By: Akanksha 

Can a woman’s diet affect her blood pressure during pregnancy? A nationwide study looked at the effects of consuming fish before and during pregnancy, finding that eating fish before conception reduces the risk of early-onset hypertensive disorders of pregnancy (HDP), while eating fish during pregnancy helps reduce the risk of late-onset HDP. 

Published in the European Journal of Nutrition, the study examined over 86,000 singleton pregnancies within the Japan Environment and Children’s Study (JECS). Led by Takuta Inouye and Kei Hamazaki, the research team found that the protective benefits of fish consumption before and during pregnancy were especially evident in nulliparous women — those having their first child. 

Approximately 5% to 10% of pregnancies globally are affected by hypertensive disorders of pregnancy (HDP). HDP includes preeclampsia, gestational hypertension, and chronic hypertension. Developing HDP not only increases the risk of complications during pregnancy, but it also raises the risk of cardiovascular and renal diseases later in life.

How Do Omega-3 Fatty Acids Protect Against HDP?

Fish and shellfish are major sources of omega-3 polyunsaturated fatty acids (PUFAs), which include eicosatetraenoic acid (EPA) and docosahexaenoic acid (DHA). PUFAs are well-known to reduce inflammation and widen blood vessels. 

They also possess antithrombotic properties, acting similarly to the mechanism of low-dose aspirin, which is commonly prescribed to high-risk patients to reduce the risk of developing preeclampsia. Although Japan is famous for high seafood consumption, younger Japanese women have been consuming less fish in recent years. Thus, the study investigated the effects of consuming fish before and during pregnancy on maternal blood pressure. 

Also Read: New Blood Tests May Help Predict Who Is At Risk Of Preeclampsia

The study included 86,009 normotensive women to analyze their pre-pregnancy diets and 85,581 women to analyze their mid-to-late pregnancy diets. Patients with pre-existing hypertension, diabetes, renal disease, or cardiovascular disease were excluded. 

How Were the Participants’ Diets Analyzed?

Participants completed a validated food-frequency questionnaire twice throughout their pregnancies:

• Early pregnancy (around 15 weeks of gestation): To determine their dietary habits over the past year prior to pregnancy.

• Mid-to-late pregnancy (around 27 weeks of gestation): To assess their dietary intake during pregnancy.

Participants were then divided into five equal groups (quintiles) depending on their energy-adjusted daily intake. Those in the lowest quintile (Q1) consumed an average of 8.6 grams per day of fish pre-pregnancy, while those in the highest quintile (Q5) consumed an average of 52.1 grams per day.

How Were Early- and Late-Onset HDP Determined? 

Medical records were used to diagnose HDP in women whose blood pressure reached or exceeded 140/90 mmHg after 20 weeks of gestation. Early-onset HDP was defined as developing before 32 weeks of gestation, while late-onset HDP was defined as developing at or after 32 weeks. Statistical adjustments were made for maternal age, BMI, income, education, smoking, alcohol use, fertility treatments, and overall diet. 

Consuming fish at specific stages before and during pregnancy offered targeted protection against HDP:

Does Consuming Fish Pregnancy Reduce Early-Onset HDP? 

• Overall: Women in the highest quintile of pre-pregnancy fish consumption (Q5) had a 34% lower risk of developing early-onset HDP compared to those in the lowest quintile (adjusted odds ratio [aOR] 0.66).

• Nulliparous Women: First-time mothers experienced an even greater reduction in the risk of early-onset HDP. Those in the fourth and fifth quintiles had a 42% to 43% reduced risk (Q4 aOR 0.57; Q5 aOR 0.58). 

Does Consuming Fish Before Pregnancy Reduce Late-Onset HDP?

• Overall: Although overall fish consumption decreased during pregnancy, women in the fourth quintile (Q4) still maintained a 14% lower risk of overall HDP (aOR 0.86).

• Nulliparous Women: Women having their first baby had a reduced risk of overall HDP if they consumed more fish during pregnancy, an effect seen across the top three quintiles (Q3, Q4, and Q5). They also had a 21% lower risk of late-onset HDP in the third and fourth quintiles (aOR 0.79). 

• Multiparous Women: No significant reductions in risk were seen in multiparous women (those who had given birth before). This is likely due to first pregnancies already carrying a higher baseline risk for preeclampsia.

Why Did Eating Whole Fish Offer Greater Benefits Than Isolated PUFAs? 

Interestingly, looking purely at total dietary and PUFAs did not show consistent associations across all groups. Those in the highest quintile of pre-pregnancy PUFA intake had a 37% lower risk of early-onset HDP (aOR 0.63). However, the questionnaire could not differentiate between highly active marine PUFAs (EPA and DHA) and less active omega-3s (such as alpha-linolenic acid), which may have reduced the statistical significance. 

Early- and late-onset occur due to distinct underlying mechanisms: 

How Do Early- and Late-Onset HDP Differ Biologically?

• Early-onset HDP occurs mainly due to poor spiral artery remodeling and placental hypoxia. 

• Late-onset HDP occurs due to oxidative stress and maternal metabolic factors, such as obesity. 

Consuming fish regularly before pregnancy may help build up anti-inflammatory and antithrombotic stores to improve vascular development in the placenta early in pregnancy, or delay the onset of hypertension until later in gestation. 

Also Read: National Family Health Survey-6 Records Improvement in Maternal and Child Healthcare, Nutrition

What Are the Study’s Limitations, and What Can We Learn From It? 

As this was an observational study, it cannot confirm causality. Additionally, the researchers could not determine the specific species of fish consumed or the exact clinical subtype of HDP (such as preeclampsia versus gestational hypertension). 

However, sensitivity analyzes using the international cutoff of 34 weeks for early-onset HDP showed similar trends. Overall, these findings highlight that clinicians should provide dietary advice earlier rather than waiting until a positive pregnancy test. Consistently consuming fish from preconception through pregnancy provides a practical dietary strategy to improve maternal cardiovascular health. 

Reference:

Inouye, Takuya, Daisuke Higeta, Kei Hamazaki, Akira Iwase, Akiko Tsuchida, Hidekuni Inadera, Eiji Yoshioka, and the Japan Environment and Children’s Study Group. “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 65, no. 7 (2026): 249.

https://pubmed.ncbi.nlm.nih.gov/42709217/.

(Rh/APC)