The link between fish and pregnancy hypertension may start before conception

Researchers tracked dietary patterns across more than 86,000 pregnancies to examine whether when women eat fish could influence the risk of early- and late-onset hypertensive disorders.

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A Japanese study published in the European Journal of Nutrition found that higher maternal fish intake before pregnancy was associated with a lower risk of early-onset hypertensive disorders of pregnancy (HDP), while higher fish intake during pregnancy was associated with a lower risk of late-onset HDP in some intake groups among women having their first child. These associations were more evident among women who had not previously given birth.

Background

HDP, which includes gestational hypertension and pre-eclampsia, is an important cause of maternal and perinatal illness. They affect about 5–10% of pregnancies and are also associated with an increased risk of cardiovascular and metabolic disease later in life.

Fish is a major dietary source of omega-3 (n-3) polyunsaturated fatty acids (PUFAs), particularly EPA and DHA, which have anti-inflammatory, vasodilatory, and antithrombotic effects and could therefore potentially protect against HDP.

Previous observational studies have reported inconsistent associations between fish intake and HDP. There is stronger evidence that EPA and DHA intake may be protective against pre-eclampsia.

Most studies have examined dietary intake during rather than before pregnancy. In Japan, fish has traditionally been an important part of the diet, but its consumption is now falling among younger women.

The researchers therefore examined whether fish and PUFA intake before and during pregnancy was associated with the risk of HDP in the Japan Environment and Children’s Study (JECS), a large nationwide birth cohort.

Study characteristics

The analysis included 86,009 women with singleton pregnancies who participated in the JECS. Of these, 85,581 women provided information on dietary intake during pregnancy. Women with hypertension before pregnancy, diabetes, cardiovascular disease, or renal disease were excluded, as were pregnancies ending in miscarriage or stillbirth before 22 weeks, and records with incomplete dietary data. Dietary intake was assessed using a validated food-frequency questionnaire.

The first questionnaire was completed at a median gestational age of 15 weeks, assessed dietary intake over the preceding year, and was used to estimate pre-pregnancy fish and PUFA intake. A second questionnaire was completed at a median of 27 weeks to assess intake during pregnancy.

After adjusting for total energy intake, fish intake, and dietary n-3 and n-6 PUFA intake, the variables were classified into quintiles. The researchers examined associations with overall HDP, early-onset HDP (Eo-HDP; onset before 32 weeks), and late-onset HDP (Lo-HDP; onset at or after 32 weeks).

The analyses adjusted for multiple potential confounding factors, including demographic and socioeconomic (maternal age, education, household income, employment, marital status, and dietary patterns), lifestyle-related (smoking and drinking status, pre-pregnancy BMI, physical activity, the use of fatty acid supplements), and health-related (parity, assisted reproductive technology, gestational diabetes, previous HDP) factors.

The mean fish intake ranged from 8.6 g/day to 52.1 g/day in the lowest and highest quintiles, respectively. Average n-3 PUFA intake ranged from 1.1 g/day to 4.7 g/day in the lowest and highest quintiles, respectively.

Women in the higher quintiles of fish, n-3, and n-6 PUFA intake were more likely to be older, to have previously given birth, to be more educated, to have a higher household income, and to be less likely to drink or smoke. They had higher rates of ART and gestational diabetes mellitus">GDM in the index pregnancy.

Prepregnancy fish intake

Pre-pregnancy fish intake was not significantly associated with overall HDP or Lo-HDP. However, it was linked to 34% lower odds of Eo-HDP in the highest quintile.

When only women who had not previously given birth were included, the odds of Eo-HDP were approximately 43% lower in the fourth and fifth quintiles.

Pregnancy fish intake

Fish intake during pregnancy was associated with 14% lower odds of overall HDP in the fourth quintile. For women expecting their first child, higher intake in pregnancy was linked to lower odds of HDP across the third, fourth, and fifth quintiles, and 21% lower odds of Lo-HDP in the third and fourth quintiles.

A significant trend in overall HDP was observed with increasing fish intake among women having their first child, although the corresponding trend for Lo-HDP did not reach statistical significance.

The pattern of associations therefore differed according to when dietary intake was assessed: pre-pregnancy intake was more strongly associated with Eo-HDP, whereas intake during pregnancy was associated mainly with Lo-HDP, particularly among women having their first child.

PUFA intake

Less consistent associations were observed between PUFA intake and HDP.

Higher pre-pregnancy n-3 PUFA intake was associated with 37% lower odds of Eo-HDP in the highest intake group overall, although there was no significant trend across increasing intake. Conversely, n-6 PUFA intake was linked to an 87% increase in Eo-HDP odds among women who had previously given birth, but only in the second intake quintile. The n-6/n-3 PUFA ratio was associated with higher odds of HDP and Eo-HDP only in the third quintile.

Thus, significant associations were not consistently observed across quintiles of prepregnancy intake. Moreover, fish intake declined during pregnancy in this cohort, which may have affected the analysis.

When onset before 34 (rather than 32) weeks of gestation was used as the cutoff for Eo-HDP, the main findings remained similar.

Interpretation

These findings, therefore, add to the evidence that fish intake may be linked to a lower risk of HDP and are consistent with some previous epidemiological studies. However, there was no clear signal supporting the protective effect of total dietary n-3 PUFA intake against HDP.

The researchers suggest that the difference between early- and late-onset HDP may partly explain the timing-specific findings. Eo-HDP is more closely associated with abnormalities in placental development and spiral artery remodeling, while Lo-HDP has stronger links with maternal metabolic factors. The anti-inflammatory and antithrombotic properties of n-3 PUFAs could potentially influence processes involved in early placental dysfunction.

They also suggest that increased prepregnancy fish intake may have shifted the onset of some Eo-HDP cases to later in gestation.

The different pattern observed for fish intake during pregnancy may instead reflect differences in the timing of dietary exposure. Because maternal obesity and related metabolic factors are major risk factors for Lo-HDP, the authors suggest that the influence of pre-pregnancy fish intake on this form of HDP may be relatively modest.

Moreover, pregnancy is often associated with reduced fish intake, which may affect the analysis.

The stronger effects observed among women who had not previously given birth could reflect the higher risk of HDP associated with a first pregnancy, while differences in baseline risk among women with previous births may have made dietary associations harder to detect.

Limitations

The study was observational, so it cannot establish that fish consumption prevents HDP. Although the analyses adjusted for many potential confounders, residual confounding may have persisted.

Fish and PUFA intake estimated from the food-frequency questionnaires and food-composition tables may not have precisely reflected individual dietary intake. Individual PUFA subtypes could not be evaluated separately. The FFQ could not identify fish species in detail, and PUFA intake from non-marine fish could not be estimated separately.

The study also could not distinguish between specific HDP phenotypes such as gestational hypertension and pre-eclampsia. The primary analysis also defined early-onset HDP using a 32-week cutoff rather than the more commonly used 34-week threshold, which may limit comparisons with other studies. The researchers did not assess potential non-linear associations, so the study could not identify an optimal level of fish or PUFA intake. Finally, the large number of statistical comparisons could have led to spurious associations.

Conclusion

This study showed lower odds of certain forms of HDP associated with fish intake before and during pregnancy. The associations were more evident among women who had not previously given birth.

Higher fish intake during pregnancy was associated with a lower risk of Lo-HDP in some intake groups among women having their first child, while pre-pregnancy fish intake was linked to a reduced risk of Eo-HDP. Associations with total dietary n-3 and n-6 PUFA intake were considerably less consistent.

The findings suggest that maintaining consistent fish intake from before conception through pregnancy may be associated with a lower risk of HDP. Future research should examine causality and distinguish the effects associated with specific types and amounts of fish or fatty acids.

Funding and competing interests

The JECS was funded by the Ministry of the Environment, Japan. One author reported receiving lecture honoraria from several pharmaceutical and wellness companies for presentations related to n-3 PUFAs; all other authors reported no conflicts of interest.

Journal reference:

• Inouye, T., Higeta, D., Hamazaki, K., et al. (2026). Association of the maternal fish and PUFA intake with the risk of hypertensive disorders of pregnancy: a nationwide birth cohort-The Japan Environment and Children’s Study (JECS). European Journal of Nutrition. DOI: 10.1007/s00394-026-04103-7, https://link.springer.com/article/10.1007/s00394-026-04103-7