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Information

Female Anatomy

In the diagram below, the uterus is shown bending forwards. This is called anteversion and represents the normal position of the uterus in relation to the other anatomy.

In 10% of women the uterus is naturally bent backwards and this is known as retroversion. In women who have suffered from pelvic inflammatory disease, the previously anteverted uterus may be 'stuck down' in a retroverted position. In both cases the retroverted position can cause pain (particularly during sex).

Diagram 1. Pelvis from side

To examine the internal organs of a female, the doctor uses a plastic or metal instrument called a speculum. The speculum is inserted in the direction shown by the arrow until it reaches the cervix. The arms of the speculum are then opened upwards and downwards to reveal , hopefully, the entrance to the cervix.

Diagram 2.

The following points relate to the menstrual cycle shown further down this page:

By convention the first day of the period is known as Day1 of the cycle. Most people have a 28 day cycle i.e.. on the 29th Day the period starts again and so this becomes Day1 again. Cycle length varies between people (and between cycles of the same person) but generally falls between 24 and 35 days. This does not have any bearing on potential fertility.

The cycle can be conveniently divided into 3 stages :

 

• Stage 1 - when the new egg is developing and the lining of the womb is regenerating (approximately Day5 to Day11).
• Stage 2 - when the egg is released and can be potentially fertilised (the release generally occurs any day between Day11 and Day18 but fertilisation must occur within 48hrs of release).
• Stage 3 - where the lining of the womb is prepared for the potential arrival of a fertilised egg. The failure of fertilisation leads to hormonal changes that bring on the period (and restarts the cycle).

 

Diagram 3.

The actual period of time during any one cycle when an egg can be fertilised is short. Most women with a 28 day cycle produce an egg somewhere between Day 11 and Day 18. Once produced the egg survives only 48 hours and can not be fertilised after that time.

This narrow 48 hr window probably explains why if 100 couples with normal fertility had unprotected sex at random throughout the cycle only 30 pregnancies would occur. In other words the chance of you falling pregnant, even when you are trying, is only 30% per month.

Sperm can survive for approximately 5 days once ejaculated so having unprotected sex on Day 7 of your cycle could ,in theory, result in a pregnancy if the egg was released by Day 12 but not if the egg was released on Day 18 (by which time the sperm would have died).

 

Unfortunately, unless you have a series of ultrasound scans at the first stage of the cycle (which is clearly not practical for someone wanting contraceptive protection every month), it is impossible to be absolutely sure when an egg will be produced before it is actually released.

 

Diagram 1. Modified from "The Sourcebook of Medical Illustration", Medical College of St Bartholomews Hospital, London 1989.

Diagram 2, 3. Copyright drthom.com.