Diagnosing rhesus disease

Rhesus disease is usually diagnosed during the routine screening tests you're offeredduring pregnancy.

Blood tests

A Blood tests should becarried outearly on in your pregnancy to test for conditions such as anaemia , rubella , HIV and hepatitis B .

Your blood will also be tested to determine which blood group you are, and whether your blood is rhesus (RhD) positive or negative (see causes of rhesus disease for more information).

If you're RhD negative, your blood will be checked forthe antibodies (known as anti-D antibodies)that destroy RhD positive red blood cells. You may have become exposed to themduring pregnancy if your baby has RhD positive blood.

If no antibodies are found, your blood will be checked again at 28 weeks of pregnancy and you'll beoffered an injection ofa medication called anti-D immunoglobulin to reduce the risk of your baby developing rhesus disease (see preventing rhesus disease for more information).

If anti-D antibodies aredetectedin your blood during pregnancy, there's a risk that yourunbornbaby will be affected by rhesus disease. For this reason, you and your baby will be monitored more frequently than usual during your pregnancy.

In some cases, a blood test to check the father's blood type may be offered if you have RhD negative blood. This isbecause your babywon't beat risk of rhesus disease if both the mother and father have RhD negative blood.

Checkingyour baby's blood type

It's possible to determine if an unborn baby is RhD positive or RhD negative by taking a simple blood test during pregnancy.

Genetic information (DNA) from the unborn baby can be found in the mother'sblood, which allows the blood group of the unborn baby to bechecked without any risk. It's usually possible to get a reliable result from this testafter 11-12 weeks ofpregnancy, which islong before the baby is at risk from the antibodies.

Ifyour baby is RhD negative,they'renot at risk of rhesus disease and no extra monitoring or treatment will be necessary. If they're found to be RhD positive, the pregnancy will be monitored more closely so that any problems that may occur can be treated quickly.

In the future, RhD negative womenwho haven't developed anti-D antibodies may be offered this test routinely, tosee if they're carrying an RhD positive or RhD negative baby, toavoid unnecessary treatment.

Monitoring during pregnancy

If your baby is at risk of developing rhesus disease, they'll be monitored by measuring the blood flow in their brain. If your baby is affected, their blood may be thinner and flow more quickly. This can be measured using a type of ultrasound scan called a Doppler ultrasound.

If a Doppler ultrasound shows your babys blood is flowing faster than normal, a procedure called fetal blood sampling (FBS) can be used to check whether your baby is anaemic . This procedure involves inserting a needle through your abdomen (tummy) to remove a small sample of blood from your baby. The procedure is performed under local anaesthetic , usually on an outpatient basis, so you can go home on the same day.

There's a small (usually 1-3%) chance that this procedure could cause you to lose your pregnancy, so it should only be carried out if necessary.

If your baby is found to be anaemic, they can be given a transfusion of blood through the same needle. This is known as an intrauterine transfusion (IUT) and it may require an overnight stay inhospital.

FBS andIUT are only carried out in specialist units, so you may need to be referred to a different hospital to the one where you were going to have your baby.

This is to check their blood group and see if the anti-D antibodies have been passed into their blood. This is called a Coombs test.

If you're known to have anti-D antibodies, your babys blood will also be tested for anaemia and jaundice .

Content supplied by the NHS Website

Medically Reviewed by a doctor on 28 Nov 2016