Progestogen only contraceptives
“Progestogen contraceptives occupy a growing position in the control of female fertility. Their advantage is that they do not provoke the feelings of discomfort and the complications associated with the use of the oestroprogestogenic pill and that they can be used during lactation with no risk to the baby. They are the following:
- the minipill, or low-dose pill;
- quarterly injectable contraceptives (Depo-Provera);
- contraceptives in the form of subcutaneous implants (Norplant)”.
“Progestogens act:
- by partially inhibiting ovulation mechanisms; this inhibition is only partial, irregular and varies from one case to the next.
- by making the cervical mucus that is secreted by the cervical glands thicker, more viscous, less abundant. There is no or little sperm penetration through this mucus. Sperm penetration reaches its lowest level three hours after the intake of progestogen, and then rises again. It was long thought that the contraceptive action of the mini-pill was due almost exclusively to this action on the cervical mucus, but it is now acknowledged that some spermatozoa may still succeed in going up from the vagina toward the Fallopian tubes through this barrier. The high frequency of ectopic pregnancies obliges us to acknowledge that, in progestogen “contraception”, fertilization continues to take place;
- by disturbing the motility of the fallopian tubes: the egg transit is made faster, allowing little time for a possible fertilization to take place or for a fertilized egg to develop in the tube.
- and especially by making the uterine mucus non-receptive to the embryo. This effect on the uterine endometrium is predominant. Progestogens interfere with the normal cyclical development of the endometrium, causing its progressive atrophy, in a state of energy privation: under the effects of progestogens, the uterus is to some extent ‘dormant’ and incapable of receiving the embryo”.
“Are these products still contraceptive, despite their moderate effect in inhibiting ovulation? They are indeed insofar as they block spermatozoa at the cervix. But this blocking effect does not prevent the passage of some of them. And yet progestogens are efficient in preventing pregnancy. This leads to the conclusion that they are efficient in preventing pregnancies partly because they interfere with the implantation of embryos in the uterine endometrium, and this is an abortive effect”.
1. The progestogen only pill or “mini-pill”
“Progestogens administered orally, in low doses and taken continuously are called ‘mini-pill’ because of their low steroid content. Widely used today, the ‘mini-pill’ is less efficient than the traditional pill. The ‘mini-pill’ prevents ovulation only in 63% of cases. Its thickening effect on the cervical mucus does not prevent some spermatozoa from going toward the Fallopian tubes, which could explain the impressive number of ectopic pregnancies that occur when using the mini-pill as contraception (2,9-4,1% compared to 0,3-3% in general population). The mini-pill probably acts on the Fallopian tubes by increasing their motility, i.e. speeding up the non-fertilized egg’s transit, allowing less time for a possible fertilization. But the mini-pill’s primary effect is on the uterine endometrium, where it renders 84% of implantations of newly formed embryos impossible, leading to a 100% pregnancy failure”.
“As long as the mini-pill blocks ovulation only in a partial number of cases and that it is its effect on the uterine endometrium that prevails, it can be considered as both contraceptive (by thickening the cervical mucus) and abortive (by interception)”.
2. Injectable contraceptives
“Progestogen-based preparations are administered every three months by injection. The most well known and widely used are DMPA (launched on the market under the brand name Depo-Provera) and NET-EN. They provide effective contraception for women who cannot, or do not wish to, take an oral contraceptive every day”.
“The progestogen is released slowly from the injection point and has a double effect: a contraceptive effect first, by partly inhibiting ovulation and rendering the mucus impervious to spermatozoa; and an abortive effect next, by interception, radically impairing the uterine endometrium, making it unfit to receive the embryo. In addition, the embryo is transported in the fallopian tubes at abnormal speed. Their action is similar to the mini-pill’s”.
3. Implants
Subcutaneous implants are capsules made of silastic, teflon or another polymer containing micro-crystals of a progestogen or oestrogen combined with a slow-release progestogen. The hormones enter into circulation progressively as the capsules are absorbed by the organism. The first implant, marketed since the 1980’s, is Norplant. The Norplant system consists of 6 rods, each containing 36 mg of levonorgestrel, encapsulated in a flexible silicone casing. The rods are inserted in a fan-like shape beneath the skin on the inner surface of the arm, a minor procedure performed under local anaesthetic. The release of levonorgestrel is maximal in the first month of use, progressively diminishing thereafter. This product would continue to be effective even after five years. The mechanism of action of subcutaneous implants is similar to that of injectable contraceptives”.
“The progestogen released by the implant suppresses ovulation in a highly irregular manner: 11.1% of cycles are in fact ovulatory. It is not therefore the action of inhibiting ovulation which explains the efficacy of Norplant. Little is known of its action on the cervical mucus. However, the effect of the progestogen released by the implant on the uterine endometrium is very clear, and can be described as ‘dramatic’. After a few months of exposure to Norplant, 50% of women present an endometrium that is too thin to undergo biopsy. Therefore, it can be said that implants have a contraceptive action because of their effect on the ovary and on the cervical mucus, but their action appears to be primarily abortive by interception, preventing the nidation of the embryo. A further form of Norplant, Norplant II, has been developed in parallel to improve the release of the active product and hence reduce the number of implants. Two other implants have been developed more recently: Capronor and Implanon”.
Disadvantages: recurrent intermenstrual blood loss, risk of infection and local intolerance, significant vaginal bleeding, even actual haemorrhage; a surgical intervention is needed to restore fertility and it is slow to return; acne and weight gain, headaches, mood changes, and abdominal pain.