• Try not to be underweight or overweight. Both can make it difficult to conceive or maintain a pregnancy.
• General supplements are not required if you have a healthy diet. However, some are helpful: folic acid (to guard against neural tube defects) and iron supplements for some women (to avoid anaemia). Enough vitamin D is supplied by a normal diet and sunshine generally.
• Check with your doctor about becoming pregnant if you are on medication. Some can harm a foetus.
• Avoid heavy-duty cleaning products if possible.
• No current evidence says stress harms an unborn baby, says Fisher. However, a small group of people who recurrently miscarry may respond to stress reduction.
• Do not smoke if you are planning pregnancy. But if you are pregnant, it's not too late to give up the habit, says Professor Lesley McCowan, of the University of Auckland department of obstetrics and gynaecology. She has published a paper showing if women stop smoking by 3-4 months into a pregnancy complications of early birth and undernourished babies were the same as in non-smoking women.
• Fruit and vegetables are advised in the diet before conceiving. McCowan says a healthy intake of fruit helps reduce risks of pre-eclampsia. This condition can cause soaring blood pressure and swelling, seizures or organ failure in extreme cases. The babies are at risk also.
• McCowan says those with a healthy intake of greens around conception and early pregnancy have a reduced risk of small or undernourished babies.
• Fertility Plus medical director Neil Johnson recommends "no more than two strong coffees a day" and to avoid alcohol and drugs.
• He also recommends taking iodine (iodine deficiency has been linked to thyroid and brain development issues).