Materials and Methods
We performed a secondary analysis of deidentified data collected from the Consortium on Safe Labor database, a retrospective cohort study of 228,562 deliveries from 12 US clinical centers between 2002 and 2008. Data were collected from obstetric, labor progression, and newborn electronic medical records linked to hospital discharge codes. This original study received institutional review board approval from all participating institutions, and the current analysis was deemed exempt by the MedStar Washington Hospital Center’s Institutional Review Board on Oct. 17, 2013.
For the present analysis, we included women with singleton gestations, delivery gestational age ≥ 24 weeks, and vaginal deliveries. Only the patient’s first documented pregnancy in the Consortium on Safe Labor database was used for analysis. Cases with shoulder dystocia or hospitals without adequate documentation of pertinent variables were excluded ( Figure 1 ). The total number of deliveries available for analysis was 91,291.
The third stage of labor was calculated from the time of neonate delivery to the time of placental delivery as recorded in the electronic medical record. Retained placenta was defined as longer than 30 minutes. Bivariate analyses were performed to assess the relationship between a retained placenta and maternal demographic or clinical characteristics with a χ 2 test, Fisher exact test, Student t test, or Wilcoxon rank sum test, if applicable. Multivariable logistic regression analyses estimated the adjusted odds ratios and 95% confidence intervals for potential risk factors for retained placenta stratified by parity.
Risk factors for retained placenta were identified from the medical record or International Classification of Disease , 9th revision (ICD-9), codes and included parity, maternal age, gestational age, admission BMI, race, history of abortion (ICD-9), history of cesarean delivery, large for gestational age (ICD-9), intrauterine growth restriction (IUGR; ICD-9), duration of first and second stages of labor, duration of rupture of membranes to delivery, labor induction agent (misoprostol, dinoprostone, artificial rupture of membranes, or oxytocin), group B streptococcal status, chorioamnionitis, use of an epidural, episiotomy, stillbirth, hospital type, and duration of exposure to oxytocin were examined and adjusted for in the analysis.
A value of P < .05 was determined significant. Forest plots were developed to compare the odds ratios between categories of gestational age groups, based on the result of multivariable logistic regression models. All statistical analyses were performed using SAS version 9.3 (SAS Institute Inc, Cary, NC).
Results
The incidence of retained placenta in the study population was 1.12% (1047 deliveries). The demographics of the study population are described in Table 1 . Women with retained placenta compared with women without retained placenta were more likely to be older (27.5 years vs 26.6 years; P < .001), multiparous, and non-Hispanic black or Asian, but there was no difference in maternal BMI ( P < .18).
| Variable a | Retained placenta no (n = 89,765) | Retained placenta yes (n = 1047, 1.12%) | P value |
|---|---|---|---|
| Maternal age, y b | 26.64 (5.81) | 27.53 (6.43) | < .001 |
| Gravidity c | 2 (1,5) | 2 (1,5) | .700 |
| Parity c | 1 (0,3) | 1 (0,3) | .008 |
| Nulliparous | .002 | ||
| No | 50,634 (56.41%) | 541 (51.67%) | |
| Yes | 39,131 (43.59%) | 506 (48.33%) | |
| Gestational age group | < .001 | ||
| 24 wks 0 d-27 wks 6 d | 239 (0.27%) | 23 (2.20%) | |
| 28 wks 0 d-31 wks 6 d | 500 (0.56%) | 16 (1.53%) | |
| 32 wks 0 d-33 wks 6 d | 855 (0.95%) | 18 (1.72%) | |
| 34 wks 0 d-36 wks 6 d | 6190 (6.90%) | 87 (8.31%) | |
| 37 wks 0 d-38 wks 6 d | 26,702 (29.75%) | 306 (29.23%) | |
| 39 wks 0 d-40 wks 6 d | 48,503 (54.03%) | 497 (47.47%) | |
| 41 wks 0 d-41 wks 6 d | 6212 (6.92%) | 95 (9.07%) | |
| 42 wks 0 d and above | 564 (0.63%) | 5 (0.48%) | |
| BMI at admission, kg/m 2 | .184 | ||
| <18.5 | 55 (0.06%) | 1 (0.10%) | |
| 18.5–25 | 12,323 (13.74%) | 138 (13.18%) | |
| 25–30 | 30,597 (34.09%) | 357 (34.10%) | |
| 30–35 | 19,428 (21.64%) | 227 (21.68%) | |
| 35–40 | 7794 (8.68%) | 94 (8.98%) | |
| ≥40 | 4325 (4.82%) | 69 (6.59%) | |
| Missing | 15,243 (16.98%) | 161 (15.38%) | |
| Race | .039 | ||
| Non-Hispanic white | 48,848 (54.42%) | 552 (52.72%) | |
| Non-Hispanic black | 16,087 (17.92%) | 193 (18.43%) | |
| Hispanic | 14,736 (16.42%) | 204 (19.48%) | |
| Asian/Pacific Islander | 3203 (3.57%) | 25 (2.39%) | |
| Others | 1854 (2.07%) | 22 (2.10%) | |
| Unknown/declined | 5037 (5.61%) | 51 (4.87%) | |
| Stillbirth | < .001˦ | ||
| No | 89,511 (99.72%) | 1016 (97.04%) | |
| Yes | 254 (0.28%) | 31 (2.96%) | |
| Stillbirth, GA 24 wks 0 d to 27 wks 6 d | .003˦ | ||
| No | 199 (83.26%) | 11 (47.83%) | |
| Yes | 40 (16.74%) | 12 (52.17%) | |
| Stillbirth, GA 28 wks 0 d to 31 wks 6 d | .01˦ | ||
| No | 458 (91.60%) | 11 (68.75%) | |
| Yes | 42 (8.40%) | 5 (31.25%) | |
| Stillbirth, GA 32 wks 0 d to 33 wks 0 d | .042˦ | ||
| No | 819 (95.79%) | 15 (83.33%) | |
| Yes | 36 (4.21%) | 3 (16.67%) | |
| Stillbirth, GA 34 wks 0 d to 36 wks 6 d | < .001˦ | ||
| No | 6135 (99.11%) | 81 (93.10%) | |
| Yes | 55 (0.89%) | 6 (6.90%) | |
| Stillbirth, GA 37 wks 0 d to 38 wks 6 d | .001˦ | ||
| No | 26667 (99.87%) | 302 (98.69%) | |
| Yes | 35 (0.13%) | 4 (1.31%) | |
| Stillbirth, GA 39 wks 0 d to 40 wks 6 d | .355˦ | ||
| No | 48461 (99.91%) | 496 (99.80%) | |
| Yes | 42 (0.09%) | 1 (0.20%) | |
| Stillbirth, GA 41 wks 0 d to 41 wks 6 d | 1.00˦ | ||
| No | 6209 (99.95%) | 95 (100.0%) | |
| Yes | 3 (0.05%) | 0 | |
| Stillbirth, GA 42 wks 0 d and above | 1.00˦ | ||
| No | 563 (99.82%) | 5 (100.0%) | |
| Yes | 1 (0.18%) | 0 | |
| Duration of first stage of labor, h c | 6.9 (2.1, 17.1) | 495 (1.8, 24.7) | < .001 |
| Duration of second stage of labor, min c | 29 (6, 124) | 35 (7, 160) | < .001 |
| Duration of third stage of labor, min c | 5 (2, 11) | 52 (32, 1443) | < .001 |
| Hospital type | < .001 | ||
| University-affiliated teaching hospital | 27,748 (30.91%) | 444 (42.41%) | |
| Community teaching hospital | 50,498 (56.26%) | 546 (52.15%) | |
| Community nonteaching hospital | 11,519 (12.83%) | 57 (5.44%) | |
| Intrauterine growth restriction d | .183 | ||
| No | 88,270 (98.33%) | 1495 (97.80%) | |
| Yes | 1495 (1.67%) | 23 (2.20%) | |
| Large for gestational age e | .726 | ||
| No | 88672 (98.78%) | 1033 (98.66%) | |
| Yes | 1093 (1.22%) | 14 (1.34%) | |
| Use of epidural | < .001 | ||
| No | 20,211 (22.52%) | 294 (28.08%) | |
| Yes | 69,554 (77.48%) | 753 (71.92%) | |
| Chorioamnionitis | <.001 | ||
| No | 88,558 (98.66%) | 1019 (97.33%) | |
| Yes | 1207 (1.34%) | 28 (2.67%) | |
| History of cesarean delivery | .803 | ||
| No | 86,887 (96.79%) | 1012 (96.66%) | |
| Yes | 2878 (3.21%) | 35 (3.34%) | |
| Oxytocin exposure | .044 | ||
| No | 28,668 (31.94%) | 365 (34.86%) | |
| Yes | 61,097 (68.06%) | 682 (65.14%) | |
| Duration from first oxytocin use to delivery, min a | 298.8 (353.9) | 386.6 (559.5) | < .001 |
a Other variables analyzed include history of abortion, episiotomy, induction of labor agent (misoprostol, dinoprostone, artificial rupture of membranes, or oxytocin), group B streptococcal status, duration of rupture of membranes, and episiotomy; Results are presented as number of observations (percentage) with χ 2 test unless noted as follows
b Results are presented as mean (SD) with a Student t test
c Results are presented as median (10th percentile, 90th percentile) with Wilcoxon rank sum test
d Intrauterine growth restriction (ICD-9)
They were also more likely to have a stillbirth (3.0% vs 0.3%; P < .001), chorioamnionitis (2.7% vs 1.3%; P < .001), and a longer length of first and second stages of labor ( P < .001). Women with retained placenta had a significantly higher rate of postpartum hemorrhage than women without retained placenta (11.56% vs 3.13%; P < .001). However, no significant difference was found in the rate of postpartum blood transfusion between the women with a retained placenta and the women without a retained placenta (7.02% vs 5.32%; P = .092).
After stratifying by parity and adjusting for confounding factors, multiple significant risk factors for retained placenta in both nulliparous and multiparous women were identified ( Tables 2 and 3 , respectively). Regardless of parity, risk factors included increasing maternal age >30 years, early preterm delivery <27 6/7 weeks compared with 34 0/7 weeks or later ( Figures 2 and 3 ), and stillbirth and delivery in a university-affiliated or community teaching hospital. Maternal BMI, chorioamnionitis, and IUGR had no association with retained placenta.
| Nulliparous | Retained placenta | AOR b (95% CI) | |
|---|---|---|---|
| Risk factor a | No, n (%) | Yes, n (%) | |
| Age, y | |||
| <20 | 8273 (21.1) | 88 (17.4) | 0.87 (0.64–1.17) |
| 20–24 | 14,896 (38.1) | 166 (32.8) | 0.98 (0.77–1.25) |
| 25–29 | 9511 (24.3) | 109 (21.5) | Reference |
| 30–34 | 4705 (12.0) | 88 (17.4) | 1.50 (1.12–2.01) |
| 35–39 | 1479 (3.8) | 41 (8.1) | 2.02 (1.39–2.95) |
| ≥40 | 267 (0.68) | 14 (2.8) | 3.12 (1.73–5.67) |
| Gestational age, wks | |||
| 24/0–27/6 | 144 (0.37) | 11 (2.2) | Reference |
| 28/0–31/6 | 262 (0.67) | 10 (2.0) | 0.53 (0.21–1.36) |
| 32/0–33/6 | 439 (1.1) | 12 (2.37) | 0.54 (0.22–1.33) |
| 34/0–36/6 | 2789 (7.1) | 45 (8.9) | 0.44 (0.20–0.95) |
| 37/0–38/6 | 10747 (27.5) | 137 (27.1) | 0.41 (0.19–0.89) |
| 39/0–40/6 | 21139 (54.0) | 243 (48.02) | 0.39 (0.18–0.82) |
| 41–41/6 | 3365 (8.6) | 47 (9.3) | 0.39 (0.17–0.87) |
| ≥42/0 | 246 (0.63) | 1 (0.20) | 0.11 (0.01–0.93) |
| BMI at admission | |||
| <18.5 | 36 (0.1) | 1 (0.2) | 1.65 (0.21–13.12) |
| 18.5–24.9 | 6030 (15.4) | 74 (14.6) | Reference |
| 25–29.9 | 13,744 (35.1) | 175 (34.6) | 1.0 (0.76–1.32) |
| 30–34.9 | 7906 (20.2) | 99 (19.6) | 0.88 (0.65–1.20) |
| 35–39.9 | 2959 (7.6) | 40 (7.9) | 0.93 (0.62–1.38) |
| ≥40 | 1531 (9.1) | 32 (6.3) | 1.34 (0.87–2.07) |
| Missing | 6925 (17.7) | 85 (16.8) | 0.87 (0.61–1.23) |
| Race | |||
| Non-Hispanic black | 6889 (17.6) | 71 (14.0) | 0.63 (0.47–0.86) |
| Non-Hispanic white | 20,966 (53.6) | 287 (56.7) | Reference |
| Hispanic | 6161 (15.7) | 93 (18.4) | 1.11 (0.84–1.46) |
| Asian/Pacific Islander | 1668 (4.3) | 16 (3.2) | 0.80 (0.47–1.35) |
| Stillbirth | 142 (0.36) | 18 (3.6) | 5.85 (3.22–10.63) |
| Hospital type | |||
| University affiliated teaching | 12,405 (31.7) | 193 (38.1) | 2.50 (1.2–5.19) |
| Community teaching | 22,612 (57.8) | 293 (57.9) | 2.47 (1.52–4.00) |
| Community nonteaching | 4114 (10.5) | 20 (4.0) | Reference |
| Duration first stage, h c | 8.72 (3.27, 20.4) | 11.29 (4.07, 30.27) | 1.01 (1.01–1.02) |
| Duration second stage, h c | 0.98 (0.27, 2.7) | 1.23 (0.27, 3.25) | 1.06 (1.02–1.10) |
| IUGR d | 813 (2.1) | 14 (2.8) | 1.11 (0.63–1.94) |
| Chorioamnionitis | 902 (2.3) | 22 (4.35) | 1.36 (0.87–2.14) |
| Epidural | 31,961 (81.7) | 387 (76.5) | 0.70 (0.56–0.90) |
a Other risk factors analyzed but not listed above include the following: gravidity, other race, history of abortion, large for gestational age, intrauterine growth restriction, duration of rupture of membranes, method of induction, oxytocin use, and antepartum group B streptococcal status
c Results are presented as median (10th percentile, 90th percentile) with Wilcoxon rank sum test
| Multiparous a | Retained placenta | AOR (95% CI) | |
|---|---|---|---|
| Risk factor | No, n (%) | Yes, n (%) | |
| Age, y | |||
| <20 | 1362 (2.7) | 14 (2.6) | 0.92 (0.52–1.61) |
| 20–24 | 10,668 (21.1) | 128 (23.7) | 1.22 (0.95–1.56) |
| 25–29 | 17,501 (34.6) | 146 (27.0) | Reference |
| 30–34 | 13,561 (26.8) | 140 (25.9) | 1.28 (1.01–1.62) |
| 35–39 | 6207 (12.3) | 85 (15.7) | 1.59 (1.20–2.10) |
| ≥40 | 1335 (2.6) | 28 (5.2) | 2.44 (1.59–3.75) |
| Gestational age, weeks | |||
| 24/0–27/6 | 95 (0.19) | 12 (2.3) | Reference |
| 28/0–31/6 | 238 (0.5) | 6 (1.1) | 0.26 (0.09–0.77) |
| 32/0–33/6 | 416 (0.8) | 6 (1.1) | 0.18 (0.06–0.53) |
| 34/0–36/6 | 3401 (6.7) | 42 (7.8) | 0.18 (0.70–0.42) |
| 37/0–38/6 | 15,955 (31.5) | 169 (31.2) | 0.17 (0.08–0.41) |
| 39–40/6 | 27,364 (54.0) | 254 (47.0) | 0.16 (0.07–0.38) |
| 41/0–41/6 | 2847 (5.6) | 48 (8.9) | 0.25 (0.10–0.60) |
| ≥42/0 | 318 (0.6) | 4 (0.7) | 0.21 (0.06–0.79) |
| BMI at admission, kg/m 2 | |||
| <18.5 | 19 (0.1) | 0 (0) | |
| 18.5–24.9 | 6293 (12.4) | 64 (11.8) | Reference |
| 25–29.9 | 16853 (33.3) | 182 (33.6) | 1.08 (0.81–1.45) |
| 30–34.9 | 11522 (22.8) | 128 (23.7) | 1.02 (0.78–1.39) |
| 35–39.9 | 4835 (9.6) | 54 (10.0) | 1.00 (0.69–1.46) |
| ≥40 | 2794 (5.5) | 37 (6.8) | 1.16 (0.76–1.77) |
| Missing | 8318 (16.4) | 76 (14.1) | 1.04 (0.72–1.51) |
| Race | |||
| Non-Hispanic black | 9198 (18.2) | 122 (22.6) | 0.952 (0.73–1.24) |
| Non-Hispanic white | 27882 (55.1) | 265 (49.0) | Reference |
| Hispanic | 8575 (16.9) | 111 (20.5) | 1.1 (0.82–1.38) |
| Asian/Pacific Islander | 1535 (3.0) | 9 (1.7) | 0.79 (0.40–1.54) |
| Stillbirth | 112 (0.22) | 13 (2.40) | 4.47 (2.06–9.68) |
| Hospital type | |||
| University-affiliated teaching | 15343 (30.3) | 241 (46.4) | 2.22 (1.03–4.80) |
| Community teaching | 27886 (55.1) | 253 (46.8) | 1.93 (1.31–2.76) |
| Community nonteaching | 7405 (14.6) | 37 (6.8) | Reference |
| Duration first stage, h b | 5.78 (1.55, 13.8) | 6.18 (1.22, 17.3) | 1.00 (0.99–1.01) |
| Duration second stage, h b | 0.28 (0.08, 1.08) | 0.3 (0.08, 1.33) | 1.01 (0.97–1.05) |
| IUGR c | 682 (1.4) | 9 (1.7) | 1.25 (0.63–2.48) |
| Chorioamnionitis | 305 (0.6) | 6 (1.1) | 0.99 (0.41–2.43) |
| Epidural | 37,593 (74.2) | 366 (67.7) | 0.86 (0.70–1.05) |
| History of cesarean delivery | 2861 (5.7) | 35 (6.5) | 0.92 (0.65–1.32) |
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