Lack of anti-D in women at birth following antepartum immune globulin prophylaxis

Very Prolonged Anti-D: Confusion Surrounding Alloimmunization After Extra Rh Immunoglobulin: A Case Report

BACKGROUND

Rh immunoglobulin (RhIg) is usually detectable a maximum of 12 to 14 weeks after administration. Positive antibodies beyond this time frame suggests alloimmunization.

CASE

A woman had three pregnancies over a 6-month period, with two first-trimester losses. She received RhIg in the first pregnancy but not in the second. Two months after the second loss, in her third pregnancy, she received RhIg at week 6 due to first-trimester bleeding. She was subsequently anti-D antibody positive up to week 28 with antibodies too low to titre, leading to confusion about whether alloimmunization had occurred.

CONCLUSION

Rh Ig administration led to positive anti-D antibodies lasting 22 weeks, suggesting keeping this differential diagnosis in mind when suspecting alloimmunization with positive antibodies at levels too low to titre.

Risk factors for RhD immunisation despite antenatal and postnatal anti-D prophylaxis

OBJECTIVE

To identify risk factors for Rhesus D (RhD) immunisation in pregnancy, despite adequate antenatal and postnatal anti-D prophylaxis in the previous pregnancy. To generate evidence for improved primary prevention by extra administration of anti-D Ig in the presence of a risk factor.

DESIGN

Case-control study.

SETTING

Nation-wide evaluation of the Dutch antenatal anti-D-prophylaxis programme.

POPULATION

CASES

42 RhD-immunised parae-1, recognised by first-trimester routine red cell antibody screening in their current pregnancy, who received antenatal and postnatal anti-D Ig prophylaxis (gifts of 1000 iu) in their first pregnancy.

CONTROLS

339 parae-1 without red cell antibodies.

METHODS

Data were collected via obstetric care workers and/or personal interviews with women.

MAIN OUTCOME MEASURE

Significant risk factors for RhD immunisation in multivariate analysis.

RESULTS

Independent risk factors were non-spontaneous delivery (assisted vaginal delivery or caesarean section) (OR 2.23; 95% CI:1.04-4.74), postmaturity (>or=42 weeks of completed gestation: OR 3.07; 95% CI:1.02-9.02), pregnancy-related red blood cell transfusion (OR 3.51; 95% CI:0.97-12.7 and age (OR 0.89/year; 95% CI:0.80-0.98). In 43% of cases, none of the categorical risk factors was present.

CONCLUSIONS

In at least half of the failures of anti-D Ig prophylaxis, a condition related to increased fetomaternal haemorrhage (FMH) and/or insufficient anti-D Ig levels was observed. Hence, RhD immunisation may be further reduced by strict compliance to guidelines concerning determination of FMH and accordingly adjusted anti-D Ig prophylaxis, or by routine administration of extra anti-D Ig after a non-spontaneous delivery and/or a complicated or prolonged third stage of labour.