Table 3.
Associations of folic acid supplementation and dietary folate intake with the risk of small for gestational age (SGA) at ≥37 weeks of gestational age and SGA at <37 weeks of gestational age among women (n 8758) and their children enrolled in the 2010–2012 Gansu Provincial Maternity and Child Care Hospital birth cohort, Lanzhou, China
| Folic acid/folate intake duration | SGA at ≥37 weeks of gestational age | SGA at <37 weeks of gestational age | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Controls (n 7211) |
Cases (n 632) |
OR | 95 % CI | OR* | 95 % CI | Controls (n 763) |
Cases (n 152) |
OR | 95 % CI | OR* | 95 % CI | |
| Folic acid supplement | ||||||||||||
| Non-users | 1531 | 197 | 1·00 | Ref. | 1·00 | Ref. | 231 | 55 | 1·00 | Ref. | 1·00 | Ref. |
| Users | 5680 | 435 | 0·60 | 0·50, 0·71 | 0·70 | 0·58, 0·85 | 532 | 97 | 0·77 | 0·48, 1·25 | 0·76 | 0·53, 1·10 |
| ≤12 weeks | 2901 | 258 | 0·69 | 0·57, 0·84 | 0·79 | 0·64, 0·97 | 338 | 63 | 0·78 | 0·53, 1·17 | 0·77 | 0·49, 1·21 |
| >12 weeks | 2779 | 177 | 0·70 | 0·63, 0·78 | 0·77 | 0·68, 0·87 | 194 | 34 | 0·86 | 0·68, 1·08 | 0·79 | 0·59, 1·06 |
| P trend | <0·001 | <0·001 | 0·177 | 0·137 | ||||||||
| Per 2-week increase | 0·944 | 0·927, 0·961 | 0·961 | 0·943, 0·980 | 0·971 | 0·935, 1·010 | 0·966 | 0·925, 1·011 | ||||
| Before conception and during pregnancy | 2173 | 128 | 0·46 | 0·36, 0·58 | 0·59 | 0·45, 0·77 | 171 | 27 | 0·66 | 0·40, 1·10 | 0·58 | 0·32, 1·07 |
| <24 weeks | 1007 | 65 | 0·50 | 0·38, 0·67 | 0·64 | 0·46, 0·88 | 94 | 13 | 0·58 | 0·30, 1·11 | 0·47 | 0·23, 1·00 |
| ≥24 weeks | 1166 | 63 | 0·65 | 0·56, 0·75 | 0·76 | 0·64, 0·91 | 77 | 14 | 0·87 | 0·63, 1·20 | 0·84 | 0·58, 1·24 |
| P trend | <0·001 | <0·001 | 0·221 | 0·271 | ||||||||
| Per 2-week increase | 0·936 | 0·917, 0·955 | 0·953 | 0·931, 0·976 | 0·970 | 0·929, 1·015 | 0·971 | 0·921, 1·023 | ||||
| Before conception only | 266 | 25 | 0·73 | 0·47, 1·13 | 0·92 | 0·58, 1·45 | 28 | 3 | 0·45 | 0·13, 1·53 | 0·38 | 0·11, 1·47 |
| During pregnancy only | 3241 | 282 | 0·68 | 0·56, 0·82 | 0·76 | 0·62, 0·93 | 333 | 67 | 0·85 | 0·57, 1·25 | 0·80 | 0·50, 1·26 |
| ≤8 weeks | 1252 | 124 | 0·77 | 0·61, 0·98 | 0·81 | 0·64, 1·04 | 163 | 40 | 1·03 | 0·66, 1·62 | 0·95 | 0·56, 1·59 |
| >8 weeks | 1989 | 158 | 0·79 | 0·70, 0·88 | 0·86 | 0·76, 0·96 | 170 | 27 | 0·82 | 0·64, 1·05 | 0·77 | 0·57, 1·03 |
| P trend | <0·001 | 0·006 | 0·144 | 0·080 | ||||||||
| Per 2-week increase | 0·950 | 0·926, 0·975 | 0·968 | 0·941, 0·994 | 0·968 | 0·914, 1·026 | 0·947 | 0·887, 1·010 | ||||
| Dietary folate intake (µg/d) | ||||||||||||
| Before pregnancy | ||||||||||||
| Q1 < 115·63 | 1736 | 172 | 1·00 | Ref. | 1·00 | Ref. | 227 | 60 | 1·00 | Ref. | 1·00 | Ref. |
| Q2 = 115·63–157·42 | 1815 | 128 | 0·71 | 0·56, 0·91 | 0·83 | 0·65, 1·07 | 187 | 29 | 0·59 | 0·36, 0·96 | 0·59 | 0·32, 1·06 |
| Q3 = 157·42–218·91 | 1773 | 173 | 0·99 | 0·89, 1·11 | 1·09 | 0·97, 1·23 | 186 | 33 | 0·82 | 0·65, 1·04 | 0·93 | 0·70, 1·24 |
| Q4 ≥ 218·91 | 1887 | 159 | 0·95 | 0·88, 1·02 | 1·03 | 0·93, 1·13 | 163 | 30 | 0·89 | 0·76, 1·05 | 1·02 | 0·81, 1·29 |
| P trend | 0·609 | 0·194 | 0·119 | 0·718 | ||||||||
| Per 10-μg increase | 1·001 | 0·986, 1·016 | 1·020 | 0·993, 1·037 | 0·982 | 0·948, 1·017 | 0·992 | 0·953, 1·036 | ||||
| During pregnancy | ||||||||||||
| Q1 < 149·47 | 1705 | 183 | 1·00 | Ref. | 1·00 | Ref. | 266 | 57 | 1·00 | Ref. | 1·00 | Ref. |
| Q2 = 149·47–197·56 | 1788 | 146 | 0·76 | 0·61, 0·96 | 0·84 | 0·65, 1·09 | 179 | 39 | 1·02 | 0·65, 1·59 | 1·29 | 0·75, 2·24 |
| Q3 = 197·56–263·21 | 1822 | 135 | 0·83 | 0·74, 0·93 | 0·98 | 0·86, 1·12 | 166 | 31 | 0·93 | 0·74, 1·19 | 0·99 | 0·72, 1·37 |
| Q4 ≥ 263·21 | 1896 | 168 | 0·94 | 0·87, 1·00 | 1·04 | 0·93, 1·17 | 152 | 25 | 0·92 | 0·77, 1·09 | 1·35 | 0·99, 2·.01 |
| P trend | 0·063 | 0·369 | 0·276 | 0·951 | ||||||||
| Per 10-μg increase | 0·992 | 0·977, 1·007 | 1·018 | 0·998, 1·036 | 0·976 | 0·943, 1·010 | 0·988 | 0·944, 1·034 | ||||
Q, quartile; ref., reference category.
Multiplicative interaction on SGA at ≥37 weeks of gestational age: OR = 1·04 (95 % CI 0·84, 1·29), P = 0·698.
Multiplicative interaction on SGA at <37 weeks of gestational age: OR = 0·64 (95 % CI 0·38, 1·06), P = 0·085.
OR adjusted for maternal age, monthly income per capita, education level, smoking, employment, pre-pregnancy BMI, weight gain during pregnancy, pre-eclampsia, parity, caesarean section, height of child’s father, history of preterm birth, total energy intake, dietary folate intake or folic acid supplement.