Methods of birth control in humans
As little as four weeks after giving birth, it is possible though unlikely that a woman may conceive again. Frequent breastfeeding may reduce the chances of conception. Nevertheless, it would be possible to have children at about 1 year intervals. Most people do not want or cannot afford to have as many children as this. All human communities therefore practise some form of birth control to space out births and limit the size of the family.
There are four main groups of birth control methods: natural, mechanical, chemical and surgical.
- Natural methods
- Mechanical methods
- Chemical Methods
- Surgical methods
Pulling out (also known as withdrawal) is a way to prevent pregnancy by keeping semen away from the vagina. So ejaculating away from a vulva or vagina prevents pregnancy.
This is the most obvious way of preventing a pregnancy. This involves a couple avoiding sexual intercourse. In this way sperm cannot come into contact with an egg and fertilisation cannot happen.
If it were possible to know exactly when ovulation occurred, intercourse could be avoided 3-4 days before and 1 day after ovulation. At the moment, however there is no simple reliable way to recognise ovulation though it is usually 12-16 days before the onset of the next menstrual period. By keeping careful records of the intervals between menstrual periods, it is possible to calculate a potentially fertile period of about 10 days in a mid-cycle when sexual intercourse should be avoided if children are not wanted.
On its own, this method is not very reliable but there are some physiological clues that help to make it more accurate. During or soon after ovulation, a woman’s temperature rises by about 0.5∘C. It is reasonable to assume that 1 day after the temperature returns to normal, a woman will be infertile.
A thin rubber sheath is placed on the erect penis before sexual intercourse. The sheath traps the sperm and prevents them from reaching the uterus. It also prevents the transmission of sexually transmitted infections (STIs).
This is a female condom. It is a sheath or pouch, made of polyurethane or rubber, with a flexible ring at each end. The ring at the closed end of the sheath is inserted into the vagina to hold the femidom in place. The ring at the open end is placed outside the vagina. During sexual intercourse, semen is trapped inside the femidom. A femidom reduces the risk of infection by STIs.
A thin rubber disc placed in the vagina before intercourse, covers the cervix and stops sperm entering the uterus. Condoms and diaphragms, used in conjunction with chemicals that immobilise sperm are about 95% effective. However, a diaphragm does not prevent the risk of transmission of STIs.
Intra-uterine device (IUD)
A small T-shaped plastic and copper device, also known as a coil, can be inserted by a doctor or nurse into the wall of the uterus, where it probably prevents implantation of a fertilised ovum. It is about 98% effective but there is a small risk of developing uterine infection, and it does not protect against STIs.
Intra-uterine system (IUS)
This is similar to an IUD; is T-shaped and releases the hormone progestrone slowly over a long period of time (up to 5 years). The hormone prevents ovulation. An IUS does not protect against STIs.
The pill contains chemicals, which have the same effect on the body as the hormones oestrogen and progesterone. When mixed in suitable proportions these hormones suppress ovulation and so prevent conception. The pills need to be taken each day for the 21 days between menstrual periods.
There are many varieties of contraceptive pill in which the relative proportions of oestrogen and progesterone like chemicals vary. They are 99% effective, but long-term use of some types may increase the risk of cancer of the breast and cervix. The pill does not protect against STIs.
Spermicides are chemicals which, though harmless to the tissues, can kill or immobilise sperm. The spermicide, in the form of cream, gel or foam, is placed in the vagina. On their own spermicides are not very reliable but, in conjunction with condoms or diaphragms they are effective.
Vasectomy (Male sterilisation)
This is a simple and a safe surgical operation in which the man’s sperm ducts are cut and the ends sealed. This means that his semen contains the secretions of the prostate gland and seminal vesicle but no sperm, so cannot fertile an ovum. Sexual desire, erection, copulation and ejaculation are quite unaffected.
The testis continues to produce sperm and testosterone. The sperm are removed by white cells as fast as they form. The testosterone ensures that there is no loss of masculinity.
The sperm ducts can be rejoined by surgery but this is not always successful.
Laparotomy (Female sterilisation)
A woman may be sterilised by an operation in which her oviducts are tied, blocked or cut. The ovaries are unaffected. Sexual desire and menstruation continue as before, but sperm can no longer reach the ova. Ova are released but break down in the upper part of the oviduct. The operation cannot be usually reversed.
The use of hormones in fertility and contraception treatments
About 85-90% of couples trying for a baby achieve pregnancy within a year. Those that do not may be sub-fertile or infertile. Female infertility is usually caused by a failure to ovulate or a blockage or distortion of the oviducts. The later can often be corrected by surgery.
Using hormones to improve fertility
Failure to produce ova can be treated with fertility drugs. She is given hormones, including FSH and LH that cause multiple release of eggs. Administration of the drugs is timed to promote ovulation to coincide with copulation.
An artificial insemination procedure uses a thin, flexible tube (catheter) to put sperm into the woman’s reproductive tract , around the same time of ovulation.
If the problem causing the couple’s infertility is in the man (he may not be producing healthy sperms), then sperms from a donor is collected in a clinic, and can be stored at a low temperature for many months or even years. The woman can then attend the clinic and some of the sperms can be place into her reproductive tract.
Prior to insemination the sperm usually are washed and concentrated (placing unwashed sperm directly into the uterus can cause severe cramps). Concentration is accomplished by selectively choosing highly active, healthy sperm that are more capable of fertilizing an egg.
The artificial insemination may be a real help to a couple, as it allows them to have a child that they could not otherwise have.
- The man has to be able to accept that the child is not biologically his.
- When the child grows up, he may want to know who his biological father is. Some people think that the identity of the sperm donor should be given to the child. However, this may cause more problems than it solves. Many sperm donors wish to remain anonymous.
In vitro fertilisation
In vitro means literally “in glass” or, in other words, the fertilisation is allowed to take place in laboratory glassware (hence the term test-tube babies). This technique may be employed where surgery cannot be used to repair blocked oviducts.
In vitro fertilisation has received considerable publicity since the first ‘test-tube’ baby was born in 1978. The woman may be given fertility drugs, which cause her ovaries to release several mature ova simultaneously. These ova are then collected by laproscopy, i.e. they are sucked up in a fine tube inserted through the abdominal wall. The ova are then mixed with the husband’s seminal fluid and watched under the microscope to see if cell division takes place.
One or more of the dividing zygotes are then introduced to the woman’s uterus by means of a tube inserted through the cervix. Usually, only one (or none) of the zygotes develops, though occasionally there are multiple births.
The success rate for in vitro fertilisation is between 12 and 40% depending on how many embryos are transplanted. However, new research using time-lapse photography of the developing IVF embryos during the first few days of life could raise the success rate to up to 78% .