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Table 3 Mothers’ characteristics throughout three periods

From: Sociodemographic characteristics of mother’s population and risk of preterm birth in Chile

N 1991-1995 1996-2000 2001-2008  
4 392 427 1323021 1232824 1836582 aP1-P2 P2-P3 P1-P3
Age % n % n % n P b P P
<18 (292 891) 5.6 74 659 7.2 88 197 7.1 130 035 <0.001 <0.014 <0.001
18-38 (3 910 271) 91.0 1 204 514 88.8 1 095 027 87.7 1 610 730 <0.001 <0.001 <0.001
>38 (189 265) 3.3 43 848 4.0 49 600 5.2 95 817 <0.001 <0.001 <0.001
Marital Status          
Living with partner 62.1 821 803 54.9 544 980 42.3 775 989 <0.001 <0.001 <0.001
(2 142 772)   
Not living with partner 37.9 501 218 45.1 446 808 57.7 1 060 593 <0.001 <0.001 <0.001
(2 008 619)   
Parity          
Primipara (1 849 118) 40.6 537 524 42.1 519 250 43.1 792 344 <0.001 <0.001 <0.001
Multipara (2 471 351) 57.2 756 413 56.2 692 944 55.7 1 021 994 <0.001 <0.001 <0.001
Grand Multipara 19.0 25 410 15.0 19 004 12.0 21 580 <0.001 <0.001 <0.001
(65 994)   
  1. Chile, Singleton Live Births, 1991–2008.
  2. aPeriods : P1 : 1991–1995, P2 : 1996–2000, P3 :2001–2008.
  3. bPearson’s chi-square test with significance level for P < 0.05.