Pregnancy weeks are counted from the first day of your last period. Although we usually say a pregnancy lasts about 40 weeks, you’re technically pregnant for “only” 38 weeks—266 days—because fertilization takes place in week 2+0 or, in other words, the third week of your pregnancy.
From the moment you know that you’re expecting, it’s important to give up alcohol, nicotine and drugs completely. It’s also a good idea to do this when you’re trying for a baby as the fetus is particularly delicate during the first few weeks.
Another good idea is to take 400 micrograms of folic acid (vitamin B9) per day as this reduces the risk of conditions such as spina bifida in the fetus. Ideally, you should start taking folic acid a few months before you want to conceive.