Conception occurs when sperm are deposited in the vagina during intercourse. The sperm swim through the neck of the womb (cervix), up through the womb itself (the uterus) and along the fallopian tubes leading off the womb. If the woman has recently produced an egg from her ovary, this travels down along one of the fallopian tubes and therefore meets the sperm coming in the opposite direction. Production of an egg (ovulation) usually occurs about 14 days before the next period is due. One of the sperm fertilises the egg, which then travels down the remainder of the tube, and into the cavity of the womb where it sticks itself (implants) into the lining of the womb. This journey usually takes about 3 days. Once it is 'bedded down' into the womb lining it begins to receive nourishment from the womb and gradually develops into a foetus. Anything which interferes with one or more parts of this process will act as a possible contraceptive and it is on this basis that contraceptives work.
The rhythm method
The rhythm method of contraception is based on the fact that if intercourse only takes place at a time when ovulation is unlikely to have occurred, then there will be no egg available for the sperm to fertilise. This time in a woman's cycle is sometimes referred to as the 'safe period'. As mentioned above, ovulation usually takes place 14 days before the next period is due. This means that for a woman who has a normal 28 day cycle (i.e. 28 days between the start of one period and the first day of the next one) ovulation will take place on the 14th day (day one being the first day of her last period). However, if her cycle is normally 34 days long, ovulation will probably take place on the 20th day of her cycle.
Another factor in the calculation of the 'safe period' is the fact that sperm are capable of surviving inside the fallopian tube for about 4 or 5 days and the egg is able to be fertilised for 1 or 2 days after ovulation. This means that if a woman normally ovulates on day 14 of her cycle, sperm from intercourse on day 10 could still be viable on the 14th day and an egg released on day 14 could still be capable of fertilisation on day 16. Therefore, it follows that in a regular 28 day cycle the 'safe' period is from day 1 to day 9 and from day 17 to day 28. If the cycle is irregular it makes calculation more difficult although there are some body changes which women can be taught to recognise to help them to tell when they are around the time of ovulation.
The advantage of this method is that it is very natural and does not involve taking any form of drug but the disadvantage is that ovulation can be difficult to predict resulting in a failure rate of about 5% unless the couple are very disciplined in its use.
This method involves the man withdrawing his penis from the vagina just before ejaculation. The only advantage of this method is that it does not involve any medication but its main disadvantage is its unreliability since it depends on self-discipline and also some sperm may be produced before ejaculation, or may be spilled onto the opening of the vagina and still manage to swim far enough to fertilise an egg.
The sheath (condom)
There are now male and female condoms. The male condom is placed over the erect penis whereas the female condom is placed inside the vagina before intercourse. They act as a barrier preventing the sperm from entering the vagina. Often the condom is lubricated with a spermicide (a substance designed to kill sperm) making it more effective. Advantages of this method include the fact that it only needs to be used at the time ie it is spontaneous and that it reduces the risk of the transmission of sexually transmitted diseases such as AIDS. As a result it is recommended that this method is used in addition to other methods if there is a risk of disease transmission eg in casual relationships. If used correctly the male condom has a 98% effective rate and the female condom a 95% effective rate.
The main disadvantage is the risk of the condom bursting or falling off during intercourse. It is less reliable than most other methods although its reliability can be increased if the woman inserts a spermicide into the vagina while the man is putting on the condom.
The diaphragm or cap
The diaphragm/cap is another type of barrier method. There are caps which fit over the neck of the womb (the cervix), but the more commonly used device is a circular diaphragm which fits inside the vagina and is inserted before intercourse after the woman has covered both sides with spermicidal gel or cream. The diaphragm is then left inside the vagina for at least six hours after intercourse to allow the spermicide to work. The correct size of diaphragm has to be used and the woman must be instructed in how to insert it correctly. For this reason she needs to visit her doctor or family planning clinic before she is able to use this method. The advantage of this method is that it can be inserted before any sexual activity occurs and is more reliable than the condom. However, the disadvantages include the lack of spontaneity and the fact that the woman needs to be well motivated in its use.
Intra-uterine contraceptive devices (IUCDs)
These are often referred to as 'coils' and these days are usually made of plastic in a shape which fits inside the cavity of the womb with two nylon threads at the bottom. These are left protruding through the neck of the womb to enable the coil to be removed by the doctor who pulls on the threads. Most types also have a small amount of copper on them which makes them more effective. They are thought to work by preventing the fertilised egg from implanting on the lining of the womb but there may be other effects involved as well. They need to be fitted by a doctor and most types need changing every 3-5 years. The advantages are the fact that the woman does not need to think about it other than to remember to have it changed, although some women do like to learn how to check that it is still in the right place. It is also instantly reversible since the woman is fertile as soon as the coil has been removed. Disadvantages are that it may make some women's periods heavier and there is a slightly higher risk of the woman getting an infection in her fallopian tubes or an ectopic pregnancy (a pregnancy in the tube) thus possibly affecting future fertility. It has a 1-2% failure rate.
There is now an interuterine system called Mirena. This flexible plastic device contains the hormone Progesterone which is released at a slow consistent rate. It is more than 99% efective. It has also been used for women with heavy periods as it makes the periods lighter by thinning the lining of the womb.
The combined oral contraceptive pill (The pill)
This is called the combined pill because it contains a combination of two female hormones - oestrogen and progesterone. It is usually taken for 21 days each month with a 7 day break (during which the woman has a period) followed by another 21 days of the pill and so on. It works in a variety of ways but the main effect is the prevention of ovulation. Taken correctly it is a very effective method having about a 0.5% failure rate but like any drug it is not without side effects and a certain amount of risk to health although for most women these side effects and risks are very small. One of the most serious risks (although rare) is of thrombosis (formation of a blood clot inside a blood vessel). As a result there are some women who should not take the pill and others who need careful medical advice before taking it.
However for most women it is a very safe, effective method of contraception.
Advantages of the pill are its effectiveness and general safety whereas disadvantages include occasional side-effects such as weight gain, acne, nausea and reduction in sex drive and the fact that the woman has to remember to take the pill within the same 12 hour time period each day. Also remember that other medications, such as antibiotics, may interfere with the effectivenss of the pill so you should discuss this with your physician if being prescribed any other medications.
The Progesterone only pill (mini-pill)
Instead of containing two hormones the progesterone only pill contains just progesterone. It acts by making the mucus at the entrance to the womb thicker thereby acting as a barrier to the movement of sperm into the womb. Other differences from the combined pill include the fact that it is taken every single day without a break and that it must be taken within the same 3 hour time band each day. Advantages are that it is physically safer for the woman than the combined pill, has fewer side-effects and can be taken whilst breast-feeding. The disadvantages are that it is less effective than the normal pill, having a failure rate of about 2-3%, and can upset the period pattern.
Depot hormone injections ('the injection')
This method involves an injection of progesterone every 10-12 weeks which acts as a long-acting contraceptive. Advantages are that the woman needs only to remember to have the injection and can forget about contraception in between and that it is physically safe and does not prevent breast feeding since it contains no oestrogen and it is reported to have a low failure rate. Disadvantages are that it can cause a disturbed menstrual pattern, and possible weight gain and that any side effects cannot be stopped immediately since the woman has to wait until the injection wears off. Another possible problem is that it can take many months for fertility to return once the injections have been stopped.
Emergency ('morning after') contraception
There are two main methods of emergency contraception. The so-called morning-after pill can, in fact, be started within 72 hours of unprotected intercourse and usually consists of four pills in total: two taken as soon as possible after the event and two taken twelve hours later. The pills are high dose combined oral contraceptive pills. Another method of emergency contraception is the insertion of a coil (IUCD) within 5 days of unprotected intercourse. This has the added advantage that it also provides a method of long-term contraception at the same time. These methods both have a failure rate of about 1%.
Male sterilisation (vasectomy): This is usually performed under local anaesthetic and is a simple procedure where a small cut is made either side of the top of the scrotum. The spermatic cord which carries the sperm is identified, cut and sutured to prevent it from re-joining. The cuts are then sutured. Usually the individual is fit to return to work after a day or two. The man must then provide semen samples until they are found to be clear of sperm. It is only then that the couple can discontinue other methods of contraception.
Female sterilisation: This is performed under a general anaesthetic either through a laparoscope (a special telescope inserted into the abdomen) or a small cut into the abdomen. The fallopian tubes are found, cut and sutured or clipped with specially designed clips.
The most important aspect of choosing sterilisation as a method of contraception is that it must be considered to be irreversible ie it must be thought of as a permanent procedure since reversal of sterilisation is a difficult operation and generally has a low success rate in terms of a resulting pregnancy.
In October 1995 there was a 'pill scare' which was based on some findings that certain pills (those containing the types of progesterone called gestodene or desogestrel) possibly doubled the risk of a woman developing venous thromboembolism (clots in the veins of the legs). This seemed to be especially true for certain 'high risk' women such as those who are significantly overweight or who have a close family history of thromboembolism.
However this must be weighed against the evidence that these same pills may be safer in terms of heart attack risk than pills without these hormones. Also the risk of thromboembolism in a woman who is pregnant is double that of a woman on these pills and so women who were so alarmed at the scare that they stopped these types of pill and became pregnant as a result, in fact put themselves at a greater risk than if they had continued taking the pills.
A fairly recent development is an implant in the form of several rods containing progesterone which is placed under the skin of the upper arm. This is called Norplant and is effective for up to 5 years but is removable before this time if a woman wishes to become pregnant. Its most troublesome side-effect is irregular bleeding.
New coils now exist which contain a progesterone which is slowly released into the woman's womb cavity. The advantage over other types of intra-uterine contraceptive device is that it may make periods lighter and less painful and may protect against ectopic pregnancies. However it can be more difficult to insert but lasts up to 3 years.
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Last updated 15 November 2011