Table 2

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
Overall48/2654 (1.81)43/2674 (1.61)1.13 (0.74, 1.71)†
DHA status0.05
 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 status0.02
 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 status0.007
 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.