什麼是避孕

人類生理學術語，指有意防止懷孕的措施。最常見的方法是絕育術，手術簡單，但有效率超過99%。許多避孕方法會損害健康；最安全的方法包括使用阻隔式避孕器以及危險期推算法。避孕藥是利用雌激素或孕酮來抑制卵巢排卵。「事後丸」是含有大劑量的雌激素和孕激素或僅有後者的藥片，是在性交後避孕的方法之一。口服避孕藥最嚴重的副作用就是可能會造成血栓疾病。子宮內避孕器（IUD）是植入子宮內的塑膠或金屬器械，引起子宮內膜發生輕度炎症，從而抑制了排卵，防止了受精，或防止了受精卵着牀。1970年代和1980年代，有的避孕器被禁止販賣，因爲發現它們的副作用是高危險性的骨盆炎症、異位妊娠和自發性敗血性流產等疾病。保險套、陰道海綿條、陰道隔膜和子宮帽等阻隔式避孕器，以阻止精入進入子宮。保險套還可以預防性傳染病（STD）的流傳。殺精劑可協助防止精子越過這些阻隔，因此可提高這些器械的效力使之接近100%。危險期推算法是估算排卵期，這樣就可在這每月中婦女最易受孕的大約六天內避免性交。除記錄個人月經週期外，還可每日測體溫，因爲基礎體溫升高時就意味排卵。這兩種方法還常再結合第三種方法，即觀察子宮頸黏液的變化，這可預示易孕時期。正在實驗中且使用較少的節育法還有男性口服避孕藥。

contraception

Birth control by prevention of conception or impregnation. The most common method is sterilization. The most effective temporary methods are nearly 99% effective if used consistently and correctly. Many methods carry health risks; barrier devices and avoidance of intercourse during the most fertile period are safest. Hormonal contraceptives use estrogen and/or progesterone to inhibit ovulation. The “morning-after pill” (high-dose hormones) is effective even after intercourse. The most serious side effect of oral contraceptives is the risk of blood-clotting disorders. Intrauterine devices (IUDs) are placed inside the uterus and appear to cause a mild endometrial inflammation that either inhibits fertilization or prevent a fertilized egg from implanting. Certain types were taken off the market in the 1970s and '80s when it was found that their side effects included a high incidence of pelvic inflammatory disease, ectopic pregnancies, and spontaneous septic abortions. Barrier devices, such as condoms, diaphragms, cervical caps, female condoms (vaginal pouches), and vaginal sponges, prevent sperm from entering the uterus. Condoms also prevent sexually transmitted diseases. Used with spermicides, condoms are nearly 100% effective. Fertility awareness techniques have evolved from keeping track of the menstrual cycle (the so-called “rhythm method”; see menstruation) to avoid intercourse around the time of ovulation; tracking body temperature and cervical mucus consistency can raise effectiveness to more than 80%. Experimental forms of birth control include an oral contraceptive for men.