The female reproductive system is almost entirely internal.

The vagina is the canal that leads from the outside of the body to the cervix, the opening to the uterus. The cervix contains cells that produce mucus, which around the time of ovulation creates channels for sperm to swim through.

The uterus is the muscular organ in which a fertilised egg can develop into a baby. It is the size and shape of a small pear and lined with a blood-rich and nourishing lining, the endometrium. The endometrium thickens after ovulation to provide a potential bed for an embryo to implant and grow a placenta. The drop in hormones approximately 14 days after ovulation results in the shedding of this lining. The myometrium is the muscular layer that contracts during a period, which for some women can cause significant pain.

The Fallopian tubes extend from the ovaries to the top of the uterus. The ovaries contain the eggs and are about the size of walnuts.

The eggs in each ovary are made before a woman is born. They reside in the ovaries as immature eggs until they die off or are selected to mature. Every month from puberty to menopause, eggs begin to mature inside several fluid filled 'cysts' called follicles. Each group of eggs begins development 3 months prior to an ovulation so that waves of maturing eggs occur throughout a woman's life. Only one follicle from each group will become dominant, while the others will shrink away. The dominant follicle releases an egg at ovulation, which then travels down the Fallopian tube toward the uterus.

Sperm swim up to fertilise an egg as it travels down the Fallopian tube. The developing embryo then travels down the Fallopian tube to the uterus, where it implants in the endometrium approximately one week after ovulation.

For more information see The Path to Pregnancy – Know your cycle

Hormones control the highly complex sequence of events leading to ovulation and those that prepare the endometrium for a potential pregnancy. The main ones are – follicle stimulating hormone (FSH), luteinizing hormone (LH), oestrogen and progesterone. Other hormones that affect the reproductive system include testosterone and prolactin. These hormones can be a problem for women with polycystic ovarian syndrome (PCOS) and irregular cycles respectively. Click here to read more about infertility.

The pituitary gland in the brain produces FSH and LH that convey messages to the ovary. The actions of these hormones result in three phases in the monthly menstrual cycle.

Phases of the menstrual cycle:

1. Follicular phase - this begins on Day 1, the first day of menstrual bleeding. FSH stimulates the development of many follicles, but as levels of FSH gradually fall only one follicle will dominate and produce a mature egg. The developing follicle secretes oestrogen, which causes the cervical mucus to become slippery to help the sperm to swim into the uterus. Oestrogen also helps thicken the endometrium for a potential implantation.

2. Ovulatory phase - this phase is short. In response to rising oestrogen levels, the level of LH spikes up. This LH surge triggers the final maturation of the egg and the release of the egg. This usually happens 14 days before the next period is due (eg. on day 14 of a 28-day cycle).

3. Luteal phase - begins after ovulation. The follicle where the egg developed collapses and becomes the corpus luteum. This mainly produces progesterone, the hormone that transforms the endometrium so an early embryo can implant and develop. If conception does not occur, the corpus luteum stops functioning around 14 days after ovulation. Without the support of progesterone, the endometrium is shed in menstruation.

Although the 'textbook cycle' is 28-29 days, with ovulation occurring on day 14, you may experience some variation to this pattern. Your cycle may be very irregular or you may be having a period without ovulating. There are many things that can affect ovulation, some of which are outlined below.

Understanding your cycle is key to conceiving. Through detecting cervical mucus changes and measuring your basal temperature, also known as Natural Family Planning, you can identify any symptoms that may indicate irregularity or problems with ovulation. It helps you 'target' ovulation and thus make conception easier. The Path to Pregnancy – Know your cycle will provide you with all you need to understand your cycle.

If you have been on the oral contraceptive pill (The Pill) for years, your 'true' cycle will only reveal itself once you are off it. Sometimes, establishing a regular cycle can take many months and fertility may be affected for up to a year. In most cases it is only a matter of time, however in others a delay in establishing a regular cycle may indicate an underlying hormonal problem or nutritional concern.

Irregular cycles relate to irregular or absent ovulation. Herbalists widely prescribe a herb called Vitex agnus-castus to normalise the menstrual cycle and it appears to particularly help women with irregular cycles due to amenorrhoea (no ovulation), luteal phase defect (low progesterone levels after ovulation) or high prolactin levels. Raised prolactin levels are associated with menstrual cycle irregularities, absence of ovulation, PMS and cyclical breast tenderness. Women experiencing these problems often produce excessive amounts of prolactin in response to stress (physical and/or emotional). Vitex is an effective treatment for PMS (including mood changes, irritability, headaches, and breast pain or tenderness).

The Pill can cause decreased levels of vitamins B2, B6, B12, C and folic acid and zinc. Levels of these essential nutrients can take months to recover (as has been shown in the case of folate) so it is recommended to avoid conceiving immediately after coming off the Pill. You need some time to build up healthy levels of essential nutrients for conception. For example, it can take up to 5 months to build up your iodine levels.

The testes lie in the scrotum, the pouch of skin located beneath the man's penis. The testes are the organs that produce sperm and testosterone as a result of hormonal messages from the brain. Sperm slowly move through the channels of the epididymis while they mature. They then move into the vas deferens, a tube that connects the epididymis with the urethra. The entire process of sperm formation takes approximately 3 months. During this time, they are vulnerable to the effects of heat, toxins, ill-health and nutritional deficiencies. Put simply, today's ejaculation is a reflection of the man’s health over the previous 3 months.

The saying "it takes two to tango" definitely applies to preconception care and fertility. Sperm health is a reflection of a man’s general health and as such, preconception care is essential for the prospective father. For example, it is known that many illnesses, acute or chronic, can impair sperm production. If there is a fever, the declines in sperm count and quality can continue for months afterwards. Oxidative stress is implicated in all cases of male infertility and maintaining antioxidant nutrient levels may support healthy male reproduction. All the issues affecting female fertility also affect male fertility. For example, with age, sperm production and quality is reduced. The hormonal imbalance and excess heat associated with being overweight significantly reduces fertility in men. Couples have a high risk of reduced fertility if they are both either overweight or obese.

See The Path to Pregnancy – Clean up, Get Healthy, and PCC check with GP