Materials and Methods
We conducted a population-based retrospective cohort study using Washington State birth certificate data linked to deidentified maternal and neonatal hospital discharge records following delivery from the Comprehensive Hospital Abstract Reporting System (CHARS). Inclusion criteria for our subjects were nulliparity, age <25 years, singleton pregnancy, cephalic presentation, gestational age between 24-43 weeks, and delivery from 1987 through 2009. We categorized age into young adolescents aged 11-14 years, young teens aged 15-17 years, older teens aged 18-19 years, and young adults aged 20-24 years and used young adults aged 20-24 years as the reference group, in concordance with categories used by the Centers for Disease Control and Prevention for Vital Statistics reporting. A total of 2007 11- to 14-year-olds delivering from 1987 through 2009 met our inclusion criteria, matched at a 1:4 ratio with the other 3 age groups by year of delivery to improve power. The University of Washington Institutional Review Board determined that the study qualified for exempt status and did not require full institutional review board approval.
We obtained data using electronic data sources including: (1) the birth certificate database, which includes demographic, pregnancy, and delivery-related information; and (2) CHARS records, which contain International Classification of Diseases, Ninth Revision ( ICD-9 ) diagnosis and procedure codes. A covariate was classified as present if documented in at least 1 data source. Our primary outcome was method of delivery (cesarean vs vaginal). Among vaginal deliveries, we compared spontaneous vs operative vaginal delivery methods, including vacuum and forceps. Both birth certificate and CHARS records were used to capture mode of delivery, with spontaneous vaginal ( ICD-9 diagnosis code 650), operative vaginal ( ICD-9 procedure codes 72.0-72.4 and 72.7-72.9), and cesarean ( ICD-9 diagnosis code 669.7 and procedure codes 74-74.2 and 74.4-74.9).
Our secondary outcomes were maternal complications (corresponding with ICD-9 codes) including postpartum hemorrhage (666), third- and fourth-degree perineal lacerations (664.2-664.3), shoulder dystocia (660.4), and chorioamnionitis (658.4), all obtained from both birth certificate and CHARS data. We obtained information about length of stay from CHARS data, and categorized this as >3 days for a vaginal delivery (yes/no) and >5 days for a cesarean delivery (yes/no), including antepartum, intrapartum, and postpartum time. We also assessed neonatal complications using both birth certificate and CHARS data, including preterm delivery (645.10-645.13, and 645.20-645.23); low and very low birthweight (764.6-764.8, 765.6-765.8 and 764.1-764.5, 765.1-765.5, respectively); small for gestational age (SGA), or weight <10th percentile for gestational age (764); and respiratory distress syndrome (RDS) (769). Neonatal length of stay >5 or <5 days, and neonatal and infant death were obtained from CHARS data alone. Maternal complications were stratified by vaginal vs cesarean delivery. Perineal lacerations and shoulder dystocia were evaluated only among vaginal deliveries, while all other complications were evaluated among both modes of delivery.
We also evaluated demographic and pregnancy characteristics. Race, place of residence (urban, rural), insurance status, and adequacy of prenatal care were obtained using birth certificate data. Adequacy of prenatal care was measured using the Kotelchuck Index, which combines the initiation of prenatal care and number of visits compared with the expected visits, adjusted for gestational age of initiation of care and delivery. Tobacco use (306.1 and 649.0); prepregnancy weight (codes in adults and children: 649.1, 278.0-278.02, 783.2, and V85); and pregnancy comorbidities such as diabetes (648, 250), chronic hypertension (642.0-642.3, 642.9, 401), preeclampsia (642.4-642.5, 642.7) and eclampsia (642.6), and fetal anomalies (740-760) were obtained using both birth certificate and CHARS data.
We compared demographic and obstetric characteristics of the 4 age groups using χ 2 testing. To assess the risk of adverse maternal and neonatal outcomes among the youngest adolescents, we performed multivariate regression analyses and estimated the risk ratios (RRs) and 95% confidence intervals (CIs). We built separate models for each primary and secondary outcome, using logistic regression for most maternal and neonatal outcomes and Poisson regression with a robust variance estimator for common outcomes including cesarean delivery, operative delivery, maternal length of stay for vaginal and cesarean deliveries, and SGA. We adjusted for variables that we identified as potential confounders based on our literature review of factors associated with adolescent pregnancy and birth outcomes and a change in the RR estimate of >10% comparing crude and adjusted RR. We adjusted for infant birthweight in delivery method models (cesarean, operative). For maternal complications of vaginal deliveries, we adjusted for birthweight (lacerations, shoulder dystocia), maternal race (postpartum hemorrhage, chorioamnionitis), and adequacy of prenatal care (shoulder dystocia). For maternal complications of cesarean deliveries, we adjusted for maternal race (postpartum hemorrhage). For neonatal complications, we adjusted for gestational age (RDS, neonatal length of stay, neonatal death, and infant death), adequacy of prenatal care (RDS), and race (neonatal and infant death). All analyses were conducted using Stata 13.0 (Stata Corp, College Station, TX).
Results
A total of 2007 young adolescents aged 11-14 years met inclusion criteria for this study. The matched groups of those aged 15-17, 18-19, and 20-24 years each contained 8028 subjects, for a total sample of 26,091 subjects. Young adolescents 11-14 years of age were more likely to be of minority race/ethnicity, less likely to have private insurance, and less likely to be overweight compared to young adults aged 20-24 years ( Table 1 ). With regard to prenatal and intrapartum characteristics, 11- to 14-year-olds were less likely to have adequate prenatal care or to have diabetes compared to older teens and young adults. Hypertension, preeclampsia and eclampsia, and fetal malformations occurred similarly across groups.
| Demographic | Age 11-14 y n = 2007 No. (%) | Age 15-17 y n = 8028 No. (%) | Age 18-19 y n = 8028 No. (%) | Age 20-24 y n = 8028 No. (%) |
|---|---|---|---|---|
| Race/ethnicity | ||||
| Non-Hispanic White | 807 (41.4) | 4969 (63.1) | 5721 (71.5) | 6041 (76.8) |
| Hispanic | 675 (34.7) | 1564 (19.9) | 1135 (14.4) | 903 (11.5) |
| Non-Hispanic Black | 217 (11.1) | 589 (7.5) | 434 (5.5) | 291 (3.7) |
| Asian | 83 (4.3) | 302 (3.8) | 301 (3.8) | 466 (5.9) |
| Native American | 163 (8.4) | 452 (5.7) | 293 (3.3) | 162 (2.1) |
| Other | 2 (0.1) | 2 (0.0) | 5 (0.1) | 3 (0.0) |
| Place of residence | ||||
| Urban | 1381 (76.9) | 5334 (73.8) | 5537 (75.6) | 5652 (76.7) |
| Rural | 416 (23.1) | 1889 (26.2) | 1789 (24.4) | 1721 (23.3) |
| Insurance status | ||||
| Medicare/Medicaid | 1497 (74.6) | 5588 (69.6) | 5584 (69.6) | 3911 (48.7) |
| Private | 449 (22.4) | 2194 (27.3) | 2256 (28.1) | 3911 (48.7) |
| Uninsured | 61 (3.0) | 245 (3.1) | 187 (2.3) | 205 (2.6) |
| Prenatal care | ||||
| Adequate | 710 (40.5) | 3768 (52.5) | 4151 (57.8) | 4725 (65.8) |
| Inadequate | 1044 (59.5) | 3414 (47.5) | 3034 (42.2) | 2456 (34.2) |
| Tobacco use | ||||
| Yes | 306 (16.7) | 1831 (24.7) | 1883 (25.3) | 1336 (18.1) |
| No | 1528 (83.3) | 5595 (75.3) | 5550 (74.7) | 6032 (81.9) |
| Prepregnancy weight, lb | ||||
| <100 | 91 (7.1) | 254 (4.8) | 196 (3.7) | 138 (2.6) |
| 100-150 | 958 (74.7) | 3853 (72.6) | 3593 (67.0) | 3172 (59.6) |
| 150-200 | 213 (16.6) | 1041 (19.7) | 1300 (24.2) | 1513 (28.4) |
| >200 | 20 (1.6) | 156 (2.9) | 276 (5.1) | 499 (9.4) |
| Pregnancy comorbidities | ||||
| Diabetes (gestational, pregestational) | 15 (0.8) | 102 (1.3) | 145 (1.8) | 238 (3.0) |
| Chronic hypertension | 108 (5.4) | 460 (5.7) | 477 (5.9) | 569 (7.1) |
| Preeclampsia | 207 (10.3) | 686 (8.6) | 664 (8.3) | 718 (8.9) |
| Eclampsia | 25 (1.3) | 44 (0.6) | 51 (0.6) | 28 (0.4) |
| Fetal anomalies | 46 (2.3) | 199 (2.5) | 182 (2.3) | 182 (2.3) |
Young adolescents aged 11-14 years had a 27% lower risk of cesarean delivery compared to young adults aged 20-24 years (RR, 0.73; 95% CI, 0.65–0.83) ( Table 2 ), as did young teens aged 15-17 years and older teens aged 18-19 years (RR, 0.69; 95% CI, 0.64–0.74, and RR, 0.81; 95% CI, 0.76–0.86, respectively). Indications for cesarean delivery, including fetal distress, cephalopelvic disproportion, malpresentation, active genital herpes, placenta previa, and umbilical cord prolapse, did not differ among age groups (data not shown). Adolescents aged 11-14 years also had a lower risk of operative assistance with forceps or vacuum compared to 20- to 24-year-olds (RR, 0.87; 95% CI, 0.78–0.97), as did teens aged 15-17 and 18-19 years (RR, 0.76; 95% CI, 0.71–0.82, and RR, 0.82; 95% CI, 0.77–0.88, respectively).
| Variable | Age 11-14 y, n (%) | Age 15-17 y, n (%) | Age 18-19 y, n (%) | Age 20-24 y, n (%) |
|---|---|---|---|---|
| All deliveries | n = 2007 | n = 8028 | n = 8028 | n = 8028 |
| Vaginal (spontaneous or operative) | 1718 (85.6) | 6928 (86.3) | 6730 (83.8) | 6419 (80.0) |
| Cesarean | 289 (14.4) | 1100 (13.7) | 1297 (16.2) | 1609 (20.0) |
| RR (95% CI) | 0.73 (0.65–0.83) | 0.69 (0.64–0.74) | 0.81 (0.76–0.86) | 1.00 |
| Vaginal deliveries | n = 1732 | n = 7036 | n = 6833 | n = 6576 |
| Spontaneous | 1410 (82.1) | 5802 (83.8) | 5531 (82.2) | 5018 (78.2) |
| Operative | 308 (17.9) | 1126 (16.2) | 1199 (17.8) | 1401 (21.8) |
| RR (95% CI) | 0.87 (0.78–0.97) | 0.76 (0.71–0.82) | 0.82 (0.77–0.88) | 1.00 |
Among vaginal deliveries, teens aged 15-17 and 18-19 years had a decreased risk of third- and fourth-degree perineal lacerations compared to young adults (RR, 0.80; 95% CI, 0.71–0.89, and RR, 0.74; 95% CI, 0.66–0.82, respectively). Young adolescents aged 11-14 years had a similar risk of third- and fourth-degree perineal lacerations compared to young adults ( Table 3 ). Young adolescents aged 11-14 years with vaginal deliveries were 34% more likely to have a length of stay >3 days as compared to 20- to 24-year-olds (RR, 1.34; 95% CI, 1.20–1.49). Adolescents aged 11-14 years with cesarean deliveries had a 71% increased risk of hospital stay >5 days compared to 20- to 24-year-olds (RR, 1.71; 95% CI, 1.38–2.12) ( Table 4 ). Teens aged 15-17 and 18-19 years also had an increased risk of prolonged maternal length of stay compared with 20- to 24-year-olds (RR, 1.23; 95% CI, 1.05–1.45, and RR, 1.21; 95% CI, 1.04–1.42, respectively), although the risk was lower than that in the youngest group.
| Variable | Age 11-14 y, n (%) | Age 15-17 y, n (%) | Age 18-19 y, n (%) | Age 20-24 y, n (%) |
|---|---|---|---|---|
| n = 1733 | n = 7036 | n = 6834 | n = 6577 | |
| Postpartum hemorrhage a | 103 (6.0) | 346 (5.0) | 289 (4.3) | 312 (4.8) |
| RR (95% CI) | 1.07 (0.84–1.36) | 0.96 (0.81–1.13) | 0.85 (0.72–1.01) | 1.00 |
| Third- to fourth-degree perineal laceration b | 174 (8.7) | 668 (8.3) | 639 (8.0) | 812 (10.1) |
| RR (95% CI) | 0.93 (0.78–1.11) | 0.80 (0.71–0.89) | 0.74 (0.66–0.82) | 1.00 |
| Shoulder dystocia c | 32 (1.9) | 144 (2.1) | 184 (2.7) | 153 (2.4) |
| RR (95% CI) | 0.86 (0.57–1.29) | 0.96 (0.75–1.23) | 1.25 (0.99–1.58) | 1.00 |
| Chorioamnionitis a | 59 (3.4) | 235 (3.4) | 251 (3.7) | 208 (3.2) |
| RR (95% CI) | 0.95 (0.70–1.30) | 1.01 (0.83–1.23) | 1.13 (0.94–1.37) | 1.00 |
| Maternal length of stay | ||||
| >3 d d | 368 (21.4) | 1134 (16.4) | 1017 (15.1) | 974 (15.2) |
| RR (95% CI) | 1.34 (1.20–1.49) | 1.05 (0.97–1.13) | 0.98 (0.90–1.06) | 1.00 |
c Adjusted for birthweight and adequacy of prenatal care
d Adjusted for birthweight and using Poisson modeling for common outcome.
| Variable | Age 11-14 y, n (%) | Age 15-17 y, n (%) | Age 18-19 y, n (%) | Age 20-24 y, n (%) |
|---|---|---|---|---|
| n = 275 | n = 992 | n = 1195 | n = 1452 | |
| Postpartum hemorrhage a | 6 (2.1) | 17 (1.6) | 29 (2.2) | 37 (2.3) |
| RR (95% CI) | 0.68 (0.27–1.66) | 0.56 (0.31–1.03) | 0.89 (0.53–1.47) | 1.00 |
| Chorioamnionitis | 21 (7.3) | 92 (8.4) | 115 (8.9) | 144 (8.9) |
| RR (95% CI) | 0.79 (0.49–1.28) | 0.92 (0.70–1.22) | 0.98 (0.76–1.27) | 1.00 |
| Maternal length of stay | ||||
| >5 d b | 83 (28.7) | 221 (20.1) | 252 (19.4) | 250 (15.5) |
| RR (95% CI) | 1.71 (1.38–2.12) | 1.23 (1.05–1.45) | 1.21 (1.04–1.42) | 1.00 |
b Adjusted for birthweight and using Poisson modeling for common outcome.
With regard to neonatal complications, parturients aged 11-14, 15-17, and 18-19 years had an increased risk of preterm delivery and low birthweight compared to 20- to 24-year-olds ( Table 5 ). Young adolescents aged 11-14 years had a 2-fold increased risk of preterm delivery (RR, 2.11; 95% CI, 1.79–2.48) and low birthweight (RR, 2.08; 95% CI, 1.73–2.50), and a 3-fold increased risk of very low birthweight (RR, 3.25; 95% CI, 2.22–4.77) compared to young adults. In addition to the increased risk of preterm delivery and its resultant influence on birthweight in these women, young adolescents aged 11-14 years and teens aged 15-17 years also demonstrated a 25% increased risk of SGA infants, again with adolescents aged 11-14 years at highest risk (RR, 1.25; 95% CI, 1.11–1.40). Infants born to young adolescents aged 11-14 years had a nearly 4-fold risk of infant death, or death occurring from day 0-364 of life (RR, 3.90; 95% CI, 2.36–6.44). Risk of infant death was also increased for teens aged 15-17 and 18-19 years (RR, 2.18; 95% CI, 1.43–3.33, and RR, 1.62; 95% CI, 1.05–2.57, respectively).
| Indication | Age 11-14 y, n (%) | Age 15-17 y, n (%) | Age 18-19 y, n (%) | Age 20-24 y, n (%) |
|---|---|---|---|---|
| n = 2007 | n = 8028 | n = 8028 | n = 8028 | |
| Gestational age at delivery | ||||
| Preterm (<37 wk) | 235 (12.0) | 677 (8.6) | 560 (7.1) | 481 (6.1) |
| RR (95% CI) | 2.11 (1.79–2.48) | 1.45 (1.28–1.63) | 1.17 (1.04–1.33) | 1.00 |
| Birthweight at delivery | ||||
| Very low | ||||
| <1500 g | 48 (2.4) | 85 (1.1) | 62 (0.8) | 60 (0.8) |
| RR (95% CI) | 3.25 (2.22–4.77) | 1.42 (1.02–1.98) | 1.03 (0.72–1.47) | 1.00 |
| Low | ||||
| <2500 g | 182 (9.1) | 536 (6.7) | 463 (5.8) | 367 (4.6) |
| RR (95% CI) | 2.08 (1.73–2.50) | 1.49 (1.30–1.71) | 1.27 (1.10–1.46) | 1.00 |
| Small for gestational age a | 304 (16.4) | 1149 (15.4) | 1063 (14.3) | 963 (13.1) |
| RR (95% CI) | 1.25 (1.11–1.40) | 1.17 (1.08–1.26) | 1.09 (1.00–1.18) | 1.00 |
| Respiratory distress syndrome b | 43 (2.1) | 103 (1.3) | 85 (1.1) | 83 (1.0) |
| RR (95% CI) | 1.35 (0.87–2.17) | 1.05 (0.73–1.50) | 1.04 (0.72–1.49) | 1.00 |
| Neonatal length of stay c | ||||
| >5 d | 152 (8.2) | 455 (6.1) | 431 (5.7) | 387 (5.1) |
| RR (95% CI) | 1.20 (0.96–1.50) | 1.01 (0.86–1.18) | 1.05 (0.90–1.23) | 1.00 |
| Neonatal death d | 27 (1.4) | 50 (0.6) | 20 (0.3) | 26 (0.3) |
| RR (95% CI) | 2.03 (0.98–4.17) | 1.69 (0.94–3.05) | 0.79 (0.40–1.58) | 1.00 |
| Infant death d | 51 (2.5) | 88 (1.1) | 58 (0.7) | 41 (0.5) |
| RR (95% CI) | 3.90 (2.36–6.44) | 2.18 (1.43–3.33) | 1.62 (1.05–2.57) | 1.00 |
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