From: Drinking water nitrate and risk of pregnancy loss: a nationwide cohort study
 | Nitrate concentration (mg/L) | ||||
---|---|---|---|---|---|
Characteristics |  ≤ 1 |  > 1- ≤ 2 |  > 2- ≤ 5 |  > 5- ≤ 25 |  > 25 |
Total pregnanciesa, n (%) | 27,413 (29.8) | 25,753 (28.0) | 24,285 (26.4) | 10,449 (11.4) | 4,021 (4.4) |
Age at conception, mean (± SD) | 29.56 (4.29) | 29.90 (4.25) | 29.86 (4.42) | 29.44 (4.36) | 29.32 (4.35) |
Age at conception, n (%) | Â | Â | Â | Â | Â |
  < 20 | 282 (1.0) | 224 (0.9) | 261 (1.1) | 129 (1.2) | 48 (1.2) |
  ≥ 20- < 25 | 3,461 (12.6) | 2,744 (10.7) | 2,860 (11.8) | 1,443 (13.8) | 568 (14.1) |
  ≥ 25- < 30 | 11,653 (42.5) | 10,616 (41.2) | 9,719 (40.0) | 4,340 (41.5) | 1,705 (42.4) |
  ≥ 30- < 35 | 9,049 (33.0) | 9,030 (35.1) | 8,364 (34.4) | 3,386 (32.4) | 1,280 (31.8) |
  ≥ 35- ≤ 40 | 2,704 (9.9) | 2,848 (11.1) | 2,763 (11.4) | 1,056 (10.1) | 381 (9.5) |
  > 40 | 264 (1.0) | 291 (1.1) | 318 (1.3) | 95 (0.9) | 39 (1.0) |
Highest education, n (%) | Â | Â | Â | Â | Â |
  Primary school | 2,399 (8.8) | 1,592 (6.2) | 1,838 (7.6) | 926 (8.9) | 346 (8.6) |
  High school or vocational | 11,449 (41.8) | 8,721 (33.9) | 8,833 (36.4) | 4,495 (43.0) | 1,600 (39.8) |
  Basic education | 2,228 (8.1) | 1,733 (6.7) | 1,705 (7.0) | 767 (7.3) | 270 (6.7) |
  Middle education | 8,838 (32.2) | 8,548 (33.2) | 7,732 (31.8) | 3,290 (31.5) | 1,361 (33.8) |
  Higher education or Ph.D | 2,451 (8.9) | 5,102 (19.8) | 4,110 (16.9) | 950 (9.1) | 433 (10.8) |
  Missing | 48 (0.2) | 57 (0.2) | 67 (0.3) | 21 (0.2) | 11 (0.3) |
Occupation, n (%) | Â | Â | Â | Â | Â |
  Unemployedb | 2,816 (10.3) | 2,330 (9.0) | 2,311 (9.5) | 1,211 (11.6) | 471 (11.7) |
  Student | 2,036 (7.4) | 3,130 (12.2) | 2,305 (9.5) | 813 (7.8) | 378 (9.4) |
  Employee unspecified income | 2,066 (7.5) | 1,671 (6.5) | 1,637 (6.7) | 779 (7.5) | 287 (7.1) |
  Employee with low income | 10,090 (36.8) | 7,344 (28.5) | 7,747 (31.9) | 3,895 (37.3) | 1,390 (34.6) |
  Employee with middle income | 6,371 (23.2) | 6,149 (23.9) | 5,613 (23.1) | 2,255 (21.6) | 887 (22.1) |
  Chief executive or high income | 3,026 (11.0) | 4,221 (16.4) | 3,770 (15.5) | 1,147 (11.0) | 469 (11.7) |
  Owner of business | 501 (1.8) | 496 (1.9) | 474 (2.0) | 192 (1.8) | 58 (1.4) |
  Other | 507 (1.8) | 412 (1.6) |  > 422(1.7) | 157 (1.5) | 81 (2.0) |
  Missing | 0 (0.0) | 0 (0.0) |  < 5 (.) | 0 (0.0) | 0 (0.0) |
  Population densityc, mean (± SD) | 424.88 (488.63) | 1215.16 (1382.67) | 1137.34 (1306.25) | 624.18 (874.46) | 592.85 (717.16) |
Smoking in pregnancy (cigarettes/day), n (%) | Â | Â | Â | Â | Â |
  Non-smoker | 18,937 (69.1) | 17,905 (69.5) | 16,364 (67.4) | 7,038 (67.4) | 2,781 (69.2) |
  Smoked in early pregnancy | 2,061 (7.5) | 2,460 (9.6) | 2,280 (9.4) | 879 (8.4) | 295 (7.3) |
  1–9 | 2,365 (8.6) | 2,027 (7.9) | 2,045 (8.4) | 965 (9.2) | 320 (8.0) |
  10–14 | 1,172 (4.3) | 980 (3.8) | 1,066 (4.4) | 538 (5.1) | 210 (5.2) |
  > 15 | 737 (2.7) | 576 (2.2) | 712 (2.9) | 349 (3.3) | 129 (3.2) |
  Missing | 2,141 (7.8) | 1,805 (7.0) | 1,818 (7.5) | 680 (6.5) | 286 (7.1) |
Weekly alcohol consumption (units/week), n (%) | Â | Â | Â | Â | Â |
  0 | 13,860 (50.6) | 12,911 (50.1) | 12,677 (52.2) | 5,613 (53.7) | 2,121 (52.7) |
  0.5–3.5 | 10,866 (39.6) | 10,468 (40.6) | 9,276 (38.2) | 3,940 (37.7) | 1,539 (38.3) |
  4–7 | 489 (1.8) | 517 (2.0) | 447 (1.8) | 181 (1.7) |  > 65 (1.6) |
  ≥ 7.5 | 39 (0.1) | 36 (0.1) | 59 (0.2) | 20 (0.2) |  < 5 (.) |
  Missing | 2,159 (7.9) | 1,821 (7.1) | 1,826 (7.5) | 695 (6.7) | 288 (7.2) |
Body mass index (kg/m2), n (%) | Â | Â | Â | Â | Â |
  < 18.5 | 1035 (3.8) | 1,097 (4.3) | 1,098 (4.5) | 439 (4.2) | 166 (4.1) |
  18.5–25 | 16,262 (59.3) | 16,761 (65.1) | 15,371 (63.3) | 6,206 (59.4) | 2,350 (58.4) |
  25–30 | 5,238 (19.1) | 4,096 (15.9) | 4,011 (16.5) | 2,051 (19.6) | 797 (19.8) |
  > 30 | 2,360 (8.6) | 1,607 (6.2) | 1,613 (6.6) | 930 (8.9) | 369 (9.2) |
  Missing | 2,518 (9.2) | 2,192 (8.5) | 2,192 (9.0) | 823 (7.9) | 339 (8.4) |
Gravidity, n (%) | Â | Â | Â | Â | Â |
  Primigravidae | 9,604 (35.0) | 9,988 (38.8) | 8,971 (36.9) | 3,632 (34.8) | 1,517 (37.7) |
  Multigravidae |  > 17,803(64.9) | 15,765 (61.2) |  > 15,308 (63.0) |  > 6,811 (65.2) | 2,504 (62.3) |
  Missing |  < 5 (.) | 0 (0.0) |  < 5 (.) |  < 5 (.) | 0 (0.0) |
Parity, n (%) | Â | Â | Â | Â | Â |
  Nulliparous | 12,607 (46.0) | 13,825 (53.7) | 12,630 (52.0) | 4,901 (46.9) | 1,998 (49.7) |
  Multiparous |  > 14,800 (54.0) | 11,928 (46.3) |  > 11,649 (48.0) |  > 5,542 (53.1) | 2,023 (50.3) |
  Missing |  < 5 (.) | 0 (0.0) |  < 5 (.) |  < 5 (.) | 0 (0.0) |
Previous spontaneous pregnancy loss, n (%) | Â | Â | Â | Â | Â |
  0 | 21,941 (80.0) | 20,707 (80.4) | 19,547 (80.5) | 8,394 (80.3) | 3,212 (79.9) |
  1–2 | 5,283 (19.3) | 4,917 (19.1) | 4,564 (18.8) | 1,977 (18.9) | 776 (19.3) |
  > 3 |  > 183 (0.7) | 129 (0.5) |  > 168 (0.7) |  > 72 (0.7) | 33 (0.8) |
  Missing |  < 5 (.) | 0 (0.0) |  < 5 (.) |  < 5 (.) | 0 (0.0) |
Nitrosatable drug in pregnancy, n (%) | Â | Â | Â | Â | Â |
  Yes | 4,321 (15.8) | 3,726 (14.5) | 3,795 (15.6) | 1,682 (16.1) | 650 (16.2) |
  No | 23,082 (84.2) | 22,027 (85.5) |  > 20,484 (84.4) |  > 8,761 (83.9) | 3,371 (83.8) |
  Missing | 10 (0.0) | 0 (0.0) |  < 5 (.) |  < 5 (.) | 0 (0.0) |