New techniques have been developed to enhance or reduce the chances of conception. Social conventions and governing laws have developed far slower than this new technology, leading to controversy about moral, ethical, and legal grounds for the uses of such technologies.
The separation of intercourse from pregnancy uses methods blocking one of the three stages of reproduction"
- release and transport of gametes
- fertilization
- implantation
Effectiveness
Various contraceptive methods have been developed; none of which is 100% successful at preventing pregnancy or the transmission of STDs. Abstinence is the only completely effective method.
Methods
Physical prevention (most effective) include vasectomy and tubal ligation. Vasectomy: the vas deferens connecting the testes with the urethra is cut and sealed to prevent the transport of sperm. Tubal ligation: the oviduct is cut and ends tied off to prevent eggs from reaching the uterus.
Major events in a vasectomy. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
Oral contraceptives (birth control pills) usually contain a combination of hormones that prevent release of FSH and LH, inhibiting development of the follicle so that no oocytes are released. Time-release capsules (Norplant) can be implanted under the skin and offer long-term suppression of ovulation. RU-486, the so-called morning after pill, interferes with implantation of the blastula into the uterine wall. Its use as a contraceptive is very controversial.
Barrier methods employ physical (condom, diaphragm) or chemical (spermacides) means to separate the sperm from the egg. Male condoms are fitted over the erect penis; female condoms are placed inside the vagina. Only latex condoms prevent the spread of STDs. Diaphragms cap the cervix and block passage of the sperm into the uterus. Spermicidal jellies or foams kill sperm on contact and must be placed in the vagina prior to intercourse.
Reproductive Technologies Can Enhance Fertility
About 1 in 6 couples is infertile due to physical or physiological conditions preventing gamete production, implantation, or fertilization. Blocked oviducts (often from untreated STDs) are the leading cause of infertility in females. Low sperm count, low motility, or blocked ducts are common causes of male infertility.
Hormone therapy can cause increased egg production. Surgery can open blocked ducts. About 40 of the cases are due to male problems, 40 due to female problems and the remaining 20% are caused by some unknown agent(s). In vitro fertilization (test-tube babies) is a widely used technique to aid infertile couples.
Information provided by: http://gened.emc.maricopa.edu