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Maternal morbidity associated with placenta praevia among women who had elective caesarean section
European Journal of Obstetrics & Gynecology and Reproductive Biology 159 (2011) 62–66
Contents lists available at ScienceDirect
European Journal of Obstetrics & Gynecology and Reproductive Biology journal homepage: www.elsevier.com/locate/ejogrb
Maternal morbidity associated with placenta praevia among women who had elective caesarean section Chidimma Onwere a, Ipek Gurol-Urganci a,b, David A. Cromwell a,b,*, Tahir A. Mahmood a, Allan Templeton a, Jan H. van der Meulen a,b a b
Office for Clinical Research and Audit, Royal College of Obstetricians and Gynaecologists, London, UK Department of Health Services Research and Policy, London School of Hygiene and Tropical Medicine, London, UK
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 January 2011 Received in revised form 15 June 2011 Accepted 11 July 2011
Objective: Estimates of the increased risk of maternal complications after caesarean section posed by placenta praevia differ between studies and may not reflect current practice. We assess the impact of placenta praevia on maternal complications after elective caesarean section (CS). Study design: We undertook a retrospective cohort study of women who had an elective CS for a singleton at term in the English National Health Service between 1 April 2000 and 28 February 2009 using routine data from the Hospital Episode Statistics database. Multiple logistic regression was used to estimate the effect of placenta praevia on maternal complications after controlling for maternal age, parity, whether a woman had a previous CS, and gestational age. Maternal complications included postpartum haemorrhage, obstetric trauma, blood transfusion and hysterectomy. Results: Among 131,731 women having an elective CS for a singleton, 4,332 (3.3%) women had placenta praevia. Placenta praevia increased the risk of postpartum haemorrhage from 9.7% to 17.5% (adjusted odds ratio (OR) 1.91; 95% CI: 1.74 to 2.09), the risk of blood transfusion from 1.4% to 6.4% (OR 4.39; 3.76 to 5.12), and the risk of hysterectomy from 0.03% to 1% (OR 39.70; 22.42 to 70.30). Previous studies have estimated the rate of hysterectomy among women with placenta praevia to be 5%. Conclusion: Placenta praevia remains a risk factor for various maternal complications, although the increased risk of hysterectomy is lower than previously reported. ß 2011 Elsevier Ireland Ltd. All rights reserved.
Keywords: elective caesarean section maternal complications placenta praevia
1. INTRODUCTION Placenta praevia is a serious obstetric complication that affects between 0.3% and 0.5% of all live births [1]. It is implicated in around 20% of maternal deaths from haemorrhage [2] and is also associated with an increased risk of pre-term birth as well as perinatal mortality and morbidity [3]. For asymptomatic patients, an elective caesarean section for placenta praevia has been shown to improve perinatal outcome in preterm fetuses and those with malpresentations [4]. In the UK, the Royal College of Obstetricians and Gynaecologists recommend that women with placenta praevia with a placental edge less than two centimetres from the internal os are likely to need delivery by caesarean section, especially if the placenta is posterior or thick [5]. Various studies have estimated the effect of placenta praevia on maternal complication rates after delivery [1,4,6–10]. However,
* Corresponding author. Department of Health Services Research & Policy, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT Tel.: +44 0 20 78696608; fax: +44 0 20 78696644. E-mail address: [email protected] (D.A. Cromwell). 0301-2115/$ – see front matter ß 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejogrb.2011.07.008
they differ in their estimated rates of complications and the increased risk posed by placenta praevia. For example, the odds ratios for blood transfusion have ranged from 1.84 to 10.05 [6,7]. These differences reflect variation in study design, clinical practice, geographical location and improvements in care over time. For example, the period of time examined in retrospective cohorts has varied from 2 to 20 years [8,9]. In addition, not all studies have compared the outcomes in women with and without placenta praevia who underwent the same mode of delivery (i.e. caesarean section) [4,6]. A study that does not take account of the mode of delivery when comparing the outcomes of deliveries in women with and without placenta praevia is likely to be misleading because complications due to placenta praevia will be confounded with those due to caesarean section. In this paper, we describe a study which aimed to provide more accurate estimates of the risk of post-delivery complications among women with placenta praevia who were delivered at term by elective caesarean section (CS). We also examined whether various patient characteristics affected the risk of complications. We restricted the analysis to elective CS because women who have emergency CS are a heterogeneous group. The study used Hospital Episode Statistics (HES), an administrative database which
C. Onwere et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 159 (2011) 62–66
includes the records of all births in English National Health Service (NHS) hospitals. 2. MATERIALS AND METHODS We used data extracted from HES to identify all singleton deliveries in NHS hospitals between 1 April 2000 and 28 February 2009. The HES dataset contains records of all patient admissions to English NHS hospitals, and its core fields describe patient demographics, clinical information, and hospital administrative data. Diagnostic information is coded using the International Classification of Diseases, tenth revision (ICD10) and operative procedures are coded using the UK Office for Population Censuses and Surveys classification, fourth revision (OPCS4). For delivery episodes, HES also has a ‘‘maternity tail’’, which allows hospitals to record parity, birth weight, gestational age and pregnancy outcome. However, not all records of delivery have this information completed. We included NHS acute trusts (which consist of one or more hospitals) if they had entered, for at least 50% of all deliveries, valid
63
values for gestational age and parity in the maternity tails of their HES delivery records. An NHS trust was judged to have valid parity information if the proportion of nulliparous women delivering within it was between 25% and 55% (which corresponded to the overall proportion in England and Wales 15% [10]). It was judged to have valid gestation data if the median gestation was between 38 and 40 weeks. Data were allocated to the NHS trusts that existed in February 2009 to take account changes in the local organisation of hospitals between April 2000 and February 2009. Deliveries by elective caesarean section were defined as episodes containing the OPCS4 procedure code R17. We excluded pre-term deliveries in which the CS was performed before 37 weeks gestation. Women were defined as having placenta praevia if any of the diagnosis fields contained ICD10 code O44. Complications of postpartum haemorrhage, obstetric trauma, puerperal sepsis and other puerperal infections were identified from the diagnosis fields. However, information on the occurrence of hysterectomy and blood transfusion could be coded in both diagnosis and procedure fields and so were defined using both ICD10 and OPCS4 codes (see Appendix 1).
Fig. 1. Selection of the patient cohort.
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C. Onwere et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 159 (2011) 62–66
The rate of each complication was expressed per 1000 deliveries for women with and without placenta praevia. The risks of complications associated with placenta praevia were estimated using a multiple logistic regression model and were expressed as an odds ratios with 95% confidence intervals. The odds ratios were adjusted for maternal age (35 years or under, over 35 years), parity (0, 1-3, 4+), previous caesarean section, and gestational age at the time of the elective caesarean section (38 weeks or before, 39 weeks or after). We considered that an elective CS at 38 weeks or before may be a marker for a high-risk subset of women and an interaction term was included in the model to test whether the relative risk associated with placenta praevia was related to the timing of elective CS. Statistical calculations were performed in STATA version 11. All p-values were two-sided and values lower than 0.05 were judged to be statistically significant. The chi-square test was used to test the differences between proportions. 3. RESULTS In England, there were 4,981,495 singleton deliveries in 144 English NHS trusts between 1 April 2000 and 28 February 2009. Elective CS was performed to deliver 449,872 (9.0%) of these singletons and, among these, 14,944 women had placenta praevia (33.2 per 1000 elective CS). Removing the NHS trusts that had entered insufficient information on gestational age and parity data into the maternity tail reduced the dataset to 159,482 elective CS deliveries. A further 20,121 women (4.5%) were omitted because their individual record lacked either gestation or parity data.
Finally, 7,630 women (1.7%) were omitted because the elective CS was performed for a preterm baby (before 37 weeks gestation). This left a sample of 131,731 elective CS for term infants, which corresponded to 29.3% of the elective CS deliveries for the nine year period (Figure 1). There were 4,332 women among the 131,731 elective CS who had placenta praevia at term, giving a rate for the cohort of 32.9 per 1000 elective CS. The difference in the placenta praevia rates between included and excluded elective CS deliveries was not statistically significant (3.29% v 3.34%, p = 0.42). Table 1 summarises the characteristics of the women. Women with placenta praevia tended to be older and more had their caesarean before 39 weeks gestation. Among women without placenta praevia, 67,092 (52.7%) women had previous CS (uterine scar) as the indication for elective CS while, for another 26,574 (20.9%) women, the indication was breech presentation. These indications were less common among the women who had placenta praevia, with previous CS and breech presentation occurring among 627 (14.5%) and 246 (5.7%) women, respectively. The complication rates for elective CS deliveries at term for women with and without placenta praevia are shown in Table 2. With adjustment for differences in maternal age, parity, and previous CS, women with placenta praevia were found to have double the risk of postpartum haemorrhage and obstetric trauma, and roughly four times the risk of a blood transfusion. There were no episodes of puerperal sepsis in the placenta praevia group, and the difference in the rates of other puerperal infections was not statistically significant. However, 1% of women with placenta
Table 1 Characteristics of women with and without placenta praevia who had an elective caesarean section (CS) at term for a singleton baby. Patient characteristic
Women with placenta praevia
Number of women
1
4,332
Women without placenta praevia
Statistical significance1
127,399
Age (years)
Under 20 20 to 25 26 to 30 31 to 35 Over 35
33 264 780 1,618 1,613
(0.8) (6.1) (18.1) (37.6) (37.4)
2,577 13,530 28,812 44,022 37,961
(2.0) (10.7) (22.7) (34.7) (29.9)
p < 0.001
Ethnicity
White Asian Afro-Caribbean Other Unknown
2,710 460 181 178 803
(62.6) (10.6) (4.2) (4.1) (18.5)
84,005 10,181 5,336 4,104 23,773
(65.9) (8.0) (4.2) (3.2) (18.7)
p < 0.001
Gestational age
37-38 weeks 39+ weeks
3,340 (77.1) 992 (22.9)
61,614 (48.4) 65,785 (51.6)
p < 0.001
Parity
1 2 3 or more
1,341 (31.0) 1,356 (31.3) 1,635 (37.7)
25,523 (20.0) 50,471 (39.6) 51,405 (40.4)
p < 0.001
Statistical significance as measured by Pearson Chi-squared test.
Table 2 The impact of placenta praevia on complication rates among women who had an elective caesarean section (CS) at term for a singleton baby. Complications of delivery
Number of women Postpartum haemorrhage** Third-stage haemorrhage Other immediate PH Delayed and secondary PH Obstetric trauma Puerperal sepsis Other puerperal infections Blood transfusion Hysterectomy
Number of cases (rate per thousand elective CS) Women with placenta praevia
Women without placenta praevia
4,332 758 (175.2) 68 (15.7) 658 (151.9) 34 (7.8) 35 (8.1) 0 (0) 42 (9.7) 277 (63.9) 44 (10.2)
127,399 12,382 (97.2) 568 (4.5) 11,303 (88.7) 516 (4.1) 395 (3.1) 18 (0.1) 1014 (8.0) 1735 (13.6) 34 (0.3)
Adjusted OR for Placenta Praevia (95% CI)*
1.91 (1.74-2.09) 2.87 (2.15-3.84) 1.80 (1.63-1.99) 1.67 (1.12-2.51) 2.34 (1.50-3.65) undefined 1.30 (0.91-1.85) 4.39 (3.76-5.12) 39.70 (22.42-70.30)
* Odds ratios adjusted for maternal age, parity, previous caesarean section, and the timing of delivery (before/after 39 weeks) ** Some women had more than one type of postpartum haemorrhage coded which results in the total being less than the sum of the different types.
C. Onwere et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 159 (2011) 62–66
praevia had a hysterectomy, a substantially higher proportion than for women without this disorder (0.03%). For none of the outcomes was the risk of a complication related to the timing of the elective CS (ie, none of the interaction terms for the timing of the CS and placenta praevia had an odds ratio that was statistically significant). 4. COMMENTS This study used a large administrative dataset to derive precise estimates of maternal complications among women with term singletons with placenta praevia who had an elective CS. We found that women with placenta praevia had twice the risk of postpartum haemorrhage and obstetric trauma, although the absolute rates remained low. In contrast, the presence of placenta praevia still represented a substantial increase in the relative risks of hysterectomy. Hysterectomy occurred in 1% of these women compared to only 0.03% of women without placenta praevia. We also found that the timing of an elective CS did not alter the relative risks associated with placenta praevia. Strengths of this study include its large sample size, and its widespread coverage of English NHS acute trusts. But being based on data from an administrative database introduces various limitations. First, it is possible that the women with incomplete data in the maternity tail differed from women included in the study in terms of their characteristics and pregnancy risks. However, the risk of selection bias appears to be small. We found that the distributions of maternal age and mode of delivery were similar in the episodes with good quality data and omitted episodes. The rates of complications among the included and excluded organisations were also similar. The rates of postpartum haemorrhage were 17.5% and 19.4% (p = 0.01), the rates of blood transfusion were 6.39% and 6.63% (p = 0.59), and the rates of hysterectomy were 1.02% and 1.32% (p = 0.13), respectively. Second, the coding of the method of delivery is potentially inaccurate. We minimised possible errors from this by using the three character OPCS code for elective CS (R17), an approach shown to be more reliable than using specific 4-character OPCS codes [11]. High-levels of agreement between administrative databases and medical records have also been reported for the coding of elective caesarean section (kappa > 0.90) [12]. Third, our results may be influenced by the quality of diagnostic coding. Under-reporting complications would have lowered the absolute rates but would only influence the estimated odds ratios if the coding of a complication was dependent upon the characteristics of a patient. There is no reason to suppose this was the case. The occurrence of placenta praevia might also have been under-reported. This would lead to the relationship between complications and placenta praevia to be underestimated rather than overestimated due to an effect known as ‘‘regression dilution’’ [13]. However, it is likely that under-reporting of placenta praevia was small because the overall incidence rate of placenta praevia in HES was 0.57%, which is similar to incidence rates in other studies. The ICD-10 codes within O44 do not distinguish between major and minor placenta praevia. In elective CS procedures, injury to bowel, bladder, ureters and blood vessels are well documented complications [14]. Our results show that the risk of these injuries during elective CS with placenta praevia was doubled. The reason for this is unclear, and increased parity and previous CS did not increase the risk of obstetric trauma as might have been expected [14,15]. Further investigation of this finding should be undertaken in other studies. While postpartum haemorrhage has been highlighted as a complication of placenta praevia, estimates of its incidence have ranged from 1.3% to 25.8% [4,7]. The estimated postpartum
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haemorrhage rate in this study was 17.5% for women with placenta praevia. This variation could reflect differences in the population selection although this seems unlikely. The studies with the highest and lowest haemorrhage rates were both limited to singleton deliveries. An alternative explanation is that the variation reflects differences in the definition of both postpartum haemorrhage and placenta praevia. However, the estimated relative risks associated with women with placenta praevia have tended to be similar across studies and suggest these women had twice the risk of bleeding, however severe [4,6,7]. With the increased risk of haemorrhage, it is not surprising that we also found an increased risk of blood transfusion among women with placenta praevia. The adjusted odds ratio of 4.39 was lower than estimates from older studies [6,8]. The use of blood transfusion has been interpreted as a marker for the severity of haemorrhage [16] and might suggest that, amongst women with placenta praevia, the frequency of severe haemorrhage has reduced over time. However, it may also reflect different attitudes among obstetricians to the use of blood transfusions [17]. Hysterectomy represents a serious complication of delivery and previous studies have reported that this outcome is experienced by 5% of women with placenta praevia undergoing caesarean section [6,8]. Our study found that hysterectomy occurred in only 1% of these women and perhaps reflects recent improvements in the safety of caesarean section [14]. The lower rates of blood transfusion and caesarean hysterectomy observed in our study may also reflect changes in clinical practice, such as the greater obstetric and anaesthetic consultant presence on labor wards [1,18]. In conclusion, placenta praevia remains an important risk factor for obstetric complications but our results suggest the increased relative risk of blood transfusion and caesarean hysterectomy may be lower than previous reports. These refined estimates should be used for antenatal counselling and planning delivery. 5. CONDENSATION Placenta praevia remains a risk factor for maternal complications after elective caesarean section but the risk of hysterectomy is lower than estimated in previous studies. Acknowledgements We thank the Department of Health for providing the Hospital Episode Statistics data used in this study. Appendix 1: Definitions of patient characteristics and complications of delivery ICD10 diagnosis codes Elective caesarean section delivery Placenta praevia Postpartum haemorrhage Third-stage haemorrhage Other immediate postpartum haemorrhage Delayed and secondary postpartum haemorrhage Obstetric trauma Puerperal sepsis Other puerperal infections Hysterectomy Blood transfusion
OPCS4 procedure codes R17
O44 O72.0-.2 O72.0 O72.1 O72.2 O71.5, O71.8, O71.9 O85 O86 O82.2 R25.1, Q07, Q08 Z51.3, Y63.0 X33.2, X33.3, X33.8, X33.9, X34
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REFERENCES [1] Iyasu S, Saftlas AK, Rowley DL, Koonin LM, Lawson HW, Atrash HK. The epidemiology of placenta praevia in the United States, 1979 through 1987. Am J Obstet Gynaecol 1993;168(5):1424–9. [2] Lewis G (ed). The Confidential Enquiry into Maternal and Child Health (CEMACH). Saving Mothers’ Lives: reviewing maternal deaths to make motherhood safer 2003-2005. The Seventh Report on Confidential Enquiries in Maternal Deaths in the United Kingdom. London: CEMACH, 2007. [3] Crane JM, van den Hof MC, Dodds L, Armson A. Neonatal outcomes with placenta praevia. Obstet Gynaecol 1999;93(4):541–4. [4] Sheiner E, Shoham-Vardi I, Hallak M, Hershkowitz R, Katz M, Mazor M. Placenta praevia: Obstetric risk factors and pregnancy outcome. J Matern Fetal Med 2001;10(6):414–9. [5] Royal College of Obstetricians and Gynaecologists. Management of placenta praevia/accreta. Guideline No.27. London: RCOG, 2005. [6] Crane JM, van den Hof MC, Dodds L, Armson A. Maternal Complications with placenta praevia. Am Journal of Perinatol 2000;17(2):101–5. [7] Tuzovic L. Complete versus incomplete placenta praevia and obstetric outcome. Int J Gynaecol Obstet 2006;93(2):110–7. [8] Takayama T, Minakami H, Koike T, Watanabe T, Sato I. Risks associated with caesarean sections in women with placenta praevia. J Obstet Gynaecol Res 1997;23(4):375–9. [9] Bergholt T, Stenderup JK, Vedsted-Jakobsen A, Helm P, Lenstrup C. Intraoperative surgical complication during caesarean section: an observational study of the incidence and risk factors. Acta Obstet Gynecol Scand 2003;82(3):251–6. [10] McShane PM, Heyl PS, Epstein MF. Maternal and perinatal morbidity resulting from placenta praevia. Obstet Gynecol 1985;65(2):176–82.
[11] Dixon J, Sanderson C, Elliott P, Walls P, Jones J, Petticrew M. Assessment of the reproducibility of clinical coding in routinely collected hospital activity data: a study in two hospitals. J Public Health Med 1998;20(1): 63–9. [12] Roberts CL, Bell JC, Ford JB, Morris JM. Monitoring the quality of maternity care: how well are labour and delivery events reported in population health data? Paediatr Perinat Epidemiol 2009;23(2):144–52. [13] MacMahon S, Peto R, Cutler J, Collins R, Sorlie P, et al. Blood pressure, stroke, and coronary heart disease. Part 1, Prolonged differences in blood pressure: prospective observational studies corrected for the regression dilution bias. Lancet 1990;335:765–74. [14] National Institute for Clinical Excellence. Caesarean section. London: RCOG Press, 2004. [15] Allen VM, O’Connell CM, Liston RM, Baskett TF. Maternal morbidity associated with caesarean delivery without labor compared with spontaneous onset of labor at term. Obstet Gynecol 2003;102(3):477–82. [16] Roberts CL, Ford JB, Algert CS, Bell JC, Simpson JM, Morris JM. Trends in adverse maternal outcomes during childbirth: a population-based study of severe maternal morbidity. BMC Pregnancy Childbirth 2009;9:7. [17] Knight M, Callaghan WM, Berg C, Alexander S, Bouvier-Colle MH, Ford JB, Joseph K, Lewis G, Liston RM, Roberts CL, Oats J, Walker J. Trends in postpartum haemorrhage in high resource countries: a review and recommendations from the International Postpartum Haemorrhage Collaborative Group. BMC Pregnancy Childbirth 2009;9:55. [18] Royal College of Obstetricians and Gynaecologists, Royal College of Midwives, Royal College of Anaesthetists, Royal College of Paediatricians and Child Health. Towards Safer Childbirth: Minimum standards for the organisation and delivery of care in labour. London: RCOG press; 2007.
Contents lists available at ScienceDirect
European Journal of Obstetrics & Gynecology and Reproductive Biology journal homepage: www.elsevier.com/locate/ejogrb
Maternal morbidity associated with placenta praevia among women who had elective caesarean section Chidimma Onwere a, Ipek Gurol-Urganci a,b, David A. Cromwell a,b,*, Tahir A. Mahmood a, Allan Templeton a, Jan H. van der Meulen a,b a b
Office for Clinical Research and Audit, Royal College of Obstetricians and Gynaecologists, London, UK Department of Health Services Research and Policy, London School of Hygiene and Tropical Medicine, London, UK
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 January 2011 Received in revised form 15 June 2011 Accepted 11 July 2011
Objective: Estimates of the increased risk of maternal complications after caesarean section posed by placenta praevia differ between studies and may not reflect current practice. We assess the impact of placenta praevia on maternal complications after elective caesarean section (CS). Study design: We undertook a retrospective cohort study of women who had an elective CS for a singleton at term in the English National Health Service between 1 April 2000 and 28 February 2009 using routine data from the Hospital Episode Statistics database. Multiple logistic regression was used to estimate the effect of placenta praevia on maternal complications after controlling for maternal age, parity, whether a woman had a previous CS, and gestational age. Maternal complications included postpartum haemorrhage, obstetric trauma, blood transfusion and hysterectomy. Results: Among 131,731 women having an elective CS for a singleton, 4,332 (3.3%) women had placenta praevia. Placenta praevia increased the risk of postpartum haemorrhage from 9.7% to 17.5% (adjusted odds ratio (OR) 1.91; 95% CI: 1.74 to 2.09), the risk of blood transfusion from 1.4% to 6.4% (OR 4.39; 3.76 to 5.12), and the risk of hysterectomy from 0.03% to 1% (OR 39.70; 22.42 to 70.30). Previous studies have estimated the rate of hysterectomy among women with placenta praevia to be 5%. Conclusion: Placenta praevia remains a risk factor for various maternal complications, although the increased risk of hysterectomy is lower than previously reported. ß 2011 Elsevier Ireland Ltd. All rights reserved.
Keywords: elective caesarean section maternal complications placenta praevia
1. INTRODUCTION Placenta praevia is a serious obstetric complication that affects between 0.3% and 0.5% of all live births [1]. It is implicated in around 20% of maternal deaths from haemorrhage [2] and is also associated with an increased risk of pre-term birth as well as perinatal mortality and morbidity [3]. For asymptomatic patients, an elective caesarean section for placenta praevia has been shown to improve perinatal outcome in preterm fetuses and those with malpresentations [4]. In the UK, the Royal College of Obstetricians and Gynaecologists recommend that women with placenta praevia with a placental edge less than two centimetres from the internal os are likely to need delivery by caesarean section, especially if the placenta is posterior or thick [5]. Various studies have estimated the effect of placenta praevia on maternal complication rates after delivery [1,4,6–10]. However,
* Corresponding author. Department of Health Services Research & Policy, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT Tel.: +44 0 20 78696608; fax: +44 0 20 78696644. E-mail address: [email protected] (D.A. Cromwell). 0301-2115/$ – see front matter ß 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejogrb.2011.07.008
they differ in their estimated rates of complications and the increased risk posed by placenta praevia. For example, the odds ratios for blood transfusion have ranged from 1.84 to 10.05 [6,7]. These differences reflect variation in study design, clinical practice, geographical location and improvements in care over time. For example, the period of time examined in retrospective cohorts has varied from 2 to 20 years [8,9]. In addition, not all studies have compared the outcomes in women with and without placenta praevia who underwent the same mode of delivery (i.e. caesarean section) [4,6]. A study that does not take account of the mode of delivery when comparing the outcomes of deliveries in women with and without placenta praevia is likely to be misleading because complications due to placenta praevia will be confounded with those due to caesarean section. In this paper, we describe a study which aimed to provide more accurate estimates of the risk of post-delivery complications among women with placenta praevia who were delivered at term by elective caesarean section (CS). We also examined whether various patient characteristics affected the risk of complications. We restricted the analysis to elective CS because women who have emergency CS are a heterogeneous group. The study used Hospital Episode Statistics (HES), an administrative database which
C. Onwere et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 159 (2011) 62–66
includes the records of all births in English National Health Service (NHS) hospitals. 2. MATERIALS AND METHODS We used data extracted from HES to identify all singleton deliveries in NHS hospitals between 1 April 2000 and 28 February 2009. The HES dataset contains records of all patient admissions to English NHS hospitals, and its core fields describe patient demographics, clinical information, and hospital administrative data. Diagnostic information is coded using the International Classification of Diseases, tenth revision (ICD10) and operative procedures are coded using the UK Office for Population Censuses and Surveys classification, fourth revision (OPCS4). For delivery episodes, HES also has a ‘‘maternity tail’’, which allows hospitals to record parity, birth weight, gestational age and pregnancy outcome. However, not all records of delivery have this information completed. We included NHS acute trusts (which consist of one or more hospitals) if they had entered, for at least 50% of all deliveries, valid
63
values for gestational age and parity in the maternity tails of their HES delivery records. An NHS trust was judged to have valid parity information if the proportion of nulliparous women delivering within it was between 25% and 55% (which corresponded to the overall proportion in England and Wales 15% [10]). It was judged to have valid gestation data if the median gestation was between 38 and 40 weeks. Data were allocated to the NHS trusts that existed in February 2009 to take account changes in the local organisation of hospitals between April 2000 and February 2009. Deliveries by elective caesarean section were defined as episodes containing the OPCS4 procedure code R17. We excluded pre-term deliveries in which the CS was performed before 37 weeks gestation. Women were defined as having placenta praevia if any of the diagnosis fields contained ICD10 code O44. Complications of postpartum haemorrhage, obstetric trauma, puerperal sepsis and other puerperal infections were identified from the diagnosis fields. However, information on the occurrence of hysterectomy and blood transfusion could be coded in both diagnosis and procedure fields and so were defined using both ICD10 and OPCS4 codes (see Appendix 1).
Fig. 1. Selection of the patient cohort.
64
C. Onwere et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 159 (2011) 62–66
The rate of each complication was expressed per 1000 deliveries for women with and without placenta praevia. The risks of complications associated with placenta praevia were estimated using a multiple logistic regression model and were expressed as an odds ratios with 95% confidence intervals. The odds ratios were adjusted for maternal age (35 years or under, over 35 years), parity (0, 1-3, 4+), previous caesarean section, and gestational age at the time of the elective caesarean section (38 weeks or before, 39 weeks or after). We considered that an elective CS at 38 weeks or before may be a marker for a high-risk subset of women and an interaction term was included in the model to test whether the relative risk associated with placenta praevia was related to the timing of elective CS. Statistical calculations were performed in STATA version 11. All p-values were two-sided and values lower than 0.05 were judged to be statistically significant. The chi-square test was used to test the differences between proportions. 3. RESULTS In England, there were 4,981,495 singleton deliveries in 144 English NHS trusts between 1 April 2000 and 28 February 2009. Elective CS was performed to deliver 449,872 (9.0%) of these singletons and, among these, 14,944 women had placenta praevia (33.2 per 1000 elective CS). Removing the NHS trusts that had entered insufficient information on gestational age and parity data into the maternity tail reduced the dataset to 159,482 elective CS deliveries. A further 20,121 women (4.5%) were omitted because their individual record lacked either gestation or parity data.
Finally, 7,630 women (1.7%) were omitted because the elective CS was performed for a preterm baby (before 37 weeks gestation). This left a sample of 131,731 elective CS for term infants, which corresponded to 29.3% of the elective CS deliveries for the nine year period (Figure 1). There were 4,332 women among the 131,731 elective CS who had placenta praevia at term, giving a rate for the cohort of 32.9 per 1000 elective CS. The difference in the placenta praevia rates between included and excluded elective CS deliveries was not statistically significant (3.29% v 3.34%, p = 0.42). Table 1 summarises the characteristics of the women. Women with placenta praevia tended to be older and more had their caesarean before 39 weeks gestation. Among women without placenta praevia, 67,092 (52.7%) women had previous CS (uterine scar) as the indication for elective CS while, for another 26,574 (20.9%) women, the indication was breech presentation. These indications were less common among the women who had placenta praevia, with previous CS and breech presentation occurring among 627 (14.5%) and 246 (5.7%) women, respectively. The complication rates for elective CS deliveries at term for women with and without placenta praevia are shown in Table 2. With adjustment for differences in maternal age, parity, and previous CS, women with placenta praevia were found to have double the risk of postpartum haemorrhage and obstetric trauma, and roughly four times the risk of a blood transfusion. There were no episodes of puerperal sepsis in the placenta praevia group, and the difference in the rates of other puerperal infections was not statistically significant. However, 1% of women with placenta
Table 1 Characteristics of women with and without placenta praevia who had an elective caesarean section (CS) at term for a singleton baby. Patient characteristic
Women with placenta praevia
Number of women
1
4,332
Women without placenta praevia
Statistical significance1
127,399
Age (years)
Under 20 20 to 25 26 to 30 31 to 35 Over 35
33 264 780 1,618 1,613
(0.8) (6.1) (18.1) (37.6) (37.4)
2,577 13,530 28,812 44,022 37,961
(2.0) (10.7) (22.7) (34.7) (29.9)
p < 0.001
Ethnicity
White Asian Afro-Caribbean Other Unknown
2,710 460 181 178 803
(62.6) (10.6) (4.2) (4.1) (18.5)
84,005 10,181 5,336 4,104 23,773
(65.9) (8.0) (4.2) (3.2) (18.7)
p < 0.001
Gestational age
37-38 weeks 39+ weeks
3,340 (77.1) 992 (22.9)
61,614 (48.4) 65,785 (51.6)
p < 0.001
Parity
1 2 3 or more
1,341 (31.0) 1,356 (31.3) 1,635 (37.7)
25,523 (20.0) 50,471 (39.6) 51,405 (40.4)
p < 0.001
Statistical significance as measured by Pearson Chi-squared test.
Table 2 The impact of placenta praevia on complication rates among women who had an elective caesarean section (CS) at term for a singleton baby. Complications of delivery
Number of women Postpartum haemorrhage** Third-stage haemorrhage Other immediate PH Delayed and secondary PH Obstetric trauma Puerperal sepsis Other puerperal infections Blood transfusion Hysterectomy
Number of cases (rate per thousand elective CS) Women with placenta praevia
Women without placenta praevia
4,332 758 (175.2) 68 (15.7) 658 (151.9) 34 (7.8) 35 (8.1) 0 (0) 42 (9.7) 277 (63.9) 44 (10.2)
127,399 12,382 (97.2) 568 (4.5) 11,303 (88.7) 516 (4.1) 395 (3.1) 18 (0.1) 1014 (8.0) 1735 (13.6) 34 (0.3)
Adjusted OR for Placenta Praevia (95% CI)*
1.91 (1.74-2.09) 2.87 (2.15-3.84) 1.80 (1.63-1.99) 1.67 (1.12-2.51) 2.34 (1.50-3.65) undefined 1.30 (0.91-1.85) 4.39 (3.76-5.12) 39.70 (22.42-70.30)
* Odds ratios adjusted for maternal age, parity, previous caesarean section, and the timing of delivery (before/after 39 weeks) ** Some women had more than one type of postpartum haemorrhage coded which results in the total being less than the sum of the different types.
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praevia had a hysterectomy, a substantially higher proportion than for women without this disorder (0.03%). For none of the outcomes was the risk of a complication related to the timing of the elective CS (ie, none of the interaction terms for the timing of the CS and placenta praevia had an odds ratio that was statistically significant). 4. COMMENTS This study used a large administrative dataset to derive precise estimates of maternal complications among women with term singletons with placenta praevia who had an elective CS. We found that women with placenta praevia had twice the risk of postpartum haemorrhage and obstetric trauma, although the absolute rates remained low. In contrast, the presence of placenta praevia still represented a substantial increase in the relative risks of hysterectomy. Hysterectomy occurred in 1% of these women compared to only 0.03% of women without placenta praevia. We also found that the timing of an elective CS did not alter the relative risks associated with placenta praevia. Strengths of this study include its large sample size, and its widespread coverage of English NHS acute trusts. But being based on data from an administrative database introduces various limitations. First, it is possible that the women with incomplete data in the maternity tail differed from women included in the study in terms of their characteristics and pregnancy risks. However, the risk of selection bias appears to be small. We found that the distributions of maternal age and mode of delivery were similar in the episodes with good quality data and omitted episodes. The rates of complications among the included and excluded organisations were also similar. The rates of postpartum haemorrhage were 17.5% and 19.4% (p = 0.01), the rates of blood transfusion were 6.39% and 6.63% (p = 0.59), and the rates of hysterectomy were 1.02% and 1.32% (p = 0.13), respectively. Second, the coding of the method of delivery is potentially inaccurate. We minimised possible errors from this by using the three character OPCS code for elective CS (R17), an approach shown to be more reliable than using specific 4-character OPCS codes [11]. High-levels of agreement between administrative databases and medical records have also been reported for the coding of elective caesarean section (kappa > 0.90) [12]. Third, our results may be influenced by the quality of diagnostic coding. Under-reporting complications would have lowered the absolute rates but would only influence the estimated odds ratios if the coding of a complication was dependent upon the characteristics of a patient. There is no reason to suppose this was the case. The occurrence of placenta praevia might also have been under-reported. This would lead to the relationship between complications and placenta praevia to be underestimated rather than overestimated due to an effect known as ‘‘regression dilution’’ [13]. However, it is likely that under-reporting of placenta praevia was small because the overall incidence rate of placenta praevia in HES was 0.57%, which is similar to incidence rates in other studies. The ICD-10 codes within O44 do not distinguish between major and minor placenta praevia. In elective CS procedures, injury to bowel, bladder, ureters and blood vessels are well documented complications [14]. Our results show that the risk of these injuries during elective CS with placenta praevia was doubled. The reason for this is unclear, and increased parity and previous CS did not increase the risk of obstetric trauma as might have been expected [14,15]. Further investigation of this finding should be undertaken in other studies. While postpartum haemorrhage has been highlighted as a complication of placenta praevia, estimates of its incidence have ranged from 1.3% to 25.8% [4,7]. The estimated postpartum
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haemorrhage rate in this study was 17.5% for women with placenta praevia. This variation could reflect differences in the population selection although this seems unlikely. The studies with the highest and lowest haemorrhage rates were both limited to singleton deliveries. An alternative explanation is that the variation reflects differences in the definition of both postpartum haemorrhage and placenta praevia. However, the estimated relative risks associated with women with placenta praevia have tended to be similar across studies and suggest these women had twice the risk of bleeding, however severe [4,6,7]. With the increased risk of haemorrhage, it is not surprising that we also found an increased risk of blood transfusion among women with placenta praevia. The adjusted odds ratio of 4.39 was lower than estimates from older studies [6,8]. The use of blood transfusion has been interpreted as a marker for the severity of haemorrhage [16] and might suggest that, amongst women with placenta praevia, the frequency of severe haemorrhage has reduced over time. However, it may also reflect different attitudes among obstetricians to the use of blood transfusions [17]. Hysterectomy represents a serious complication of delivery and previous studies have reported that this outcome is experienced by 5% of women with placenta praevia undergoing caesarean section [6,8]. Our study found that hysterectomy occurred in only 1% of these women and perhaps reflects recent improvements in the safety of caesarean section [14]. The lower rates of blood transfusion and caesarean hysterectomy observed in our study may also reflect changes in clinical practice, such as the greater obstetric and anaesthetic consultant presence on labor wards [1,18]. In conclusion, placenta praevia remains an important risk factor for obstetric complications but our results suggest the increased relative risk of blood transfusion and caesarean hysterectomy may be lower than previous reports. These refined estimates should be used for antenatal counselling and planning delivery. 5. CONDENSATION Placenta praevia remains a risk factor for maternal complications after elective caesarean section but the risk of hysterectomy is lower than estimated in previous studies. Acknowledgements We thank the Department of Health for providing the Hospital Episode Statistics data used in this study. Appendix 1: Definitions of patient characteristics and complications of delivery ICD10 diagnosis codes Elective caesarean section delivery Placenta praevia Postpartum haemorrhage Third-stage haemorrhage Other immediate postpartum haemorrhage Delayed and secondary postpartum haemorrhage Obstetric trauma Puerperal sepsis Other puerperal infections Hysterectomy Blood transfusion
OPCS4 procedure codes R17
O44 O72.0-.2 O72.0 O72.1 O72.2 O71.5, O71.8, O71.9 O85 O86 O82.2 R25.1, Q07, Q08 Z51.3, Y63.0 X33.2, X33.3, X33.8, X33.9, X34
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