physiology

Female physiology

The menstrual cycle is influenced by the sex hormones - oestrogen and progesterone. These hormones cause physiological changes in a woman's body, which can be monitored using the following clinical indicators:

• Changes in the basal body or waking temperature
• Changes in cervical mucus secretion
• Changes in the cervix
• The length of menstrual cycles
• Abdominal pain and breast changes.

With education and experience a woman is able to accurately assess the fertile and infertile phases of her cycle and use this knowledge to plan or avoid pregnancy

Male physiology

• The testes produce sperm continuously
• At ejaculation, between two and five millilitres of seminal fluid is released, containing around 100 million sperm per millilitre
• Semen quality and quantity may impact the ability of sperm to successfully fertilise the egg. Sperm mobility is equally  an important factor and even with a low count, men who have highly mobile sperm may still be fertile.
• Sperm will survive for 3-5 days or longer in a woman's cervix in the presence of fertile mucus
• A thick sticky mucus plug blocking the cervix during the infertile phase of a woman's menstrual cycle impedes sperm penetration.
  Sperm remaining in the vagina are destroyed within hours by the acidity of the vaginal secretions
• Sperm may be contained in the small amount of lubricating fluid a man releases prior to ejaculation.
  For this reason genital contact or withdrawal method ('being careful') could cause pregnancy if fertile mucus is present at the vaginal entrance