Table 4.
Risk of Spontaneous Preterm Birth According to Timing of Study Enrollment and Use of Micronutrient Supplements Among Pregnant Women in Northern China, 2006–2009
| Timing of Enrollment and Supplement Group | SPB Category |
|||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| All SPBs (20–36 Weeks) |
Late SPBs (32–36 Weeks) |
Early SPBs (20–31 Weeks) |
||||||||||
| No. of Cases | Incidencea, % | RR | 95% CI | No. of Cases | Incidencea, % | RR | 95% CI | No. of Cases | Incidencea, % | RR | 95% CI | |
| Enrollment at ≥12 gestational weeks | ||||||||||||
| FA | 193 | 6.9 | 1 | Referent | 171 | 6.1 | 1 | Referent | 22 | 0.8 | 1 | Referent |
| IFA | 207 | 7.2 | 1 | Referent | 186 | 6.5 | 1 | Referent | 21 | 0.8 | 1 | Referent |
| MMN | 180 | 6.4 | 1 | Referent | 158 | 5.7 | 1 | Referent | 22 | 0.8 | 1 | Referent |
| Enrollment at <12 gestational weeks | ||||||||||||
| FA | 142 | 4.6 | 0.66 | 0.52, 0.82 | 116 | 3.8 | 0.60 | 0.47, 0.77 | 26 | 0.9 | 1.05 | 0.60, 1.86 |
| IFA | 127 | 4.2 | 0.59 | 0.47, 0.74 | 102 | 3.4 | 0.53 | 0.41, 0.68 | 25 | 0.8 | 1.02 | 0.57, 1.81 |
| MMN | 122 | 3.9 | 0.55 | 0.44, 0.70 | 104 | 3.4 | 0.53 | 0.42, 0.68 | 18 | 0.6 | 0.72 | 0.38, 1.34 |
Abbreviations: CI, confidence interval; FA, folic acid; IFA, iron + folic acid; MMN, multiple micronutrients; RR, risk ratio; SPB, spontaneous preterm birth.
a
Calculation of the incidence of certain types of preterm birth did not include other subtypes of preterm birth in the denominator.