At your very 1st NHS antenatal appointment, you'll have some blood tests to find out your 'rhesus status'. If you're rhesus positive, you probably won't hear any more about it. But if you're 'rhesus negative', your midwife will let you know, either in a letter or at your next antenatal appointment.


It's (almost always) nothing to worry about. But we know – from the kind of thing MFM mums say on our Chat forum – that finding our you're rhesus negative can often be confusing. It certainly was for jellyfishpink:

"My midwife told me [I am] rhesus negative. She told me I need to have some anti-D injections later in the pregnancy and asked if I knew my husband's blood group (I don't). She said something about a blood transfusion if I have another baby and I'm just very confused! What does it really mean? And how will it affect me with this baby – and if I decide to have another baby?"

So, if you're rhesus negative, here's our guide to what it means, what these anti-D injections are – and what else you need to know.

What does rhesus negative mean?

As you probably already know, everybody's blood can be grouped into 1 of 4 groups: A, B, AB and O. What you may not know is that your blood also has a rhesus factor – making you either rhesus positive or rhesus negative. It's usually signified by a + or - sign after your blood group, so you could be, for example, A+ or O-.

More like this

How common is it? Not that common: about 15% of women are rhesus negative.

What does it mean for me? Is my baby at risk?

People who are rhesus positive have a substance known as D antigen on the surface of their red blood cells. But rhesus negative people do not.

If you're rhesus negative and your baby is rhesus negative, there's no problem.

If your baby is rhesus positive (inheriting his/her positive rhesus status from his/her dad), this isn't usually a problem either – during a 1st pregnancy.

But there can be problems if you become pregnant again with another rhesus-positive baby. And that's because your 1st baby's rhesus-positive blood cells will have mingled with your own rhesus-negative blood cells at the birth – triggering a process called 'sensitisation', where your body starts making antibodies against what it sees as 'foreign' rhesus-positive blood cells.

These antibodies will then cross your placenta and attack your unborn baby's rhesus-positive blood red blood cells – and that can result in anaemia and a serious condition called rhesus disease or haemolytic disease of the newborn.

Sounds scary? Sounds complicated? We don't blame you!

But the good news is that, these days, a few simple anti-D injections can sort everything out. And your baby – and any future babies – should be absolutely fine.

What is anti-D?

Anti-D – or anti-D immunoglobulin, to give it its full name – works by neutralising any rhesus-positive antigens that may have entered your bloodstream during your pregnancy.

This means your body is never triggered to make those antibodies, so a rhesus-positive baby would be quite safe.

When do you have the injections? Where do you have them?

The anti-D injections are usually given at in 2 separate doses at 28 weeks and 34 weeks, although some hospitals give one double dose at 28 to 30 weeks.

The reason they're done at this point is that your baby's blood wouldn't normally mix with your own until the last trimester of pregnancy (when there may be some small but otherwise harmless bleeds from your placenta) and the actual birth (whether it's vaginal or C-section).

You may also have another anti-D injection after your baby's born – if your baby turns out to be rhesus positive (a sample of blood will be taken for testing from your baby's umbilical cord). If you do need this extra injection, it should be given within 72 hours of the birth.

Your midwife will inject the anti-D into a muscle – either your upper arm or your buttock. It might sting a bit – and (be warned) the needle will probably look bigger than you're used to for other blood tests and jabs, as MFM forum mum xxAJBplus1xx explains:

"Well, I have just come back from having my 1st Anti D Injection. It was absoultely fine, I was a little nervous about it but I didn't even feel anything when the needle went in – no stinging or anything – although my partner said it was the biggest needle he has ever seen!"

Is anti-D safe? Anti-D comes from donated human plasma (the clear yellowy fluid part of blood) and will have been screened for HIV, hepatitis and treated to inactivate any viruses, such as vCJD.

It won't harm your baby. Very, very occasionally, women have an allergic reaction to immuglobulin A (IgA) – which is present in the jab in tiny amounts – so your midwife will ask you to stay in the clinic or doctor's surgery for 20 minutes after your jab, just to make sure all is OK.

Do I have to have the injections?

No. You are entitled to refuse them (and then the antibody levels in your blood will be carefully monitored throughout your pregnancy) but your midwife will strongly recommend that you do have them because of the very real risk of your subsequent babies developing rhesus disease.

But my partner's rhesus negative like me. Do I still need the injections?

Well, you'd think not – because if both you and your partner are rhesus negative, it shouldn't be possible to have a rhesus positive baby together.

But hospital policy is generally to ignore the rhesus status of a male partner and give anti-D injections, regardless, to every pregnant woman who's rhesus-negative.

Midwives will often say this is because it's not always certain your current male partner is the actual father of your baby (yes, really!), so it's best to err on the side of caution.

But it's also because, according to US geneticists at Stanford School of Medicine, there is the teeniest, tiniest chance that 2 people who test as rhesus negative can produce a rhesus positive baby: it's all to do with the fact that the test used to screen for rhesus status only screens for 1 of the rhesus genes, so it is (mathematically) possible to be given rhesus negative status when you actually have some rhesus positive genes. So again, it's best to err on the side of caution.

Will I need the injections with every pregnancy?


Is there anything I need to be careful about?

There are way other, more uncommon, ways your blood and your baby's blood could mix, in addition to the small 3rd placental bleed and the birth. If you have any of the following, after your 12th week of pregnancy, you should tell your midwife, who will probably want to give you an anti-D injection as soon as possible (preferably within 3 days):

  • Trauma or a blow to, or a fall onto, your tummy
  • Vaginal bleeding (after 20 weeks)
  • Severe stomach pains

You should also automatically be given an anti-D injection if you have:

  • Chorionic villus sampling (CVS) or amniocentesis
  • A miscarriage or termination
  • A procedure, called external cephalic version (ECV) to try to turn your baby from the breech position to a head-down one

What happens if I already have these antibodies in my blood?

This doesn't happen often, as the anti-D injections are so effective (and are usually routinely given after miscarriages and terminations, too).

However, if you do already have the antibodies in your blood, this will be picked up during your routine antenatal blood test. Your blood will then put though a different and more complicated test (after about 12 weeks) to see if there's enough DNA from your baby in it (they're usually is) to find out your baby's blood type is.

If your baby is rhesus negative, all is well – and no further treatment will be needed (or you get pregnant again).

If your baby is rhesus positive, your baby is a risk of developing rhesus disease. You will be closely monitored throughout your pregnancy, particularly with a type of ultrasound scan called a Doppler.

If there are any worries about your baby's blood flow, you will be referred to a specialist unit (maybe in a different hospital), where you may have a procedure called fetal blood sampling (FBS) to check whether your baby is anaemic.

FBS is done by inserting a needle into your belly to remove a small sample of blood. It's carried out under local anaesthetic and, as it carries with it a 1 to 3% chance of miscarriage, it's only done when really necessary.

"If the baby is shown to have serious anaemia," says Dr Geetha Venkat, of the Harley Street Fertility Clinic, "he or she can be given an intra-uterine blood transfusion (given to your baby, in the womb, through the same needle), will need to be considered."

Once your baby is born (he or she may need to be delivered early, by induction or C-section), he or she will be monitored closely. Around half of all cases are mild and don't need further treatment.

If your baby does need further care, this may be phototherapy – placing your baby under a halogen or fluorescent lamp (eyes covered) – and/or treatment with intravenous immunoglobulin and maybe more blood transfusions. "The blood transfusions," says Dr Venkat, "have a good success rate. Complications from rhesus diseases are very treatable with, generally, limited side effects."