Blood TestA new non-invasive blood test for rhesus disease may drastically cut down on injections and save the NHS more than £500,000 a year.

Currently, all women at risk of having a rhesus-D positive baby undergo anti-D immunoglobin treatment, which substantially reduces the possibility of sensitisation occurring if they give birth to a baby with the opposite blood type (rhesus D negative), but brings with it all the risks associated with injecting blood products. Although women carrying rhesus-D negative babies do not require these injections, the only reliable way to test a baby’s blood type is to extract DNA from the umbilical cord after birth. As a result, an estimated 40,000 women are receiving this treatment unnecessarily.

The new method, which extracts the unborn baby’s DNA from a sample of the mother’s blood, comes recommended in draft guidance recently published by the National Institute for Health and Care Excellence (NICE). Developed by the NHS Blood and Transplant authority, high-throughput non-invasive prenatal testing (NIPT) can identify a foetus’s rhesus-D status early in pregnancy, saving time, money, and limited stocks of anti-D immunoglobin.

Approximately 17% of pregnant women in England and Wales have the blood type rhesus-D negative, over half of whom will give birth to a baby with the opposite blood type (rhesus-D positive). If this is the woman’s first pregnancy, there is usually no threat to either mother or child, as the mother’s immune system reacts to the child’s blood in a process called sensitisation.

However, subsequent pregnancies with women who have been sensitised to the rhesus-D antigen can cause significant problems for rhesus-D positive babies. The mother’s antibodies attack the baby’s blood, which may lead to haemolytic disease of the foetus and newborn – also known as rhesus disease.

Although rhesus disease only develops in 1% of cases, the consequences can be severe. Babies with the disease can develop anaemia or jaundice, and in extreme cases it may lead to miscarriage or stillbirth.

The Director of the Centre for Health Technology Evaluation at NICE, Professor Carole Longson, hopes that the new test will encourage expectant mothers to consider anti-D immunoglobin treatment – also known as anti-D prophylaxis – should they need it.

NIPT “may lead to better adherence as these women know that if they do not have anti-D prophylaxis there is a risk of problems in future pregnancies,” she said.