Plasma long-chain omega-3 fatty acid status and risk of recurrent early spontaneous preterm birth: a prospective observational study.

INTRODUCTION: A 2018 Cochrane review found that omega-3 supplementation in pregnancy was associated with a risk reduction of early preterm birth of 0.58; prompting calls for universal supplementation. Recent analysis suggests the benefit may be confined to women with a low baseline omega-3 fatty acid status. However, the contemporary omega-3 fatty acid status of pregnant women in the UK is largely unknown. This is particularly pertinent for women with a previous preterm birth, in whom a small relative risk reduction would have a larger reduction of absolute risk. This study aimed to assess the omega-3 fatty acid status of a UK pregnant population and determine the association between the long-chain omega-3 fatty acids and recurrent spontaneous early preterm birth. MATERIAL AND METHODS: A total of 283 high-risk women with previous early preterm birth were recruited to the prospective observational study in Liverpool, UK. Additionally, 96 pregnant women with previous term births and birth ≥39+0  weeks in the index pregnancy provided a low-risk population sample. Within the high-risk group we assessed the odds ratio of recurrent early preterm birth compared with birth at ≥37+0  weeks of gestation according to plasma eicosapentaenoic acid plus docosahexaenoic acid (EPA+DHA) at 15-22 weeks of gestation. RESULTS: Our participants had low EPA+DHA; 62% (143/229) of women with previous preterm birth and 69% (68/96) of the population sample had levels within the lowest two quintiles of a previously published pregnancy cohort. We found no association between long-chain omega-3 status and recurrent early preterm birth (n = 51). The crude odds ratio of a recurrent event was 0.91 (95% CI 0.38-2.15, p = 0.83) for women in the lowest, compared with the highest three quintiles of EPA+DHA. CONCLUSIONS: In the majority of our participants, levels of long-chain omega-3 were low; within the range that may benefit from supplementation. However, levels showed no association with risk of recurrent early spontaneous preterm birth. This could be because our population levels were too low to show benefit in being omega-3 "replete"; or else omega-3 levels may be of lesser importance in recurrent early preterm birth.