Contraception (Edexcel GCSE Biology: Combined Science)

• Birth control methods are important in keeping family sizes small and in limiting the increase in human population
• Humans can use mechanical, chemical, surgical and natural contraceptive methods to prevent a pregnancy
• Some birth control methods also give protection from sexually transmitted infections

Natural

• Abstinence
  • Avoiding sexual intercourse completely

• Rhythm method
  • Avoiding sexual intercourse during the fertile period of the menstrual cycle when ovulation occurs
  • The exact time ovulation happens can be worked out by monitoring body temperature and quality of cervical mucus
  • This is the least reliable method of birth control and is, instead, a better method used to determine the best time to conceive rather than a method of contraception

Chemical

• IUD / IUS
  • An intrauterine device or intrauterine system is a small device fitted inside the uterus by a doctor or nurse
  • It releases sex hormones which thicken the mucus produced in the cervix, making it difficult for sperm to swim into the uterus
  • It also thins the lining of the uterus, making it more difficult for a fertilised egg to implant
  • An IUD also interferes with passage of sperm through the uterus, in which way it is acting as a barrier method of birth control

• Contraceptive pill, implant, injection
  • May contain just progesterone or a mixture of progesterone and oestrogen
  • Very effective when taken regularly
  • The hormones can also be delivered from a small skin implant or an injection, both of which last several months and increase the effectiveness as they remove the risk of forgetting to take a pill regularly
  • They work by mimicking some of the hormone levels during pregnancy
  • By raising the levels of progesterone and oestrogen, the uterus lining is maintained and development of another egg cell is prevented
  • This means that sex at any time of the month cannot cause pregnancy as no egg is released to be fertilised

Barrier

These all work by preventing sperm from reaching the egg

• Condom
  • Latex sheath worn over the penis
  • Prevents sperm entering the vagina as ejaculate remains in condom
  • Also protects against STIs

• Femidom
  • Latex sheath inserted into the vagina
  • Prevents entry of sperm into the vagina

• Diaphragm
  • A rubber cap that fits over the entrance to the cervix
  • Prevents entry of sperm into uterus
  • Often used with a spermicide (cream which kills sperm)

Surgical

• Vasectomy
  • The sperm ducts are cut, meaning that no sperm is present in the semen when ejaculation occurs
  • Very effective but difficult to reverse

• Female sterilisation (tubal ligation)
  • The oviducts are cut or tied off, preventing eggs from reaching the uterus or sperm from reaching the eggs
  • Very effective but difficult to reverse

Types of birth control