Before you were pregnant, you probably got by with some simple food know-how, usually along the lines of eat more fruit and veg, drink plenty of water and stay away from the hot chips and family packs of chocolate. Now that you're eating for two, most of these rules still apply, but there are some new ones you'll need to adopt, too.

Eating for two

As tempting as it is to bulk up for bub, you actually don't need to eat more than usual in the first trimester. In the second trimester, you need to consume an additional 1400 kilojoules, and in the last trimester you need an additional 1900 kilojoules. Nutritionist Dr Joanna McMillan recommends eating three small snacks between meals to keep your blood sugar and energy levels even. "Try wholegrain crackers spread with peanut butter for morning tea, a handful of nuts and a banana for afternoon tea and a warm cocoa drink made with milk, pure cocoa powder and a stick of cinnamon in the evening after dinner," she says.

Even though you may be hungrier, especially in your last trimester, try to make every mouthful count and avoid energy-dense, but nutrient-poor sugary and processed fatty foods. "Your baby needs more of almost all nutrients, so it's crucial that you plan proper, balanced meals," says Joanna. "Research clearly shows that a low-GI diet is beneficial to both baby and mum, so avoid refined starches with meals and include instead whole grains and legumes, along with a protein-rich food, stacks of vegetables and a few healthy fats."

Additional nutrients

Along with avoiding certain foods, pregnancy is also a time when you and your baby will benefit from extra nutrients. The key ones are folate, iron and iodine.

• Supplement with 400mcg of folate (folic acid) a day, as well as eating a healthy diet rich in folate for at least a month before conception and in the first three months of pregnancy. This is recommended by health authorities because it has been shown to reduce the risk of spina bifida.

• Studies reveal Australians are mildly deficient in iodine, which is necessary for your baby's brain development.This is why the National Health and Medical Research Council advises pregnant women to take a 150mcg iodine supplement every day.

• Your body also needs more iron during pregnancy because blood volume increases to accommodate your placenta and growing baby.

Some pregnant women become iron deficient or anaemic. If this is your case, your doctor will recommend you take iron supplements until your iron levels are adequate. You'll also be advised to include plenty of iron-rich foods in your diet, like red meat, legumes, green leafy vegetables and iron-fortified cereals.

Eat more fish

Fish, particularly oily fish, is a great food for pregnant women as it's packed with omega-3 fats, which are essential for your baby's central nervous system and brain development. However there has been some concern over mercury contamination, leading to conflicting advice on how much to eat.

Much of the confusion has been due to the varying levels of mercury reported in fish from around the world. "Here in Australia we are lucky to have our fish tested and very clear advice provided on its consumption," says Joanna.

The NSW Food Authority recommends you eat two to three serves of fish each week, with the exception of catfish, orange roughy, shark, swordfish and marlin. Atlantic salmon, canned salmon, mackerel, herring and sardines are rich sources of omega-3 fats and are safe to eat. Canned tuna is also safe and a great convenient food for you to include, although the omega-3 levels are not as high as the oily fish above.

As long as it's well cooked and eaten hot, seafood is generally safe to eat. Pregnant women, however, are advised to avoid eating raw seafood, store-bought sushi, ready-to-eat chilled peeled prawns and smoked salmon.

A note about eggs

High in protein and rich in important nutrients, including omega-3 fats, eggs are a great addition to your pregnancy diet. There is a small risk of eggs carrying salmonella, so it's recommended pregnant women cook their whites and yolks well to reduce the risk of food poisoning. Salmonella poisoning will make you ill and, in rare cases, could cause miscarriage.

"For this reason the advice is to play safe and only eat well-cooked eggs. Perhaps try scrambled or omelettes instead of poached for now," says Joanna. "Supermarket mayonnaise is pasteurised so perfectly safe, but do be careful with homemade mayonnaise made with raw eggs."

Cap the caffeine

Good news: your mid-morning latte isn't banned just yet! But it's recommended you limit your caffeine intake while pregnant as high levels of caffeine have been linked to miscarriage and premature birth. The NSW Food Authority advises pregnant women to have no more than 200mg of caffeine daily, an amount found in three cups of instant coffee, one cup of espresso-style coffee or four cups of medium-strong tea.

Ditch the deli

Many deli-style foods may carry listeria, a bacteria that can cause a nasty flu-like illness. If transmitted to your unborn baby, listeria could lead to miscarriage, premature labour or stillbirth. To reduce this risk, food authorities recommend you stay clear of deli-style foods during the whole nine months of pregnancy.

Foods off the menu include smoked salmon and processed meats such as salami, ham, pressed turkey and chicken. Pâté is not recommended, nor bean sprouts or prepared salads from salad bars. Always cook meat well and prepare your own salads, washing ingredients well. Refrigerate leftovers and use within a day or so.

Soft white cheeses like camembert, feta and ricotta also have a higher risk of listeria contamination, so avoid these, too, unless they're cooked above 65°C, such as on pizzas.

Strong bones

Growing babies need calcium to create skeletons and teeth, so make sure your dairy intake is adequate. If you're not consuming enough calcium in your diet, your baby will draw on your body's reserves for her needs.

"As your baby's needs are prioritised, your teeth and bone health may suffer, so aim to get at least 1000mg of calcium a day," says Joanna. This is about three serves of dairy, which is the same recommended calcium intake for non-pregnant women. This is because when you are pregnant, your body becomes more efficient at using calcium.
Hard cheeses, yoghurt and milk are all rich in calcium.

If you're not a dairy eater, try eating calcium-fortified, non-dairy sources such as fish with small bones, (think canned salmon or sardines) figs, almonds, tofu and leafy green vegetables.

Foodie fixes

Nausea, heartburn and constipation are just some of the pregnancy discomforts that can be eased by eating the right foods. First-trimester nausea can feel worse if there is nothing in your stomach. "Try eating little and often, rather than having big meals," says Joanna. "Dry, crunchy foods like wholegrain toast or crackers can really help. Ginger is also fantastic for nausea." Try ginger tea or use ginger as an ingredient when making meals at home.

Hormonal changes in pregnancy can also bring on an unwelcome side effect in your bowels, namely constipation. This condition is caused when your intestinal tract relaxes, meaning food doesn't move along as quickly as usual. To ease constipation, eat high-fibre foods and drink lots of water. "Your gut slows down in pregnancy, so constipation is common. Consuming plenty of the three different types of fibre – insoluble, soluble and resistant starch – will help," says Joanna. "Eat legumes, whole grains, nuts, seeds and plenty of fruit and vegetables to get all three types."

In your later trimesters heartburn is a common complaint. Fatty and fried foods can make this worse, as can caffeine. "Try eating smaller, more regular meals and stay sitting upright after eating to help reduce heartburn," says Joanna. "You can also try consuming more liquid, nutritious drinks such as homemade smoothies, vegetable-based juices and soups."