Table 1 Distribution of the conception season in women with different characteristics
Characteristics | Total | Season of conception | |||
|---|---|---|---|---|---|
Spring | Summer | Autumn | Winter | ||
Demographic characteristics | Â | Â | Â | Â | Â |
Age (years) | Â | Â | Â | Â | Â |
 18–20 | 15,541 (100.0) | 4075 (26.2) | 3978 (25.6) | 3524 (22.7) | 3964 (25.5) |
 21–25 | 78,227 (100.0) | 21,730 (27.8) | 17,954 (23.0) | 15,821 (20.2) | 22,722 (29.0) |
 26–30 | 67,951 (100.0) | 18,575 (27.3) | 16,354 (24.1) | 14,317 (21.1) | 18,705 (27.5) |
 31–35 | 23,515 (100.0) | 6477 (27.5) | 5856 (24.9) | 4786 (20.4) | 6396 (27.2) |
 36–49 | 8848 (100.0) | 2477 (28.0) | 2258 (25.5) | 1798 (20.3) | 2315 (26.2) |
Ethnicity* | Â | Â | Â | Â | Â |
 Han | 120,309 (100.0) | 33,463 (27.8) | 28,428 (23.6) | 24,822 (20.6) | 33,596 (27.9) |
 Minority | 73,497 (100.0) | 19,803 (26.9) | 17,918 (24.4) | 15,359 (20.9) | 20,417 (27.8) |
Education* | Â | Â | Â | Â | Â |
 Primary school or below | 40,113 (100.0) | 10,664 (26.6) | 10,057 (25.1) | 8569 (21.4) | 10,823 (27.0) |
 Junior high school | 104,967 (100.0) | 29,087 (27.7) | 24,796 (23.6) | 21,860 (20.8) | 29,224 (27.8) |
 Senior high school | 26,219 (100.0) | 7323 (27.9) | 6049 (23.1) | 5175 (19.7) | 7672 (29.3) |
 College or higher | 20,309 (100.0) | 5578 (27.5) | 4945 (24.3) | 4066 (20.0) | 5720 (28.2) |
Occupation* | Â | Â | Â | Â | Â |
 Farmer | 178,213 (100.0) | 48,938 (27.5) | 42,497 (23.8) | 36,993 (20.8) | 49,782 (27.9) |
 Worker | 8846 (100.0) | 2483 (28.1) | 2212 (25.0) | 1777 (20.1) | 2374 (26.8) |
 Other | 5147 (100.0) | 1385 (26.9) | 1265 (24.6) | 1056 (20.5) | 1441 (28.0) |
Reproductive characteristics | Â | Â | Â | Â | Â |
First gestation* | 75,615 (100.0) | 21,696 (28.7) | 17,094 (22.6) | 14,434 (19.1) | 22,391 (29.6) |
Primipara | 93,979 (100.0) | 26,820 (28.5) | 21,265 (22.6) | 18,014(19.2) | 27,880 (29.7) |
History of preterm birth | 731 (100.0) | 184 (25.2) | 178 (24.4) | 161(22.0) | 208 (28.5) |
History of spontaneous abortion | 7063 (100.0) | 1845 (26.1) | 1733 (24.5) | 1584(22.4) | 1901(26.9) |
History of induced abortion | 45,628 (100.0) | 12,288 (26.9) | 10,851 (23.8) | 9531 (20.9) | 12,958 (28.4) |
History of stillbirth | 1696 (100.0) | 405 (23.9) | 422 (24.9) | 373 (22.0) | 496 (29.2) |
Health status | Â | Â | Â | Â | Â |
Body-mass index (kg/m2)* | Â | Â | Â | Â | Â |
 < 18.5 | 23,513 (100.0) | 6491 (27.6) | 5564 (23.7) | 4783 (20.3) | 6675 (28.4) |
 18.5–23.9 | 137,343 (100.0) | 37,779 (27.5) | 32,798 (23.9) | 28,454 (20.7) | 38,312 (27.9) |
 24.0–27.9 | 24,520 (100.0) | 6619 (27.0) | 5965 (24.3) | 5207 (21.2) | 6729 (27.4) |
 ≥ 28.0 | 5477 (100.0) | 1519 (27.7) | 1309 (23.9) | 1168 (21.3) | 1481 (27.0) |
Anemia* | 46,043 (100.0) | 12,367 (26.9) | 10,989 (23.9) | 9561 (20.8) | 13,126 (28.5) |
HBsAg positive* | 4767 (100.0) | 1283 (26.9) | 1158 (24.3) | 1030 (21.6) | 1296 (27.2) |
Living habits during pregnancy | Â | Â | Â | Â | Â |
Eating meat and eggs | 192,443 (100.0) | 52,872 (27.5) | 46,025 (23.9) | 39,924 (20.7) | 53,622 (27.9) |
No eating vegetables | 765 (100.0) | 215 (28.1) | 203 (26.5) | 161 (21.0) | 186 (24.3) |
Smoking* | 710 (100.0) | 199 (28.0) | 179 (25.2) | 148 (20.8) | 184 (25.9) |
Drinking alcohol* | 4376 (100.0) | 1156 (26.4) | 1080 (24.7) | 974 (22.3) | 1166 (26.6) |
Taking folic acid* | 184,547 (100.0) | 50,775 (27.5) | 44,001 (23.8) | 38,152 (20.7) | 51,619 (28.0) |