Whether you are already pregnant or trying to become pregnant, mercury should be avoided. Higher blood mercury concentration is linked to infertility in both men and women. Mercury can also harm an unborn baby’s developing nervous system. High levels of mercury are found in fish such as shark, swordfish, king mackerel and tilefish. However, fish and shellfish are part of a healthy diet so the FDA recommends eating up to 12 ounces a week of fish and shellfish that are lower in mercury. Some healthy, low-mercury fish are shrimp, canned light tuna, salmon, pollock and catfish.