什么是避孕

人类生理学术语，指有意防止怀孕的措施。最常见的方法是绝育术，手术简单，但有效率超过99%。许多避孕方法会损害健康；最安全的方法包括使用阻隔式避孕器以及危险期推算法。避孕药是利用雌激素或孕酮来抑制卵巢排卵。「事後丸」是含有大剂量的雌激素和孕激素或仅有後者的药片，是在性交後避孕的方法之一。口服避孕药最严重的副作用就是可能会造成血栓疾病。子宫内避孕器（IUD）是植入子宫内的塑胶或金属器械，引起子宫内膜发生轻度炎症，从而抑制了排卵，防止了受精，或防止了受精卵着床。1970年代和1980年代，有的避孕器被禁止贩卖，因为发现它们的副作用是高危险性的骨盆炎症、异位妊娠和自发性败血性流产等疾病。保险套、阴道海绵条、阴道隔膜和子宫帽等阻隔式避孕器，以阻止精入进入子宫。保险套还可以预防性传染病（STD）的流传。杀精剂可协助防止精子越过这些阻隔，因此可提高这些器械的效力使之接近100%。危险期推算法是估算排卵期，这样就可在这每月中妇女最易受孕的大约六天内避免性交。除记录个人月经周期外，还可每日测体温，因为基础体温升高时就意味排卵。这两种方法还常再结合第三种方法，即观察子宫颈黏液的变化，这可预示易孕时期。正在实验中且使用较少的节育法还有男性口服避孕药。

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.