Page 433 - Essential Haematology

Chapter 30 Pregnancy and neonatal haematology / 419

lead to their destruction. Anti - D antibody is respon- needed. In addition, at birth the babies of Rh
sible for most cases of severe HDN although anti - c, D - negative women who do not have antibodies
anti - E, anti - K and a wide range of other antibodies must have their cord blood grouped for ABO and
’
are found in occasional cases (see Table 29.2 ). Rh. If the baby s blood is Rh D - negative, the mother
Although antibodies against the ABO blood group will require no further treatment. If the baby is Rh
system are most frequent cause of HDN this is D - positive, prophylactic anti - D should be adminis-
usually mild. tered at a minimum dose of 500 units intramuscu-
larly within 72 hours of delivery. A Kleihauer test
is performed. This uses differential staining to esti-

R h h aemolytic d isease of the n ewborn

mate the number of fetal cells in the maternal cir-
When an Rh D - negative woman has a pregnancy culation (Fig. 30.5 a). If the Kleihauer is positive
with an Rh D - positive fetus, Rh D - positive fetal red many centres will perform flow cytometry for a

cells cross into the maternal circulation (especially more accurate estimate of the volume of feto -
at parturition and during the third trimester) and maternal haemorrhage (FMH) (Fig 30.5 b). Th e
sensitize the mother to form anti - D. Th e mother chance of developing antibodies is related to the

could also be sensitized by a previous miscarriage, number of fetal cells found. The dose of anti - D is
amniocentesis or other trauma to the placenta or by increased if there is > 4 mL transplacental haemor-
blood transfusion. Anti - D crosses the placenta to rhage. Anti - D IgG (125 units) is given for each
the fetus during the next pregnancy with an Rh 1 mL of FMH greater than 4 mL.
D - positive fetus, coats the fetal red cells and results
in reticuloendothelial destruction of these cells,
Sensitizing e pisodes d uring p regnancy
causing anaemia and jaundice. If the father is het-
Anti - D IgG should be given to Rh D - negative
erozygous for D antigen, there is a 50% probability
women who have potentially sensitizing episodes
that the fetus will be D - positive. The fetal Rh D

during pregnancy: 250 units is given if the event
genotype can be established by polymerase chain
occurs up to week 20 of gestation and 500 units
reaction (PCR) analysis for the presence of Rh D in
thereafter, followed by a Kleihauer test. Potentially
a maternal blood sample.
sensitizing events include therapeutic termination
Th e main aim of management is to prevent
of pregnancy, spontaneous miscarriage after 12
anti - D antibody formation in Rh D - negative
weeks ’ gestation, ectopic pregnancy and invasive
mothers. This can be achieved by the administration

antenatal diagnostic procedures.
‘
of small amounts of anti - D antibody which mop
up ’ and destroy Rh D - positive fetal red cells before
they can sensitize the immune system of the mother Treatment of e stablished a nti - D

to produce anti - D. s ensitization
If anti - D antibodies are detected during pregnancy

they should be quantified at regular intervals. Th e
Prevention of R h i mmunization

clinical severity is related to the strength of anti - D
At the time of booking, all pregnant women should present in maternal serum but is also aff ected by
have their ABO and Rh group determined and such factors as the IgG subclass, rate of rise of anti-
serum screened for antibodies at least twice during body and past history. The development of haemo-

the pregnancy. All non - sensitized Rh D - negative lytic disease in the fetus can be assessed by
women should be given at least 500 units (100 μ g) velocimetry of the fetal middle cerebral artery by

of anti - D at 28 and 34 weeks ’ gestation to reduce Doppler ultrasonography as increased velocities cor-
the risk of sensitization from fetomaternal haemor- relate with fetal anaemia (Fig. 30.6 ). If anaemia is
rhage. Fetal Rh D typing from DNA in maternal detected, fetal blood sampling and intrauterine
blood can be used before 28 weeks. If the fetus is transfusion of irradiated Rh D - negative packed red
Rh D - negative, no further anti - D prophylaxis is cells may be indicated.