Fish, in particular oily fish, has gained a lot of publicity in recent years over its role in preventing cardiovascular disease. The omega-3 fatty acids that these fish contain are also highly beneficial for all stages of pregnancy. They’re known for their fertility-boosting qualities, supporting your baby’s brain development and mental performance, reducing the risk of premature birth, and lowering the rate of maternal depression during and after pregnancy.

So what’s the catch?

The increasing level of water pollution has had a significant impact on marine life. Fish and other sea life have been exposed to different types of contaminants over the past decades, leading to some safety concerns over their consumption.

Sea pollution manifests in different ways, mainly as contamination with rubbish, oil, radioactive waste, sewage, heavy metals and pesticides. The majority of fish are not affected and do not pose a health risk if consumed. In addition, our bodies are designed to deal with small amounts of contaminants present in our food. Pregnancy, however, is a vulnerable period, requiring extra care to prevent the absorption of pollutants that might affect the development of your baby.

Know your enemy


Mercury is the most common toxin found in fish and other seafood. Although it exists naturally in the environment, the majority of the mercury pollution occurs as a result of man’s activities, including coal-burning power plants, industrial boilers, steel production and cement manufacture. Mercury that enters the water is converted into another, highly toxic, form known as methylmercury, which can be easily absorbed by the aquatic bodies. Most fish do not constitute a health risk as they only contain small levels of the toxin. However certain species, mainly the older and larger predatory types, contain much higher concentration of methylmercury due to bioaccumulation. The picture below explains the path of mercury contamination in fish.

© Bretwood Higman, Ground Truth Trekking

High mercury exposure during conception and pregnancy can lead to abnormalities in the development of your baby’s brain and nervous system. Current recommendations from the Food Standards Agency (FSA) advise women trying to conceive and expectant mums to avoid shark, marlin and swordfish and limit their intake of fresh tuna to no more than 140g per week. Canned tuna intake can be a bit higher, up to four 140g portions per week, as some of the mercury it contains is removed during the canning process.

Although the recommendations for the general population are more relaxed, if you think you might get pregnant in the next few years you should also limit your intake of fish high in mercury as it has the ability to accumulate in your body over time.

Dioxins and dioxin-like PCBs

Dioxins and polychlorinated biphenyls (PCBs) are further types of environmental toxins that can be found in fish. They are released in a variety of industrial and combustion processes, including waste incineration and fires. These days the industrial production of dioxins and PCBs is heavily controlled. There are a number of pollution prevention control measures in place, which have led to a steady decline in emissions over the past few decades.

Both compounds are known as persistent toxins, which means that they’re resistant to biodegradation and take a long time to break down. In the aquatic environment, they can easily accumulate in the fatty tissue of fish, with oily fish being the most affected due to the higher proportion of fat in their bodies. Similarly, diets high in foods known to contain dioxins and PCBs can cause a build up in the fatty tissue of our bodies, leading to possible health consequences such as an increased risk of cancer, as well as hormonal and immune disturbances. There is also some evidence that foetal exposure to both types of toxins can have developmental effects on your offspring, including impaired reproductive system and motor skills, and low birth weight.

But don’t empty your fridge just yet. According to the Food Standards Agency, “it is not necessary, nor possible, to avoid foods with dioxins”. As has already been mentioned, it usually takes years for the toxins to accumulate in your fatty tissue and therefore reducing the intake of oily fish prior to or during pregnancy will not have any significant effect on the level of dioxins and PCBs already present in your body.

Also, we are not exposed to the same amount of toxins as the individuals or laboratory animals used for the studies that measured the adverse health effects. Most people on a healthy and varied diet keep their intake of dioxins below the Tolerable Daily Intake, which measures the maximum amount of a toxin that can be taken over a lifetime without causing any harm. In addition, the amount of dioxins and PCBs has been reduced significantly over the years, lowering environmental emissions and, as a result, their levels in foods we consume.

Finally, oily fish are not the only source of dioxins and PCBs in our diet, you can also find them in meat, eggs and dairy, therefore avoiding fish will not eliminate the contaminants. Besides, the benefits of fish consumption outweigh the possible health side effects and it is recommended that women trying to conceive and expectant mums consume two portions of fish, one of which should be oily. These include salmon, mackerel, fresh tuna (not canned), trout, sardines and herring.


Fish can also contain small amounts of pesticides, which are used to destroy pests such as insects, rats or weeds, in order to protect the food production. Pesticides can be released into the aquatic environments by fish farmers, for example in salmon farms to control sea lice parasites, or through remnants in the air and soil. The risk of harm to pregnant women and their unborn children is considered to be minimal and no greater than that of general population. The amount of pesticides we are exposed to in the diet is closely monitored through regular safety assessments, including the foods that are imported from non-EU countries. If the level of pesticide residue exceeds the legal limit, the foods are removed from the market. You can find more information on the Food Standards Agency’s website.

How about breastfeeding?

Although breastfeeding mums can pass a small amount of environmental contaminants through breast milk, the research suggests that they present no health risk to the baby. As a result, breastfeeding women are allowed a maximum of one portion of shark, marlin or swordfish, or two portions of oily fish per week.


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