The main components of amniotic fluid include water (98–99%); organic components of glucose, fat, protein and protein derivatives, bilirubin, metabolites, fetal AFP, hormones secreted by the placenta and fetus, enzymes (aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, etc.); inorganic components such as electrolytes; and cells detached from the surface of the fetus. Serum potassium, AFP, tissue factors, and lamellar bodies are considered markers of amniotic fluid. We selected serum potassium, AFP and SCs as markers of amniotic fluid in this study.
This study has shown the efficiency of the washing stage of the cell salvage machine, AF contaminants can be effectively reduced when used in combination with a leucodepletion filter, but amniotic fluid on blood recovery still have some effects on HbF.
The AFP level in sample III was significantly lower than that in sample I and sample II in the two groups. K + in sample III was significantly lower than that in sample I in group 2; however, the reduction of K + in group 1 was not significant, which might be due to the use of the nonparametric rank sum test. SCs still existed in sample III in the two groups.
Durand et al. found that the cell saver could not completely remove fetal cell debris. Another study showed that in filtered blood samples, AFP was completely removed, while the SC component still existed. Such reports have raised concerns about amniotic fluid embolus (AFE) after autologous blood transfusion. All of the abovementioned studies are consistent with the results of our study, which suggest that SCs require further clearance. In recent years, the concentrations of SCs and lamellar bodies have decreased significantly with the application of leukocyte filters. Elagamy et al. reported that after using a double suction system and a leukocyte filter, median squamous cell counts (0 [0–1] versus 8 [3–12]/high power field) were significantly lower postfiltration compared to prewash values. Sullivan et al. reported similar results.
The leukocyte depletion filter (LDF) effect
Different LDF materials result in different filtration effects on the components of amniotic fluid. Catling et al. reported combining the Haemonetics-5 Cell Saver system (American blood, Haemonetics 5+) with a Pall RC 100 LDF (Pall RC 100, Pall Biomedical, Portsmouth, UK). The AFP level was significantly decreased postfiltration, while SCs were not effectively filtered and still existed in nearly half of the filtered samples. Using the same cell saver and the new Pall RS filter (LeukoGuard RS, Pall Biomedical Products Co., East Hills, NY), Waters  reported significantly fewer SCs and lamellar bodies.
In this study, a Pall SB leukocyte filter (American blood, LipiGuard SB), which is composed of a polyester non-woven cloth, was used as a filter material. WBCs in sample IV were significantly reduced and almost negligible compared with in sample I and sample III in the two groups. In addition, K + and AFP levels in sample IV were significantly reduced compared with in sample I. SCs in sample IV were significantly reduced compared with in sample III, and there was no significant difference compared with sample I, proving that SCs could be effectively removed by LDF, especially collected with amniotic fluid.
Amniotic fluid on blood recovery effects
Within the last 10 years, the application of intraoperative cell salvage (IOCS) in obstetrics has attracted increasing attention[9–12]. IOCS is already one technique that can be applied to treat obstetric hemorrhage in the UK; the United States Association of Obstetricians and Gynecologists (ACOG) also promotes the use of IOCS with bleeding due to placenta accreta[13–14]. In recent discussions on "perioperative blood conservation," the Italy Immunology and Transfusion Medical Commission (SIMIT) recommended that IOCS be used in obstetric emergencies with bleeding or a risk of bleeding, but added leukocyte depletion filtration after the recovery of blood cells. However, these guidelines have not mentioned the effect of amniotic fluid in the recovery of blood loss.
In 1999, Catling et al.  divided 27 females into two groups, 13 in whom a single suction device was used for all the blood loss and amniotic fluid. Two suction devices were used in another group of 14 patients, and the suction device was switched to an autologous blood device for blood loss after the amniotic fluid had been completely absorbed by normal suction. After the test, they showed that the use of two separate suction devices significantly reduced amniotic fluid composition, and in the single-suction device group, SCs were still visible in the recovered blood. In 2008, Sullivan et al.  also randomly divided 34 females into two groups. Similar to the results obtained with and without the amniotic fluid, AFP, Hb and SC levels showed no significant differences between prewash, postwash and postfiltration samples. Tanqueray advocated using a separate suction system from the time of amniotic membrane rupture until the complete delivery of the fetus and placenta in cesarean sections in order to minimize amniotic fluid contamination of the collected blood. Nevertheless, at several large maternity units, all intraoperatively lost blood is collected, which improves the volume of RBCs salvaged.
In this study, we randomly divided the samples into two groups: A single suction device was used in group 1 for all blood loss in addition to amniotic fluid. Two suction devices were used in group 2 after the beginning of surgery, with an ordinary suction tube used for net absorption of amniotic fluid until the baby was delivered, and the suction device subsequently switched to an autologous blood recovery device for intraoperative blood loss. We found that AFP in prewash samples, SCs in prewash and postwash samples, and HbF in postwash and postfiltration samples showed significant differences between the two groups. However, there was no significant difference in other samples between the two groups, which confirmed that in addition to HbF, amniotic fluid or no recovery had no significant effect on the components of postfiltration blood.
HbF and alloimmunization
The cell saver system could not distinguish between fetal and maternal red cells, and thus, any aspirated fetal red cells will be retransfused. Previously, Durand found that the HbF approached 1% in 7 recovered blood samples out of 15 patients, and Rainaldi found that the HbF approached 1.8%, or 2%, in 3 recovered blood samples out of 15 patients. Many studies have confirmed that fetal red blood cells are present in postfiltration blood[7, 8, 20], thereby increasing the risk of maternal alloimmunization when there is incompatibility between maternal and fetal red cell antigens.
Due to fewer antigenic sites, antibodies may be produced three to six months after birth, and the ABO antigen did not completely develop in neonates. Thus, the clinical significance of the ABO blood group incompatibility is low. In the case of maternal blood group incompatibility, Rh blood group incompatibility should be considered. In pregnant females with Rh-negative blood group incompatibility, the maternal anti-D immunoglobulin can neutralize the immune reactions. The dose of anti-D immunoglobulin is mainly based on the matrix determined by the amount of fetal red blood cells.
Catling determined that the maximum number of fetal red blood cells in the maternal sample was 19 ml (between 2–19 ml) using IOCS, and 500–2500 IU anti-D immune globulin was potentially required. In 2011, Ralph filtered leukocytes using IOCS in 70 females after infusion of autologous blood into maternal fetal red blood cells, where the median was 0.8 ml (between 0.2–12.9 ml) . As pregnancy progresses, fetal red blood cells in maternal circulation will increase to more than 2.5 ml in nearly 1% maternal, 0.3% even more than 15ml . Ralph found that the median fetal red blood cell antepartum in the maternal circulation was approximately 0.48 ml (between 0-4.6 ml) up to 9 ml postpartum. This finding suggests that the 0.2–12.9 ml of fetal red blood cells in recovered blood was essentially the same amount of fetal red blood cells in maternal circulation after delivery [7–8]. Moreover, when volume of fetal red blood cells is no more than 4 ml, 500 units of anti-D immune globulin can prevent alloimmunization but are required within 72 hours after delivery. Thus, rapid measurement of the amount of fetal red blood cells in maternal circulation is important, and if necessary, supplementation with anti-D immunoglobulin to prevent the occurrence of alloimmunization may be required . Considering the risk of alloimmunization, patients infused with anti-D immunoglobulin should be followed-up to assess the antibody response in three to six months, while the establishment of a central database to collect summary information is recommended .
In this study, the HbF of samples III in the two groups were significantly higher than that in samples I. However, the samples III were nearly the same as the samples IV in the two groups without significant differences compared with the samples I, potentially due to the use of the nonparametric rank correlation test. However, HbF levels of sample III and sample IV were higher in Group 1 than in Group 2, means more anti-D immunoglobulin needed, so two suction devices are recommended to reduce HbF pollution.
Although the sample size was calculated after the pre-test, it only considered the measurement of SCs and AFP, and a small trial sample was used. Due to the very low incidence of AFE, a larger sample size is needed to determine the safe use of IOCS in obstetrics.
Thirty-four patients who underwent a cesarean section were randomly selected to participate in this study, and the average blood loss was 547 ml. Furthermore, 71% of patients lost less than 350 ml. Due to the small amount of blood loss in some patients, some bias toward lower Hb levels was introduced due to the dilution effect introduced by the recycling machine during the filtration process.