Table 1

Temporal trends in maternal demographic characteristics and risk factors for birth trauma among singleton infants, Washington State, USA, 2004–2013

Maternal and infant characteristicsBirth year
2004–2006
(n=213 270)
2007–2010
(n=301 508)
2011–2013
(n=218 040)
P value* Rate ratio
(95% CI)†
n (%)n (%)n (%)
Maternal age (years)
  15–1917 844 (8.4)24 380 (8.1)13 313 (6.1)<0.0010.73 (0.71 to 0.75)
  20–29111 509 (52.3)157 445 (52.2)109 527 (50.2)<0.0010.96 (0.96 to 0.97)
  30–3977 941 (36.6)111 085 (36.8)88 445 (40.6)<0.0011.11 (1.10 to 1.12)
 ≥405976 (2.8)8598 (2.9)6755 (3.1)<0.0011.11 (1.07 to 1.14)
Race
  Non-Hispanic white153 872 (72.4)213 846 (71.1)155 618 (71.6)<0.0010.99 (0.99 to 0.99)
  African-American7775 (3.7)12 201 (4.1)9699 (4.5)<0.0011.22 (1.19 to 1.26)
  Native American4445 (2.1)6123 (2.0)4320 (2.0)0.0060.95 (0.91 to 0.99)
  Hispanic25 871 (12.2)37 531 (12.5)23 387 (10.8)<0.0010.88 (0.87 to 0.90)
  Other20 649 (9.7)31 131 (10.3)24 324 (11.2)<0.0011.15 (1.13 to 1.17)
Maternal education
(<high school)
9800 (4.6)11 318 (3.7)6032 (2.8)<0.0010.60 (0.58 to 0.62)
Smoking during pregnancy20 834 (9.9)29 206 (9.8)19 635 (9.0)<0.0010.91 (0.89 to 0.93)
Not married67 109 (31.6)104 035 (34.6)75 055 (34.5)<0.0011.09 (1.08 to 1.10)
Parity
 Nullipara85 407 (40.0)124 799 (41.4)88 428 (40.6)0.0101.01 (1.01 to 1.02)
 Para 1–3110 757 (51.9)159 444 (52.9)117 743 (54.0)<0.0011.04 (1.03 to 1.05)
 Grand multipara
 (≥4 births)
17 106 (8.0)17 265 (5.7)11 869 (5.4)<0.0010.68 (0.66 to 0.69)
Body mass index (kg/m2)
 Underweight (<18.5)6240 (2.9)8332 (2.8)6230 (2.9)0.0450.98 (0.94 to 1.00)
 Normal (18.5 to 24.9)89 369 (41.9)131 590 (43.6)94 093 (43.1)<0.0011.03 (1.02 to 1.04)
 Overweight (25 to 29.9)46 074 (21.6)72 295 (24.0)53 849 (24.7)<0.0011.14 (1.13 to 1.16)
 Obese (≥30)39 752 (18.6)65 239 (21.6)51 806 (23.8)<0.0011.27 (1.26 to 1.29)
 Missing31 842 (14.9)24 052 (8.0)12 062 (5.5)<0.001
Assisted conception1470 (0.7)2702 (0.90)2249 (1.0)<0.0011.47 (1.38 to 1.57)
Diabetes mellitus
(types 1 and 2)
1578 (0.7)2591 (0.9)2151 (1.0)<0.0011.33 (1.25 to 1.42)
Gestational diabetes12 255 (5.75)19 160 (6.3)16 382 (7.5)<0.0011.31 (1.28 to 1.34)
Chronic hypertension2489 (1.2)3783 (1.3)2815 (1.3)<0.0011.09 (1.03 to 1.15)
Hypertension in pregnancy10 857 (5.1)15 304 (5.1)12 010 (5.5)<0.0011.08 (1.06 to 1.11)
Infant sex (male)109 744 (51.5)154 777 (51.3)112 326 (51.5)0.8461.00 (1.00 to 1.01)
Preterm birth
 <34 weeks3042 (1.4)4372 (1.4)3255 (1.5)0.1041.05 (1.00 to 1.10)
 <37 weeks15 006 (7.0)20 067 (6.7)14 265 (6.5)<0.0010.93 (0.91 to 0.95)
Birth weight (g)
 <25009414 (4.4)13 448 (4.5)10 186 (4.7)<0.0011.06 (1.03 to 1.09)
 2500–299929 718 (14.0)43 033 (14.3)31 990 (14.7)<0.0011.05 (1.04 to 1.07)
 3000–3999149 045 (70.1)211 901 (70.3)151 953 (69.7)0.0021.00 (0.99 to 1.00)
 4000–449920 754 (9.8)28 051 (9.3)20 094 (9.2)<0.0010.95 (0.93 to 0.96)
 ≥45003731 (1.75)4819 (1.6)3640 (1.7)0.0050.95 (0.91 to 1.00)
Caesarean delivery
 Primary with labour19 965 (9.4)27 960 (9.3)18 323 (8.4)<0.0010.90 (0.88 to 0.92)
 Primary no labour16 310 (7.6)23 314 (7.7)15 930 (7.3)<0.0010.96 (0.94 to 0.98)
 Repeat with labour1227 (0.6)1939 (0.6)1961 (0.9)<0.0011.56 (1.46 to 1.68)
 Repeat no labour16 931 (7.9)28 281 (9.4)22 366 (10.3)<0.0011.29 (1.27 to 1.32)
Vaginal delivery
 Spontaneous144 931 (68.0)203 513 (67.5)149 270 (68.5)<0.0011.01 (1.00 to 1.01)
 Forceps1698 (0.8)2185 (0.7)1416 (0.6)<0.0010.82 (0.76 to 0.88)
 Vacuum12 208 (5.7)14 316 (4.7)8774 (4.0)<0.0010.70 (0.68 to 0.72)
Previous caesarean delivery
 One prior delivery16 198 (7.6)25 871 (8.6)21 049 (9.6)<0.0011.27 (1.25 to 1.30)
 Two or more4518 (2.1)8821 (2.9)8069 (3.7)<0.0011.75 (1.68 to 1.81)
Labour induction50 584 (24.2)69 022 (23.1)48 530 (22.3)<0.0010.92 (0.91 to 0.93)
PROM (>12 hours)8435 (4.1)16 232 (5.5)13 246 (6.1)<0.0011.50 (1.46 to 1.54)
Precipitous labour (<3 hours)6323 (3.1)9595 (3.2)6486 (3.0)0.4750.98 (0.95 to 1.01)
Prolonged labour3206 (1.5)7759 (2.6)5691 (2.6)<0.0011.69 (1.62 to 1.77)
Cephalopelvic disproportion6669 (3.1)7873 (2.6)4374 (2.0)<0.0010.64 (0.62 to 0.67)
Obstructed labour16 256 (7.6)21 224 (7.0)13 524 (6.2)<0.0010.81 (0.80 to 0.83)
  • Breech delivery excluded.

  • *Cochran-Armitage test for trend.

  • †Rate ratio comparing periods 2011–2013 versus 2004–2006.

  • PROM, premature rupture of membranes.