Fetomaternal hemorrhage (FMH) is blood mixing between fetus and mother during sensitizing events. Anti-D immunoglobulin is administered in Rh-negative women to prevent isoimmunization. Dosing guidelines differ across countries. UK and US have differing dosing schemes. Little is known about the FMH occurring with dilation and evacuation. There is a resource and cost savings incentive to use the smallest dose that covers the FMH.
This study describes the amount of FMH occurring with dilation and evacuation from 15w0d to 23w6d gestation using Kleihauer-Betke (KB) tests, which detects fetal red blood cells in maternal red blood cells. This study also describes pre-procedure FMH, and the proportion of subjects with FMH over and under the amounts covered by UK and US doses.
Women with singleton pregnancies between 15w0d and 23w6d gestation were recruited. We obtained blood pre-procedure and again 30-120minutes post-procedure for KB testing. Three hundred pre- and post-procedure pairs of KB tests were completed. KB used to calculate volume of fetal blood in the maternal circulation, before and after dilation and evacuation.
Results: The median gestational age was 20w0d. Nine percent were Rh-negative. Five samples had FMH greater than 10 mL, two of which also had high baseline FMH over 10 mL. Average pre- and post-procedure KB tests showed FMH of 0.42 mL and 1.65 mL, respectively. Eight-eight percent had no detectable FMH pre-procedure, and 39.6% post-procedure. All of the participants below 18w0d had post-procedure FMH less than UK dosing. Over 98% of FMH through 23w6d fell below UK dosing.
Conclusion: Over 98% of post-procedure FMH with dilation and evacuation through 23w6d are sufficiently treated with the UK dosing scheme. These data support the UK dosing scheme for procedures through 18w0d. Additional studies are needed in this age range to determine if the guidelines warrant amendment.