Table 3

Results of interaction analyses involving alcohol use, parity and their combination as predictors of the effect of omega-3 supplementation on PTB

Any previous births ≥20 weeksDrank alcohol in 3 months leading up to pregnancyOmega-3 n/N (%)
Preterm
Control n/N (%)
Preterm
OR (95% CI)Interaction P value
OverallOverall169/2654 (6.37)209/2674 (7.82)0.80 (0.65, 0.99)*
NoOverall84/1170 (7.18)81/1164 (6.96)1.03 (0.75, 1.42)0.04
YesOverall84/1473 (5.70)128/1502 (8.52)0.65 (0.49, 0.87)
OverallNo68/1196 (5.69)103/1161 (8.87)0.62 (0.45, 0.86)0.04
OverallYes100/1446 (6.92)106/1505 (7.04)0.97 (0.73, 1.30)
NoNo25/454 (5.51)42/451 (9.31)0.57 (0.34, 0.95)†0.02†
NoYes59/716 (8.24)39/713 (5.47)1.54 (1.01, 2.34)†
YesNo43/742 (5.80)61/710 (8.59)0.66 (0.44, 0.99)†
YesYes41/730 (5.62)67/791 (8.47)0.64 (0.43, 0.97)†
  • ORs are comparing the omega-3 group to the control group. ORs >1 indicate the odds of preterm birth are higher in the omega-3 group, while ORs <1 indicate the odds of preterm birth are higher in the control group. Unless otherwise indicated, ORs are based on a logistic regression model including treatment group, alcohol use/parity and an interaction between treatment group and alcohol use/parity, with adjustment for enrolment centre and use of omega-3 supplements in the last 3 months.

  • *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.

  • †ORs are based on a logistic regression model including treatment group, alcohol use, parity, all two-way interactions and a three-way interaction, with adjustment for enrolment centre and use of omega-3 supplements in the last 3 months. Interaction p value is for the three-way interaction.

  • PTB, preterm birth.