Blood transfusion and cesarean delivery.

OBJECTIVE: To evaluate risks for intraoperative or postoperative packed red blood cell transfusion in women who underwent cesarean delivery. METHODS: This was a 19-university prospective observational study. All primary cesarean deliveries from January 1, 1999, to December 31, 2000, and all repeat cesareans from January 1, 1999, to December 31, 2002, were included. Trained, certified research nurses performed systematic data abstraction. Primary and repeat cesarean deliveries were analyzed separately. Univariable analyses were used to inform multivariable analyses. RESULTS: A total of 23,486 women underwent primary cesarean delivery, of whom 762 (3.2%) were transfused (median 2 units, 25th% to 75th% 2-3 units). A total of 33,683 women underwent repeat [corrected] cesarean delivery, and 735 (2.2%) were transfused (median 2 units, 25th% to 75th% 2-4 units). Among primary cesareans, general anesthesia (odds ratio [OR] 4.2, 95% confidence interval [CI] 3.5-5.0), placenta previa (OR 4.8, CI 3.5-6.5) and severe (hematocrit less than 25%) preoperative anemia (OR 17.0, CI 12.4-23.3) increased the odds of transfusion. Among repeat cesareans, the risk was increased by general anesthesia (OR 7.2, CI 5.9-8.7), a history of five or more prior cesareans (OR 7.6, CI 4.0-14.3), placenta previa (OR 15.9, CI 12.0-21.0), and severe preoperative anemia (OR 19.9, CI 14.5-27.2). CONCLUSION: Overall, the risk of transfusion in association with cesarean is low. However, both severe preoperative maternal anemia and placenta previa are associated with markedly increased risks. The former argues for optimizing maternal antenatal iron status to avoid severe anemia and the latter for careful perioperative planning when previa complicates cesarean. LEVEL OF EVIDENCE: II-2.

Dwight J. Rouse, md, msph, Cora MacPherson, PhD, Mark Landon, md, Michael W. Varner, md, Kenneth J. Leveno, md, Atef H. Moawad, md, Catherine Y Spong, md, Steve N. Caritis, md, Paul J. Meis, md, Ronald J. Wapner, md, Yoram Sorokin, md, Menachem Miodovnik, md, Marshall Carpenter, md, Alan M. Peaceman, md, Mary Jo O'Sullivan, md, Baha M. Sibai, md, Oded Langer, MD,John M. Thorp, md, Susan M. Ramin, md, and Brian M. Mercer, md, for the National Institite of Child Health and Human Development Maternal-Fetal Medicine Units Network * OBJECTIVE: To evaluate risks for intraoperative or post­operative packed red blood cell transfusion in women who underwent cesarean delivery. METHODS: This was a 19-university prospective obser­vational study. All primary cesarean deliveries from Jan­uary 1, 1999, to December 31, 2000, and all repeat See related article on page 885. * For members of the National Institute of Child Health and Human Develop­ment Maternal-Fetal Medicine Units Network, see the Appendix. From the Departments of Obstetrics and Gynecology, the University of Alabama at Birmingham, Birmingham, Alabama; the George Washington University Biostatistics Center, Washington, DC; Ohio State University, Columbus, Ohio; University of Utah, Salt Lake City, Utah; University of Texas Southwestern Medical Center, Dallas, Texas; University of Chicago, Chicago, Illinois; the National Institute of Child Health and Human Development, Bethesda, Maryland; University of Pittsburgh, Pittsburgh, Pennsylvania; Wake Forest University School of Medicine, Winston-Salem, North Carolina; Thomas Jefferson University, Philadelphia, Pennsylvania; Wayne State University, Detroit, Michigan; University of Cincinnati, Cincinnati, Ohio; Brown Univer­sity, Providence, Rhode Island; Northwestern University, Chicago, Illinois; University of Miami, Miami, Florida; University of Tennessee, Memphis, Tennessee; University of Texas Health Science Center at San Antonio, San Antonio, Texas; University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; University of Texas Health Science Center at Houston, Houston, Texas; and Case Western Reserve University, Cleveland, Ohio. Supported by grants From the National Institute of Child Health and Human Development (HD21410, HD21414, HD27860, HD27861, HD27869, HD27905, HD27975, HD27977, HD34776, HD34722, HD34736, HD34208, HD34270, HD40500, HD40485, HD40544, HD40545, HD40560, HD40572, and HD36807). The following core committee members participated in protocol development and coordination between clinical research centers (F. Johnson andJ. McCampbell'}, protocol and data management and statistical analysis (Elizabeth Thom), and protocol development and oversight (John Hauth). Presented at the annual meeting of the Society for Gynecologic Investigation, Toronto, Ontario, Canada, March 22-26, 2006. Corresponding author: Dwight J. Rouse, MD, MSPH, Department of Obstetrics and Gynecology, University of Alabama at Birmingham, 679 79th St. South, OHB 457, Birmingham, AL 35249-7333; e-mail: [e-mail]. © 2006 by The American College of Obstetricians and Gynecologists. Published by Lippincott Williams & Wilkins. ISSN: 0029-7844/06 cesareans from January 1, 1999, to December 31, 2002, were included. Trained, certified research nurses per­formed systematic data abstraction. Primary and repeat cesarean deliveries were analyzed separately. Univariable analyses were used to inform multivariable analyses. RESULTS: A total of 23,486 women underwent primary cesarean delivery, of whom 762 (3.2%) were transfused (median 2 units, 25th% to 75th% 2-3 units). A total of 33,683 women underwent primary cesarean delivery, and 735 (2.2%) were transfused (median 2 units, 25th% to 75th% 2-4 units). Among primary cesareans, general anesthesia (odds ratio [OR] 4.2, 95% confidence interval [Cl] 3.5-5.0), placenta previa (OR 4.8, Cl 3.5-6.5) and severe (hematocrit less than 25%) preoperative anemia (OR 17.0, Cl 12.4-23.3) increased the odds of transfusion. Among repeat cesareans, the risk was increased by gen­eral anesthesia (OR 7.2, Cl 5.9-8.7), a history of five or more prior cesareans (OR 7.6, Cl 4.0-14.3), placenta previa (OR 15.9, Cl 12.0-21.0), and severe preoperative anemia (OR 19.9, Cl 14.5-27.2). CONCLUSION: Overall, the risk of transfusion in asso­ciation with cesarean is low. However, both severe preoperative maternal anemia and placenta previa are associated with markedly increased risks. The former argues for optimizing maternal antenatal iron status to avoid severe anemia and the latter for careful perioper­ative planning when previa complicates cesarean. (Obstet Gynecol 2006;108:891-7) LEVEL OF EVIDENCE: II-2 I__I emorrhage is second only to embolism as a I I cause of pregnancy-related mortality in the United States.1 Much of the existing data on cesarean- associated transfusion was retrospectively collected and is not contemporary. In this investigation, we have more precisely defined risk factors for the ad­ministration of packed red blood cells in association with cesarean delivery in a recently assembled, large prospective cohort. Our hope was that these data, VOL. 108, NO. 4, OCTOBER 2006 OBSTETRICS & GYNECOLOGY 891 Copyright© American College of Obstetricians and Gynecologists ( reflective of current transfusion practices in a broadly representative sample of U.S. women, might be useful in patient counseling, perioperative planning, and even perhaps in reducing the risk of transfusion. MATERIALS AND METHODS Subjects were identified as part of a 19-center observa­tional study of cesarean delivery for the four-year period January 1, 1999, to December 31, 2002. Each clinical center and the data coordinating center had institutional review board approval for this study, and the require­ment for informed consent was waived. For the first 2 years of the study, women who underwent cesarean delivery were identified on a daily basis by trained, certified research personnel who abstracted data from hospital records and logs onto standardized forms. For the final 2 years of the study, only women who under­went repeat cesarean delivery were identified and had their data collected. This change occurred because the primary focus of this observational study was trial of labor after cesarean. Although planned as only a 2-year study, the declining rate of trial of labor after cesarean necessitated 2 more years of data collection to meet the sample size goal for this group. Gestational age was assigned based on the best estimate of the local caregiv­ers (and in 28%, 46%, and 11%, respectively, included a 1st, 2nd, or 3rd trimester ultrasound). In all of the participating centers, some form of prophylaxis against uterine atony was routinely employed. However, we did not collect information on specific prophylactic regi­mens for individual women. Data lacking unique patient identifiers were trans­mitted weekly from each of the 19 clinical centers by telecommunications link to the data coordinating center where they were edited for missing, out of range, and inconsistent values. Weekly, edit reports were transmitted to each center for correction or clarification. Data were also compared across forms at regular intervals, and corrections and clarifications were requested from the centers as appropriate. The independent variable for this study was transfusion of packed red blood cells, intraoperatively or postoperatively before hospital discharge ("trans­fusion"). Because the 1) obstetric characteristics and clinical situations in which primary and repeat cesar­eans were performed differed substantially (eg, the former most often experienced labor and the latter did not); 2) outcomes associated with certain condi­tions (eg, placenta previa) were predicted to be de­pendent on whether the cesarean was a primary or a repeat; and 3) data collection period for the two conditions was not synchronous, we analyzed pri­mary and repeat cesarean deliveries separately. Categorical variables were compared by the x1 test, Fisher exact test, or Mantel-Haenszel test of trend, as appropriate. Continuous variables were compared using the Wilcoxon rank sum test. Variables found to be significant in univariable analysis were entered into a multivariable logistic regression model. Backward selec­tion was used to retain only those variables with Pvalues less than .05. Nominal two-tailed Pvalues are reported with no adjustments made for multiple comparisons. For this analysis a P value less than .05 was considered statistically significant. All analyses of multiple gestation were predicated only on the first infant delivered. SAS 8 software (SAS Institute, Inc., Cary, NC) was used for analysis. RESULTS Primary Cesareans A total of 23,486 pregnancies were analyzed. Seven hundred sixty-two women (3.2%) were transfused (me­dian 2 units, 25th to 75th % 2-3 units). In 114 (15%) women, the transfusion was given only intraoperatively, in 556 (73%) it was given only postoperatively, and in 92 (12%) women it was given during both periods. The mean (plus or minus standard deviation) maternal age was 27 (±7) years. Forty-two percent were white, 31% African American, 21% Hispanic, and 5% other. Most (68%) were nulliparous. Mean body mass index (BMI) at delivery was 32.5 kg/m2 (±7.1). Fifty-five percent had government-funded (or no) insurance and 45% private insurance. Mean gestational age at delivery was 38 (±4) weeks, and mean birth weight 3,039 (±943) gm. Seventy-five percent experienced labor. The predom­inant cesarean indication was abnormally progressive labor (37%), followed by nonreassuring fetal heart rate status (23%). In univariable analyses, several continuous vari­ables were significantly associated with transfusion (Ta­ble 1). Compared with women who did not undergo transfusion, women who did were, on average, approx­imately one-half year younger, had a slightly lower BMI, and had a preoperative hematocrit that was 4% lower. Their mean gestational age at delivery was nearly 2 weeks earlier; if induced, their median induction time was 2 hours longer; and if they received oxytocin, it was administered for almost 2 hours longer. The average birth weight of their infants was 338 g lighter. We also analyzed hematocrit as a continuous variable: for each percentage point increase in hematocrit, the odds ratio (OR) for transfusion was 0.8 (95% confidence interval [CI] 0.79-0.82). In univariable analyses of categorical variables, significant risk factors for transfusion included nonwhite race, multiparity (and progressively higher parity), mul- 892 Rouse et al Blood Transfusion and Cesarean Delivery OBSTETRICS & GYNECOLOGY Copyright© American College of Obstetricians and Gynecologists ( Table 1. Primary Cesarean Deliveries-Univariable Analysis of Risk Factors for Packed Red Blood Cell Transfusion: Continuous Variables Variable Transfusion (n=762) No Transfusion (n=22,724) P Maternal age (y) 26.3±7.0 26.8±6.5 .012 Gestational age (wk) 36.2±4.7 37.9±3.8 <.001 BMI at delivery (kg/m2) 31,0±6.6 32.6±7.1 <.001 Maternal hematocrit (%) 31,4±5.3 35.3 ±3.8 <.001 Labor duration (h) Spontaneous 6.5 (2.9-13.0) 7.3(3.9-12.5) .377 Induced 18.1 (10.5-28.5) 16.1 (10.6-23.7) .038 Augmented 18.1 (13.1-23.2) 17.1 (12.6-22.3) .220 Duration of oxytocin (h) 12.4±9.2 10.7 ±8.4 .001 Infant birth weight (g) 2,712± 1,058 3,050±936 <.001 BMI, body mass index. Data are presented as mean (plus or minus standard deviation) or median (25-75th percentile) tiple gestation, hypertensive disorders, clinically diag­nosed chorioamnionitis,2 placental abruption, placenta previa, general anesthesia, mild (preoperative hemato­crit 25-29%) and severe (preoperative hematocrit less than 25%) anemia, hysterotomy other than low trans­verse, and prematurity (gestational age less than 37 weeks, Table 2). We combined factors from the above univariable analyses into a multivariable logistic regression model. In the final multivariable model, African American or Hispanic race, multiple gestation, preeclampsia, chorio­amnionitis, placental abruption, mild preoperative ma­ternal anemia (hematocrit 25-29%), general anesthesia, eclampsia or hemolysis, elevated liver enzymes, low platelets syndrome, placenta previa, and severe preop­erative maternal anemia (hematocrit less than 25%) were significantly associated with transfusion in a pro­gressively stronger fashion (Table 3). Repeat Cesareans A total of 33,683 pregnancies were analyzed. Seven hundred thirty-five women (2.2%) were transfused (me­dian 2 units, 25th% to 75th% 2-4 units). In 169 (23%) women, the transfusion was given only intraoperatively, in 436 (59%) it was given only postoperatively, and in 130 (18%) women it was given during both periods. The mean (plus or minus standard deviation) maternal age was 30 (±6) years. Thirty-nine percent were white, 26% African American, 31% Hispanic, and 4% other. Me­dian parity was 1. Mean BMI at delivery was 33.4 kg/m2 (±7.2). Fifty-seven percent had government-funded (or no) insurance, and 43% had private insurance. Mean gestational age at delivery was 38 (±3) weeks, and mean birth weight 3261 (±723) gm. Twenty-nine percent experienced labor. The predominant cesarean indica­tion was elective repeat (63%). In univariable analyses, several continuous vari­VOL. 108, NO. 4, OCTOBER 2006 ables were significantly associated with transfusion (Table 4). Compared with women who did not un­dergo transfusion, women who underwent transfusion were, on average, of lower BMI, and had a preoper­ative hematocrit that was almost 4% lower. Their mean gestational age at delivery was almost 2 weeks earlier and the mean birth weight of their infants was 427 g lighter. If their labor was augmented, the duration of augmentation was shorter. For each per­centage point increase in hematocrit, the OR for transfusion was 0.8 (95% Cl 0.77-0.80). In univariable analyses of categorical variables, significant risk factors for transfusion included nonwhite race, parity of 3 and above, multiple gestation, three or more prior cesareans, hypertensive disorders, clinically diagnosed chorioamnionitis, placental abruption, pla­centa previa, general anesthesia, mild (preoperative hematocrit 25-29%) and severe (preoperative hemato­crit less than 25%) anemia, hysterotomy other than low transverse, and prematurity (Table 5). We combined significant factors from the above univariable analyses into a multivariable regression model and found preeclampsia, African-American or Hispanic race, race category "other," chorioamnioni­tis, placental abruption, mild preoperative maternal anemia (hematocrit 25-29%), general anesthesia, 5 or more prior cesareans, placenta previa, and severe preoperative maternal anemia (hematocrit less than 25%) were significantly associated with transfusion in a progressively stronger fashion (Table 6). DISCUSSION In this contemporary, prospectively assembled cohort of approximately 57,000 women undergoing cesarean delivery, we have confirmed that overall the risk of cesarean-associated packed red blood cell transfusion is relatively low: 3.2% for primary cesarean and 2.2% Rouse et al Blood Transfusion and Cesarean Delivery 893 Copyright© American College of Obstetricians and Gynecologists ( Table 2. Primary Cesarean Deliveries-Univariable Analysis of Risk Factors for Packed Red Blood Cell Transfusion: Categorical Variables Variable n Transfusion n (%) P Maternal race White 9,887 208 (2.1) <.001 African American 7,338 296 (4.0 Hispanic 4,993 212 (4.2 Other 1,268 46 3.6 Nulliparous No 7,394 333 (4.5 <.001 Yes 15,983 420 2.6 Parity 0 15,983 420 2.6 <.001* 1 3,819 126 3.3 2 1,960 89 (4.5 3 881 63 (7.2 4 375 22 5.9 5 or more 359 33 9.2 Multiple gestation Singleton Twins 21,849 676 3.1 <.001* 1,465 72 (4.9 Triplets or higher order 172 14 (8.1 Any multifetal gestation 1,637 86 5.3 <.001 Hypertensive disorder None 18,778 522 (2.8 <.001 Chronic 253 8 3.2 Gestational 1,015 30 (3.0 Preeclampsia 3,084 154 (5.0 Eclampsia 82 8 9.8 HELLP syndrome 271 40 (14.8) Diabetes^ Yes 2,082 64 (3.1) .650 No 21,389 697 3.3) Chorioamnionitis Yes 2,387 113 (4.7) <.001 No 21,098 649 3.1) Placental abruption Yes 807 115 (14.3 <.001 No 22,678 647 2.9) Placenta previa Yes 506 76 (15.0 <.001 No 22,980 686 3.0) Labor None 5,972 244 (4.1) <.001 Induced 6,753 205 (3.0 Augmented 5,772 147 (2.5 Spontaneous 4,985 166 (3.3 rorceps or vacuum attempt Yes 646 26 4.0 .256 No 22,840 736 3.2) Complete cervical dilation Yes 3,360 103 (3.1 .913 No 16,469 499 3.0) Anesthesia type Regional " 20,603 438 (2.1) <.001 General 2,836 323 11.4) Preoperative hematocrit (%) Less than 25 236 84 (35.6 <.001* 25-29 1,615 174 (10.8 30 or more 19,629 469 2.4) Hysterotomy type* Low transverse 22,108 659 (3.0 <.001 Other 1,378 103 7.5 Birth weight (g) Less than 4,000 20,718 688 (3.3 .038* 4,000-4,500 2,152 61 (2.8 More than 4,500 596 12 (2.0 Gestational age (wk) 37 or more 17,191 422 (2.5 <.001* 35-36 2,071 73 (3.5 32-34 1,852 113 (6.1 Less than 32 2,305 145 (6.3) HELLP, hemolysis, low platelets, elevated liver enzymes * P value from test, of trend, t Pregestational and gestational. T Collected during the first 2 years of the study only. 894 Rouse et al Blood Transfusion and Cesarean Delivery OBSTETRICS & GYNECOLOGY Copyright© American College of Obstetricians and Gynecologists ( Table 3. Primary Cesarean Deliveries-Multivariable Analysis of Risk Factors for Packed Red Blood Cell Transfusion Variable n (%) OR for PRBC Transfusion (95% Cl) African-American or Hispanic Race 12,331 (52.5) 1.3 (1.1-1.6) Multiple gestation 1,637 (7.0) 1.7 (1.3-2.1) Preeclampsia 3,084 (13.1) 1.9 (1.6-2.3) Chorioamnionitis 2,387(10.2) 2.5 (2.0-3.2) Placental abruption 807 (3.4) 2.9 (2.2-3.7) Mild anemia (hematocrit 25-29%) 1,615 (7.5) 3.4 (2.8-4.2) General anesthesia 2,836 (12.1) 4.2 (3.5-5.0) Eclampsia or HELLP syndrome 353 (1.5) 4.3 (3.1-6.2) Placenta previa 506 (2.2) 4.8 (3.5-G.5) Severe anemia (hematocrit<25l)/o) 236 (1.1) 17.0 (12.4-23.3) OR, odds ratio; PRBC, packed red blood cell transfusion; Cl, confidence interval; HKLLP, the syndrome of hemolysis, elevated liver enzymes, and low platelets. Table 4. Repeat Cesarean Deliveries-Univariable Analysis of Risk Factors for Packed Red Blood Cell Transfusion: Continuous Variables Variable Transfusion (n=735) No Transfusion (n =32,948) P Maternal age (y) 29.6±6.2 29.5±5.8 .956 Gestational age (wk) 36.4±4.0 38.3±2.5 <.001 BMI at delivery (kg/m2) 33.1 ±8.3 33.5 ±7.2 .005 Maternal hematocrit (%) 31.1 ±5.0 34.9±3.7 <.001 Labor duration (h) Spontaneous 7.8 (4.0-12.3) 7.5 (4.6-12.3) .757 Induced 13.9 (9.5-23.3) 13.7(9.0-22.0) .804 Augmented 11.8 (8.7-18.8) 15.4 (11.2-20.6) .042 Duration of oxytocin (h) 6.3 (3.0-11.8) 7.3 (3.7-11.8) .432 Infant birth weight (g) 2,843±9G0 3,270±714 <.001 BMI, body mass index. Data are mean (plus or minus standard deviation) or median (25-75t.h percentile) for repeat. These rates are comparable to the contem­poraneous rate of 3.3% (primary and repeat cesareans combined) reported in a four-hospital Danish study and a single hospital study in which a rate of 3.2% was reported for 1987.3,4 In addition to the large size of the cohort, a major strength of this study is that all data for the project were abstracted by trained and certified research nurses before hospital discharge using uniform crite­ria, and ongoing, systematic procedures for data quality control were employed. The major weakness of these data is that they are observational and do not reflect standardized transfusion practices. Nor did the analyses we performed take into account specific prophylactic regimens for the prevention of uterine atony, because this information was not collected. Our analysis has revealed multiple factors that are associated with an increased risk of transfusion for women undergoing both a primary and a repeat cesarean delivery. Some of these factors have been previously identified, although from much smaller cohorts.-' Most notably, among women who under­went primary cesarean, a preoperative hematocrit of less than 25% was associated with a 36% risk of transfusion. Among women who underwent repeat cesarean, this degree of anemia also was associated with a high risk of transfusion (28%), as was the occurrence of placenta previa (32% risk). These risks argue for optimizing maternal antenatal iron status to avoid severe anemia, because iron deficiency is the most common cause of anemia during pregnancy,(l and they suggest that informing severely anemic iron deficient women about their high risk of transfusion should they undergo cesarean might enhance compli­ance with iron supplementation. These data also argue for careful perioperative planning when pla­centa previa complicates repeat cesarean. As have others, we found that nontransverse hyste­rotomy was associated with an increased risk of transfu­sion, but with multivariable analysis this association was not statistically significant.' Also as have others, we found that general anesthesia was independently associ- VOL. 108, NO. 4, OCTOBER 2006 Rouse et al Blood Transfusion and Cesarean Delivery 895 Copyright© American College of Obstetricians and Gynecologists ( Table 5. Repeat Cesarean Deliveries-Univariate Analysis of Risk Factors for Packed Red Blood Cell Transfusion: Categorical Variables Variable n Transfusionn (%) P Maternal race White 13,028 183 (1.4) <.001 African American 8,599 315 3.7 Hispanic 10,439 197 1.9 Other 1617 40 (2.5) Parity 1 18,099 252 (1.4) <.001* 2 9,726 220 2.3 3 3,565 149 4.2 4 1,218 55 4.5 5 or more 861 58 (6.7) Multiple gestation Singleton 32,840 703(2.1) .001* Twins 811 30 3.7 Triplets or higher 32 2 6.3 All multiple gestations 843 32 (3.8) .001 Number of prior cesareans 1 23,579 427(1.8) <.001* 2 7,902 202 2.6 3 1,754 75 4.3 4 323 15 4.6) 5 or more 110 16 (14.6) Hypertensive disorder ^None 30,135 614(2.0) <.001 Chronic 509 10 2.0 Gestational 944 25 2.7 Preeclampsia 1,925 72 3.7 Eclampsia 31 3 9.7 11E1.1 .i 137 10(7.3) Diabetes'1' Yes 3,479 81 (2.3) .518 No 30,194 652 (2.2) Chorioamnionitis Yes 561 32 (5.7) <.001 No 33,121 703(2.1) Placental abruption 71 (14.1) Yes 504 <.001 No 33,178 664 (2.0) Placenta previa Yes 394 127(32.2) <.001 No 33,289 608(1.8) Labor None 23,953 461 (1.9) <.001 Induced 1,554 51 3.3 Augmented 1,538 42 2.7 Spontaneous 6,638 181 (2.7) Forceps or vacuum attempt 95 5 (5.3) .057 Yes No 33,588 730 (2.2) Complete cervical dilation Yes 761 25 (3.3) .088 No 17,003 395 (2.3) Anesthesia type Regional 31,986 458 (1.4) <.001 General 1,654 273(16.5) Preoperative hematocrit (%) Less than 25 279 79 (28.3) <.001* 25-29 2,662 184 6.9 30 or more 28,790 421 (1.5) Hysterotomy type* 14,866 275(1.9) <.001 Low transverse Other 922 88 (9.5) Birth weight Less than 4,000 g 29,771 668 (2.2) .059* 4,000-4,500 £ 3,125 47 1.5 More than 4,£>00 g Gestational age (weeKs) 773 17(2.2) 37 or more 28,201 439(1.6) <.001* 35-36 2,629 104 4.0 32-34 1,569 89 5.7 Less than 32 1,235 102 8.3 HKLLP, hemolysis, low platelets, elevated liver enzymes. * P value from test, of trend, t Pregestational and gestational. T Collected during the first two years of the study only. 896 Rouse et al Blood Transfusion and Cesarean Delivery OBSTETRICS & GYNECOLOGY Copyright© American College of Obstetricians and Gynecologists ( Table 6. Repeat Cesarean Deliveries-Multivariable Analysis of Risk Factors for Packed Red Blood Cell Transfusion Variable n (%) OR for PRBC Transfusion (95% Cl) Preeclampsia 1,925 (5.7) 1.6 (1.2-2.1) African-American or Hispanic Race 19,038 (56.5) 1.7 (1.4-2.0) Race category "other" 1,617(4.8) 2.0 (1.4-2.9) Chorioamnionitis 561 (1.7) 2.5 (1.7-3.8) Placental abruption 504 (1.5) 2.6 (1.8-3.7) Mild anemia (hematocrit 25-29%) 2,662 (8.4) 3.8 (3.1-4.6) General anesthesia 1,654 (4.9) 7.2 (5.9-8.7) 5 or more prior cesareans 110 (0.3) 7.6 (4.0-14.3) Placenta previa 394 (1.2) 15.9 (12.0-21.0) Severe anemia (hematocrit <25%) 279 (0.9) 19.9 (14.5-27.2) OR, odds ratio; PRBC, packed red blood cell transfusion; CI, confidence interval. ated with an increased risk of transfusion.8 10 In our study, the odds were quadrupled for women undergoing primary cesarean, and increased seven-fold for women undergoing repeat cesarean. In addition to the well- recognized risk of aspiration and failed intubation asso­ciated with general anesthesia, our data suggest that, all other things being equal, avoidance of transfusion, espe­cially in the face of severe anemia, may be another reason to choose regional anesthesia for cesarean. REFERENCES 1. Chang J, Elam-Evans LD, Berg CJ, Herndon J, Flowers L, Seed KA, et al. Pregnancy-related mortality surveillance-United States, 1991-1999. MMWR Surveill Summ 2003;52:1-8. 2. Rouse DJ, Landon M, Leveno KJ, Leindecker S, Varner MW, Caritis SN, et al. The Maternal-Fetal Medicine Units cesarean registry: chorioamnionitis at term and its duration-relationship to outcomes. Am J Obstet Gynecol 2004;191:211-6. 3. Larsen R, Titlestad K, Lillevang ST, Thomsen SG, Kidholm K, Georgsen J. Cesarean section: is pretransfusion testing for red cell alloantibodies necessary? Acta Obstet Gynecol Scand 2005;84:448-55. 4. Camann WR, Datta S. Red cell use during cesarean delivery. 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APPENDIX In addition to the authors, other members of the National Institute of Child Health and Human Development Mater­nal- Fetal Medicine Units Network are as follows: Ohio State University-J. lams, F. Johnson, S. Meadows, H. Walker University of Alabama at Birmingham-J. Hauth, A. Northen, S. Tate University of Texas Southwestern Medical Center-S. Bloom, J. McCampbell, D. Bradford University of Utah-M. Belfort, F. Porter, B. Oshiro, K. Anderson, A. Guzman University of Chicago-J. Hibbard, P. Jones, M. Ramos- Brinson, M. Moran, D. Scott University of Pittsburgh-K. Lain, M. Cotroneo, D. Fischer, M. Luce Wake Forest University-M. Harper, M. Swain, C. Moorefield, K. Lanier, L. Steele Thomas Jefferson University- A. Sciscione, M. DiVito, M. Talucci, M. Pollock Wayne State University-M. Dombrowski, G. Norman, A. Millinder, C. Sudz, B. Steffy University of Cincinnati-T. Siddiqi, H. How, N. Elder Columbia University-Y. Malone, M. D'Alton, V. Pem­berton, V. Carmona, H. Husami Brown University-H. Silver, J. Tillinghast, D. Catlow, D. Allard Northwestern University-M. Socol, D. Gradishar, G. Mallett University of Miami- G. Burkett, J. Gilles, J. Potter, F. Doyle, S. Chandler University of Tennessee-'W. Mabie, R. Ramsey University of Texas at San Antonio-O. Langer, S. Barker, M. Rodriguez University of North Carolina-K. Moise, K. Dorman, S. Brody, J. Mitchell University of Texas at IIouston-'L. Gilstrap, M. Day, M. Kerr, E. Gildersleeve Case Western Reserve University-H. Ehrenberg, C. Mil- luzzi, B. Slivers, C. Santori The George Washington University Biostatistics Center-E. Thom, S. Gilbert, H. Juliussen-Stevenson, M. Fischer National Institute of Child Health and Human Develop- ment-D. McNellis, K. Howell, S. Pagliaro VOL. 108, NO. 4, OCTOBER 2006 Rouse et al Blood Transfusion and Cesarean Delivery 897 Copyright© American College of Obstetricians and Gynecologists (