Pregnancy Guide Helping you through pregnancy

Congratulations, you're going to have a baby. Though the average pregnancy lasts 266 days - 38 weeks from the time of conception - your expected date of delivery is calculated from the first day of your last period. This is 40 weeks, which doctors divide into three 'trimesters', each lasting three months.

Here is your comprehensive guide to those 40 vital weeks. Midwife and holistic health guru, Zita West - whose clients include actress Kate Winslet - tells you about the changes in you and your baby throughout your pregnancy: how you will feel, what you should be doing and what complementary therapies and good nutrition can do to help you have a happy, healthy pregnancy and perfect baby.

Week 1-3

The egg has been fertilised by the sperm and is a cluster of dividing cells, known as the blastocyst. It is only the size of a pinhead but multiplying fast.

Three layers of cells are starting to develop, which will divide into the different parts and organs of the body, including the skeleton, nervous system, brain, lungs and kidneys.

Also beginning to form are the first cells of the placenta, the mass of tissue that provides oxygen and nutrients for your baby, as well as transferring waste products out of the body via the mother's body.

This, however, does not kick into action until the blastocyst has become a fully formed foetus - aboutweeks 13-14. And all these changes will be starting to happen before you even realise you've missed your period.