BIRTH CONTROL

HEALTH INFO

How do Contraceptives Work?

Contraceptives are methods of preventing or ending pregnancy, also referred to as “birth control,”and work in three ways:

Prevent Fertilization. Fertilization is the union of a man’s sperm and woman’s egg. Some contraceptives create a physical barrier to block sperm from reaching an egg. Male and female condoms and the diaphragm are examples.
Make the Uterus Hostile to Implantation.* Contraceptives can attempt to prevent a baby from implanting in the mother’s uterus after fertilization by creating a hostile environment. Intra-uterine Devices (IUDs) and chemical methods are in this category.
Alter Body Chemistry.* Typically referred to as “hormonal” contraceptives, synthetic steroids like the pill mimic hormones to prevent pregnancy by changing a woman’s body chemistry, which has three impacts:

Prevent ovulation, the release of the egg each menstrual cycle.
Produce less and thicker mucus in the cervix so that sperm cannot easily enter the uterus.
Thin the lining of the uterus, making it more difficult for a fertilized egg to implant.

Chemical contraceptives include the oral birth control pill, Depo-Provera injection, patch, and implant. Chemical methods provide no protection against STDs and can actually increase your risk of getting an STD by making your reproductive tract more vulnerable to infection. [See Birth Control and STDs]

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*Note: Methods in categories 2 and 3 can be ‘abortifacient,’ meaning that they end the life of a developing baby.

More Birth Control Information

A woman tends to choose birth control based on what she considers to be the most convenient and effective method for her. However, it’s important to weigh carefully the risks and side effects of each method.

Using contraceptives cannot guarantee the prevention of pregnancy. Contraceptives were used during the month of conception in 48% of unintended pregnancies.1

Male Condom

82-98% effective at preventing pregnancy2
60-79% effective at preventing STDs3

Female Condom

79-95% effective at preventing pregnancy4

Diaphragm or Cervical cap

84-94% effective at preventing pregnancy5
Increases risk of vaginal infection, making a woman more vulnerable to contracting STDs6

Birth Control Pill

91-99% effective at preventing or terminating pregnancy7
Makes a woman’s reproductive tract more suseptible to infection, increasing her risk of contracting an STD by 30%.8
Multiplies risk of heart attack by up to 2.3 and risk of stroke by up to 2.29
Increases risk of glioma, a rare brain cancer, by 50% with short-term use. Five years of birth control pill use doubles a woman’s risk.10
Listed by the World Health Organization as a Class 1 carcinogen for increased risk of breast and liver cancers11
For nearsighted women, six months of using the pill has been shown to increase nearsightedness 2 or 3 times.12

Depo-Provera Shot

94-99% effective at preventing pregnancy13
Associated with decreased bone mineral density, weight gain and increased risk of breast cancer14

The Patch

91-99% effective at preventing pregnancy15
Multiplies risk of stroke by 3.216

Implant / IUD

99% effective at preventing or terminating pregnancy17
47% of implant users experience adverse effects, including severe acne and weight gain18

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Finer LB, Henshaw SK (2006). Disparities in rates of unintended pregnancy in the United States, 1994 and 2001. Perspect Sex Repro H, 38(2): 90-6.