Hormonal contraceptives primarily alter the reproductive hormones that are released during the menstrual cycle. Therefore in order to understand how they prevent pregnancy, it is important to understand the normal menstrual cycle.
The menstrual cycle is counted from the first day of menstrual bleeding, with that being day 1 of the cycle. The cycle in general lasts an average of 28 days (day 1 of one cycle to day 1 of the next cycle) but this duration may vary from once cycle to another. This variation forms the basis for the description of menstrual cycles are regular or irregular. In general, many women experience variations of a few days between the longest and shortest cycle. However, if this variation is more than 7 days, then they cycles are said to be irregular. The actual duration of menstruation (bleeding) also varies, ranging from 2 to 7 days. Most discussions of the menstrual cycle are based on a 28-day cycle.
The menstrual cycle is divided into 3 broad phases;
The follicular phase (day 1 to 13) – during this phase, the growth of a follicle in the ovary is stimulated by one of the reproductive hormones, referred to as follicle-stimulating hormone (FSH). This follicle once mature is the one that releases the ovum (egg). The FSH also stimulates the growth of the lining of the uterus (womb) in preparation for pregnancy.
Ovulation phase (day 13 to 16) – during this phase, another reproductive hormone called luteinizing hormone (LH) triggers the release of the ovum from the mature follicle. This release is what is referred to as ovulation. Once released, the ovum travels into the fallopian tubes, where if sperms are present, fertilization will take place.
The Luteal phase (day 16 to 28) – at this stage, the 3rd reproductive hormone, progesterone is released. If the ovum was fertilized, the progesterone continues to be produced to sustain the pregnancy. If there was no fertilization, progesterone production of progesterone ceases and the lining of the uterus is shed as menstrual blood.
The hormonal contraceptives usually have progesterone only or are combined having both progesterone and estrogen. Examples of the hormonal contraceptives are as follows:
Progesterone only contraceptives – pills (e.g. microlut), implants (e.g. Norplant, Jadelle, Implanon), Injectables (e.g. Depo)
Combined oral contraceptives - These contain both progesterone and estrogen e.g. femiplan,
These contraceptives work as follows:
They reduce the production of FSH and LH. This means that the follicle in the ovary does not develop and ovulation does not occur (no ovum is released).
They cause thickening of the mucus produced by the cervix, which makes prevents or makes the penetration of sperm into the uterus difficult.
They prevent the development of the lining of the uterus, hence making it less conducive for implantation of an ovum.
They slow down the transportation of the ovum in the fallopian tubes. This means that by the time the ovum gets to the fallopian tubes, it is unlikely to find living sperms.
The most commonly used are the male and female condom. As the name suggests, these provide a physically bar the sperms from entering the female reproductive tract (if used correctly). The female condom is especially tricky to use and needs to be inserted into the vagina before sexual intercourse.
Intrauterine devices (coils)
These are small T-shaped devices that are inserted into the uterus, and may be plain copper-based or it may be lined with the hormone progesterone (which works in the same way outlined above). The device prevents implantation of ovum in the uterus, and also thickens the cervical mucus which interrupts movement of sperm.
This is a permanent method of contraception, which involves cutting and tying off the cut ends of the fallopian tubes (in females) and the vas deferens (in males). In males, vasectomy prevents the transportation of sperm from the testes, and hence the ejaculate does not contain any sperm. In females, the tubal ligation prevents the ovum from getting to the uterus, and the sperm from reaching the ovum. Once question commonly raised is where then do the sperms and the ova go once produced? These are readily broken down and reabsorbed by the body without any adverse effect.