Mears E, Vessey M P, Andolsek L, Oven A
Br Med J. 1969 Jun 21;2(5659):730-4. doi: 10.1136/bmj.2.5659.730.
One hundred and seventy-five women took part in a comparative clinical trial of four progestogen-only oral contraceptives and were followed for either a year or until treatment was discontinued. Megestrol acetate 0.25 mg. was found to be a very ineffective contraceptive, 21 out of 43 women becoming pregnant. One, three, and four pregnancies occurred during treatment with norethisterone acetate 0.3 mg., norgestrel 0.05 mg., and chlormadinone 0.5 mg., respectively, corresponding to pregnancy rates of 4, 9, and 12 per 100 woman-years of use.All three effective progestogens were very much less acceptable than modern low-dose combined oral contraceptives. Discontinuation of treatment for medical reasons (particularly menstrual disturbances) during the course of only one year affected 24% receiving norethisterone acetate, 38% receiving norgestrel, and 46% receiving chlormadinone.
175名女性参与了四种仅含孕激素的口服避孕药的对比临床试验，并随访了一年或直至治疗中断。发现0.25毫克醋酸甲地孕酮是一种非常无效的避孕药，43名女性中有21人怀孕。在使用0.3毫克醋酸炔诺酮、0.05毫克炔诺孕酮和0.5毫克氯地孕酮治疗期间，分别发生了1例、3例和4例妊娠，相当于每100妇女年的妊娠率为4%、9%和12%。所有三种有效的孕激素都远不如现代低剂量复方口服避孕药易于接受。在仅一年的疗程中，因医学原因（特别是月经紊乱）而中断治疗的情况在接受醋酸炔诺酮治疗的患者中占24%，接受炔诺孕酮治疗的患者中占38%，接受氯地孕酮治疗的患者中占46%。
