WOMEN’S BODIES: ORAL CONTRACEPTION: QUESTIONS ABOUT PILL

Posted on Wednesday, March 11th, 2009 at 4:47 pm

How does the Pill work?

There are three effects that together make the combined Pill highly effective. First and most important, when taken correctly the hormones in the Pill prevent ovulation. How can hormones taken by mouth do this? You will see that high blood levels of ovarian hormones produced during the natural menstrual cycle stop the pituitary from releasing the hormone (FSH) that triggers the development of ovarian follicles in the next cycle. If you put enough ovarian hormones into your blood by swallowing them, pituitary hormones are suppressed in the same way and ovarian follicles don’t develop: no egg – no pregnancy! Second, the lining of the uterus is altered by the Pill’s progestogen so that it is less suitable for a fertilised egg to implant and develop. Third, progestogen causes the mucus produced in the cervix to become thicker and stickier, making it harder for sperm to get through.

When I was working at Sydney University in the early 1950s and my colleagues and I read that overseas researchers were studying the use of oral hormones to prevent ovulation, we thought it a very cheeky attempt to interfere with nature, and that it would neither work nor ‘catch on’. How wrong we were! But you must admit that hormonal contraception very cleverly uses knowledge of reproductive physiology.

How reliable is the Pill?

If it’s taken according to instructions, the combined Pill is more than 99 per cent effective in preventing pregnancy. Most accidental pregnancies on the Pill are the result of mistakes in use.

How is the Pill used?

All combined Pills are taken for three weeks, followed by a week off. These four weeks are called a Pill ‘cycle’. After the week off, the Pill is taken for another cycle of three weeks on and one week off, and so on. Each pack of the Pill contains enough tablets for one cycle.

Most Pills come in both 21- and 28-day (or ED, standing for Every Day) packs. The 28-day packs contain 7 ‘dummy’ tablets that are taken when women using the 21-day packs would be having their week off. The dummies are a different colour to distinguish them from the hormone tablets. Many women prefer the 28-day packs, finding it easier to remember when to start a new cycle if there is no break in taking the tablets. Whether you are using the 21-day or 28-day pack, you will be taking cycles of 21 hormone tablets followed by 7 days of no hormones.

What is the reason for the ‘week off?

When the Pill was first devised it was intended to be taken continuously. With no fall in hormone levels, the endometrium wouldn’t die and be shed. It was expected (by the men who designed the Pill) that women would be pleased not to have regular vaginal bleeding. However, many women felt ‘wrong’ without periods. What’s more, since missed periods have always been associated with pregnancy, many women couldn’t feel sure that the Pill had ‘worked’. The missed period was particularly confusing with the early higher dose Pills, which often caused side-effects (such as nausea and breast enlargement) that were just like the symptoms of early pregnancy.

Studies showed that contraception was no less effective if a break of no more than 7 days was taken between courses of hormones that lasted no less than 21 days. It was decided that the Pill would be more acceptable if there was a short break between courses. During the break the fall in blood hormones results in some bleeding resembling menstruation (called ‘withdrawal bleeding’), usually starting 24-72 hours after the last hormone tablet is taken. It is usually shorter and lighter, with less bright bleeding than your natural period.

The decision to use the ‘three weeks on, one week off scheme for taking the Pill was quite arbitrary. It fits in with most people’s idea that vaginal bleeding about every four weeks is ‘normal’, provides regular evidence that there’s no pregnancy, and Pills for a four-week cycle could be packaged on a convenient-sized card. However, it could have been 47 days on and three days off, or whatever you like.

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