Is swordfish safe during pregnancy?

No. The US Food and Drug Administration and the Environmental Protection Agency list swordfish among the Choices to Avoid, the fish with the highest mercury levels, for people who are pregnant or breastfeeding. The same advice asks for 8 to 12 oz a week of lower-mercury seafood. The European Food Safety Authority puts swordfish in its list of high-mercury species. Nobody has run a trial of swordfish in pregnancy, so this answer rests on agency advice, on how much mercury the fish carries, and on cohort studies of mercury before birth.

Not for everyone. If you are pregnant or breastfeeding, swap swordfish for a lower-mercury fish and keep eating fish. US advice names swordfish alongside king mackerel, marlin, orange roughy, shark, tilefish from the Gulf of Mexico and bigeye tuna as the choices to avoid.

What the trials found

There are no randomized trials of swordfish in pregnancy, and we found no systematic review of it either. The trials that exist test the other side of the question, which is why the advice says to switch species rather than give up fish.

The strongest evidence is a Cochrane review of 70 randomized trials in 19,927 pregnant women. Omega-3 fats, given mostly as capsules and in some trials as foods such as fish, lowered preterm birth before 37 weeks from 13.4 to 11.9 percent, a risk ratio of 0.89 (95% CI 0.81 to 0.97) across 26 trials in 10,304 women, on high-quality evidence. Early preterm birth before 34 weeks fell from 4.6 to 2.7 percent. Swordfish was not among the foods tested.

One randomized trial fed a real fish. In Norway, 137 pregnant women were assigned 14 oz (400 g) of cod a week for 16 weeks or their usual diet. Afterward the median mercury in their hair was 554 mcg/kg against 485 in the usual-diet group, a gap that was not statistically significant (p = 0.186). Cod is lean and low in mercury. That reassurance belongs to cod and does not carry over to swordfish.

Who should be careful

The concern is methylmercury. In a survey of 177 fish and lobster samples bought in New York State, swordfish had the highest average mercury of any species, 1,190 ng/g. The abstract does not say how many of the samples were swordfish.

What that mercury does before birth comes from observational studies, and none of them gave swordfish to anyone. A pooled analysis of three large cohorts estimated that prenatal methylmercury raising the mother's hair mercury by 1 mcg/g at birth goes with 0.7 fewer IQ points in the child. That is a 2005 model built on cohorts eating whale meat and fish. A systematic review of 19 studies found mercury from the mother's diet consistently linked to lower birth weight and lower scores on developmental tests, with no pooled size of the effect. In 62,941 Norwegian pregnancies, women in the top fifth of mercury from diet had babies 34 g lighter (95% CI 22 to 46 g lighter) than those in the bottom fifth, and odds of a small baby for gestational age of 1.19 (1.08 to 1.30). Mercury there was calculated from food questionnaires and never measured. In 917 children in the Faroe Islands, whose mothers ate pilot whale meat, prenatal methylmercury went with weaker language, attention and memory at age 7. Those links held after excluding children whose mothers had hair mercury above 10 mcg/g.

Two reports from one Italian cohort are the only outcome data on swordfish itself in pregnancy that we found. Of 412 pregnant women followed to a year after birth, postpartum thyroiditis affected 22 of 92 who mainly ate swordfish, 23.9 percent, and 4 of 85 who mainly ate oily fish, 4.7 percent. That is a single center, the women chose their own fish, and we read only the abstract. In an earlier report on 236 women from the same cohort, those who mainly ate swordfish had the highest rates of thyroid antibodies through pregnancy and early postpartum, and oily fish eaters the lowest. Antibodies were not measured before pregnancy, so the order of events is unknown.

Unsettled. Whether swordfish itself harms a pregnancy is unknown in the sense a trial would settle. The agencies do not wait for that trial. They act on the mercury the fish carries and on cohorts linking prenatal mercury to smaller babies and lower test scores. The swordfish thyroid findings come from one center in Italy and have not been repeated elsewhere.

What expert bodies say

The US FDA and EPA advise people who are pregnant or breastfeeding to eat between 8 and 12 oz a week of a variety of seafood from choices lower in mercury, and put swordfish on the list of choices to avoid. The European Food Safety Authority names swordfish, pike, tuna and hake as species with high mercury content, and says women of childbearing age should stay under the tolerable weekly intake for methylmercury to protect the fetus, getting the benefits of fish from low-mercury species. The two bodies frame it differently, one as a species list and one as a weekly limit, and agree on the direction.

How we searched

What would change this answer

• Not much, in the direction of eating it. The advice rests on mercury content, and a trial that fed swordfish to pregnant women is unlikely ever to be run.
• Repeating the Italian thyroid findings in another population, with antibodies measured before pregnancy, would show whether that signal is real or a quirk of one center.
• Measured mercury from swordfish eaten in pregnancy, linked to the child's outcomes. The cohorts here used whale meat, mixed seafood or mercury calculated from diet.

More on the fish itself: Swordfish.

Sources

1. ev-swpr-01 · Position of an expert body · agency consumer advice · n = —
   Those who are pregnant or breastfeeding consume between 8 and 12 ounces per week of a variety of seafood from choices that are lower in mercury.
   
   Who: people who are pregnant or breastfeeding
   Effect: 8 to 12 oz/week of lower-mercury seafood; Choices to Avoid (highest mercury): king mackerel, marlin, orange roughy, shark, swordfish, tilefish (Gulf of Mexico), bigeye tuna
   Certainty: T2, level E. Swordfish listing confirmed in the chart on the same page in a second request.
   US FDA/EPA, Advice about Eating Fish (page updated 03/05/2024) · checked 2026-10-07 · we read the section
2. ev-swpr-02 · Position of an expert body · agency scientific statement (news summary of EFSA opinions 2014-2015) · n = —
   This particularly applies to countries where fish/seafood species with a high mercury content – such as swordfish, pike, tuna and hake – are consumed regularly.
   
   Who: women of childbearing age, pregnant women, toddlers and children
   Effect: high-mercury species: swordfish, pike, tuna, hake; women of childbearing age should meet fish benefits with low-methylmercury species and stay under the TWI
   Certainty: T2, level E. Agrees with FDA/EPA in direction; EFSA frames it as a TWI, FDA/EPA as a species list.
   EFSA, Fish: scenarios indicate benefits versus risks (news, 22 January 2015) · checked 2026-10-07 · we read the section
3. ev-swpr-03 · Observational data · market survey of contaminant levels · n = 177 samples
   The highest average mercury level (1,190 ng/g) was found in swordfish.
   
   Who: 177 fish and lobster samples from stores and markets in New York State
   Effect: swordfish mean total Hg 1,190 ng/g, highest of all species
   Certainty: Number of swordfish samples not given in the abstract.
   J Food Prot, 2010 · checked 2026-10-07 · we read the abstract
4. ev-swpr-04 · Observational data · prospective cohort · n = 412
   Overall, PPT prevalence was 63/412 (15.3%), but 22/92 in group A (23.9%), 4/85 in group B (4.7%; P < 0.0001 vs. group A), 17/108 (15.7%) in group C, and 16/117 (13.7%) in group D.
   
   Who: pregnant women in Italy with stable fish-eating habits, followed to month 12 postpartum
   Effect: postpartum thyroiditis 22/92 (23.9%) swordfish group vs 4/85 (4.7%) oily fish group, P < 0.0001; first-trimester TPOAb 21.7% vs 4.7%
   Certainty: Single center, fish groups self-selected, no adjustment details in the abstract; pollutant mechanism inferred by authors. no_pmc.
   Endocrine, 2019 · checked 2026-10-07 · we read the abstract
5. ev-swpr-05 · Observational data · prospective cohort · n = 236
   Positivity rates and serum concentrations of both antibodies were the greatest in group A and the lowest in group B (P < 0.001 and P < 0.05 to < 0.001, respectively).
   
   Who: thyroid disease-free, nonsmoking pregnant women with stable diets; 48 swordfish, 52 oily fish, 68 mixed, 68 other fish
   Effect: TgAb and TPOAb positivity highest in swordfish group, lowest in oily fish group (P < 0.001); antibody level rose with monthly swordfish intake
   Certainty: Earlier report of the same cohort as ev-swpr-04; antibodies not measured before pregnancy. no_pmc.
   Endocrine, 2016 · checked 2026-10-07 · we read the abstract
6. ev-swpr-06 · Observational data · quantitative pooled analysis of prospective cohorts (Harvard Center for Risk Analysis panel) · n = 3 cohorts
   It finds that prenatal MeHg exposure sufficient to increase the concentration of mercury in maternal hair at parturition by 1 microg/g decreases IQ by 0.7 points.
   
   Who: children in three major prospective cohorts of prenatal methylmercury exposure
   Effect: -0.7 IQ points per 1 ug/g maternal hair mercury at parturition; plausible range 0 to 1.5 points
   Certainty: 2005 model on cohorts with whale meat and fish exposure; not swordfish-specific; observational.
   Am J Prev Med, 2005 · checked 2026-10-07 · we read the abstract
7. ev-swpr-07 · Observational data · systematic review of observational studies (PRISMA) · n = 19 studies
   Prenatal exposure to mercury was consistently associated with lower birth weight, but only one study reported a negative association with length at birth.
   
   Who: fetuses, neonates and children up to 8 years with measured maternal dietary methylmercury exposure
   Effect: consistent association with lower birth weight; lower neuropsychological and developmental test scores; no pooled effect size
   Certainty: Narrative synthesis, observational, so C. Authors note fish nutrients may offset mercury toxicity.
   Nutr Rev, 2022 · checked 2026-10-07 · we read the abstract
8. ev-swpr-08 · Observational data · prospective birth cohort · n = 62,941
   Women in the highest quintile compared with the lowest quintile of Hg exposure delivered offspring with 34 g lower birth weight (95 % CI -46 g, -22 g) and had an increased risk of giving birth to small-for-gestational-age offspring, adjusted OR = 1·19 (95 % CI 1·08, 1·30).
   
   Who: pregnant women in the Norwegian Mother and Child Cohort (MoBa) with a validated FFQ
   Effect: birth weight -34 g (95% CI -46 to -22) top vs bottom quintile of Hg exposure; SGA adjusted OR 1.19 (1.08 to 1.30); seafood 88% of Hg exposure
   Certainty: Mercury calculated from diet, not measured; OR is odds, not risk.
   Public Health Nutr, 2014 · checked 2026-10-07 · we read the abstract
9. ev-swpr-09 · Observational data · prospective birth cohort · n = 917
   These associations remained after adjustment for covariates and after exclusion of children with maternal hair mercury concentrations above 10 microgram(s) (50 nmol/g).
   
   Who: children from 1,022 consecutive singleton births in the Faroe Islands, 1986 to 1987
   Effect: mercury-related deficits in language, attention and memory, lesser in visuospatial and motor; persisted after excluding maternal hair mercury above 10 ug/g
   Certainty: Exposure from whale meat, not swordfish; effect sizes not in abstract.
   Neurotoxicol Teratol, 1997 · checked 2026-10-07 · we read the abstract
10. ev-swpr-10 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of RCTs with GRADE · n = 19,927
    Preterm birth < 37 weeks (13.4% versus 11.9%; risk ratio (RR) 0.89, 95% confidence interval (CI) 0.81 to 0.97; 26 RCTs, 10,304 participants; high-quality evidence) and early preterm birth < 34 weeks (4.6% versus 2.7%; RR 0.58, 95% CI 0.44 to 0.77; 9 RCTs, 5204 participants; high-quality evidence) were both lower in women who received omega-3 LCPUFA compared with no omega-3.
    
    Who: women at low, mixed or high risk of poor pregnancy outcomes; omega-3 LCPUFA supplements or food vs placebo or no omega-3
    Effect: preterm birth <37 wk RR 0.89 (95% CI 0.81 to 0.97; 26 RCTs, 10,304 participants; high quality); early preterm <34 wk RR 0.58 (0.44 to 0.77)
    Certainty: Mostly capsule trials; swordfish not tested. Supports eating fish in pregnancy, but from lower-mercury species.
    Cochrane Database Syst Rev, 2018 · checked 2026-10-07 · we read the abstract
11. ev-swpr-11 · Randomized controlled trial(s) · randomized controlled trial · n = 137
    Post-intervention, the intervention group had median (inter-quartile range) THHg concentrations of 554 (392-805) µg/kg, and the control group 485 (341-740) µg/kg (p = 0.186).
    
    Who: pregnant women in Norway, gestational week 20 to 36, 400 g cod fillets per week vs habitual diet
    Effect: post-intervention hair mercury median 554 vs 485 ug/kg (p = 0.186)
    Certainty: Contrast case: lean low-mercury fish; does not transfer to swordfish.
    Environ Int, 2020 · checked 2026-10-07 · we read the abstract