Results of interaction analyses involving blood biomarkers of omega-3 status in early pregnancy as predictors of the effect of omega-3 supplementation on EPTB
| Omega-3 status in early pregnancy* | Omega-3 n/N (%) Early preterm | Control n/N (%) Early preterm | OR (95% CI) | Interaction P value |
| Overall | 48/2654 (1.81) | 43/2674 (1.61) | 1.13 (0.74, 1.71)† | |
| DHA status | 0.05 | |||
| Low (<2.0%) | 4/189 (2.12) | 8/239 (3.35) | 0.63 (0.19, 2.14) | |
| Moderate (2.0%–2.9%) | 30/1533 (1.96) | 31/1478 (2.10) | 0.93 (0.56, 1.55) | |
| Replete (>2.9%) | 13/803 (1.62) | 3/828 (0.36) | 4.50 (1.28, 15.83) | |
| EPA+DHA status | 0.02 | |||
| Low (<2.6%) | 5/340 (1.47) | 11/406 (2.71) | 0.54 (0.19, 1.55) | |
| Moderate (2.6%–3.4%) | 26/1310 (1.98) | 27/1234 (2.19) | 0.91 (0.53, 1.57) | |
| Replete (>3.4%) | 16/875 (1.83) | 4/905 (0.44) | 4.17 (1.39, 12.54) | |
| Total omega-3 status | 0.007 | |||
| Low‡ (<4.2%) | 4/421 (0.95) | 15/491 (3.05) | 0.30 (0.10, 0.93) | |
| Moderate (4.2%–4.9%) | 20/1053 (1.90) | 18/994 (1.81) | 1.05 (0.55, 2.01) | |
| Replete (>4.9%) | 23/1051 (2.19) | 9/1060 (0.85) | 2.60 (1.20, 5.64) |
ORs are comparing the omega-3 group to the control group within each category of omega-3 status (low, moderate or replete). ORs >1 indicate the odds of early preterm birth are higher in the omega-3 group, while ORs <1 indicate the odds of early preterm birth are higher in the control group. Unless otherwise indicated, ORs are based on a logistic regression model including treatment group, omega-3 status and an interaction between treatment group and omega-3 status, with adjustment for enrolment centre and use of omega-3 supplements in the last 3 months.
*DHA, EPA+DHA and total omega-3 status were measured as a percentage of total fatty acids in whole blood at baseline and categorised as low, moderate or replete according to cut-offs identified in Simmonds et al.5
†OR is based on a logistic regression model including treatment group, with adjustment for enrolment centre and use of omega-3 supplements in the last 3 months.
‡Results differ slightly from Simmonds et al5 since cut-offs were applied here after rounding to one decimal place (consistent with how cut-offs have been applied in practice) and ORs are presented here instead of relative risks.
DHA, docosahexaenoic acid; EPA, eicosapentaenoic acid; EPTB, early preterm birth.