Background
Despite that anti-D prophylaxis regimens to prevent alloimmunisation
during pregnancy are used for fifty years, and are shown effective,
anti-D is the most common red cell antibody causing severe hemolytic
disease of the fetus and newborn (HDFN).1 Intrauterine
transfusions are in the majority of cases due to anti-D
immunisation.2
Postnatal anti-D immunoglobulin prophylaxis to RhD negative women with a
newborn blood typed RhD positive was introduced in the late 1960s and
reduced the risk of immunisation of RhD negative women from
approximately 15% to 1-1.5%. 3,4In the 1990s many
countries added routine antenatal anti-D prophylaxis (RAADP) in the
third trimester to all RhD negative women, further minimising the risk
of immunisation to an incidence of 0.2-0.4%.5 During
the last decade fetal RHD -typing combined with targeted RAADP
only to those carrying an RHD positive fetus, has been proven
effective and is implemented in many countries.6 The
strategies of doses and timing of administration of RAADP vary between
countries, one single dose of anti-D; 1000-1500 IU in gestational week
28-30 or two doses of 500-625 IU at 28 and 34 weeks are the most common
routines.7,8,9 A second or third dose anti-D is given
postdelivery, usually a dose of 1000-1500 IU. In some programs, testing
of fetomaternal hemorrhage (FMH) is recommended at delivery, to
determine if additional doses of anti-D are
required.10
It is known, that one single dose anti-D in gestational week 28 is not
detectable at delivery in a proportion of women, varying from 39-56%
and up to 78% for those who deliver after 40 weeks of
gestation.7,8 thus not protecting them from
immunisation at the end of the third trimester, when the risk of
immunisation is increased.9,11,12 The two-dose
strategy gives a higher rate of detectable anti-D at term, 85%, but is
associated to higher costs and lower compliance of receiving the two
doses.13,14
In Sweden the recommendations are to perform fetal RHD screening
in the first trimester, and to administer targeted RAADP, 1500 IU in
gestational week 28 and a second dose of anti-D 1500 IU
postdelivery,15,16 and at situations carrying an
increased risk of fetomaternal hemorrhage during pregnancy.
Today, when fetal RHD typing is widely implemented and theRHD type of the fetus is known with high accuracy6 an alternative strategy could be to administer two
RAADP doses, at gestational week 28 and 38, the latter to cover term and
post term of the pregnancy. If the postdelivery anti-D dose could be
excluded, this strategy could be cost effective and have the potential
of high compliance.
The aim of this study was to retrospectively analyse the proportion of
women with undetectable levels of prophylactic anti-D at the time of
delivery after one dose of RAADP (1500 IU) at gestational week 28.
Secondly, in a prospective study, to investigate if a strategy with
administration of the second dose of anti-D in gestational week 38,
instead of postdelivery, would improve the protection at term and if the
protection would be enough after delivery.