TABLE 2.
Association between tertiles of folate species at <16 wk and risk of preterm birth (PTB) and spontaneous preterm birth (sPTB)1
| Term | PTB | Adjusted RR (95% CI)2 | Term | sPTB | Adjusted RR (95% CI)3 | |
| n (%) | n (%) | n (%) | n (%) | |||
| Total folate | ||||||
| T1 (16.8 ng/mL)4 | 89 (86) | 15 (14) | 1.0 (ref) | 89 (88) | 12 (12) | 1.0 (ref) |
| T2 (24.7 ng/mL)4 | 86 (82) | 19 (18) | 1.3 (0.7, 2.4) | 86 (88) | 12 (12) | 1.0 (0.5, 2.2) |
| T3 (38.9 ng/mL)4 | 98 (94) | 6 (6) | 0.4 (0.1, 0.9) | 98 (97) | 3 (3) | 0.2 (0.1, 0.8) |
| 1-SD (12-ng/mL) increase | 0.7 (0.5, 1.0) | 0.6 (0.4, 0.9) | ||||
| 5MeTHF | ||||||
| T1 (10.2 ng/mL)4 | 89 (84) | 17 (16) | 1.0 (ref) | 89 (86) | 14 (14)5 | 1.0 (ref) |
| T2 (15.8 ng/mL)4 | 90 (86) | 15 (14) | 0.9 (0.5, 1.7) | 90 (91) | 9 (9) | 0.7 (0.3, 1.5) |
| T3 (25.1 ng/mL)4 | 94 (92) | 8 (8) | 0.5 (0.2, 1.1) | 94 (96) | 4 (4) | 0.3 (0.1, 0.8) |
| 1-SD (7.9 ng/mL) increase | 0.8 (0.5, 1.1) | 0.6 (0.4, 0.9) | ||||
| 5FoTHF | ||||||
| T1 (3.7 ng/mL)4 | 90 (87) | 13 (13) | 1.0 (ref) | 90 (94) | 6 (6) | 1.0 (ref) |
| T2 (7.8 ng/mL)4 | 91 (88) | 13 (12) | 1.1 (0.5, 2.2) | 91 (88) | 13 (12) | 2.0 (0.8, 5.2) |
| T3 (15.5 ng/mL)4 | 92 (87) | 14 (13) | 1.2 (0.6, 2.4) | 92 (92) | 8 (8) | 1.3 (0.5, 3.6) |
| 1-SD (12 ng/mL) increase | 0.9 (0.7, 1.2) | 0.9 (0.7, 1.14) |
1
T1, bottom tertile; T2, middle tertile; T3, upper tertile; RR, risk ratio; ref, reference; 5MeTHF, 5-methyltetrahydrofolate; 5FoTHF, 5-formyltetrahydrofolate.
2
Adjusted for race-ethnicity, education, smoking, and obesity.
3
Adjusted for education and smoking.
4
Values in parentheses are median values for the tertile.
5
P < 0.05 (test of trend).