If a woman is considering pregnancy, she should consult her obstetrician or midwife to discuss diet, general health, stress, and others factors to be considered. Prenatal vitamins are an important part of a healthy pregnancy and a healthy baby, and should not be left out of the discussion. The importance of taking a daily prenatal vitamin cannot be stressed enough, its your baby's future.
Women are now encouraged to take them before getting pregnant to prevent birth defects, as well as throughout the pregnancy and breastfeeding to ensure a healthy baby. Prenatal vitamins are a supplement to the diet and should not be substituted for healthy food choices.
A conception chart is a bit more useful for having a child than for avoiding having one, though they can be used for both. The western conception chart only claims to be able to predict cycles of ovulation and tell you when you will be the most fertile so that you can be sure to have sex on those days, while the chinese conception chart claims much greater powers. The chinese conception chart claims to actually be able to predict the child's gender based on the phase of the moon, the mothers age, and a variety of other factors, but most people are skeptical to say the least.
The other day, my married daughter and I met for coffee. She walked in a few minutes after me. She walked up to the table I had chosen and asked "am I pregnant". I asked her what she meant. She rattled off a list of symptoms that she had been experiencing. After she was done with her list she asked again "am I pregnant". I told her that there are so many reliable tests available over the counter that she should go and buy one and find out. She has been trying to get pregnant for close to two years, so she is much in tune with her body.