Skip to main content

Table 1 Characteristics of the study population, Manitoba, Canada, 1980-2016a

From: Revisiting the association between maternal and offspring preterm birth using a sibling design

  Population Cohort Mothers without sisters Mothers with sisters
Discordant sisters Concordant sisters
Mother Born Preterm Mother Born at term Index mothers born preterm with sisters born at term Index mothers born at term with sisters born preterm All born preterm All born at term
Number of mothers (%)b 39,573 (100.0) 1328 (3.4) 26,805 (67.7) 455 (1.2) 578 (1.5) 69 (0.2) 10,338 (26.1)
Number of infants (%)b 79,198 (100.0) 2565 (3.2) 50,647 (63.9) 1069 (1.4) 1430 (1.8) 137 (0.2) 23,350 (29.5)
Infant’s preterm birth 4913 (6.2) 198 (7.7) 3025 (6.0) 109 (10.2) 143 (10.0) 18 (13.1) 1420 (6.1)
Infant’s preterm birth type
 Provider-initiated 1489 (1.9) 44 (1.7) 912 (1.8) 34 (3.2) 53 (3.7) < 6c 443 (1.9)
 Spontaneous 3424 (4.3) 154 (6.0) 2113 (4.2) 75 (7.0) 90 (6.3) c 977 (4.2)
Infant’s Birth Year, mean(SD) 2010 (4.3) 2010 (4.4) 2010 (4.3) 2010 (4.2) 2009 (4.4) 2009 (4.3) 2010 (4.2)
Male infant 40,624 (51.3) 1290 (50.3) 26,037 (51.4) 547 (51.2) 765 (53.5) 70 (51.1) 11,915 (51.0)
Infant’s Birth Order
 1 39,069 (49.3) 1321 (51.5) 26,495 (52.3) 449 (42.0) 567 (39.7) 67 (48.9) 10,170 (43.6)
 2 22,505 (28.4) 727 (28.3) 14,559 (28.8) 281 (26.3) 374 (26.1) 42 (30.7) 6522 (27.9)
 3 9930 (12.5) 299 (11.7) 5727 (11.3) 165 (15.4) 212 (14.8) 17 (12.4) 3510 (15.0)
 4+ 7694 (9.7) 218 (8.5) 3866 (7.6) 174 (16.3) 277 (19.4) 11 (8.0) 3148 (13.5)
Mother’s Age
  < 20 17,467 (22.1) 504 (19.6) 10,306 (20.3) 251 (23.5) 422 (29.5) 29 (21.2) 5955 (25.5)
 20–24 28,714 (36.3) 915 (35.7) 17,654 (34.9) 438 (41.0) 581 (40.6) 51 (37.2) 9075 (38.9)
 25–29 23,741 (30.0) 812 (31.7) 15,856 (31.3) 281 (26.3) 321 (22.5) 38 (27.7) 6433 (27.6)
 30 + 9276 (11.7) 334 (13.0) 6831 (13.5) 99 (9.7) 106 (7.4) 19 (13.9) 1887 (8.1)
Neighborhood SES tertiles
 P0-P33 (Lowest SES) 25,940 (32.8) 753 (29.4) 13,341 (26.3) 560 (52.4) 794 (55.5) c 10,444 (44.7)
 P34-P66 25,244 (31.9) 870 (33.9) 16,983 (33.5) 298 (27.9) 373 (26.1) 57 (41.6) 6663 (28.5)
 P67-P100 (Highest SES) 25,219 (31.8) 846 (33.0) 18,266 (36.1) 197 (18.4) 240 (16.8) 27 (19.7) 5643 (24.2)
 Unknown 2795 (3.5) 96 (3.7) 2057 (4.1) 14 (1.3) 23 (1.5) < 6 c 600 (2.6)
Location of Neighborhood
 Urban 35,674 (45.0) 1364 (53.2) 25,017 (49.4) 398 (37.2) 514 (35.9) 75 (54.7) 8306 (35.6)
 Rural South 17,364 (21.9) 483 (18.8) 11,079 (21.9) 196 (18.3) 246 (17.2) 22 (16.1) 5338 (22.9)
 Rural Mid 11,891 (15.0) 362 (14.1) 7378 (14.6) 182 (17.0) 237 (16.6) 22 (16.1) 3710 (15.9)
 Rural North 14,269 (18.0) 356 (13.9) 7173 (14.2) 293 (27.4) 433 (30.3) 18 (13.1) 5996 (25.7)
Mother moved in Year before Birth of Child 20,819 (26.3) 728 (28.4) 13,518 (26.7) 295 (27.6) 378 (26.4) 34 (24.8) 5866 (25.1)
Mother had a Substance Abuse Diagnosis in Year before Birth of Child 2111 (2.7) 67 (2.6) 1174 (2.3) 37 (3.5) 67 (4.7) < 6 c 761 (3.3)
Mother had no partnerd 6400 (8.52) 220 (8.92) 4120 (8.55) 83 (8.84) 113 (9.28) 11 (9.65) 1853 (8.70)
Mother smoked during pregnancyd 19,257 (26.0) 688 (27.91) 11,435 (23.74) 317 (33.76) 438 (35.96) 34 (29.82) 6345 (29.78)
Inadequate prenatal cared 13,548 (18.26) 406 (16.47) 7270 (15.09) 271 (28.86) 378 (31.03) 22 (19.30) 5201 (24.41)
Employment income assistance d 15,631 (21.06) 578 (23.45) 9383 (19.48) 334 (27.42) 246 (26.20) 32 (28.07) 5058 (23.74)
Maternal educationd
 12 years or less 17,692 (23.84) 541 (21.95) 9829 (20.40) 336 (35.78) 481 (39.49) 20 (17.54) 6485 (30.44)
 More than 12 years 42,885 (57.79) 1496 (60.69) 30,512 (63.34) 379 (40.36) 426 (34.98) 80 (70.18) 9992 (46.90)
 Unknown 13,637 (18.38) 428 (17.36) 7831 (16.26) 224 (23.86) 311 (25.53) 14 (12.28) 4829 (22.66)
  1. Abbreviations: SD Standard Deviation, SES Socioeconomic Status
  2. aFrequencies are expressed as N (column %) unless otherwise specified
  3. bRow percent
  4. cSuppressed due to small cell size
  5. dInformation available for births occurred from 2000 to 2016 (Population cohort: 38,212 mothers, 74,214 children; sibling subcohort: 951 mothers, 2157 children)