Objective
Although a history of postpartum hemorrhage (PPH) is a recognized risk factor for PPH in subsequent pregnancies, little is known about how the risk accumulates over multiple pregnancies, how recurrence varies by PPH subtype, and whether recurrence can be explained by chronic maternal conditions.
Study Design
Risks of PPH were assessed according to a history of PPH, severity, and subtype (atony, retained placenta, or lacerations) in 538,332 primiparous women whose data were included in the Swedish Medical Birth Register from 1997-2009. The role of stable maternal risk factors was evaluated in regression models that predicted probability of recurrent PPH in second and third pregnancy.
Results
Women with a history of PPH had a 3-fold increased risk of PPH in their second pregnancy compared with unaffected women (15.0% vs 5.0%, respectively). Adjustment for stable maternal risk factors did not attenuate this risk significantly (adjusted relative risk, 3.0; 95% confidence interval, 2.9–3.1). In a third pregnancy, the risk of PPH was 26.6% after 2 previously affected pregnancies, compared with 4.4% in women with no previous PPH. A history of a specific type of PPH predicted recurrence of PPH in the second pregnancy, not only of the same type but other causes as well.
Conclusion
PPH risk is highest among women with >1 previously affected delivery and in those with a previous severe PPH. Chronic conditions that are known to be risk factors for PPH do not explain the recurrence risks. The recurrence patterns across PPH subtypes may point to shared pathologic mechanisms underlying the varying PPH causes.
Postpartum hemorrhage (PPH) is a leading cause of maternal morbidity and death in both the developing and developed world. The incidence of PPH has increased substantially in developed countries over the past decade, even after adjustment for temporal trends in risk factors such as advanced maternal age, obesity, and obstetric practice. Common causes for PPH include uterine atony, retained or adherent placenta, and lacerations. Major risk factors for PPH include conditions that overdistend the uterus, labor induction and augmentation, previous cesarean delivery, hypertensive disorders of pregnancy, fibroid tumors, placenta previa, coagulopathy, and obesity.
Although a history of PPH is a recognized risk factor for PPH in subsequent pregnancies, much remains unknown about the causes and patterns of recurrence. In particular, there are few data available regarding the accumulation of risk after several affected pregnancies and how the risk of recurrence varies by the severity of previous PPHs. The role of PPH subtype for risks of recurrence is understood poorly and of importance because each cause may have different underlying pathophysiologic conditions and risk factors.
Identification of the patients with a history of PPH who are at the highest risk for recurrence may have crucial implications in guiding clinical treatment. Referral of patients to high-risk medical centers has been suggested as a means of improving outcomes for certain high-risk obstetric conditions and may be appropriate for some patients with a history of PPH. Recurrence risk data may also inform counseling regarding the risks of delivering outside of a hospitalized setting. Finally, it may affect the decision by clinicians about whether to place intravenous lines or to order blood products in anticipation of possible PPH.
To further understand the epidemiologic condition of recurrent PPH, we studied recurrence of PPH in women of the Swedish Medical Birth Register. In addition to describing overall PPH recurrence patterns in this nationwide sample, we specifically sought to (1) determine whether PPH recurrence could be explained by known PPH risk factors that are expected to be present in all pregnancies and (2) to evaluate the impact of PPH subtype (atony, retained placenta, lacerations) and severity on recurrence risk.
Materials and Methods
The Medical Birth Register contains information on 96-99% of all live births in Sweden since 1973 and stillbirths that occurred after 28 weeks of gestation (and from 22 weeks of gestation since June 2008). Information is retrieved from prenatal and delivery records and includes baseline characteristics of the mother. Onset of delivery is recorded routinely according to standardized categories of either spontaneous, induced vaginal, or cesarean delivery. At the time of discharge, the obstetrician records potential pregnancy or delivery-related complications according to the International Classification of Diseases , version 10 (ICD-10) coding. Since 1997, procedures could further be recorded with the Swedish version of the Nordic Medico-Statistical Committee Classification of Surgical Procedures.
PPH was identified through the ICD-10 code O72 and was specified further as occurring before or immediately after the delivery of the placenta (codes O72.0 and O72.1, respectively) or >2 hours after the delivery of the placenta (code O72.2). The diagnosis is applied by clinicians when blood loss is estimated to be in excess of 1000 mL. In the Swedish version of the ICD-10, PPH that occurs after the delivery of the placenta can be classified further as either because of atony (A), lacerations (B), or unknown reasons (Z). In the present study, we considered subgroups of PPH because of retained placenta (code O72.0), atony (code O72.1A), or lacerations (code O72.1B). If >1 specific diagnosis was given for 1 delivery, the hemorrhage was classified as not otherwise specified (together with hemorrhages of unknown reason). For cesarean delivery, hemorrhage generally was coded as a diagnosis of excessive (>1000 mL) perioperative bleeding, without further information on cause (eg, atony, retained placenta). We therefore included these as PPH in the setting of cesarean delivery in the overall analyses and performed analyses restricted to vaginal deliveries (for which the cause of PPH was generally coded). The distributions of diagnoses that were set in the study population are illustrated in Table 1 . We defined severe PPH as hemorrhage that led to coagulopathy (code O72.3) and/or with a concurrent coding of blood transfusion during the delivery hospitalization. Because of changes of the clinical definition of PPH after the transition from ICD-9 (>600 mL bleeding) to ICD-10 (>1000 mL), the evaluation of PPH recurrence was restricted to births that occurred after the implementation of ICD-10 in Sweden (from 1997, except in the county of Skåne where it was implemented from 1998).
| Variable | Postpartum hemorrhage, n | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Specified | Unspecified | Any | ||||||||
| Retained placenta | Atony | Lacerations | Unknown | Several specific | Late (>2 hrs) | Leading to coagulopathy | Incomplete code | Perioperative bleeding | With blood transfusion | |
| International Classification of Diseases –10 code | O72.0 | O72.1A | O72.1B | O72.1X | O72.0 + O72.1A/B | O72.2 | O72.3 | O72.? | O67.8 | Z51.3 |
| Vaginal delivery | ||||||||||
| First, n (%) | 8837 (2.01) | 9872 (2.25) | 4250 (0.97) | 3536 (0.80) | 461 (0.10) | 788 (0.18) | 23 (0.01) | 40 (0.01) | 4523 (1.03) | |
| Second, n (%) | 4069 (1.54) | 5439 (2.05) | 1174 (0.44) | 1281 (0.48) | 183 (0.07) | 487 (0.18) | 13 (0.00) | 15 (0.01) | 1771 (0.67) | |
| Third, n (%) | 676 (1.35) | 1128 (2.26) | 100 (0.20) | 179 (0.36) | 31 (0.06) | 92 (0.18) | 1 (0.00) | 1 (0.00) | 282 (0.56) | |
| Cesarean delivery | ||||||||||
| First, n (%) | 146 (0.15) | 995 (1.00) | 74 (0.07) | 190 (0.19) | 13 (0.01) | 375 (0.38) | 30 (0.03) | 4 (0.00) | 7996 (8.07) | 1295 (1.31) |
| Second, n (%) | 61 (0.14) | 321 (0.72) | 39 (0.09) | 89 (0.20) | 8 (0.02) | 167 (0.37) | 12 (0.03) | 4025 (8.97) | 615 (1.37) | |
| Third, n (%) | 13 (0.15) | 63 (0.74) | 6 (0.07) | 18 (0.21) | 34 (0.40) | 4 (0.05) | 709 (8.36) | 101 (1.19) | ||
To study the recurrence of PPH, we first identified all deliveries to primiparous women in the Medical Birth Register between 1997 and 2009. These 583,332 women were observed with respect to subsequent deliveries; the result was a total of 914,939 deliveries in the study period, of which 1.5% were multiples (n = 13,626). Frequency of PPH was assessed after first, second, and third delivery, which represented population risks of PPH. Among those with and without a diagnosis in their first pregnancy, we estimated the proportion of women who undertook a second pregnancy and the risk of PPH in that pregnancy; we then repeated the procedure for a third pregnancy. Probabilities of subsequent delivery, given PPH experience, were compared with the χ 2 test, and probability values of < .05 were considered statistically significant. Next we obtained relative risks of PPH, given previous PPH history, from log-linear regression models that estimated the probability of PPH in the second and third pregnancy, respectively. Analyses were performed for all deliveries and then restricted to vaginal deliveries, which were also stratified according to specific subtype of PPH. To further assess the influence of known chronic risk factors for PPH (ie, factors expected to be present across a woman’s reproductive life), we adjusted for fixed demographic factors (measured during the first pregnancy) such as year of birth, maternal age, civil status, country of origin, and diagnosis of chronic hypertension (code I10-15; code O10-11, which can predispose to superimposed preeclampsia), diabetes mellitus (code E10-14; codes O24.0-24.3, which can predispose to macrosomia and polyhydramnios), coagulopathy (code D66-69), or fibroid tumors (code D25). We also evaluated the presence of ≥1 of these risk factors in the second pregnancy of women with PPH in the first pregnancy.
Last, we assessed whether the type of hemorrhage (any, specific type, severe) that had been experienced in the first pregnancy influenced the risk and type of hemorrhage recurrence in the second pregnancy. Permission for the study was obtained from the Regional Ethical Review Board at Karolinska Institutet, Stockholm, Sweden.
Results
Table 1 shows the distribution of PPH diagnoses in the first 3 pregnancies to all women who gave birth from 1997-2009, stratified by birth order and mode of delivery. In this sample of 906,607 deliveries, there were 58,082 cases of PPH (6.4%). The risk of PPH was higher in the first delivery (7.0%) than in subsequent deliveries (5.5%). This pattern of highest risk in first delivery was observed for all subtypes, except for PPH that was associated with uterine atony, where risk remained largely unchanged across pregnancies.
In the same population, the risk of PPH was assessed in relation to maternal characteristics that were obtained in the corresponding pregnancy ( Table 2 ). Risk of PPH was associated positively with maternal age and maternal chronic conditions that included diabetes mellitus, hypertension, coagulopathy, and uterine fibroid tumors. In contrast, women who were single or who were born outside of Scandinavia were at less risk of PPH than women who lived with the father or who were born in Scandinavia, respectively. There was also a trend of increasing occurrence of PPH in the 13-year study period.
| Maternal characteristics | n | Postpartum hemorrhage | ||
|---|---|---|---|---|
| n | % | Odds ratio (95% CI) | ||
| Age at delivery, y | ||||
| <20 | 20,757 | 843 | 4.06 | 1.00 |
| 20-34 | 756,554 | 46,944 | 6.20 | 1.56 (1.46–1.68) |
| ≥35 | 129,262 | 10,294 | 7.96 | 2.0 (1.90–2.20) |
| Parity | ||||
| Primiparous | 538,468 | 37,651 | 6.99 | 1.00 |
| Multiparous | 368,139 | 20,431 | 5.55 | 0.78 (0.77–0.80) |
| Civil status | ||||
| Living with father | 812,033 | 52,022 | 6.41 | 1.00 |
| Living alone | 15,840 | 833 | 5.26 | 0.81 (0.76–0.87) |
| Unknown | 28,207 | 1,575 | 5.58 | 0.86 (0.82–0.91) |
| Country of origin | ||||
| Scandinavian | 771,783 | 49,814 | 6.45 | 1.00 |
| Non-Scandinavian | 134,069 | 8,233 | 6.14 | 0.95 (0.92–0.97) |
| Diabetes mellitus | ||||
| No | 900,986 | 57,597 | 6.39 | 1.00 |
| Yes | 5621 | 485 | 8.63 | 1.38 (1.26–1.52) |
| Chronic hypertension | ||||
| No | 901,484 | 57,667 | 6.40 | 1.00 |
| Yes | 5123 | 415 | 8.10 | 1.29 (1.16–1.43) |
| Coagulopathy | ||||
| No | 903,221 | 57,776 | 6.40 | 1.00 |
| Yes | 3386 | 306 | 9.04 | 1.45 (1.29–1.64) |
| Fibroid tumors | ||||
| No | 905,723 | 57,956 | 6.40 | 1.00 |
| Yes | 884 | 126 | 14.25 | 2.43 (1.99–2.97) |
Table 3 shows the risk of PPH in subsequent deliveries according to PPH history at first and second delivery. For both deliveries overall and when restricted to vaginal deliveries, the risk in a given pregnancy was increased greatly in women with a history of PPH. In the second pregnancy, this was reflected by a 3-fold higher risk in women with a history of PPH compared with those with no history (relative risk all = 3.0; 95% confidence interval, 2.9–3.1). In the third pregnancy, women with PPH in each of their 2 previous pregnancies had a 6-fold higher risk of PPH than women with no history (relative risk all = 6.1; 95% confidence interval, 5.1–7.2). Restricting our search to vaginal deliveries further strengthened the risks of recurrence. Adjustment for stable risk factors that potentially could explain the recurrence had little effect on the estimates. When each PPH subtype was considered separately (among vaginal deliveries only) similar patterns of recurrence were seen for PPH because of retained placenta and atony; the most pronounced recurrence was seen for hemorrhage because of retained placenta (results not shown).
| Pregnancy history | Recurrence in all deliveries | Recurrence in vaginal deliveries | |||||||
|---|---|---|---|---|---|---|---|---|---|
| First pregnancy | Second pregnancy | n | % | RR (95% CI) | RR (95% CI) a | n | % | RR (95% CI) | RR (95% CI) a |
| No | — | 289,982 | 5.0 | 1.0 | 1.0 | 226,310 | 3.7 | 1.0 | 1.0 |
| Yes | — | 19,853 | 15.0 | 3.0 (2.9–3.1) | 3.0 (2.9–3.1) | 13,552 | 14.2 | 3.8 (3.6–4.0) | 3.7 (3.6–3.9) |
| No | No | 52,847 | 4.4 | 1.0 | 1.0 | 41,631 | 3.5 | 1.0 | 1.0 |
| Yes | No | 2782 | 9.9 | 2.3 (2.0–2.5) | 2.3 (2.0–2.6) | 1937 | 9.4 | 2.7 (2.3–3.1) | 2.7 (2.3–3.2) |
| No | Yes | 2405 | 15.0 | 3.4 (3.1–3.8) | 3.4 (3.0–3.8) | 1443 | 15.3 | 4.4 (3.8–5.0) | 4.2 (3.7–4.9) |
| Yes | Yes | 406 | 26.6 | 6.1 (5.1–7.2) | 6.2 (5.2–7.3) | 247 | 26.7 | 7.6 (6.2 9.4) | 7.6 (6.1–9.5) |
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