Articles

578 www.thelancet.com Vol 369 February 17, 2007

Maternal seafood consumption in pregnancy and 

neurodevelopmental outcomes in childhood 

(ALSPAC study): an observational cohort study

Joseph R Hibbeln, John M Davis, Colin Steer, Pauline Emmett, Imogen Rogers, Cathy Williams, Jean Golding

Summary

Background Seafood is the predominant source of omega-3 fatty acids, which are essential for optimum neural 

development. However, in the USA, women are advised to limit their seafood intake during pregnancy to 340 g per 

week. We used the Avon Longitudinal Study of Parents and Children (ALSPAC) to assess the possible benefi ts and 

hazards to a child’s development of diff erent levels of maternal seafood intake during pregnancy.

Methods 11 875 pregnant women completed a food frequency questionnaire assessing seafood consumption at 32 weeks’ 

gestation. Multivariable logistic regression models including 28 potential confounders assessing social disadvantage, 

perinatal, and dietary items were used to compare developmental, behavioural, and cognitive outcomes of the children 

from age 6 months to 8 years in women consuming none, some (1–340 g per week), and >340 g per week.

Findings After adjustment, maternal seafood intake during pregnancy of less than 340 g per week was associated with 

increased risk of their children being in the lowest quartile for verbal intelligence quotient (IQ) (no seafood consumption, 

odds ratio [OR] 1·48, 95% CI 1·16–1·90; some, 1·09, 0·92–1·29; overall trend, p=0·004), compared with mothers who 

consumed more than 340 g per week. Low maternal seafood intake was also associated with increased risk of suboptimum 

outcomes for prosocial behaviour, fi ne motor, communication, and social development scores. For each outcome 

measure, the lower the intake of seafood during pregnancy, the higher the risk of suboptimum developmental outcome.

Interpretation Maternal seafood consumption of less than 340 g per week in pregnancy did not protect children from 

adverse outcomes; rather, we recorded benefi cial eff ects on child development with maternal seafood intakes of more 

than 340 g per week, suggesting that advice to limit seafood consumption could actually be detrimental. These results 

show that risks from the loss of nutrients were greater than the risks of harm from exposure to trace contaminants in 

340 g seafood eaten weekly.

Introduction

Optimum fetal neurodevelopment is dependent on 

specifi c nutrients derived solely from dietary sources, 

including docosahexaenoic acid (DHA), an omega-3 

essential fatty acid, of which seafood is a major source.1

Low seafood intake during pregnancy could lead to fetal 

defi ciency in essential long-chain omega-3 fatty acids 

such as DHA and eicosapentaenoic acid, (EPA) resulting 

in adverse eff ects on neurodevelopment.2

 DHA defi ciency 

leads to reduced dendritic arborisation3

 and impaired 

gene expression for regulation of neurogenesis, 

neurotransmission, and connectivity.4

 In severe 

conditions of DHA deprivation, such as Zellweger 

disease and peroxisomal disorders, mental retardation is 

common, yet restoration of dietary DHA intake improves 

clinical outcomes and neuronal myelination.5–7

In 2004, advice8

 was issued jointly by two US Federal 

Government agencies for pregnant women or women 

likely to become pregnant to restrict their overall 

consumption of seafood to 340 g per week,8

 to avoid 

fetal exposure to trace amounts of neurotoxins. 

However, such control of seafood consumption could 

cause intake of long-chain omega-3 fatty acids to 

fall below quantities adequate for best fetal neurodevelopment.9,10 We analysed an observational cohort 

study, the Avon Longitudinal Study of Parents and 

Children (ALSPAC), to assess whether the advice is 

successful in providing protection from adverse 

neurodevelopmental outcomes. 

Methods

ALSPAC was designed to assess environmental factors 

(including diet) during and after pregnancy that might 

aff ect the development, health, or wellbeing of the child. All 

pregnant women living in Bristol, UK, and surrounding 

areas, with an expected delivery date between April 1, 1991 

and Dec 31, 1992 were eligible for inclusion.11 Of 

14 541 pregnancies, 13 988 children survived for at least 

12 months. About 85% of eligible expectant mothers participated; recruitment, dropout, and other methodologies 

have been described elsewhere.11,12 Mothers were sent postal 

questionnaires four times during pregnancy and then at 

specifi c time points11,12 after birth of the child to obtain 

information about diet, education, social circumstances, 

behavioural, and developmental outcomes. The 

investigation used singleton and fi rst-twin births for whom 

data were available for 28 key social, demographic, and 

other confounding variables (n=8946). Mothers answered 

questions about development or behaviour of their children 

at ages 6, 18, 30, 42, and 81 months (number completing at 

Lancet 2007; 369: 578–85

See Comment page 537

Laboratory of Membrane 

Biophysics and Biochemistry, 

US National Institute on 

Alcohol Abuse and Alcoholism, 

US National Institutes of 

Health, Bethesda, MD 20952, 

USA (J R Hibbeln MD); 

University of Illinois at 

Chicago, Chicago, IL, USA

(J M Davis MD); and 

Department of Community 

Based Medicine, University of 

Bristol, UK (C Steer MSc, 

P Emmett PhD, I Rogers PhD, 

C Williams PhD, 

J Golding FMedSci)

Correspondence to:

Joseph R Hibbeln, Laboratory of 

Membrane Biophysics and 

Biochemistry, US National 

Institute on Alcohol Abuse and 

Alcoholism, US National 

Institutes of Health, 31 Center 

Drive Rm. 31/1B58, MSC 2088, 

Bethesda, MD 20952, USA

jhibbeln@mail.nih.gov
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www.thelancet.com Vol 369 February 17, 2007 579

least one valid response and having all confounders=8801), 

and their children had their intelligence quotient (IQ) 

measured by the Weschler Intelligence Scale for Children 

IIIUK (WISC-IIIUK) at age 8 years (n=5449). All ALSPAC 

studies were done voluntarily under ethical review as 

previously described.11 Mothers volunteeres to take part on 

the understanding that they were under no obligation and 

could drop out whenever they wished. The study had the 

approval of the ALSPAC Ethics and Law Advisory 

Committee and local ethics committees.

Seafood exposure

Data for food consumption were obtained at 32 weeks’ 

gestation by a self-completed detailed food-frequency 

questionnaire, which was also used to calculate nutrient 

and energy intakes.13 Three questions assessed seafood 

consumption: “How many times nowadays do you eat 

(a) white fi sh (cod, haddock, plaice, fi sh fi ngers, etc), (b) 

dark or oily fi sh (tuna, sardines, pilchards, mackerel, 

herring, kippers, trout, salmon, etc), and (c) shellfi sh 

(prawns, crabs, cockles, mussels etc)?”. Each response 

was chosen from fi ve predefi ned categories: Never or 

rarely; once in 2 weeks; 1–3 times per week; 4–7 times 

per week; and more than once a day. These were scored 

as portions per week as follows: rarely or never=0; once 

in 2 weeks=0·5; 1–3 times per week=2; 4–7 times per 

week=5·5; or more than once a day=10.

Portion sizes were based on typical eating patterns in 

the UK with consideration of relative proportions of 

processed and fresh seafood commonly consumed 

(webpanel 1). Total seafood consumption per week was 

calculated as the total number of portions, multiplied by 

the portion size for each type of fi sh. A mother who ate 

seafood three times a week would typically have a fi sh 

intake of 347 g per week (range 297–358 g per week). 

Fatty acid values were based on profi les of typical species 

of British seafood (webpanel 1).14 Intake of omega-3 fatty 

acids for each portion were estimated as follows: white 

fi sh, 0·32 g; oily fi sh, 0·89 g; shellfi sh, 0·34 g.14 Derived 

estimates of the intake of omega-3 fats from seafood 

(α-linolenic, eicosapentaenoic, docosapentaenoic, and 

docosahexaenoic acids) were calculated as total amounts 

and as proportions of total energy intake. The 

questionnaire also asked about intake of other foods 

(meats, poultry, vegetables, fruits, potatoes etc); 

the social variations in diet have been described 

previously.15

The frequency of seafood consumption has previously 

been validated in relation to two biochemical markers 

in subpopulations of ALSPAC.16–18 First, seafood 

consumption association with predicted erythrocyte 

fatty acid composition was established in a thorough 

statistical analysis with smile plots to correct for multiple 

analyses of 40 fatty acids.16 The frequency of oily-fi sh 

consumption positively correlated with erythrocyte 

DHA content in a dose-response eff ect (p<0·0001).16,17

Second a further biochemical marker of seafood 

consumption is umbilical cord mercury content, since 

seafood is a major dietary source of methyl-mercury 

(MeHg). Umbilical MeHg concentrations also showed a 

positive relation to reported seafood intake.18 These 

direct biochemical comparisons are consistent with 

other studies that validated the use of similar food 

frequency questionnaires and derived nutrient intake 

data (eg, those used in pregnancy).19 See Online for webpanel 1

Confounder Maternal seafood consumption in pregnancy p

None (n=1059) 1–340 g per week 

(n=5770)

>340 g per week 

(n=2087)

Maternal education

Low 392 (37%) 1521 (26%) 329 (16%) <0·0001

Middle 345 (33%) 2164 (38%) 727 (35%)

High 322 (30%) 2085 (36%) 1031 (49%)

Housing 

Mortgaged/owned 740 (70%) 4650 (81%) 1809 (87%) <0·0001

Council 167 (16%) 594 (10%) 121 (6%)

Other 152 (14%) 526 (9%) 157 (8%)

Crowding at home 

<1 person/room 821 (78%) 4879 (85%) 1866 (89%) <0·0001

1+ person/room 238 (22%) 891 (15%) 221 (11%)

Life events

0–7 965 (91%) 5369 (93%) 1929 (92%) 0·0766

8–18 94 (9%) 401 (7%) 158 (8%)

Partner

No 39 (4%) 73 (1%) 16 (0·8%) <0·0001

Yes 1020 (96%) 5697 (99%) 2071 (99%)

Maternal age

<20 years 48 (5%) 130 (2%) 28 (1%) <0·0001

≥20 years 1011 (95%) 5640 (98%) 2059 (99%)

Maternal smoking in pregnancy

Non-smoker 643 (61%) 4063 (70%) 1612 (77%) <0·0001

Stopped 162 (15%) 751 (13%) 234 (11%)

Still smoking 254 (24%) 956 (17%) 241 (12%)

Maternal alcohol use in pregnancy

Non-drinker 123 (12%) 366 (6%) 88 (4%) <0·0001

Stopped 485 (46%) 2431 (42%) 873 (42%)

Still drinking 451 (43%) 2973 (52%) 1126 (54%)

Parity

0 521 (49%) 2510 (44%) 891 (43%) 0·0026

1 339 (32%) 2145 (37%) 762 (7%)

2+ 199 (19%) 1115 (19%) 434 (21%)

Breast-feeding

Yes 766 (72%) 4564 (79%) 1821 (87%) <0·0001

No 293 (28%) 1206 (21%) 266 (13%)

Gender

Boy 553 (52%) 2986 (52%) 1060 (501%) 0·6835

Girl 506 (48%) 2784 (48%) 1027 (49%)

Ethnic origin

White 1036 (98%) 5711 (99%) 2058 (99%) 0·0092

Black 10 (0·9%) 35 (0·6) 18 (0·9)

Asian 13 (1%) 24 (0·4%) 11 (0·5)

Table 1: Characteristics of confounders used in the analyses by seafood intake groups (n=8916) with 

tests of the diff erences between the three groups
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580 www.thelancet.com Vol 369 February 17, 2007

Outcome measures

An estimate of the child’s abilities used a scale developed 

by ALSPAC, including items from the Denver 

Developmental Screening Test.20 A set of questions 

completed by the mother at home was used to calculate a 

continuous score with four domains (gross motor, fi ne 

motor, communication, and social skills). The scales 

were completed by parents when the children were 6, 18, 

30 and 42 months of age. A comparison of the selfcompletion results with the Griffi ths scale21 (administered 

under controlled conditions by trained psychologists) 

done on a representative subpopulation of the cohort 

(n=1045) at 18 months, gave a correlation coeffi cient of 

0·54 (p<0·0001).

Suboptimum development was defi ned as scores at the 

lower end of the distribution closest to 25% for the total 

score and for each of the four component scores. Because 

the communication scores at age 6 months were clustered, 

the percentage with sub-optimum development deviated 

substantially from this target, being closer to 15%. 

Assessments from the questionnaires at 6 months of age 

were susceptible to small diff erences in ages, and we 

therefore corrected these scores for the age of the child.

The Strengths and Diffi culties Questionnaire22 was 

completed by the mothers for their children at age 

81 months. The questionnaire has well-established 

consistency, reliability, and diagnostic predictability, 

surpassing the Child Behaviour Checklist for inattention 

and hyperactivity.23,24 The scale consists of 25 questions 

with fi ve subscales (prosocial [ie, positive social 

interactions], hyperactivity, emotional symptoms, conduct 

problems, and peer problems) and a total diffi culties score. 

Age of child 

when tested

Maternal seafood consumption Risk of suboptimum outcomes†

None* 1–340 g per 

week*

>340 g per 

week*

None vs

>340 g per week

1–340 g per week 

vs >340 g per week

Trend test‡

OR (95%CI) OR (95%CI) p n

Cognition

Verbal IQ 8 yr 31·0% (46.3) 22·9% (42.0) 17·2% (37.8) 2·16 (1·72–2·71) 1·43 (1·21–1·68) <0·0001 5407

Performance IQ 8 yr 27·4% (44.6) 25·1% (43.3) 22·2% (41.5) 1·33 (1·05–1·67) 1·18 (1·01–1·37) 0·0104 5042

Total IQ 8 yr 28·9% (45.4) 24·9% (43.2) 18·6% (38.9) 1·78 (1·40–2·25) 1·45 (1·23–1·71) <0·0001 5000

Behaviour

Prosocial 7 yr 11·9% (32.4) 9·7% (29.6) 8·1% (27.3) 1·54 (1·15–2·05) 1·22 (0·99–1·50 0·0032 6582

Peer problems 7 yr 18·7% (39.0) 13·3% (34.0) 11·9% (32.4) 1·69 (1·33–2·15) 1·13 (0·95–1·35) <0·0001 6581

Hyperactivity 7 yr 13·3% (33.9) 10·0% (30.0) 9·4% (29.1) 1·48 (1·13–1·94) 1·07 (0·88–1·30) 0·0091 6575

Emotional 7 yr 15·1% (35.9) 12·2% (32.7) 11·7% (32.1) 1·35 (1·05–1·73) 1·05 (0·88–1·26) 0·0369 6582

Conduct 7 yr 13·1% (33.8) 9·7% (29.6) 8·5% (27.8) 1·63 (1·24–2·15) 1·16 (0·94–1·42) <0·0001 6586

Total behavioral 7 yr 13·3% (33.9) 9·6% (29.4) 8·3% (27.6) 1·69 (1·28–2·23) 1·17 (0·95–1·44) 0·0004 6570

ALSPAC early development tests

Gross motor skills 6 mo 22·8% (42.0) 22·7% (41.9) 19·7% (39.8) 1·20 (1·00–1·44) 1·19 (1·05–1·35) 0·0151 8764

18 mo 30·5% (46.1) 31·7% (46.5) 31·5% (46.5) 0·95 (0·80–1·13) 1·01 (0·90–1·13) 0·6827 8227

30 mo 27·5% (44.7) 28·4% (45.1) 27·0% (44.4) 1·02 (0·86–1·23) 1·07 (0·95–1·21) 0·5683 7720

42 mo 24·2% (42.9) 24·8% (43.2) 23·6% (42.5) 1·03 (0·86–1·25) 1·07 (0·94–1·21) 0·5534 7603

Fine motor skills 6 mo 23·7% (42.5) 26·7% (44.2) 23·2% (42.2) 1·03 (0·86–1·23) 1·21 (1·07–1·36) 0·2165 8746

18 mo 25·3% (43.5) 21·8% (41.3) 19·1% (39.3) 1·44 (1·20–1·73) 1·18 (1·04–1·34) 0·0001 8228

30 mo 29·0% (45.4) 28·3% (45.0) 24·2% (42.8) 1·28 (1·07–1·53) 1·23 (1·09–1·40) 0·0015 7728

42 m 29·7% (45.7) 24·8% (43.2) 20·1% (40.1) 1·68 (1·39–2·02) 1·31 (1·15–1·49) <0·0001 7596

Social skills 6 mo 24·8% (43.2) 23·2% (42.2) 20·7% (40.5) 1·27 (1·06–1·51) 1·16 (1·03–1·32) 0·0048 8743

18 mo 24·9% (43.3) 24·9% (43.2) 22· %4 (41.7) 1·15 (0·96–1·38) 1·15 (1·01–1·30) 0·0600 8226

30 mo 27·6% (44.7) 26·2% (44.0) 22·5% (41.8) 1·31 (1·09–1·58) 1·22 (1·08–1·38) 0·0011 7711

42 mo 26·4% (44.1) 25·7% (43.7) 21·1% (40.8) 1·34 (1·11–1·62) 1·30 (1·14–1·48) 0·0003 7592

Communication skills 6 mo 17·7% (38.1) 15·6% (36.3) 12·7% (33.3) 1·48 (1·20–1·82) 1·27 (1·10–1·48) 0·0001 8745

18 mo 28·7% (45.2) 25·3% (43.5) 22·9% (42.0) 1·35 (1·14–1·61) 1·14 (1·01–1·29) 0·0007 8237

yr=years. mo=months.*Data are mean (SD) of percentage of children in the lowest quartile for Wechsler intelligence scale for children (WISC-IIIUK) and ALSPAC early 

development test subscales or in the suboptimum range of behavioural scores for the Strengths and Diffi culties Questionnaire (SDQ): peer problems (proportion in 

highest 13%), prosocial (proportion in lowest 9.0%) hyperactivity (proportion in highest 10%), emotional disorders (proportion in highest 12.1%), conduct disorders 

(proportion in highest 9.7%), total behavioural problems (proportion in highest 10.2%). For communications skills subscale, clustered scores prevented selection of 

lowest 25%, thus adverse (suboptimum) outcomes were defi ned by selecting the lowest 15%. †Suboptimum outcomes were defi ned as the odds ratio (OR) comparing no 

seafood intake and (1–340 g per week) with >340 g per week, using logistic regression analyses unadjusted for covariates. ‡A test for trend was made on the assumption that 

the three fi sh intake categories were equally spaced.

Table 2: Children with suboptimal outcomes and their corresponding maternal seafood consumption (unadjusted)
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See Online for webpanel 2

These scores were prorated according to Goodman’s22

instructions and as previously described for the cohort,25

such that the low tails of the distribution of gender-specifi c 

scores (closest to 10%) were chosen to create the binary 

outcome, indicating sub-optimum behavioural outcomes 

for each subscale. 

IQ was estimated with an abbreviated form of the WISCIIIUK, a well-standardised assessment of full-scale, verbal, 

and performance intelligence,26 which was given to 8-yearold children at the ALSPAC research clinic with standard 

neuropsychological testing procedures.12 Suboptimum 

cognitive outcomes were defi ned as the lowest 25% of 

scores for full scale, verbal, and performance subscales. 

Statistical analyses

To evaluate the 2004 US advice, we used three categories 

of seafood consumption: none; consumption of 1–340 g 

per week (ie, up to three portions per week); and 

consumption of more than 340 g per week. Categories of 

intake of omega-3 fatty acids were created, with women 

whose estimated intake was zero as one category, and the 

remainder were divided into equal groups. The relation of 

these categories of omega-3 intake to each outcome 

measure to estimate dose-response was assessed for nonlinearity by plotting residuals and iterative curve-fi tting 

analyses including linear, power, exponential, quadratic, 

and logarithmic models (Sigma Plot version 8.02). We did 

logistic regression analyses with those who ate more than 

340 g of seafood per week as the unity or reference category 

(SPSS version 11.0.1). p values are provided for trend.

We identifi ed potential confounding variables by review 

of published data (table 1). Two continuous variables were 

used to assess the cumulative eff ects of adverse social and 

developmental factors during defi ned developmental 

periods: the family adversity index during pregnancy and a 

measure of parenting, one based on facilities for child care 

in the home27 at 6 months of age. The family adversity 

index was calculated from the scores of 38 adverse factors 

(webpanel 2). Perinatal variables were birthweight (<2500 g; 

≥2500 g), and gestation at delivery (<37 weeks, ≥37 weeks). 

Additionally, 12 individual categorical covariates were 

included: sex of the child, age of the mother (<20 years or 

≥20 years), parity, highest maternal educational attainment, 

educational attainment (based on the UK examination 

system, and referred to qualifi cations that the parent might 

have obtained at school or at later ages,28 catergorised as 

low, medium, or high), housing status (council [subsidised 

public housing], other rented, owned/mortgaged), 

crowding (≤1 or >1 person per room), stressful life events 

at 18 weeks of gestation (upper 10%, lower 90% of cohort), 

had partner at time of birth (no, yes), smoking status 

during pregnancy (never, smoked before but not at 

18 weeks of gestation, or still smoking at 18 weeks of 

gestation), alcohol use during pregnancy (non-drinker, 

drank before 18 weeks of gestation, still drinking alcohol at 

18 weeks of gestation), breastfeeding (none, some) and 

ethnicity (white, black, Asian). Perinatal variables were low 

0

15

20

25

30

n=584

Verbal IQ

children suboptimum (%)

n=3493 n=1330

A 35

B

C

D

0

15

20

25

30

n=875

Fine motor

children suboptimum (%)

n=4923 n=1798

35

0

5

10

n=739

Prosocial

children suboptimum (%)

n=4260 n=1583

15

0

15

20

25

30

n=875

None

Maternal seafood consumption in pregnancy

0–340 g

per week

>340 g

per week

Social development

children suboptimum (%)

n=4919 n=1798

35

Figure 1: Suboptimum outcomes in children according to mothers’ seafood 

consumption

Means and 95% CI of the percentage of children with suboptimum outcomes. 

Suboptimum outcomes are defi ned as the lowest quartile for verbal IQ , fi ne motor 

control, and social skills and by scores in the suboptimum range for prosocial 

behaviour. A=suboptimum verbal IQ in 8-year-old children. B=suboptimum fi ne 

motor score in 42-month-old children. C=suboptimum prosocial score in 7-yearold children. D=suboptimum social development score in 42-month-old children.
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582 www.thelancet.com Vol 369 February 17, 2007

birthweight (<2500 g, ≥2500 g), and preterm delivery 

(<37 weeks, ≥37 weeks).

To investigate the possibility that seafood intake might 

be a marker for other diff erences in diet aff ected by social 

patterning, we also adjusted for 12 other food groups 

noted to be socially patterned in a previous analysis of diet 

in pregnancy in this cohort (sausages/burgers, pies/

pasties, red meat, poultry, green leafy vegetables, other 

vegetables, salad, chips, fresh fruit, fruit juice, crisps, and 

biscuits).15 All these 28 confounding variables (12 categorical 

and two continuous social variables, two perinatal 

variables, plus 12 dietary food groups) were used uniformly 

for all multivariable logistic regression analyses. 

To assess whether the outcomes of families with social 

disadvantage who did not complete the study were diff erent, 

we used the national test results (standardised assessment 

tasks) at age 7. These tests are administered to all children 

enrolled in British Government-funded schools.

Role of the funding source

The sponsor of the study had no role in study design, data 

collection, data analysis, data interpretation, or writing of 

the report. The US National Insititute of Alcohol Abuse 

and Alcoholism contributed to scientifi c review of the 

report. The corresponding author had full access to all the 

data in the study and had fi nal responsibility for the 

decision to submit for publication.

Results

Maternal seafood consumption ranged from 0 to 3268 g 

per week (mean 235 g per week, SD 202), resulting in 

estimated intakes of omega-3 fatty acids from seafood 

ranging from 0 to 15·6 g per week, (mean 1·06 g per 

week, SD 1·05). In total 12% of women were eating no 

fi sh during pregnancy, 65% 1–340 g per week, and 

23% more than 340 g per week.

As shown in table 1, low seafood consumption by 

mothers was more likely in homes with evidence of social 

disadvantage (high level of family adversity, crowding, low 

maternal education levels, not being a home owner, and 

being a single parent) and less than ideal lifestyles (smoker, 

low parenting scores, and not breastfeeding). 

The proportions of children with suboptimum behaviour 

and development scores by maternal seafood intake are 

shown in table 2. The unadjusted data consistently show 

that children of mothers who ate more than 340 g per week 

of seafood had outcomes that were no worse than children 

of women who ate less seafood. However, these unadjusted 

data clearly show that children of mothers who reported no 

seafood intake often had the greatest risk of adverse or 

suboptimum outcomes. Additionally, when seafood intake 

was moderate (1–340 g per week) the risk of suboptimum 

outcomes in the children were between those of no seafood 

consumption and those eating more than 340 g per week. 

This result can be seen for four outcomes in fi gure 1.

Greater maternal intake of omega-3 fatty acids was 

associated with lower risk of suboptimum verbal IQ in a 

non-linear dose-response curve (fi gure 2). Much the 

same protective dose-response patterns were seen for 

nearly all of the outcomes signifi cant in unadjusted and 

adjusted analyses (data not shown).

Table 3 shows results after adjustment for the factors 

shown in table 1, plus the two perinatal factors and 12 food 

categories. Consumption of seafood in pregnancy was 

signifi cantly associated with nine of the 23 outcomes—in 

each case the higher the maternal seafood intake the less 

likely the infant was to have a suboptimum score.

Since specifi c nutrient defi ciencies could contribute to 

defi cits in verbal development, a separate analysis was 

done using 30 co-variates with maternal intakes of 

14 specifi c nutrients, instead of 12 categories of food. The 

risks for low verbal IQ were greater when using the data 

for 14 specifi c nutrients (Odds ratio [OR] 1·67 [95% CI 

1·28–2·13]) than when using the food category data (OR 

1·48 [1·16–1·90]) in analyses comparing children whose 

mothers ate no seafood with children whose mothers ate 

more than 340 g seafood per week. These results suggest 

that our use of the food category data could lead to 

underestimation of the risks of low maternal seafood 

consumption; we chose to use food category data because 

it does not make assumptions about the nutrient content 

of food as does data for specifi c nutrients. 

In a further attempt to allow for potential confounders, 

we repeated the earlier analysis with our standard 

28 factors but included paternal seafood consumption 

0 0·05 0·10 0·15 0·20 0·25

Estimated omega-3 fatty acids from seafood in pregnancy (en %)

0·30 0·35 0·40 0·45 0·50 0·55 0·60

12

0

14

16

18

20

22

24

26

28

30

32

34

36

Percentage of children

Figure 2: Prevalence of children with low verbal IQ according to mothers’ omega-3 fatty acid from seafood

Estimated maternal consumption of long chain omega-3 fatty acids is expressed as proportion of total calories 

(en %). Maternal seafood consumption was grouped into six categories: mothers with no reported consumption 

plus fi ve equal groups of remaining population. Means and 95% CI for proportion of children in the lowest quartile 

for verbal IQ . Best curve fi t for categorical means was r=0·96, r

2

=0·92, f=19·2, p=0·017, with the following 

equation: f=20·6229+12·7575*exp (–12·7934*x). 
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as a proxy for social confounding. Even though this 

could be regarded as an over-control, maternal seafood 

consumption was still signifi cantly associated with 

verbal IQ, although the eff ect sizes were slightly reduced 

(for no maternal fi sh compared with >340 g per week, 

OR dropped from 1·48 [1·16–1·90] to 1·39 [1·04–1·86].

We did not do a detailed analysis of fi sh oil supplements. 

They were consumed in pregnancy by only 205 (1·7%)

women in the study. The outcomes of infants of mothers 

who took supplements, but did not eat seafood were close 

to those of mothers who did eat fi sh (data not shown). 

There was no trend toward benefi t in any childhood 

outcome variable associated with a seafood intake less than 

340 g per week, irrespective of statistical model used.

Discussion

The information obtained in ALSPAC shows no evidence 

that consumption of more than three portions of seafood 

a week during pregnancy has an adverse eff ect on the 

behaviour or development of the child. By contrast, 

maternal consumption of more than 340 g seafood a week 

was benefi cial for the child’s neurodevelopment. These 

results were unexpected since the 2004 advisory8

 was 

formulated on the basis of an assessment of development 

in the verbal domain, the Boston naming test.29 The 

relevant measures in ALSPAC were verbal IQ and 

communication skills. The relation between maternal 

seafood intake and the child’s communication skills at 

ages 6 and 18 months and verbal IQ are the opposite to 

those anticipated by the US advisory. 

In any observational study the possibility exists that 

relevant confounders have not been taken into account. 

As we show in table 1, there are notable social diff erences 

between groups. We tried to account for these diff erences 

by allowing for many factors. Another possibility is that by 

measuring seafood consumption, we are measuring only 

the eff ects of a healthy diet. For this reason, we also took 

account of 12 socially patterned food categories15 but there 

was no change in the direction of the results (table 3). 

Further analyses allowed for all estimated nutrients in the 

mother’s diet, but again this analysis made little diff erence 

to the outcomes.

Seafood intake in the ALSPAC cohort is unlikely to have 

resulted in a lower exposure to MeHg than in the US 

general population. ALSPAC is reasonably representative 

of the British population,11 which has a higher mean 

consumption of mercury (0·05 μg/kg bodyweight30), than 

does the US population (0·02 μg/kg bodyweight31). 

Seafood eaten in Avon, UK, was therefore likely to have 

contained greater quantities of MeHg32 than the species 

from the USA that were used to formulate the 2004 US 

advice.29,31,33 Such seafood obtained in the UK would be 

expected to put children at greater risk of suboptimum 

development outcomes than in the USA, in contrast with 

the fi ndings presented here. However, the UK has less 

contamination by polychlorinated biphenyls than other 

developed countries.34 

Diff erences between the children who continued in the 

study and those who did not could provide a possible 

explanation for the discrepancy between our results and 

the outcomes anticipated when following the advisory. 

Attrition was disproportionately high in families with 

social disadvantage and lower seafood intake. To assess 

whether their outcomes were diff erent we used the national 

test results (standard ised assessment tasks) at age 7 years. 

These tests are administered to all children enrolled in 

British govern ment funded schools (more than 90% of the 

co hort). 

For attrition bias to have an eff ect in the direction of 

trend, the group of children who dropped out of the study 

must have had the highest standardised assessment scores 

of the children whose mothers who ate no seafood. 

However, the lower standardised test scores were in the 

same direction and more pronounced in children who 

Outcomes† Age None vs >340 g per week 1–340 g per week vs

>340 g per week

Trend*

OR (95 % CI)‡ OR (95 % CI)‡ p n

Cognition

Verbal IQ 8 yr 1·48 (1·16–1·90) 1·09 (0·92–1·29) 0·0041 5407

Performance IQ 8 yr 0·98 (0·76–1·27) 0·99 (0·84–1·18) 0·9015 5042

Full scale IQ 8 yr 1·29 (0·99–1·69) 1·19 (0·99–1·42) 0·0389 5000

Behaviour

Prosocial 7 yr 1·44 (1·05–1·97) 1·16 (0·93–1·44) 0·0249 6582

Hyperactivity 7 yr 1·13 (0·84–1·53) 0·91 (0·73–1·12) 0·6293 6575

Emotional 7 yr 1·09 (0·83–1·44) 0·96 (0·80–1·17) 0·6810 6582

Conduct 7 yr 1·21 (0·89–1·64) 1·01 (0·81–1·25) 0·2869 6586

Peer problems 7 yr 1·25 (0·96–1·62) 0·97 (0·80–1·16) 0·1753 6581

Total score 7 yr 1·17 (0·86–1·60) 0·98 (0·79–1·22) 0·3832 6570

Child development

Gross motor skills 6 mo 1·10 (0·90–1·34) 1·06 (0·92–1·21) 0·3262 8764

18 mo 1·02 (0·85–1·22) 1·01 (0·89–1·13) 0·8420 8227

30 mo 0·97 (0·80–1·18) 1·03 (0·90–1·17) 0·9402 7720

42 mo 0·96 (0·78–1·18) 0·99 (0·87–1·13) 0·7159 7603

Fine motor skills 6 mo 1·01 (0·83–1·23) 1·12 (0·99–1·28) 0·5191 8746

18 mo 1·25 (1·04–1·51) 1·09 (0·96–1·23) 0·0222 8228

30 mo 1·04 (0·85–1·27) 1·04 (0·91–1·19) 0·6163 7728

42 mo 1·35 (1·09–1·66) 1·14 (0·98–1·31) 0·0053 7596

Social development 6 mo 1·15 (0·95–1·40) 1·01 (0·89–1·16) 0·2173 8743

18 mo 1·01 (0·83–1·24) 1·01 (0·88–1·15) 0·8937 8226

30 mo 1·24 (1·01–1·53) 1·12 (0·98–1·29) 0·0326 7711

42 mo 1·21 (0·98–1·50) 1·17 (1·01–1·35) 0·0377 7592

Communication 6 mo 1·30 (1·04–1·63) 1·15 (0·98–1·35) 0·0184 8745

18 mo 1·26 (1·03–1·53) 1·02 (0·90–1·17) 0·0485 8237

yr=years. mo=months. *A test for trend was made on the assumption that the three fi sh intake categories were equally 

spaced. Deviation from the trend was assessed as between fi sh intake group χ2 statistic (2 df) and the trend χ2 (1 df). 

Because of transformation inherent in logistic regression, linear trend was tested against log OR. Results with 

signifi cant trend associations had no signifi cant deviations. †Outcomes variables are as described in table 2 legend. 

‡Results of logistic regression analyses adjusted for 28 variables : 12 categorical and two continuous social variables as 

outlined in table 1, birthweight (≤2500 g, >2500 g), preterm delivery (≤37 weeks, >37 weeks) 12 non-fi sh food 

groups.15

Table 3: Maternal seafood consumption and suboptimum childhood outcomes:logistic regression 

models adjusted for 28 factors
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584 www.thelancet.com Vol 369 February 17, 2007

dropped out of the cohort (n=2454): mothers who ate no 

seafood (mean 7·1; SD 3·8); mothers who ate 1–340 g per 

week (8·4; 3·7); mothers who ate more than the advisory 

limit (8·8; 3·8); compared with the scores of children who 

remained in the cohort (n=7081): mothers who ate no 

seafood (mean 9·2; SD 3·6); mothers who ate 1–340 g per 

week (9·7; 3·5); and mothers who ate more than the 

advisory limit (10·2; 3·4] )(p=0·0091, unadjusted ANOVA 

by mother’s consumption and attrition status).

We noted that the disproportionate attrition of socially 

disadvantaged participants probably caused an underestimation of the association of suboptimum development 

with low seafood consumption.

Nearly all assessments of dietary intakes are diffi cult. 

Here we did not have information about specifi c species 

of seafood or portion sizes. However, our food frequency 

questionnaire, which was specially developed for ALSPAC, 

has been validated in comparison with two biochemical 

markers for seafood consumption in a subpopulation of 

this cohort.16–18 Food frequency questionnaires for seafood 

have also been validated in other studies.19,35,36 Similarly, 

the maternal reports of child development and behaviour 

are prone to reporting bias. Although the ALSPAC 

development score that was completed by the parents does 

not have the sensitivity suitable for a screening test, it does 

have high specifi city for detection of damage.37 Additionally, 

when compared with development scores based on a 

diff erent test administered by psychologists, the resulting 

correlation (r=0·54) was close to what is generally seen in 

comparisons between two diff erent tests purporting to 

measure a similar trait.

Advice that limits seafood consumption might reduce 

the intake of nutrients necessary for optimum neurological 

development. Findings reported here are consistent with 

reports that lower omega-3 fatty acid intakes in pregnancy 

predict lower verbal IQ.38,39 Adverse outcomes associated 

with insuffi cient intakes of long chain omega-3 fatty acids 

during pregnancy include: intrauterine growth 

retardation,40 delayed or suboptimum depth perception,17

adverse neurodevelopmental measures,18 residual defi cits 

in fi ne motor skills, speed of information processing in 

infants,41 and irreversible defi cits in serotonin and 

dopamine release.42 Thus, other evidence suggests that 

omega-3 fatty acids in pregnancy could be directly 

responsible for the benefi cial fi ndings shown here. The 

2004 US advisory8

 however, aimed to reduce the potential 

harm from pollutants in seafood, specifi cally methylmercury. Although methylmercury undoubtedly has 

harmful eff ects on the developing brain, the harm is 

unlikely to be greater than the overall benefi ts of nutrients 

at the concentrations usually present in seafood. These 

data show that the risks from losing the benefi ts of 

nutrients essential to neurodevelopment exceeds the risk 

of exposure to trace concentrations of contaminants in 

340 g seafood eaten weekly.

In conclusion, we recorded no evidence to lend support 

to the warnings of the US advisory8

 that pregnant women 

should limit their seafood consumption. By contrast, we 

noted that children of mothers who ate small amounts 

(<340 g per week) of seafood were more likely to have 

suboptimum neurodevelopmental outcomes than 

children of mothers who ate more seafood than the 

recommended amounts.

Contributors

P Emmett designed the food frequency questions. P Emmett and 

I Rogers developed the nutrient coding scheme. J Hibbeln, J M Davis, 

C Steer, and J Golding analysed data. All authors contributed to writing 

the manuscript.

Confl ict of interest statement

We declare that we have no confl ict of interest.

Acknowledgments

We thank all parents and children who took part and, the midwives for 

their cooperation and help in recruitment; the whole ALSPAC study 

team, including interviewers, computer technicians, laboratory 

technicians, clerical workers, research scientists, volunteers, and 

managers who continue to make our study possible. ALSPAC received 

fi nancial support from the Medical Research Council, the Wellcome 

Trust, the University of Bristol, UK government departments, medical 

charities, and other sources. The statistical analyses presented here were 

supported by the Intramural Research Program of the National Institute 

on Alcohol Abuse and Alcoholism, NIH and National Institute of Mental 

Health Grant No 1 P01MH68580-01 CFDA#93.242 through 

John M Davis. The ALSPAC study is part of the WHO initiated 

European Longitudinal Study of Pregnancy & Childhood.

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