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Table 1 Characteristics of Mother-Infant pairs according to delivery type

From: Prepregnancy body mass index and risk of preterm birth: association heterogeneity by preterm subgroups

  Medically-induced PTBsa Spontaneous PTBsa Term birthsb p-valuec
  (N = 466) (N = 930) (N = 3281)  
  Mean (SD)  
Maternal age (years) 29.5 (6.8) 28.0 (6.6) 27.8 (6.4) <0.001
Gestational age at birth (weeks) 33.7 (3.0) 33.7 (3.4) 39.5 (1.3) <0.001
Prepregnancy BMI (kg/m2) 27.1 (6.6) 25.5 (6.0) 25.8 (6.1) <0.001
Birth weight (grams) 1989 (734) 2237 (716) 3239 (563) <0.001
  N (%)  
Prepregnancy BMI (kg/m2)     <0.001
  <18.5 13 (2.8) 54 (5.8) 149 (4.5)
  18.5-24.9 188 (40.3) 444 (47.7) 1613 (49.2)
  25.0-29.9 136 (29.2) 269 (28.9) 915 (27.9)
  ≥ 30.0 129 (27.7) 163 (17.5) 604 (18.4)
Hypertensive disorders of pregnancy     <0.001
  None 179 (38.7) 850 (92.1) 3004 (92.2)
  Chronic hypertension 19 (4.1) 27 (2.9) 71 (2.2)
  Mild preeclampsia 60 (13.0) 24 (2.6) 123 (3.8)
  Severe hypertensive disorders (severe pre-eclampsia, eclampsia, HELLP syndrome) 205 (44.3) 22 (2.4) 61 (1.9)
Chorioamnionitis     <0.001
  None 125 (26.8) 252 (27.1) 1265 (38.6)
  Subclinical chorioamnionitis 117 (25.1) 157 (16.9) 578 (17.6)
  Clinical chorioamnionitis 35 (7.5) 239 (25.7) 302 (9.2)
Unknown 189 (40.6) 282 (30.3) 1136 (34.6)
Glucose tolerance     <0.001
  No 401 (86.4) 855 (92.3) 3090 (94.5)
  Gestational diabetes 39 (8.4) 46 (5.0) 145 (4.4)
  Diabetes mellitus before index pregnancy 24 (5.2) 25 (2.7) 35 (1.1)
Gestational weight gain per 2009 IOM     <0.001
  Inadequate 50 (10.7) 118 (12.7) 479 (14.6)
  Adequate 38 (8.2) 115 (12.4) 635 (19.4)
  Excessive 148 (31.8) 306 (32.9) 853 (26.0)
  Unknown 230 (49.4) 391 (42.0) 1314 (40.0)
Married 159 (34.2) 250 (26.9) 1183 (36.2) <0.001
Household income     0.13
  < $30,000/yr 213 (45.7) 475 (51.1) 1580 (48.2)
  ≥ $30,000/yr 69 (14.8) 100 (10.8) 387 (11.8)
  Unknown 184 (39.5) 355 (38.2) 1314 (40.0)
Education     0.02
  < High school 138 (29.6) 310 (33.3) 1100 (33.5)
  High school 176 (37.8) 336 (36.1) 1055 (32.2)
  > High school 152 (32.6) 284 (30.5) 1126 (34.3)
Maternal race/ethnicity     0.003
  White 52 (11.2) 130 (14.0) 342 (10.4)
  Black 260 (55.8) 482 (51.8) 1646 (50.2)
  Hispanic 106 (22.7) 213 (22.9) 892 (27.2)
  Other 48 (10.3) 105 (11.3) 401 (12.2)
Maternal smoking 3 months before or during index pregnancy 98 (21.0) 275 (29.6) 591(18.0) <0.001
Maternal stress during pregnancy     <0.001
  No stress 144 (31.1) 304 (33.1) 1269 (38.9)
  Average stress 194 (41.9) 396 (43.1) 1385 (42.4)
  Very stressful 125 (27.0) 218 (23.7) 612 (18.7)
Any illicit drug use during pregnancy 76 (16.5) 218 (23.5) 432 (13.2) <0.001
Alcohol use during pregnancy 30 (6.5) 65 (7.0) 211 (6.4) 0.84
Parity     0.02
  Nulliparous 207 (44.4) 385 (41.4) 1381 (42.1)
  Primiparous 119 (25.5) 239 (25.7) 977 (29.8)
  Multiparous 140 (30.0) 306 (32.9) 923 (28.1)
Cervical incompetence 16 (3.4) 64 (6.9) 37 (1.1) <0.001
Placenta previa 22 (4.7) 29 (3.1) 32 (1.0) <0.001
Preterm premature rupture of membranes 0 (0.0) 439 (47.2) 0 (0.0) N/A
Mode of delivery     <0.001
  Vaginal 136 (29.2) 695 (74.8) 2302 (70.2)
  Cesarean section 330 (70.8) 234 (25.2) 977 (29.8)
Delivery type     N/A
  Medically-induced 466 (100.0) 0 (0.0) 971 (29.6)
  Spontaneous 0 (0.0) 930 (100.0) 2310 (70.4)
PTB according to gestational age    N/A N/A
  Early PTB (<34 weeks) 189 (40.6) 320 (34.4)
  Late PTB (34–36 weeks) 277 (59.4) 610 (65.6)
Infant sex- female 247 (53.0) 447 (48.1) 1656 (50.5) 0.20
  1. PTB = Preterm Birth; BMI = Body Mass Index; IOM = Institute of Medicine; HELLP = hemolysis, elevated liver enzymes, low platelets.
  2. aPTBs include births at 23–36 weeks gestation.
  3. bTerm Births include births at 37–44 weeks gestation.
  4. cP-values calculated from chi-square tests for categorical variables and ANOVA for continuous variables.