As soon as a pregnancy is revealed, friends and family often flock to offer their advice: what not to drink, whether you should exercise and which books to read.

If a pregnancy is planned, healthy eating should actually start far before the test comes back positive. “Six months before getting pregnant is when women should get their bodies in shape and iron levels checked,” said Leslie Beck, a registered nutritionist and author of several books, including Leslie Beck’s Nutrition Guide to a Healthy Pregnancy. “It is important for women to get into the eating habits that are important when they do become pregnant well before conceiving,” added Beck.

Although most women know the importance of healthy eating and giving up after-work cocktails, it can be confusing to determine what to include and exclude from their diet. Many women dramatically alter their eating habits and aim to adopt a healthy lifestyle to keep themselves and their baby strong. This probably also has a hand in giving them that fresh ‘pregnancy glow’.

The paranoia that bugs many expecting mothers is not at all unfounded; not only is it as natural to be concerned for your baby’s health as it is to crave pickles and ice cream, but food born pathogens are a real threat.

“Listeria food poisoning can be lethal to a baby,” said Beck. Bacteria that normally wouldn’t harm you may have a chance to flourish during pregnancy, thanks to your altered immune system.

Listeria is found in several different foods, such as soft, ripened cheeses (feta, brie and camembert) and deli-meats. Refrigerated pate, uncooked seafood and smoked seafood should also be avoided. They are only safe if they are heated until they are steaming hot. It is better to avoid those dishes that are no longer palatable after being heated; oysters and sushi are not part of a safe pregnancy menu. “Pregnant women are twenty times more likely to get Listeria poisoning,” said Beck, so avoiding the risk altogether is sensible decision.

There are other risks lurking in the grocery aisles, aside from food poisoning: certain food additives have proven to be harmful to your unborn child. If reaching for a Diet Coke, there is more women should beware of than the caffeine intake alone, specifically, what sweetens the beverage.

Many diet products are sweetened with saccharine instead of sugar. “Saccharine is in the food supply, so it could be in anything marketed as ‘diet’, like diet pop or Crystal Light,” said Beck, “these should be avoided.” The types of sweeteners used should be right on the front of the packaging and easy to spot, according to Beck, so before giving into a craving, check that snacks or drinks are sweetened with sugar, Aspartame or Sucralose, which are considered safe during pregnancy.

The nutrients expecting mothers should make sure to include in their diet are as important as the ones to avoid. To start, women should start taking a supplement with 0.6 mg of folic acid when they are planning to conceive. All prenatal supplements contain a range of B vitamins, which reduce the risks of spinal defects.

Iron needs also increase during pregnancy, especially in the second and third trimester. “Most women are iron deficient,” said Beck, and it is important to get iron levels checked by a doctor before or early on in pregnancy. “Iron is tough to get, especially for vegetarian women who are pregnant,” adds Beck.

To help with brain and retinal development it is important for women to consume adequate amounts of omega-3 acid, DHA. These fatty acids are found in fish, with salmon and trout being the best sources, according to Beck. If the baby is being breastfed, then it is still important for the mom to keep up on her fatty acid intake. Fish that are high in mercury should be avoided though. These include tuna steaks, swordfish and shark.

“Omega-3 fats are especially important in the third trimester.” Said Beck. “If women don’t eat fish, I recommend fish oil capsules to meet this need. Fish liver oil capsules should however be avoided, as they are high in vitamins A and D, and consuming too much vitamin A has side effects, such as decreased bone density.”

Exercise should always be part of a balanced lifestyle, but it is best to check with a doctor before starting any exercise program while expecting, said Beck. Mild activity, such as a brisk walk or swimming, is recommended. In her book, Leslie Beck also suggests waiting until the second trimester and consulting with a doctor if women have not started an exercise regime prior to conceiving. An active lifestyle during pregnancy will help avoid many pregnancy-related discomforts and increase much needed strength.

Beck added that becoming pregnant changes a woman’s life dramatically, and with a little dedication, it can also be a great motivator in transforming a woman’s diet if their lifestyle needs a healthy boost.