In a recent study published in the Neurotoxicology journal, researchers explored the benefits of fish consumption in pregnant women.

There are rising concerns regarding contaminants like mercury in fish that may have negative impacts during pregnancy, despite solid evidence that eating fish while pregnant is helpful. Despite being generally recommended for pregnant women, there is a caveat that pregnant women should not eat fish with high mercury levels. As a result, pregnant women have generally reduced their seafood consumption.

Study: The benefits of fish intake: Results concerning prenatal mercury exposure and child outcomes from the ALSPAC prebirth cohort. Image Credit: Monkey Business Images / Shutterstock

About the study

In the present study, researchers compared two studies using community samples that included measures of prenatal mercury exposure and frequent follow-ups on the children.

Pregnant women from a specific geographical area were enrolled in the pre-birth cohort Avon Longitudinal Study of Parents and Children (ALSPAC) study from 1990–1992, and their pregnancies were followed. Furthermore, their offspring were followed up through childhood, adolescence, and adulthood. The following were used as data sources: (a) self-report questionnaires that were initially filled out by the mother and her partner and later by their children; (b) links to medical records; (c) biological sample tests; physical examinations; (d) various environmental measures of subsamples; and (e) links to geographic sources of pollution obtained with geographic information systems (GIS).

In almost 99.7% of pregnancies for whom a blood measurement was made, the team noted the gestational age of the subject at the time of collecting blood samples. The amount of mercury in whole blood was measured. When the baby was born, the midwife collected cord tissue samples.

The Sheffield assays used a convenience sample of children wherein the total mercury content in the umbilical cord tissue was determined. In phase 1, the majority of samples were analyzed using inductively coupled plasma-optical emission spectrometry (ICP-OES) for the detection of approximately 13 elements, including magnesium, iron, manganese, zinc, and copper. Atomic fluorescence techniques were used to measure the amounts of selenium and mercury.

The Danish analysis involved the examination of an ALSPAC umbilical cord sub-sample to evaluate mercury contents using a different approach. The samples were chosen from individuals who had a suitably-sized cord sample as well as genome-wide association study (GWAS) data at the time. Mercury was identified after cord tissue samples were freeze-dried. The amount of mercury found in the umbilical cord was used as a proxy for prenatal exposure to methylmercury.

Using a food frequency questionnaire (FFQ) in the last trimester of pregnancy, estimates of maternal diet were acquired for over 11,000 pregnant women. Three questions regarding seafood consumption were included in the FFQ, which queried how frequently the pregnant women had white fish, oily fish, and shellfish. This data made it possible to estimate the total amount of fish consumed, along with data on typical portion sizes and the total energy intake.

Results

Six sociodemographic factors and the pregnant woman's reported dietary intake of 103 items were compared with the mother's total blood mercury levels. The study results showed more significant levels of mercury for women who were pregnant for the first time, older women, those who were employed in higher-status occupations, those with higher levels of education, and those who owned (or were purchasing) homes. An additional 6.5% of the variation in the total blood mercury was caused by the number of amalgam fillings in the woman's mouth at the beginning of pregnancy and the number of such fillings that had been withdrawn and replaced throughout pregnancy.

The findings showed unadjusted favorable correlations between Hg and the three birth measures. The difference between the adjusted birth weights of the children of women who did and did not consume fish was statistically significant. However, after adjusting for whether or not the mother consumed fish, the team noted a difference such that if the mother had fish, there was no association between Hg and birthweight. In contrast, if she did not, there was a negative association.

At two to four ages, there was a positive correlation between the maternal blood Hg level and the overall score in preschoolers. Only one of the 20 tests that examined the relationship between maternal blood Hg level, fish consumption, and the Denver Developmental Screening Test (DDST) was significant. There were no signs of harmful correlations between maternal Hg levels and cognition.    

Overall, the study findings highlighted positive correlations between the degree of Hg exposure in utero and the capacity for complex cognition and reasoning in the ALSPAC offspring of pregnant women who consumed fish.

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.