How do contraceptive hormones prevent pregnancy?

Contraceptive hormones prevent pregnancy by inhibiting ovulation, altering cervical mucus, and changing the uterine lining.

Contraceptive hormones, such as those found in birth control pills, patches, injections, and intrauterine devices (IUDs), work primarily by suppressing the body's natural hormonal cycle to prevent ovulation. Ovulation is the process where an egg is released from the ovaries for fertilisation. If no egg is released, there is nothing for sperm to fertilise, thus preventing pregnancy.

These hormones, typically a combination of synthetic oestrogen and progesterone, trick the body into thinking it's already pregnant, which stops the ovaries from releasing an egg. They do this by maintaining consistent levels of these hormones in the body, which inhibits the production of follicle-stimulating hormone (FSH) and luteinising hormone (LH). These two hormones are crucial for the maturation and release of the egg.

In addition to inhibiting ovulation, contraceptive hormones also work by altering the consistency of the cervical mucus. The hormones thicken the mucus at the cervix, making it difficult for sperm to swim through and reach an egg. This provides an additional barrier to fertilisation.

Lastly, these hormones can also change the lining of the uterus, making it less receptive to a fertilised egg. Even if an egg were to be fertilised, the changes in the uterine lining would make it difficult for the egg to implant and begin growing. This three-pronged approach – inhibiting ovulation, altering cervical mucus, and changing the uterine lining – makes hormonal contraceptives highly effective at preventing pregnancy.

It's important to note that while contraceptive hormones are effective at preventing pregnancy, they do not protect against sexually transmitted infections. Therefore, they should be used in conjunction with barrier methods, such as condoms, for comprehensive sexual health protection.