Mechanisms of action and terminology
The function of birth control can be classified by the stage of reproduction during which it is active. A form of birth control which prevents the sperm from fertilizing the egg is a contraceptive agent. A form of birth control which acts after fertilization to prevent or interrupt the implantation of the embryo into the uterine lining is a contragestive agent. After implantation has occurred, an agent which ends gestation by terminating the pregnancy is an abortifacient.
The term contraception is a contraction of contra, which means against, and the word conception, meaning fertilization. The word contragestion is likewise a combination of contra and gestation. French scientist Étienne-Émile Baulieu coined the word in 1985 because he felt that there was a need for a technical term to describe the prevention of implantation, which did not fit the traditional definitions of either contraception or abortion. Since 18 U.S. states define pregnancy as beginning at conception, describing methods of birth control in terms of their potential means of action allows one to be technically accurate while using language that is neutral with regard to the abortifacient versus contraceptive controversy.
These mechanisms of action are not always mutually exclusive. One substance or device can have more than one potential effect depending upon when it is used. For example, while mifepristone is best known as an abortifacient, it can also function as a contragestive agent. Likewise, the IUD can be used as a contraceptive or a contragestive depending upon when it is inserted.
Contraception
Contraception include barrier methods, such as condoms or diaphragm, injectable contraceptives, and hormonal contraception, also known as oral contraception. The most common methods of hormonal contraception include the combined oral contraceptive pill and the minipill. Hormonal emergency contraception can be both contraceptive and contragestive.
Contragestion
Contragestives include intrauterine devices placed inside the uterus and some forms of hormonal "emergency contraception".
An intrauterine device.
Sterilization
Surgical sterilization is available in the form of tubal ligation for women and vasectomy for men. Although sterilization is considered a permanent procedure due to the uncertainty of reversal possibility, it is possible to attempt a tubal reversal to reconnect the Fallopian tubes in females or a vasectomy reversal to reconnect the vasa deferentia in males. The rate of success depends on the type of sterilization that was originally performed and damage done to the tubes as well as the patient's age.
Behavioral methods
Behavioral methods involve regulating the timing or methods of intercourse to prevent the introduction of sperm into the female reproductive tract, either altogether or when an egg may be present.
Lactational
From ancient times women tried to extend breastfeeding in order to avoid a new pregnancy. The lactational amenorrhea method, or LAM, gives guidelines for determining the length of a woman's period of breastfeeding infertility.
Fertility awareness
Symptoms-based methods of fertility awareness involve a woman's observation and charting of her body's fertility signs, to determine the fertile and infertile phases of her cycle. Charting may be done by hand or with the assistance of fertility monitors. Most methods track one or more of the three primary fertility signs: changes in basal body temperature, in cervical mucus, and in cervical position. If a woman tracks both basal body temperature and another primary sign, the method is referred to as symptothermal. Other bodily cues such as mittelschmerz are considered secondary indicators.
Calendar-based methods such as the rhythm method and Standard Days Method estimate the likelihood of fertility based on the length of past menstrual cycles. To avoid pregnancy with fertility awareness, unprotected sex is restricted to the least fertile period. During the most fertile period, barrier methods may be availed, or she may abstain from intercourse.
The term natural family planning (NFP) is sometimes used to refer to any use of fertility awareness methods. However, this term specifically refers to the practices that are permitted by the Roman Catholic Church — breastfeeding infertility for example. FA methods may be used by NFP users to identify these fertile times.
Coitus interruptus
Coitus interruptus (literally "interrupted sexual intercourse"), also known as the withdrawal or pull-out method, is the practice of ending sexual intercourse ("pulling out") before ejaculation. The main risk of coitus interruptus is that the man may not perform the maneuver correctly, or may not perform the maneuver in a timely manner. Although concern has been raised about the risk of pregnancy from sperm in pre-ejaculate, several small studies have failed to find any viable sperm in the fluid.
Avoiding semen near vagina
Non-penetrative sex is used to avoid pregnancy, but pregnancy can still occur with Intercrural sex and other forms of penis-near-vagina sex (genital rubbing, and the penis exiting from anal intercourse) where semen can be deposited near the entrance to the vagina and can itself travel along the vagina's lubricating fluids.
Sexual abstinence
Though some groups advocate total sexual abstinence, by which they mean the avoidance of all sexual activity, in the context of birth control the term usually means abstinence from vaginally penetrative sexual activity.
Abstinence is 100% effective in preventing pregnancy; however, not everyone who intends to be abstinent refrains from all sexual activity, and in many populations there is a significant risk of pregnancy from nonconsensual sex. As a public health measure, it is estimated that the protection provided by abstinence may be similar to that of condoms. Some authorities recommend that those using abstinence as a primary method have backup method(s) available (such as condoms or emergency contraceptive pills).
Abortion
Surgical abortion methods include suction-aspiration abortion (used in the first trimester) or dilation and evacuation (used in the second trimester). Medical abortion methods involve the use of medication that is swallowed or inserted vaginally to induce abortion. Medical abortion can be used if the length of gestation has not exceeded 8 weeks. Some herbs are considered abortifacient.
Methods in development
For females
Praneem is a polyherbal vaginal tablet being studied in India as a spermicide, and a microbicide active against HIV.
BufferGel is a spermicidal gel being studied as a microbicide active against HIV.
Duet is a disposable diaphragm in development that will be pre-filled with BufferGel. It is designed to deliver microbicide to both the cervix and vagina. Unlike currently available diaphragms, the Duet will be manufactured in only one size and will not require a prescription, fitting, or a visit to a doctor.
The SILCS diaphragm is a silicone barrier that is still in clinical testing. It has a finger cup molded on one end for easy removal. Unlike currently available diaphragms, the SILCS diaphragm will be available in only one size.
A longer acting vaginal ring is being developed that releases both estrogen and progesterone, and is effective for over 12 months.
Two types of progestogen-only vaginal rings are being developed. Progestogen-only products may be particularly useful for women who are breastfeeding. The rings may be used for four months at a time.
A progesterone-only contraceptive is being developed that would be sprayed onto the skin once a day.
Quinacrine sterilization (non-surgical) and the Adiana procedure (similar to Essure) are two permanent methods of birth control being developed.
For males
Other than condoms and withdrawal, there is currently only one common method of birth control available. This option is undergoing a vasectomy, a minor surgical procedure wherein the vasa deferentia of a man are severed, and then tied/sealed in a manner which prevents sperm from entering the seminal stream (ejaculate). Several methods are in research and development:
As of 2007, a chemical called Adjudin was in Phase II human trials as a male oral contraceptive.
Reversible inhibition of sperm under guidance is an experimental injection into the vas deferens that coats the walls of the vas with a spermicidal substance. The method can potentially be reversed by washing out the vas deferens with a second injection.
Experiments in vas-occlusive contraception involve an implant placed in the vasa deferentia.
Experiments in heat-based contraception involve heating the testicles to a high temperature for a short period of time.