Screening Rhesus antibodies

You are now in your third trimester — such an exciting milestone! While you’re preparing more and more for your baby’s arrival, your body is also working hard behind the scenes. One of the things we monitor more closely in a small number of pregnancies is the development of antibodies against the baby’s blood type. That’s why some women receive an extra blood test around 27 weeks. Here we explain how that works.

A quick look back

Around 11 weeks pregnant, we tested your blood. We checked:

• Your ABO blood type (A, B, AB or O)
• Your Rhesus D and Rhesus c blood type
• Whether you already had antibodies against blood groups

For most pregnant women, this first test is all that’s needed. But if you are Rhesus D‑negative or Rhesus c‑negative, we will schedule a second blood test around week 27.

Why only for Rhesus D‑negative and Rhesus c‑negative?

If you are Rhesus D‑negative or Rhesus c‑negative and your baby has a positive blood type, your body may produce antibodies against the baby’s blood. These antibodies can break down the baby’s red blood cells, which may cause anaemia.

That’s why this extra test is important — and only needed — for people with a Rhesus D‑ or c‑negative blood type.

What does the laboratory check at 27 weeks?

1. Have you developed blood group antibodies?
   We check this again — even if there were no antibodies earlier in pregnancy. If antibodies are found, we will discuss what this means and whether extra monitoring is needed.
2. What is the baby’s Rhesus D blood type? (only if you are Rhesus D‑negative)
   Using DNA from your baby that naturally circulates in very small amounts in your blood, the lab can determine whether your baby is Rhesus D‑positive.

Rhesus D‑negative: what does that mean for you?

If you are Rhesus D‑negative and your baby is Rhesus D‑positive, you will receive an injection with anti‑D antibodies around week 30. This prevents your own body from developing antibodies against the baby’s blood. You will receive a second injection after birth. 
These injections are safe and fully covered by health insurance.

Rhesus c‑negative: what happens then?

If you are Rhesus c‑negative, we will again check whether antibodies have developed. Important: there is no preventive injection for Rhesus c, unlike Rhesus D. This makes careful monitoring extra important. If antibodies are found, we will schedule additional check‑ups to closely monitor your baby.

How common are Rhesus antibodies?

Very rare — they occur in less than 1% of Rhesus‑negative pregnancies. In the vast majority of pregnancies, the body does not form antibodies against the baby’s blood.
When it does happen, it usually follows a clear event such as abdominal trauma or strong impact: falling off a bike, a hard kick to the belly, an airbag deployment, or heavy vibrations like landing on the lower back when slipping down stairs.

These situations may allow a tiny amount of baby’s blood to enter your bloodstream. If this happens — whether before or after week 27 — we take extra blood to check whether antibody formation has started. This allows early treatment if needed.

Costs

• The week‑27 blood test is free of charge.
• If follow‑up testing or treatment is needed, it’s covered by basic insurance. You may pay part of your deductible if it isn’t used yet.
• Testing or treatment for your baby is fully covered.
• If the biological father’s blood also needs to be tested, these costs are covered by the government.

What do you need to do?

• You don’t need to do anything — we will remind you if this blood test applies to you.
• If you have fallen hard onto your belly or experienced strong impact or vibrations (for example slipping down stairs), please call our emergency number! We will assess whether extra testing is necessary.