Midwife, nutritionist, and acupuncturist Zita West has helped many women - including several celebrities - achieve a healthy pregnancy. Fertility and Conception is the complete guide to getting pregnant. Check out our ovulation chart, which may help you work out your cycle.

Below, an exclusive extract from Zita's book:

Fertility Facts
Many women and men don't think much about reproduction and fertility until they want a baby. You would be surprised at just how many couples I see do not fully appreciate how their systems work. In knowledge lies the ability to improve your own chances of conception. The starting points are the basic details of the female and male reproductive systems and how they relate to the all-important issue of fertility and aging.

Reproduction in women
A woman's supply of eggs - several million initially - is created while she herself is in the womb. By puberty, between a quarter and a half million remain. During her life only 400 or so of those will be released via ovulation.

The ovaries are roughly the size of small plums and they contain a lifetime's supply of immature eggs. Each month, an egg develops to maturity and is released from one ovary, ready for fertilization. The ovaries also produce oestrogen and progesterone. The average menstrual cycle is 28 days long and has two distinct phases. The first is the follicular phase, associated with the production of oestrogen which stimulates the egg to develop within the ovary until it is released (ovulation). The second is the luteal phase, associated with progesterone. During this phase the womb lining grows so that a fertilized egg can implant in it and be nourished.

Reproduction in men
Unlike women, men are fertile all the time. From puberty, they manufacture sperm constantly: an adult male produces many millions of them every day.

Hormonal processes are similar in men and women. In both, the hypothalamus releases gonadotrophin-releasing hormone (GnRH). This occurs every 60 to 90 minutes in men, triggering the pituitary gland to release follicle stimulating hormone (FSH) and luteinizing (LH) hormone. A man produces FSH and LH at an even rate throughout the month, enabling cells to be produced and matured constantly. So, in theory, he is always fertile. This fertility does, however, depend upon a perfect balance between FSH and LH being maintained at all time.