In 1960, the U.S. Food and Drug Administration (FDA) authorized birth control in the form of an oral contraceptive for women in order to be used as a way to prevent pregnancy. Over 16 million U.S. women use birth control, according to pregnancy-info.net. There are some instances in which women on low dose birth control have become pregnant. Some of the low dose pills on the market are Micrette, YAZ, Alesse, Lybrel, LoEstrin1/20, Yasmin, Seasonale, Seasonique and Lo/Ovral; containing between 20 and 35 mcg (microgram) of estrogen and progestin, according to Health.com.
How Birth Control Works
Birth control pills are comprised of two artificial hormones that are able to hinder ovulation (release of an egg each month); progesterone and estrogen, according to healthywomen.org. The natural cycle of ovulation begins at the start of every menstrual cycle. First, estrogen levels increase for about 14 days and cause the walls of the uterus to thicken in order to be able to maintain the egg when it arrives. When estrogen levels reach its climax, the egg is released and sent to the uterus. The levels of the hormone progesterone rises, also thickening the lining of the uterus in preparation for when it becomes implanted. Essentially, birth control is able to maintain the hormones at a certain level in order to trick the body into not releasing a healthy egg to be fertilized. The consistent thick walls of the uterus prevent sperm from reaching the egg, as well.
In instances where women have been on a low dose birth control and have become pregnant, it may be because the dosage was too low for their particular body, rendering the oral contraceptive ineffective. The common pill dose is, for the most part, the proper amount to work effectively; however, it is not enough for all, reports epidemiologist Victoria Holt, who led a study on factors that can cause pregnancy while on the pill.
Switching Birth Controls
When switching from one birth control to another, it also leaves a window of an increased risk to become pregnant. A woman needs time for her body to adjust accordingly to the new drug, in order for it to work properly.
Birth Control Schedule
Women who have trouble taking birth control pills on a consistent, regular basis; will increase their chances of becoming pregnant from 0.1 to 5 percent, states LaborOfLove.com. Missing a pill, failing to take the pill at the same time each day, or starting the pill late; all escalate the chances of a woman becoming pregnant while taking oral contraceptives.
Some factors can reduce the impact of low dose birth control pills. Taking other drugs including seizure medications (phenytoin, carbamazepine, primidone, phenobarbital, topiramate, oxcarbazepine, barbiturates), tuberculosis medication (rifampin), an antifungal drug (griseofulvin), bronchodilators (theoyphylline) and St. John's wort, according to healthywomen.org, can make the low dose pill less effective. Talk with your doctor about whether or not any prescribed medications might lower the effectiveness of the birth control pill.
If a woman immediately throws up after taking the oral contraceptive, it renders the medication ineffective. It takes about 30 minutes for the birth control to enter the bloodstream. A heavy sickness that causes vomiting and diarrhea will cause the birth control to leave the body before it has time to be absorbed properly.
Women who are considered overweight have a 60 to 70 percent higher risk of becoming pregnant, even though they are taking birth control, reports Holt. While the exact reason the oral contraceptive is not as effective on larger women as it is on smaller women is not clear. Overweight women have a high metabolism rate, which may lead to decreasing the length the medication is supposed to last. Also, an increase in weight leads to an increase in liver enzymes, which end up ridding drugs from the body. Another possible factor is that the estrogen and progesterone are possibly more prone to be caught in body fat in overweight women, instead of moving freely around in the bloodstream, claims Holt.
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