Postpartum hemorrhage after vaginal birth: an analysis of risk factors.

Objective: To determine, in a single tertiary obstetric hospital, the incidence of and risk factors for postpartum hemorrhage (PPH) after a vaginal birth.

Methods: PPH was defined as measured blood loss greater than 1,000mL and/or need for a transfusion.

Results: Over a 4-year period, 13,868 of 19,476 women delivered vaginally, with a PPH rate of 5.15%. Identified risk factors for PPH were Asian race, maternal blood disorders, prior PPH, history of retained placenta, multiple pregnancy, antepartum hemorrhage, genital tract lacerations, macrosomia (>4 kg), and induction of labor, as well as chorioamnionitis, intrapartum hemorrhage, still birth, compound fetal presentation, epidural anesthesia, prolonged first/second stage of labor, and forceps delivery after a failed vacuum.

Conclusions: Identification of risk factors for PPH after a vaginal delivery may afford prophylactic treatment of such women with reduction of morbidity.

**********

Postpartum hemorrhage (PPH) is responsible for 25% of the 515,000 maternal pregnancy-related deaths reported by the World Health Organization. (1) The average blood loss for a vaginal delivery is approximately 500 mL, a calculation determined in an investigation using chromium-labeled red blood cells in 1962. (2) Although most women can tolerate blood losses between 500 to 1,000 mL at the time of delivery, women with marginal blood stores or other medical problems may have significant morbidity associated with losses in excess of these amounts. Accordingly, investigators have attempted to identify those women at greatest risk for an excessive blood loss at the time of delivery.

Significant associated risk factors after a vaginal delivery for blood loss greater than 1,000 mL in the first 24 hours after delivery include labor longer than 12 hours, macrosomia (>4 kg), episiotomy, and retained placenta. (3,4) Other studies have identified low parity, advanced maternal age, female circumcision, antenatal hospitalizations, twins, induction/augmentation of labor, prolonged second and third stages of labor, anesthesia, and Asian or Hispanic ethnicity as risk factors for a postpartum hemorrhage. (5-9) Previous investigations of post-partum hemorrhage after vaginal delivery are limited by the methodology used in the estimation of blood loss, the combining of vaginal and operative abdominal delivery for analysis, the sample size evaluated, data from a number of hospitals with varying techniques of blood loss assessment, and failure to account for other factors that may have influenced the evaluation of the blood loss.

The purpose of this investigation was to accurately describe blood loss after vaginal delivery in a single tertiary obstetric hospital, and to determine the factors influencing PPH.

Materials and Methods

An extensive obstetric database was created in 1998 at King Edward Memorial Hospital, Perth, Australia, which records multiple fields of information on each pregnancy, including maternal demographics, past obstetric history, current medical conditions, antenatal diagnostic procedures and fetal conditions, antepartum complications, intrapartum events, mode of birth, and immediate postpartum events. Immediately after each delivery, the required intrapartum fields of information were entered by the attending midwife as well as the intrapartum and immediate postpartum events of that delivery. This information is then correlated with antepartum records, postpartum records, and neonatal records before the patient's discharge from the hospital or soon thereafter by the database coordinator. The accuracy of those records is also verified by the database coordinator. This study was initiated to assess the rate of postpartum hemorrhage and compare it with hospitals delivering similar number of patients with comparable maternal demographics. This study was determined to be exempt from institutional review approval by the Ethics Committee at King Edward Memorial Hospital.

Blood loss at vaginal delivery was calculated by collecting and measuring the blood in collection devices used specifically for vaginal birth and then weighing sheets, drapes, and sponges after delivery. Postpartum hemorrhage was defined as blood loss in excess of 1,000 mL and/or need for red blood cell transfusion because of maternal anemia and/or hemodynamic instability. Admission and postdelivery hematocrits were not obtained on all admissions; therefore the criteria used in this study for a postpartum hemorrhage was measured blood loss in excess of 1,000 mL and need for blood transfusion. All vaginal deliveries beyond 20 weeks of gestation were evaluated. Only one pregnancy from each subject was used in this analysis.

Multiple variables that have been linked with postpartum hemorrhage and other variables that have not previously been assessed were evaluated for a possible connection with postpartum hemorrhage. Medical conditions evaluated included chronic hypertension, insulin-dependent diabetes, alcohol or drug addiction, maternal obesity, circulatory system disorders (history of heart surgery, heart valve prosthesis, pulmonary embolus, vascular disease, and heart disease), blood disorders (sickle cell anemia, thalassemia, thrombocytopenia, coagulation defects, and thrombophilia), vaginal or cervical problems (cervical cone biopsy, cervical suture, colposcopy with biopsies), and leiomyomata. Past obstetric problems assessed included uterine/vaginal anomalies, contracted maternal inlet/outlet, antenatal procedures (chorionic villus sampling, amniocentesis, fetal reduction, fetal transfusion), fetal anomalies, history of a previous fetal loss, and prior postpartum hemorrhage. Antepartum events evaluated included antenatal care, single versus multiple gestation, oligohydramnios (defined as amniotic fluid index of 5), hydramnios (defined as amniotic fluid index > 18), placenta location, antepartum bleeding (placental abruption, placenta previa, or bleeding of unknown cause after 20 weeks of pregnancy), threatened abortion, preterm labor, preterm rupture of the membranes, and preeclampsia/eclampsia. Intrapartum events assessed included maternal transfer, presentation at delivery, onset of labor (spontaneous or induced), type of analgesia, location of delivery (labor and delivery at the hospital or the attached family birthing center), the length of the first stage of labor (prolonged latent phase labor > 20 hours in nulligravida and > 14 hours in multigravida, prolonged active phase labor of < 1.2 cm per hour in nulligravida and < 1.4 cm in multiparous patient), the length of the second stage of labor (> 2 hours without epidural and > 3 hours with epidural), length of the third stage of labor > 30 minutes), use of oxytocin for induction or augmentation, chorioamnionitis (temperature > 38[degrees]C, which is persistent and uterine tenderness/irritability), gestational age at delivery, excessive intrapartum bleeding, intrauterine fetal demise (IUFD), trauma of the genital tract at delivery, and neonatal birth weight.

Prepregnancy medical conditions, antepartum, intrapartum, and immediate postpartum events were evaluated by univariate analysis for an association with PPH. All of the identified variables associated with PPH were then entered into a logistic regression model in a hierarchical fashion. At each step, the Wald [chi square] was inspected, and only variables that had a high probability of association (P < 0.3) were retained before the next set of variables were added to the model. Once all the variables had been added, categoric variables with a Wald [chi square] probability of greater than 0.2 were collapsed into the baseline category. Odds ratios (OR) and 95% confidence intervals (CI) were then calculated for all variables and categories that were still in the model. A P value of less than 0.05 was considered significant.

Results

Between July 1 of 1998 and June 30 of 2002, there were 18,735 women giving birth to 19,476 infants at this tertiary obstetric hospital. There were 4,867 women delivered by cesarean and 13,868 delivered vaginally. Postpartum hemorrhage was identified in 714 of the 13,868 (5.15%) of the women delivering vaginally.

The maternal demographics of the women delivering vaginally were an average age of 28.2 [+ or -] 6 years (range, 12.8 to 49) and race (80.4% white, 10.4% Asian, 9.2% others); 29.1% were primigravidas, and the median gestational age at the time of the delivery was 38 weeks (interquartile range, 38 to 40 weeks; overall range, 20 to 43 weeks). The median blood loss for the entire cohort of women delivered vaginally was a median blood loss of 250 mL (interquartile range, 150 to 350; overall range, 50 to 10,000 mL). The identified predictive factors for postpartum hemorrhage were divided into maternal demographics, medical history, and antepartum, intrapartum, and immediate postpartum events.

Table 1 shows that Asian race was the only demographic factor associated with PPH (OR, 1.8; 95% CI, 1.4 to 2.2). Past medical events associated with PPH were a history of blood disorders (OR, 1.3; 95% CI, 1.1 to 1.6) and a history of a PPH (OR, 2.2; 95% CI, 1.7 to 2.9). Antepartum factors linked with PPH included multiple pregnancy (OR, 2.2; 95% CI, 1.5 to 3.2), twin-twin transfusion syndrome (OR, 5.1; 95% CI, 1.5 to 15.7), antepartum hemorrhage (OR, 1.8; 95% CI, 1.3 to 2.3), IUFD (OR, 2.6; 95% CI, 1.1 to 5.7), and induction of labor (OR, 1.5; 95% CI, 1.2 to 1.7).

Intrapartum events associated with PPH included the use of epidural analgesia (OR, 1.3; 95% CI, 1 to 1.6), chorioamnionitis in labor (OR, 1.6; 95% CI, 1.1 to 1.7), intrapartum hemorrhage (OR, 1.5; 95% CI, 1 to 2.3), compound presentation (OR, 3; 95% CI, 1.1 to 7.3), prolonged first stage of labor (OR, 1.6; 95% CI, 1 to 1.6), prolonged second stage of labor (OR, 1.6; 95% CI, 1.1 to 2.1), delivery by forceps after an unsuccessful vacuum delivery (OR, 1.9; 95% CI, 1.1 to 3.2), trauma to the genital tract (OR, 1.7; 95% CI, 1.4 to 2.1), and prolonged third stage of labor (OR, 6.2; 95% CI, 4.6 to 8.2). In addition, neonatal birth weight in excess of 4 kg was associated with PPH (OR, 1.8; 95% CI, 1.4 to 2.3) (Table 1). The relation of risk factors for a postpartum hemorrhage after a vaginal delivery (none, one, two, and three or more) and the subsequent risk of a postpartum hemorrhage is documented (Table 2).

Discussion

Maternal mortality rate has declined markedly in the United States from 850 per 100,000 live births in 1900 to 11.8 maternal deaths per 100,000 live births in 1999. (10) Despite the frequent use of intravenous access on most laboring women in the United States and the ready availability of blood and blood products, hemorrhage related to pregnancy remains just slightly less than embolism at 17.2% and was the second leading cause of pregnancy-related maternal death in 1999. (10) The rate of postpartum hemorrhage in this investigation (5.5%) is similar to that quoted in the largest recent investigation to date that evaluated the risk of postpartum hemorrhage (3.9%). (8)

Asian race was linked with PPH in this study. This has also been previously observed with both the Asian (8) and Hispanic (11) races compared with other races. A medical history of a bleeding disorder and a prior postpartum hemorrhage were linked with PPH in the current pregnancy in this study. It is easy to understand the association of a PPH in women with a history of a bleeding disorder outside of pregnancy. Prior postpartum hemorrhage has been correlated with an increased risk of PPH in the current pregnancy, (8) but that link is not agreed on by all investigators. (5) Antepartum incidents including antepartum bleeding, multiple gestation, and an IUFD were correlated with an increased risk of PPH. Multiple gestations overdistend the uterus, and uterine atony may accompany pregnancies with twins or higher-order multiple gestations. (8) The observation of a twin pregnancy complicated by twin-twin transfusion sequence has not been described, but with the hydramnios and enlarged uterus accompanying this type of pregnancy, uterine atony at the time of delivery is easy to understand.

Genital tract trauma, vulvar and vaginal lacerations, along with lacerations of the cervix or involving the perirectal tissue, anal sphincter, or rectum, are also correlated with PPH. Genital tract trauma is a known reason for excessive blood loss at vaginal delivery. (8) We observed that delivery by forceps after an unsuccessful vacuum extraction was linked with a greater risk of PPH. The sequential use of vacuum followed by forceps has previously been correlated with PPH. Gardella et al, (12) in a study evaluating the sequential use of vacuum and forceps on neonatal and maternal outcomes, observed an association with a greater risk of PPH than the individual risk of vacuum or forceps alone. A prolonged third stage of labor in excess of 30 minutes has previously been linked with excessive blood loss at vaginal delivery. (8)

Another factor that has been related to PPH in the literature is preeclampsia. The most likely reason that preeclamptic pregnancies have an increased risk of PPH appears unrelated to the preeclampsia itself but secondary to the magnesium sulfate use, which is a known uterine relaxing agent. We did not observe preeclampsia to be associated with PPH, but that may be because of the very limited use of magnesium sulfate for seizure prophylaxis in these pregnancies. Maternal age of 30 years or greater (7,13) has been linked with PPH, and this is consistent with our study in which both a maternal age of less than 18 years was protective (OR, 0.84; 95% CI, 0.5 to 1.2) and maternal age greater than 35 years was correlated (OR, 1.1; 95% CI, 0.8 to 1.3) with PPH, although neither achieved significance. Both low parity (7) and parity of two or more (13) have been associated with PPH. We did not observe any correlation of PPH with maternal parity in this study.

The potential limitation of size in an investigation evaluating PPH is an area of concern, but with the evaluation of almost 14,000 consecutive vaginal deliveries in a single institution, this risk should be reduced. The thorough methodology used to assess the blood loss after each vaginal delivery also adds credibility to our findings. In addition, the statistical model used assists in identifying only the independent variables associated with PPH. All of these processes add strength and reliability to our investigation.

Conclusion

Despite the great strides made in the reduction of pregnancy-related maternal mortality rates over the last 100 years, hemorrhage remains a leading cause of maternal death. To further reduce the maternal mortality rate, the risk factors related to hemorrhage must be identified and measures taken to either prevent or rapidly initiate maternal resuscitation in women recognized as at-risk for significant bleeding after a vaginal delivery. This large investigation should assist in the early identification of women at high risk for postpartum hemorrhage, and may allow for prompt interventions resulting in reduced morbidity.

Table 1. Odds ratios and 95% confidence limits from logistic regression
analysis for association of factors with PPH (blood loss >1000 mL and/or
transfusion) for vaginal deliveries (a)

                                   PPH         No PPH     OR for
Effect                            n    %       n     %    PPH

Prolonged third stage of labor     77  10.8    288   2.2  6.2
Twin-twin transfusion syndrome      5   0.7     10   0.1  5.1
Compound presentation               6   0.8     29   0.2  3
IUFD                                9   1.3     34   0.3  2.6
History of PPH                     77  10.8    610   4.6  2.2
Multiple pregnancy                 40   5.6    290   2.2  2.2
Forceps delivery after             18   2.5    125   1.0  1.9
  unsuccessful vacuum delivery
Antepartum hemorrhage              82  11.5    776   5.9  1.8
Neonatal birth weight >4 kg       105  14.7  1,207   9.2  1.8
Asian race                        109  15.3  1,325  10.1  1.8
Genital tract trauma at delivery  136  19.0  1,689  12.8  1.7
Prolonged first stage of labor     96  13.4  1,240   9.4  1.6
Prolonged second stage of labor    54   7.6    501   3.8  1.6
Intrapartum hemorrhage             36   5.0    310   2.4  1.5
Induction of labor                 22   3.1    202   1.5  1.5
Epidural                          213  29.8  3,158  24.0  1.3
Chorioamnionitis                   84  11.8    630   4.8  1.3
Blood disorders                   173  24.2  2,421  18.4  1.3

                                                  95%
                                               Confidence
Effect                                           limits

Prolonged third stage of labor                 4.6   8.2
Twin-twin transfusion syndrome                 1.5  15.7
Compound presentation                          1.1   7.3
IUFD                                           1.1   5.7
History of PPH                                 1.7   2.9
Multiple pregnancy                             1.5   3.2
Forceps delivery after                         1.1   3.2
  unsuccessful vacuum delivery
Antepartum hemorrhage                          1.3   2.3
Neonatal birth weight >4 kg                    1.4   2.3
Asian race                                     1.4   2.2
Genital tract trauma at delivery               1.4   2.1
Prolonged first stage of labor                 1     1.6
Prolonged second stage of labor                1.1   2.1
Intrapartum hemorrhage                         1     2.3
Induction of labor                             1.2   1.7
Epidural                                       1     1.6
Chorioamnionitis                               1.1   1.7
Blood disorders                                1.1   1.6

(a) PPH, postpartum hemorrhage; OR, odds ratios; IUFD, intrauterine
fetal death.

Table 2. Number of risk factors for postpartum hemorrhage among women
delivering vaginally with and without postpartum hemorrhage

                                                            Three or
Risk factors              Nil      One factor  Two factors    more

No postpartum hemorrhage     67      196         197          254
%                             9.4     27.5        27.6         35.6
Postpartum hemorrhage     2,920    4,779       3,507        1,941
%                            22.2     36.4        26.7         14.8

Accepted October 19, 2004.

References

1. Revised 1990 Estimates of Maternal Mortality: A New Approach by WHO and UNICEF. Geneva, World Health Organization, 2000.

2. Pritchard JA, Baldwin RM, Dickey JC, et al. Blood volume changes in pregnancy and the puerperium, II: red blood cell loss and changes in apparent blood volume during and following vaginal delivery, cesarean section, and cesarean plus total hysterectomy. Am J Obstet Gynecol 1962;84:1271-1282.

3. Stones RW, Paterson CM, Nigel J, et al. Risk factors for major obstetric hemorrhage. Eur J Obstet Gynecol Reprod Biol 1993;48:15-18.

4. Jolly MC, Seibire NJ, Harris JP, et al. Risk factors for macrosomia and its clinical consequences: a study of 350,311 pregnancies. Eur Obstet Gynecol Reprod Biol 2003;111:9-14.

5. Selo-Ojeme DO, Okonofua FE. Risk factors for primary postpartum haemorrhage: a case-control study. Arch Gynecol Obstet 1997;259:179-187.

6. McSwiney MM, Saunders PR. Female circumcision: a risk factor in postpartum hemorrhage. J Postgrad Med 1992;38:136-137.

7. Tsu VD. Postpartum haemorrhage in Zimbabwe: a risk factor analysis. Br J Obstet Gynaecol 1993;100:327-333.

8. Combs CA, Murphy EL, Laros RK. Factors associated with postpartum hemorrhage with vaginal birth. Obstet Gynecol 1991;77:69-76.

9. Allen DG, Correy JF, Marsden DE. Primary postpartum haemorrhage in Tasmania 1982-1986. Aust N Z J Obstet Gynaecol 1998;28:279-283.

10. Centers for Disease Control. Pregnancy-related mortality surveillance: United States, 1991-1999. MMWR 2003;52:1-14.

11. Petersen LA. Factors that predict low hematocrit levels in the postpartum patient after vaginal delivery. Am J Obstet Gynecol 2002;186:737-744.

12. Gardella C, Taylor M, Benedetti T, et al. The effect of sequential use of vacuum and forceps for assisted vaginal delivery on neonatal outcomes. Am J Obstet Gynecol 2001;185:896-902.

13. Xiong Q, Zhang GY, Chen HC. Analysis of risk factors of postpartum hemorrhage in rural women [Chinese]. Chin J Obstet Gynecol 1994;29:582-585.

RELATED ARTICLE: Key Points

* This study found the postpartum hemorrhage rate for women delivered vaginally was 5.15%.

* Identified risk factors for postpartum hemorrhage were Asian race, maternal blood disorders, prior postpartum hemorrhage, history of retained placenta, multiple pregnancy, antepartum hemorrhage, genital tract lacerations, macrosomia (>4 kg), labor induction, chorioamnionitis, intrapartum hemorrhage, still birth, compound fetal presentation, epidural anesthesia, prolonged first/second stage of labor, and forceps delivery after a failed vacuum.

Everett F. Magann, MD, Sharon Evans, PHD, Maureen Hutchinson, RN, RM, Robyn Collins, RN, RM, BAPPSC, CHC, Bobby C. Howard, MD, and John C. Morrison, MD

From the School of Women and Infants Health, King Edward Memorial Hospital, Perth, Australia; the Departments of Obstetrics and Gynecology, Madigan Army Medical Center, Tacoma, WA; and the University of Mississippi Medical Center, Jackson, MS.

Correspondence to Dr. John C. Morrison, Department of Obstetrics and Gynecology, University of Mississippi Medical Center, 2500 North State St., Jackson, MS 39216-4505. Email: [e-mail]