Table. Characteristics of Female Participants According to Preconception Thyrotropin Levelsa.
| Characteristic | Thyrotropin, median (IQR), mIU/L (n = 5 840 894) | Maternal preconception thyrotropin levels, mIU/L | ||||
|---|---|---|---|---|---|---|
| <0.37 (n = 223 181) | 0.37-4.87 (n = 5 470 626) | ≥4.88 (n = 147 087) | P valueb | |||
| Thyrotropin, median (IQR), mIU/L | 1.60 (1.31) | 0.21 (0.21) | 1.61 (1.24) | 5.94 (2.38) | NA | |
| Age at LMP, y | ||||||
| 20-24.9 | 1.58 (1.32) | 100 149 (44.87) | 2 360 638 (43.15) | 58 413 (39.71) | <.001c | |
| 25-29.9 | 1.60 (1.30) | 88 980 (39.87) | 2 238 871 (40.93) | 61 183 (41.60) | ||
| 30-34.9 | 1.63 (1.32) | 25 220 (11.30) | 634 559 (11.60) | 19 377 (13.17) | ||
| 35-39.9 | 1.67 (1.35) | 7547 (3.38) | 199 074 (3.64) | 6743 (4.58) | ||
| ≥40 | 1.68 (1.36) | 1281 (0.57) | 37 323 (0.68) | 1365 (0.93) | ||
| Parity | ||||||
| 0 | 1.59 (1.32) | 150 133 (67.27) | 3 553 031 (64.95) | 90 602 (61.60) | <.001 | |
| ≥1 | 1.62 (1.32) | 72 906 (32.67) | 1 912 884 (34.97) | 56 337 (38.30) | ||
| Missing data | NA | 136 (0.06) | 4544 (0.08) | 136 (0.09) | ||
| Education | ||||||
| High school or above | 1.62 (1.33) | 46 356 (20.77) | 1 058 064 (19.34) | 30 803 (20.94) | <.001 | |
| Primary school or below | 1.60 (1.31) | 175 514 (78.64) | 4 391 532 (80.27) | 115 740 (78.69) | ||
| Missing data | NA | 1331 (0.59) | 21 030 (0.38) | 544 (0.37) | ||
| Residence | ||||||
| Rural | 1.59 (1.31) | 201 412 (90.25) | 4 973 699 (90.92) | 130 494 (88.72) | <.001 | |
| Urban | 1.67 (1.37) | 21 767 (9.75) | 496 809 (9.08) | 16 590 (11.28) | ||
| Missing data | NA | 2 (<0.001) | 118 (<0.001) | 3 (<0.001) | ||
| BMI | ||||||
| Underweight (<18.5) | 1.56 (1.34) | 43 317 (19.41) | 761 952 (13.93) | 20 244 (13.76) | <.001 | |
| Normal weight (18.5-23.9) | 1.60 (1.30) | 151 541 (67.90) | 3 880 983 (70.94) | 100 679 (68.45) | ||
| Overweight (24.0-27.9) | 1.62 (1.33) | 23 085 (10.34) | 668 600 (12.22) | 20 502 (13.94) | ||
| Obesity (≥28.0) | 1.67 (1.39) | 4894 (2.19) | 152 918 (2.80) | 5470 (3.72) | ||
| Missing data | NA | 344 (0.15) | 6173 (0.11) | 192 (0.13) | ||
| Alcohol consumption | ||||||
| Yes | 1.69 (1.40) | 6158 (2.76) | 144 217 (2.64) | 4952 (3.37) | <.001 | |
| No | 1.60 (1.31) | 216 727 (97.11) | 5 318 970 (97.23) | 141 953 (96.51) | ||
| Missing data | NA | 296 (0.13) | 7439 (0.14) | 182 (0.12) | ||
| Secondhand smoke | ||||||
| Yes | 1.72 (1.46) | 28 592 (12.81) | 618 241 (11.30) | 20 769 (14.12) | <.001 | |
| No | 1.59 (1.31) | 194 253 (87.04) | 4 845 767 (88.58) | 126 124 (85.75) | ||
| Missing data | NA | 336 (0.15) | 6618 (0.12) | 194 (0.13) | ||
| Hypertension | ||||||
| Yes | 1.74 (1.45) | 3436 (1.54) | 83 584 (1.53) | 3500 (2.38) | <.001 | |
| No | 1.60 (1.31) | 219 626 (98.41) | 5 382 942 (98.40) | 143 471 (97.54) | ||
| Missing data | NA | 119 (0.05) | 4100 (0.07) | 116 (0.08) | ||
| Diabetes | ||||||
| Yes | 1.41 (1.34) | 4951 (2.22) | 61 184 (1.12) | 1835 (1.25) | <.001 | |
| No | 1.60 (1.31) | 218 110 (97.73) | 5 405 270 (98.81) | 145 128 (98.67) | ||
| Missing data | NA | 120 (0.05) | 4172 (0.07) | 124 (0.08) | ||
| History of adverse pregnancy outcomes | ||||||
| Yes | 1.62 (1.36) | 57 827 (25.91) | 1 281 488 (23.42) | 39 956 (27.16) | <.001 | |
| No | 1.60 (1.30) | 164 077 (73.52) | 4 156 610 (75.98) | 106 171 (72.18) | ||
| Missing data | NA | 1277 (0.57) | 32 528 (0.59) | 960 (0.65) | ||
Abbreviations: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); IQR, interquartile range; LMP, last menstrual period; NA, not available.
a
Data presented as number (percentage) unless otherwise indicated.
b
Multiple comparison with Bonferroni-adjusted P < .05 compared with the thyrotropin 0.37-4.87 mIU/L group (<0.37 mIU/L group vs 0.37-4.87 mIU/L group; ≥4.88 mIU/L group vs 0.37-4.87 mIU/L group).
c
The Kruskal-Wallis H test was used to examine the differences of baseline characteristics among thyrotropin groups; otherwise, the χ2 test was used.