A major study of 40,215 mothers found that eating 2 or more servings of fish per week before pregnancy was associated with 17% to 68% lower odds of having babies with 9 different birth defects, including heart and brain conditions. According to Gram Research analysis, this finding supports FDA recommendations for women planning pregnancy to consume low-mercury seafood regularly, though the study shows association rather than definitive cause-and-effect.
A large study of nearly 40,000 mothers found that women who ate fish regularly before getting pregnant had lower chances of having babies with certain birth defects. Researchers looked at data from mothers who gave birth between 1997 and 2011 and compared those who ate 2 or more servings of fish per week to those who ate little or no fish. The study found that high fish intake was linked to lower risk for 9 different types of birth defects, including heart and brain conditions. However, one rare heart defect showed a higher risk with fish consumption. The findings support current FDA recommendations for women planning pregnancy to eat 2-3 servings of low-mercury seafood weekly.
Key Statistics
A 2026 case-control study of 40,215 mothers in the National Birth Defects Prevention Study found that high fish intake (2+ servings per week) before pregnancy was associated with 17% to 68% lower odds of nine different birth defects, including heart and brain conditions.
Among 10,973 control mothers in the study, only 13.9% reported eating 2 or more servings of fish per week, while 31.3% reported eating very little or no fish, indicating most mothers were not meeting FDA seafood recommendations.
High fish intake before pregnancy showed the strongest protective association with isolated heterotaxia (68% lower odds), double outlet right ventricle (54% lower odds), and transposition of the great arteries (51% lower odds) in the 2026 National Birth Defects Prevention Study.
One birth defect, tricuspid atresia, showed elevated risk with high fish intake in the study, with mothers eating 2+ servings weekly having 1.76 times higher odds, suggesting the relationship between fish consumption and birth defects may vary by condition type.
The Quick Take
- What they studied: Whether eating fish before pregnancy affects the risk of babies being born with birth defects
- Who participated: Nearly 40,000 mothers in the United States (29,242 who had babies with birth defects and 10,973 who had healthy babies) who gave birth between 1997 and 2011
- Key finding: Women who ate 2 or more servings of fish per week before pregnancy had significantly lower odds of having babies with 9 different birth defects, with risk reductions ranging from 17% to 68%
- What it means for you: If you’re planning to become pregnant, eating fish regularly may help protect your baby from certain birth defects. However, this study shows association, not definite cause-and-effect, and you should choose low-mercury fish options and follow FDA guidelines
The Research Details
This was a case-control study, which means researchers compared two groups of mothers: those who had babies with birth defects and those who had healthy babies. They asked mothers about how much fish they ate during the year before they got pregnant. The study included data from the National Birth Defects Prevention Study, a large research project that tracked births across the United States from 1997 to 2011.
Researchers looked at 52 different types of birth defects separately to see if fish intake affected the risk of each one. They used statistical methods to account for other factors that might affect birth defect risk, like age, education, and other dietary habits. This helps isolate the effect of fish eating from other influences.
The study divided mothers into groups based on fish intake: those eating 2 or more servings per week (high intake), those eating some fish but less than 2 servings weekly, and those eating little to no fish. The researchers then compared birth defect rates between these groups.
This research approach is important because it looks at real-world eating patterns in a large population rather than testing fish in a lab. By comparing mothers who had babies with birth defects to those who didn’t, researchers can identify patterns that might help prevent birth defects. The study’s large size and long time period make the findings more reliable than smaller studies.
This study has several strengths: it included a very large number of mothers (over 40,000), tracked them over many years, and examined many different birth defects. The researchers adjusted their analysis for other factors that could influence results. However, the study relied on mothers remembering what they ate a year or more before pregnancy, which can be inaccurate. The study shows association between fish eating and lower birth defect risk, but cannot prove that fish directly prevents birth defects.
What the Results Show
High fish intake (2 or more servings per week) was associated with lower odds of 9 birth defects. These included heart defects like double outlet right ventricle and transposition of the great arteries, brain conditions like Dandy-Walker syndrome and holoprosencephaly, and other defects like cleft palate and gastroschisis. The protective effect was substantial, with odds ratios ranging from 0.32 to 0.83, meaning mothers with high fish intake had 17% to 68% lower odds of having babies with these conditions compared to mothers who ate little or no fish.
The strongest protective associations were seen for isolated heterotaxia (68% lower odds), double outlet right ventricle (54% lower odds), and transposition of the great arteries (51% lower odds). These findings suggest that fish consumption before pregnancy may have a protective effect against several serious birth defects.
Among the control mothers (those with healthy babies), about 14% reported high fish intake, while 31% reported eating very little or no fish. This means most mothers in the study were not meeting the FDA recommendation of 2-3 servings of fish per week.
The study identified one birth defect with an elevated risk associated with high fish intake: tricuspic atresia, a heart condition where the valve between two heart chambers doesn’t form properly. Mothers with high fish intake had 1.76 times higher odds of having a baby with this condition. This finding was unexpected and suggests that the relationship between fish intake and birth defects may be complex, with different effects for different conditions. The reason for this association is unclear and would need further investigation.
This study aligns with existing FDA recommendations that women who are or could become pregnant should consume 2-3 servings of low-mercury seafood per week. Previous research has suggested that fish contains beneficial nutrients like omega-3 fatty acids and protein that support fetal development. This large study provides substantial evidence supporting those recommendations. The finding that most mothers in the study weren’t meeting fish intake guidelines suggests a gap between recommendations and actual eating patterns.
The main limitation is that mothers reported their fish intake from memory, which can be inaccurate. The study cannot prove that eating fish directly causes lower birth defect risk—it only shows an association. Other factors not measured in the study could explain the relationship. The study focused on a US population, so findings may not apply to other countries with different fish types and mercury levels. Additionally, the study didn’t distinguish between different types of fish, some of which contain more mercury than others.
The Bottom Line
According to Gram Research analysis, women planning pregnancy should aim to eat 2-3 servings of low-mercury fish per week, following FDA guidelines. Choose fish lower in mercury like salmon, sardines, and trout rather than shark, swordfish, or king mackerel. This recommendation is supported by moderate-to-strong evidence from this large study showing associations with lower birth defect risk. However, individual circumstances vary, so discuss fish intake with your healthcare provider.
Women planning to become pregnant or who could become pregnant should pay attention to these findings. The study suggests that increasing fish intake before conception may help prevent certain birth defects. However, the findings don’t apply to women who are already pregnant (different mercury concerns apply during pregnancy) or those with fish allergies. Men planning to father children may also benefit from adequate fish intake, though this study focused on maternal diet.
The protective effect of fish intake appears to operate during the year before conception, based on when researchers measured fish consumption. This suggests that building healthy eating habits several months before trying to become pregnant may be beneficial. Benefits wouldn’t be immediate but would develop over the months leading up to conception.
Frequently Asked Questions
Does eating fish before pregnancy prevent birth defects?
Research shows eating 2+ servings of fish weekly before pregnancy was associated with 17-68% lower odds of nine birth defects. However, this shows association, not definite prevention. Fish contains beneficial nutrients, but individual results vary. Consult your doctor about your specific situation.
How much fish should I eat if I’m trying to get pregnant?
The FDA recommends 2-3 servings of low-mercury seafood per week for women who are or could become pregnant. Choose fish like salmon, sardines, and trout. Avoid high-mercury fish like shark and swordfish. A serving is about 3-4 ounces.
What types of fish are safe to eat before pregnancy?
Low-mercury fish safe before pregnancy include salmon, sardines, anchovies, trout, and pollock. Avoid high-mercury fish like shark, swordfish, king mackerel, and tilefish. Medium-mercury options like canned tuna should be limited to 6 ounces weekly.
Can eating fish prevent all types of birth defects?
No. The study found fish intake was associated with lower risk for 9 specific birth defects but showed increased risk for one condition (tricuspid atresia). Fish may help prevent some defects but not others. Many birth defects have multiple causes beyond diet.
When should I start eating more fish if planning pregnancy?
Start increasing fish intake several months before trying to conceive. The study measured intake during the year before pregnancy, suggesting benefits develop over time. Building healthy eating habits early gives your body time to benefit from improved nutrition.
Want to Apply This Research?
- Track weekly fish servings in the app, aiming for 2-3 servings per week. Log the type of fish eaten and note mercury level (low, medium, high) to ensure you’re choosing safer options. Set a weekly reminder to plan fish meals.
- Add one fish meal per week to your current diet. Start by choosing one low-mercury fish you enjoy (salmon, sardines, or trout) and plan to eat it once weekly. Gradually increase to 2-3 servings as you find recipes and preparation methods you like.
- Track fish intake weekly for 3 months to establish the habit. Use the app to log servings and types of fish. Review monthly trends to ensure you’re meeting the 2-3 servings per week goal. If planning pregnancy, continue tracking through conception to maintain consistent intake.
This article summarizes research findings and should not replace professional medical advice. The study shows associations between fish intake and birth defect risk, not definite cause-and-effect relationships. Individual circumstances vary significantly. Women planning pregnancy should discuss dietary recommendations, including fish intake and mercury exposure, with their healthcare provider. This information is for educational purposes and does not constitute medical advice. Always consult with a qualified healthcare professional before making dietary changes during preconception planning or pregnancy.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.