Prevalence of FMH detected
Studies have shown that some degree of fetal-maternal transplacental hemorrhage occurs in 75% of all pregnancies. This phenomenon is not dangerous to the fetus unless there is incompatibility between the mother and her fetus with respect to the D antigen of the red blood cells. FMH occurs in 3% of pregnancies in the first trimester, 12% in the second trimester, 45% in the third trimester, and 64 to 100% after delivery [1, 7]. Our result has shown that FMH occurs in 52% and 60% of our participants after delivery and other procedures when employing KBT and FCM methods, respectively.
The total volume of fetal cells in the maternal circulation is usually small and does not exceed 0.1 to 0.25 ml in most cases, but large-volume FMH occurs less often, with more than 15 ml of fetal red cells (approximately 30 ml whole blood) detected at a rate of 1.6% after cesarean section or complicated vaginal delivery and 0.7% after spontaneous vaginal delivery . Our result has indicated that around 92.5% and 87% of FMH calculated were <10 ml of fetal whole blood (<5 ml fetal RBC) whereas the remaining 7.5% and 13% were >10 ml of fetal whole blood (>5 ml fetal RBC) for KBT and FCM methods, respectively.
This result was inconsistent with the result revealed by Augustson et al. in which they concluded that 90.4% (4651/5148) of the women had FMH volume of 1.0 mL or less of Rh D-positive red cells, and 98.5% (5072/5148) had a volume of less than 2.5 mL. Only 0.4% of the cases had an FMH volume of 6.0 mL or greater (range, 6.0–92.4 mL) . The variation of the result might be due to small sample size we used in contrast to Augustson et al.
In this study FMH of >30 mL was observed in 1.3% and 2.7% of the mothers by KBT and FCM methods, respectively. It was inconsistent with Johnson et al. findings that stated in only 0.5% of deliveries FMH exceeds 25 mL .
Comparison of KBT and FCM methods
FCM may be helpful for the accurate quantitation and management of patients with large FMH and in cases where the presence of maternal hemoglobin F containing cells renders the KBT technique inaccurate. While a well standardized KBT is appropriate as a screening test for FMH, studies to assess the role of FCM for detecting FMH are warranted . Our result has shown that FMH calculated by FCM and KBT have good correlation for categorized values (r = 0.828, p < 0.005) as well as for continuous values (r = 0.897, p = 0.000). This finding was consistent with the study conducted by Pastoret et al. that revealed a good correlation between FCM and KBT (r = 0.87) . In contrast to this, a study conducted by Johnson et al. verified the correlation between KBT and FCM results was poor. In 38 (88%) cases the size of FMH quantitated by FCM was lower than that estimated using the KBT technique. In 13 (30%) cases no Rh D immunoglobulin positive cells were detected by FCM .
The agreement between the two methods was moderate with the kappa value (κ = 0.53; 95% CI, 000 to 0.039 p = 0.000) that show the two methods have agreement for calculating RhD + ve FMH. Our result was consistent with a study conducted by Savithrisowmya et al. that verified the volume of post-delivery FMH estimated by KBT and FCM correlated well (r = 0.75; ICC α = 0.73) . However, less consistent with the study conducted by Pelikan et al. which showed that the agreement between the manual KBT and FCM was fair with a weighted k, 0.40; 95% CI, 0.15-0.66 and correlation (r) of 0.69 .
Dose requirements of prophylactic RhIG
The possibility to accurately detect FMH and precisely determine its volume would enable more effective and less costly prevention of RhD alloimmunization. RhIG could be administered only in indicated cases and only in doses essentially necessary for prevention of RhD alloimmunization . As indicated the findings of our study verified FMH calculated ranges from 0.95 to 38 mL and from 0.74 to 35.7 mL with means of 1.4 ± 1.8 and 3.3 ± 3.6 for KBT and FCM respectively, so to neutralize these amounts of fetal whole blood we need administering RhIG from 50 to 300 μg and multiples of these doses.
Administration of 100 IU (20 μg) Rh D immunoglobulin has been demonstrated to protect against 1 ml of fetal red cells, 500 IU (100 μg) should protect against FMH of up to 5 ml of fetal red cells and 1,500 IU (300 μg) Rh D immunoglobulin against FMH of approximately 15 ml of fetal red cells . Before 20 weeks’ gestation 250 IU should be given. After 20 weeks’ gestation blood should be taken at least for the conventional KBT to estimate the size of the FMH and 500 IU of RhIG given . This showed for the FMH we have calculated in the current study, 500 IU (100 μg) dose of RhIG would have been sufficient for 92.5% and 87% of the 39 and 45 Rh D-negative mothers if KBT and FCM were employed, respectively. This result was consistent with a study conducted by Lubusky et al. that revealed during normal vaginal delivery as well as during delivery by cesarean section, FMH of less than 5 mL occurs in the great majority of cases, and thus for the prevention of D alloimmunization, RhIG dose of 100 μg should be sufficient .
The widespread adoption of postpartum immunoprophylaxis with a single dose of Rh D immunoglobulin dramatically reduced the incidence of Rh D immunization, and HDFN. However, despite this the incidence of Rh D immunisation during pregnancy remains at approximately 1-2%. This can partly be explained by the occurrence of a FMH of a volume larger than the protection offered by a single dose of Rh D Immunoglobulin . In our study, 1.3% and 2.7% of FMH calculated were >30 mL as quantified by KBT and FCM methods, respectively that requires a neutralizing dose of more than 300 μg RhIG.
On the other hand our result was inconsistent with Johnson et al. findings that stated in only 0.5% of deliveries FMH exceeds 25 mL. It is, therefore, important that the volume of FMH is accurately assessed so that, if necessary, a supplementary dose(s) of RhIG can be administered and maternal alloimmunisation prevented .
The result of our study has shown all expected risk factor were not associated with FMH, but gestational age 20–28 weeks was significantly different from other gestational ages by one-way ANOVA with mean and standard deviation (M = 10.9 SD = 11.1) (Figure 2). This could be because of the fact that most of our participants at this gestation age were having abortion or miscarriage of delivery. This study was consistent with the study conducted by Von Stein et al. which demonstrates an increased incidence of FMH in patients threaten to abortion compared with a gestationally matched control group .
Our results also consistent with the study conducted by Salim et al. that revealed there appears to be no difference in the incidence of large fetomaternal hemorrhage between cesarean and vaginal deliveries or between singleton and multiple deliveries . Again Pelikan et al. reported no difference between vaginal and cesarean deliveries . Besides this, David et al. identified Twin pregnancy as the only independent risk factor for severe fetal-to-maternal transfusion, but ABO-incompatibility between mother and infant seems to be protective against Rh D-alloimmunization .
Our result was inconsistent with a study conducted by Lubusky M et al. that verified delivery by cesarean section presented a higher risk of incidence of FMH of more than 2.5 mL (odds ratio, 2.2; p = 0.004) when compared with normal vaginal delivery. It did not, however, present a significant risk factor for the incidence of excessive volumes of FMH of more than 5 mL . We thought our study did not demonstrate associations with many expected risk factors because of the smaller sample size we used than many studies conducted with this title/area.
This study is sounder if it were conducted with more sample size and using anti-HgF monoclonal antibody besides the two methods.