, but your partner is rhesus positive, there’s a small chance that your baby will end up as rhesus positive,’ says Mervi Jokinen from the Royal College of Midwives.

‘This is only an issue if some of your baby’s blood enters your bloodstream because your blood cells will treat it as a foreign invader and start producing antibodies against your baby’s blood cells.’

This doesn’t matter too much during your first pregnancy, but can affect subsequent pregnancies if you haven’t received a special injection that stops your body producing these antibodies.

‘If your body produces antibodies against your baby’s blood remain in your system for life,’ says Mervi. ‘So if you go on to have another baby that is also rhesus positive, the antibodies can cross the placenta and start attacking your baby’s blood cells, which can lead to anaemia in your baby.

The outcome? After birth, your baby may have haemolytic disease of the newborn (HDN), which can cause jaundice, and if left untreated, lead to more serious health problems, but this is quite rare.

What is the treatment for rhesus factor?

The good news is that rhesus factor is easily managed so long as it’s picked up at the right time.

‘Once your midwife has checked your blood test results for your rhesus status and discovered that you’re rhesus negative, you’ll be given injections of a substance known as anti-D,’ says Mervi. ‘This prevents the body from producing antibodies if yours and your baby’s blood mixes.’

The injections are sometimes given as two doses at 28 and 34 weeks, or as one injection at 32 weeks.

‘When your baby is born, the birthing team will take a sample of blood from your baby’s umbilical cord to check what blood type he has,’ says Mervi. ‘If it’s established that he has a different rhesus status to you, you’ll be given a final anti-D injection, which has be administered within 72 hours of your baby’s birth.’

This is because when the placenta separates from your uterus after birth, there’s a chance that your baby’s blood and your blood could mix. If you have a C-section, your blood may also mix with your baby’s, so it’s important that a sample is taken from your baby’s cord so you can be treated.

If your baby’s blood type is also rhesus negative (ie, the same as yours), you won’t need the final anti-D injection.

If your midwife discovers that you already have antibodies in your system at your routine blood test (usually as a result of a previous pregnancy), you won’t receive an anti-D injection because it can only prevent antibodies from developing. If they’re already there, it won’t work. However, a specialist foetal medicine team will monitor your baby to check that he doesn’t become anaemic.

When should you see your GP or midwife?

‘Having a different blood type to your baby doesn’t usually cause any symptoms, however, if you experience any bleeds – no matter whether your rhesus status is different or not – you should contact your GP or midwife as it could potentially mean that you and your baby’s blood will have mixed,’ says Mervi.

It’s important that you don’t panic too much about the issues surrounding rhesus factor, as while it’s serious, it’s also easily treated, so long as you stay up-to-date with your routine blood tests and midwife appointments.

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