Miriam's casebook - Rhesus-negative Mother
Elena's blood group is Rhesus (Rh) negative and her partner's, Chris, is Rh positive. Their daughter is Rh positive so Elena may have developed anti-Rh-positive antibodies. Their second baby has a 50:50 chance of being Rh positive. If this second baby is Rh positive, the baby's red blood cells may be damaged by the antibodies. To prevent damage, Elena will need special antenatal care.
Mother and baby compatibility
© DK
I explained to Elena that about 85 per cent of people have the Rh factor in their red blood cells and they are Rh positive. The 15 per cent who lack the Rh factor are said to be Rh negative. A Rh-negative mother who's carrying a Rh-positive baby may develop antibodies to her baby's Rh-positive blood cells and injure them (see Rhesus disease in pregnancy). Elena's first pregnancy went without a hitch. This is usual with first pregnancies where the mother has Rh-negative blood and the baby Rh-positive blood (an incompatible pregnancy). However, when cells from this baby's blood mix with blood cells from the mother, for example during delivery, the mother's blood becomes sensitized. When the Rh factor from the baby's blood enters the mother's bloodstream, it acts as an antigen and stimulates the production of anti-Rh-positive antibodies. These attack and destroy the blood cells of her next Rh-positive (incompatible) baby. A newborn baby with Rh incompatability (see Newborn Health) may suffer from various blood conditions ranging from mild jaundice to serious, possibly fatal, anaemia (see Haemolytic disease of the newborn). Fetuses who develop haemolytic disease can often be saved by intrauterine blood transfusion.
Do all women become sensitized?
Not all Rh-negative women with Rh-positive babies become sensitized, as I explained to Elena, but there's no way of predicting which women will. All women who are Rh negative should be offered an Anti-D injection at 28 and 34 weeks of pregnancy and after delivery of a Rh-positive baby. Some units offer a double dose at 28 weeks only. Studies have yet to confirm which is the most effective.
Women who are Rh negative are also given an Anti-D injection after a late miscarriage, chorionic villus sampling, and amniocentesis or cordocentesis, especially if there's blood on the needle after it has been withdrawn from the uterus. Within 48 hours of delivering her first baby, Elena was injected with Anti-D (Rh immune-globulin) to help prevent the destructive antibodies from forming. If she'd miscarried, she would have also needed the injection, because her blood and her baby's would have mixed.
Birth expectations for a mother
I told Elena that if her antibody count remains low, she won't need further special care during her pregnancy. If the count rises moderately, her baby may be induced early to prevent serious consequences. In this case, home birth is out of the question. She'll need to deliver in hospital, probably by a Caesarean. In a very few cases the baby has to have a blood transfusion to replace his own blood cells, which have become damaged during pregnancy.
Elena's baby
Elena's baby is likely to be fit and healthy, thanks to the Anti-D injections. His cord blood will be tested for his group. If he is negative, no further Anti-D is needed. If he is positive, Anti-D will be given to Elena within 72 hours of delivery. The dose of Anti-D will be assessed by the amount of fetal cells in Elena's circulation.
If he is affected by Rh incompatibility, his bilirubin levels will rise quickly after birth because his liver can't get rid of it. A high level of bilirubin will make him look yellow. This can be treated by placing him under ultraviolet “bili” light, which converts bilirubin into a harmless substance. He may also need a transfusion - blood can be withdrawn from the baby via the umbilical vein and replaced with donor blood that's compatible with his mother's blood. If severe haemolytic disease had been predicted before he was born, he may have been successfully treated by a transfusion while in the womb.
Miriam's top tips
A mother who is Rh negative will be monitored closely throughout her pregnancy. Remember that:
- all women who are Rh negative should be offered an Anti-D injection at 28 and 34 weeks and after delivery of a Rh-positive baby
- any increasing levels of antibodies will be picked up by regular antenatal blood tests
- from 16 weeks, a test for bilirubin (a by-product of red blood cell destruction) can be done which allows doctors to decide if blood transfusions are needed.
Posted 30.06.2010
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