Structured Abstract
Please note: In 2003, the CTF updated its Grades of
Recommendations to include an "I Recommendation" for situations where
insufficient evidence exists to allow a recommendation to be made.
(Formerly, these situations were captured under a "C
Recommendation".) This change is not retroactive, and all
"C Recommendations" made prior to 2003 have not been
reevaluated in light of the new "I" recommendation grade. For a
discussion of these recommendation grades, please link to the 2003 article in
the Canadian Medical Association Journal here.
Screening for D (Rh) Sensitization in Pregnancy
Adapted by Marie-Dominique Beaulieu, MD, MSc, FCFP, Department of Family
Medicine, University of Montreal, from a report prepared for the US Preventive
Services Task Force by Carolyn DiGuiseppi, MD, MPH
These recommendations were finalized by the Task Force in June 1993
Contents
Objective
To make recommendations for screening pregnant women in Canada for D (Rh)
sensitization. This guideline is an update of the 1979 Canadian Task Force
recommendations on blood group incompatibility in pregnancy.
Burden
of Suffering
Some degree of fetal-maternal transplacental hemmorhage occurs in 75% of
all pregnancies. This phenomenon is not dangerous to the fetus unless
there is an incompatibility between the mother and her fetus with respect
to the D antigen of the red blood cells. D incompatibility exists
when a D negative woman is pregnant with a d positive fetus, which occurs
in up to 9-10% of pregnancies, depending on race. If no preventive
measures are taken, 0.7-1.8% of women will become isoimmunized antenatally,
developing D antibody through exposure to fetal blood; 8-17% will become
isoimmunized at delivery, 3-6% after spontaneous or therapeutic abortion,
and 2-5% after amniocentesis. Once isoimmunization has occurred,
the severity of fetal hemolysis varies. In 50% of the cases the fetus
is very mildly affected and does not require postpartum treatment.
However, without treatment, 25-30% of these offspring will have some degree
of hemolytic anemia and hyperbilirubinemia, another 20-25% will be hydropic
and many will die either in utero of during the neonatal period.
Options
Screening for D blood type is done using hemagglutination. Detection of
anti-D antibodies in women who have been sensitized to D-positive blood
is by the indirect antiglobulin (Coomb's) test (IGAT).
Prevention includes identification of actual or potential maternal and
fetal blood incompatibilities before isoimmunization can occur and treatment
with intravenous D immunoglobulin (D Ig) or plasma exchange, when necessary.
Treatment can occur during pregnancy or immediately after a pregnancy related
event (e.g., delivery, abortion, genetic testing).
Outcomes
Prevention of isoimmunization during pregnancy and delivery; detection
if it has occurred because of transplacental hemorrhage; and fetal anemia,
morbidity, and mortality in utero or during the neonatal period
(hemolytic disease).
Evidence
These recommendations were adapted for the Canadian context from a report/materials
prepared for the 1989 U.S. Preventive Services Task Force. MEDLINE
was searched for 1989 - 1993 using the keywords RH-HR blood group system,
RH Isoimmunization, immunoglobulins, amniocentesis, ultrasound, blood transfusion
intrauterine, erythroblastosis fetalis.
Recommendations were graded as:
|
A
|
Good evidence to support the recommendation that the condition
be specifically considered in a PHE. |
|
B
|
Fair evidence to support the recommendation that the condition
be specifically considered in a PHE. |
|
C
|
Poor evidence regarding inclusion or exclusion of the condition
in a PHE, but recommendations may be made on other grounds. |
|
D
|
Fair evidence to support the recommendation that the condition
be specifically excluded from consideration in a PHE. |
|
E
|
Good evidence to support the recommendation that the condition
be specifically excluded from consideration in a PHE. |
Quality of evidence was rated according to 5 levels:
|
I
|
Evidence from at least 1 properly randomized controlled
trial (RCT). |
|
II-1
|
Evidence from well-designed controlled trials without randomization. |
|
II-2
|
Evidence from well-designed cohort or case-control analytic
studies, preferably from more than 1 centre or research group. |
|
II-3
|
Evidence from comparisons between times or places with
or without the intervention. Dramatic results in uncontrolled experiments
could also be included here. |
|
III
|
Opinions of respected authorities, based on clinical experience,
descriptive studies or reports of expert committees. |
Values
The 13-member Task Force of experts in family medicine, geriatric medicine,
pediatrics, psychiatry and epidemiology used an evidence-based method for
evaluating the effectiveness of preventive health care interventions. Recommendations
were not based on cost-effectiveness of options. Patient preferences were
not discussed.
Background papers providing critical appraisal of the evidence and tentative
recommendations prepared by the chapter author were pre-circulated to the
members. Evidence for this topic was presented and deliberated upon in
1- to 2-day meetings, 2 to 3 times per year from January 1993 to June 1993.
Consensus was reached on final recommendations.
Benefits,
Harms, and Costs
Clinical trials done in the 1960s showed that women who received a full
dose of D Ig prophylaxis after delivery did not develop isoimmunization.
Antenatal isoimmunization has been shown to be prevented by D Ig at 28
weeks' gestation in non-randomized controlled trials; this reduces the
incidence of isoimmunization to 0.2% of women at risk. Case series and
non-randomized trials showed that D Ig reduced isoimmunization after amniocentesis
(from 5.2% to 0%) and after termination of pregnancy (from 2.6% to 0.4%).
Postpartum doses of D Ig can be based on the amount of fetal blood estimated
to have been transferred during delivery: 300 micrograms of D Ig will prevent
sensitization to 30 mL of fetal blood. Combined antenatal and postnatal
prophylazis will prevent isoimmunization in 96% of women at risk.
D Ig has few side effects although some fetuses develop weak direct-antiglobulin-positivity
after antenatal administration, but resulting anemia and hyperbilirubinemia
in the newborn infant are rare.
Ultrasound-guided cordiocentesis can detect fetal hemoglobin and D blood
type but complications can occur (2% to 7%) including fetal mortality (0.5%
to 1.0%).
Severe fetal anemia can be treated with ultrasound-guided intravascular
transfusion at experienced centres with success rates of 62% to 86% for
hydropic infants and > 90% success for those without hydrops. After pulmonary
maturity has been established, early delivery and exchange transfusion
can occur with only 1% mortality risk.
Recommendations
Recommendation grade [A, B, C, D, E] and level of evidence
[I, II-1, II-2, II-3, III] are indicated after each recommendation. Citations
in support of individual recommendations are identified in the guideline
text.
-
Good evidence exists to support screening for ABO and D blood antibodies
during antenatal and prenatal visits (first prenatal visit and within 72
h of delivery of a D-positive infant). [A,
I].
-
Fair evidence exists to support additional screening at 24 to 28 weeks'
gestation if the mother is D-negative. [B,
II-2].
-
Fair evidence exists to recommend screening after induced abortion [B,
III] and amniocentesis (possibility of bleeding) [B,
II-2].
-
Poor evidence exists to recommend the inclusion or exclusion of screening
with chorionic villus sampling [C, I].
-
Poor evidence exists to recommend the inclusion or exclusion of screening
for other obstetrical complications, procedures, or outcomes [C,
III].
Validation
This report was externally peer reviewed. The 1989 U.S. Preventive Services
Task Force recommended that all pregnant women receive ABO/Rh blood typing
testing for anti-Rh (D) antibody at their first prenatal visit. Unsensitized
Rh-negative women should receive D Ig at 28 to 29 weeks and within 72 hours
of delivery as well as after spontaneous or therapeutic abortion, ectopic
pregnancy,
amniocentesis, antepartum placental hemorrhage, or a transfusion of Rh-positive
blood products. The Society of Obstetricians and Gynecologists of
Canada and the American College of Obstetricians and Gynecologists recommend
D blood typing and antibody screening at the first prenatal visit and repeat
D antibody screening at 24 to 28 weeks of pregnancy for all D-negative
women. Both groups recommend offering D Ig to all unsensitized D-negative
women at 28 weeks gestation, and to those at increased risk for sensitization
because of delivery of a D-positive infant, antepartum hemorrhage, spontaneous
or induced abortion, amniocentesis, external version procedures or ectopic
pregnancy within 72 hours of the event. They also recommend D Ig be given
to unsensitized D-negative women who have chorionic villus sampling, cordocentesis,
antepartum fetal death, fetal surgery, or transfusion of D-positive blood
products, and measuring fetal blood cell levels in the mother when antepartum
placental hemorrhage occurs.
Sponsors
The Canadian Task Force on Preventive Health Care
developed this guideline with funding from Health Canada.
Selected
References
Source Document
Link to Full Text of this
review
Link to Summary Table of Recommendations of this review
Link to Selected References list of this review
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