Mean maternal fish intake was 1.5 (SD 1.4, range 0–7.5) servings/week, and 40 (12 percent) of mothers consumed more than 2 weekly fish servings, whereas 47 (14 percent) never consumed fish (). Mean erythrocyte total mercury was 3.8 (SD 3.8, range 0.03–21.9) ng/g, with 35 mothers above the 90th percentile of 9.1 ng/g. Mean (SD) child age at testing was 38.4 (2.2) months, and child test scores were 105.7 (13.8) for the PPVT, 99.9 (10.3) for drawing, 99.8 (10.3) for pegboard, 107.8 (14.1) for matching, and 103.2 (10.5) for WRAVMA total score.
Maternal fish intake was directly correlated with erythrocyte total mercury (spearman r = 0.42, p < 0.0001), with an unadjusted increase of 0.94 (95 percent confidence interval [CI]: 0.66, 1.21) ng/g mercury for each weekly fish serving. The likelihood of being in the top decile of erythrocyte mercury was 2 percent in those who never consumed fish but 23 percent in those who consumed fish more than twice weekly (). Otherwise, maternal or child characteristics did not significantly differ according to maternal fish intake (p> 0.05 for all characteristics in ). Among 98 mothers with available data, mean hair mercury was 0.53 (SD 0.47, range 0–2.3) mcg/g. Hair mercury was correlated with erythrocyte total mercury (Spearman r =0.46, p<0.0001) and with fish intake (r=0.49, p<0.0001). An increase of 1 ppm of hair mercury was associated with an increase in erythrocyte mercury of 4.5 (95 percent CI: 3.3, 5.8) ng/g.
Participant characteristics were generally associated with child test scores in the anticipated directions (). For example, scores were higher among children who were born with higher fetal growth, who were girls, who were firstborn, and who were older at testing ().
After adjustment for parent and child characteristics, maternal fish intake > 2 weekly servings, compared with never, was directly associated with higher child WRAVMA drawing and total scores (). Associations strengthened with adjustment for mercury levels, with the largest effects seen for the WRAVMA drawing (6.4, 95 percent CI: 2.1, 10.7) and total (6.4, 95 percent CI: 2.0, 10.8) scores, and generally positive associations also seen on the other tests ( and ). We saw no evidence for an advantage of fish consumption at or below 2 weekly servings, compared with never (). Exclusion of the four participants who reported taking prenatal fish oil supplements did not materially change results. The interaction between fish intake and breastfeeding duration was not significant (p=0.08 for PPVT model and p=0.38 for WRAVMA model).
Associations of maternal fish intake during pregnancy* with child cognitive test results at age 3 years among 341 mother-child pairs in Project Viva.
FIGURE 1 Associations of maternal 2nd trimester fish intake (> 2 weekly servings vs. never) and erythrocyte mercury levels (top decile vs. below) with child cognitive test results at age 3 years. Effect estimates are adjusted for each other as well as (more ...)
The 28 mothers (8 percent) who reported eating canned tuna at least twice weekly had children with higher scores on the PPVT (3.7, 95 percent CI: −0.9, 8.3) and WRAVMA total (5.6, 95 percent CI: 1.4, 9.8), compared with the 130 women (38 percent) who reported never eating tuna fish. The 11 mothers (3 percent) who reported consuming more than 2 weekly fish servings of fish other than canned tuna had children with higher scores on the WRAVMA total (6.1, 95 percent CI: −0.7, 12.8) but not on the PPVT (−1.4, 95 percent CI: −8.9, 6.1), compared with the 97 (28 percent) who reported eating no fish excluding tuna. Effect estimates for intake of the three fish types excluding shellfish were 4.3 (95 percent CI: −0.5, 9.0) for PPVT and 5.9 (95 percent CI: 1.6, 10.3) for WRAVMA total score.
Among children for whom we obtained clinical lead results, lead levels were not correlated with either maternal fish consumption (Spearman r = −0.01, p= 0.88) or with mercury levels (r=0.03, p=0.76). Additional adjustment for lead level in multivariable models did not alter effect estimates for fish or mercury on child cognitive test scores (results not shown).
Mean intake of DHA+EPA from fish was 128 (SD 128, range 0–843) mg/day, and mean intake from all sources was 149 (SD 154, range 0–1605) mg/day. For each 100 mg of maternal daily DHA+EPA intake from fish, children had PPVT scores that were 0.5 (95 percent CI: −0.5, 1.5) points higher, and WRAVMA total scores that were 1.1 (0.1, 2.0) points higher. Neither intake of DHA+EPA from all dietary sources, nor the DHA+EPA content of maternal erythrocytes, was associated with child cognition (data not shown).
Higher maternal erythrocyte mercury levels were associated with worse child test performance, with stronger associations after adjustment for fish intake (). We observed the strongest adverse associations of mercury levels with the PPVT (−4.5, 95 percent CI: −8.5, −0.4), WRAVMA matching (−6.0, 95 percent CI: −10.9, −1.1), and WRAVMA total (−4.6, 95 percent CI: −8.3, −0.9) tests, with associations that were somewhat less strong but still suggestive of an inverse relationship for the WRAVMA drawing and pegboard tests ( and ).
Associations of maternal 2nd trimester erythrocyte mercury levels with child cognitive test results at age 3 years among 341 mother-child pairs in Project Viva.
We next examined maternal fish intake and mercury levels simultaneously. Compared with children whose mothers reported never consuming fish, children of women with mercury below the top decile but fish intake above 2 weekly servings had higher WRAVMA total scores (5.9 points, 95 percent CI: 1.0, 10.9). Children whose mothers consumed more than 2 weekly fish servings and with mercury in the top decile also had somewhat higher WRAVMA scores, whereas children of mothers with fish intake up to 2 weekly servings and mercury in the top decile had somewhat lower WRAVMA scores ().
Child age 3 year WRAVMA total score according to maternal prenatal fish intake and mercury levels