Illustration of<unk> <unk> s primarily work by preventing fertilization. The progestogen released from hormonal<unk> s mainly works by thickening the cervical mucus, preventing sperm from reaching the fallopian tubes.<unk> s may also function by preventing ovulation from occurring but this only occurs partially. Copper<unk> s do not contain any hormones, but release copper ions, which are toxic to sperm. They also cause the uterus and fallopian tubes to produce a fluid that contains white blood cells, copper ions, enzymes, and prostaglandins, which is also toxic to sperm. The very high effectiveness of copper-containing<unk> s as emergency contraceptives implies they may also act by preventing implantation of the blastocyst.Copper-releasing IUCsWhen used as a regular or emergency method of contraception, copper-releasing IUCs act primarily to prevent fertilization. Emergency insertion of a copper IUC is significantly more effective than the use of ECPs, reducing the risk of pregnancy following unprotected intercourse by more than 99%.2,3 This very high level of effectiveness implies that emergency insertion of a copper IUC must prevent some pregnancies after fertilization.Emergency contraceptive pillsTo make an informed choice, women must know that ECPs—like the birth control pill, patch, ring, shot, and implant,76and even like breastfeeding77—prevent pregnancy primarily by delaying or inhibiting ovulation and inhibiting fertilization, but may at times inhibit implantation of a fertilized egg in the endometrium. However, women should also be informed that the best available evidence indicates that ECPs prevent pregnancy by mechanisms that do not involve interference with post-fertilization events.ECPs do not cause abortion78 or harm an established pregnancy. Pregnancy begins with implantation according to medical authorities such as the US FDA, the National Institutes of Health79 and the American College of Obstetricians and Gynecologists (ACOG).80Ulipristal acetate (UPA). One study has demonstrated that UP can delay ovulation.81... Another study found that UPA altered the endometrium, but whether this change would inhibit implantation is unknown.82p. 122:Progestin-only emergency contraceptive pills. Early treatment with ECPs containing only the progestin levonorgestrel has been show to impair the ovulatory process and luteal function.83–87p. 123:Combined emergency contraceptive pills. Several clinical studies have shown that combined ECPs containing ethinyl estradiol and levonorgestrel can inhibit or delay ovulation.107–110In 2002, a judicial review ruled that pregnancy begins at implantation, not fertilisation.8 The possible mechanisms of action should be explained to the patient as some methods may not be acceptable, depending on individual beliefs about the onset of pregnancy and abortion.Copper-bearing<unk>  (Cu-IUD). Copper is toxic to the ovum and sperm and thus the copper-bearing<unk>  (Cu-IUD) is effective immediately after insertion and works primarily by inhibiting fertilisation.9–11 A systematic review on mechanisms of action of<unk> s showed that both pre- and postfertilisation effects contribute to efficacy.11If fertilisation has already occurred, it is accepted that there is an anti-implantation effect,12,13Levonorgestrel (LNG). The precise mode of action of levonorgestrel (LNG) is incompletely understood but it is thought to work primarily by inhibition of ovulation.16,17Ulipristal acetate (UPA). UPA's primary mechanism of action is thought to be inhibition or delay of ovulation.2
Intrauterine device
Contraceptive implant
Male contraceptive
Fertility medication
Injectable birth control
Oral contraceptive pill
Combined hormonal contraception
Spermicide