Low doses of progestogen as an approach to fertility control

Effectiveness and efficacy rates of progestin-only pills: A comprehensive literature review

OBJECTIVES

To synthesize published literature on POP effectiveness and efficacy.

STUDY DESIGN

We searched PubMed Central, PubMed, and the Cochrane library through March 07, 2022. We included articles written in English reporting a Pearl Index or life table rate for pregnancy. We excluded articles only assessing formulations that: were never marketed globally, are only sold in combination with estrogen, are currently sold only for noncontraceptive purposes, or were not given to participants continuously. Four researchers independently extracted data and two analyzed data using Excel and R.

RESULTS

We included 54 studies. Among studies at low or moderate risk of bias, the median Pearl Index rate (the failure rate during typical use) was 1.63 (range 0.00-14.20, IQR 4.03) and the median method failure Pearl Index rate (the failure rate during perfect use) was 0.97 (range 0.40-6.50, IQR 0.68). Excluding the newer formulations, Desogestrel and Drospirenone, which are closer to combined oral contraceptives in that they prevent pregnancy by inhibiting ovulation, the median Pearl Index rate is 2.00 (range 0.00-14.12, IQR 2.5) and the median method failure Pearl Index rate is 1.05 (range 0.00-10.90, IQR 1.38).

CONCLUSIONS

Among studies at low or moderate risk of bias, the median Pearl Index rate during typical POP use was much lower than currently estimated (7.00), while the median perfect use rate was similar to current estimates.

IMPLICATIONS

Future research should investigate the possibility that POPs may be much more effective during typical use than currently believed.

Effects of progestin-only contraceptives on the endometrium

INTRODUCTION

The contraceptive activity of synthetic progestins is mediated through three basic mechanisms: (a) An anti-gonadotrophic action leading to the inhibition of ovulation; (b) Changes in cervical mucus characteristics that inhibit sperm penetration and (c) desynchronization of the endometrial picture necessary for implantation.

AREAS COVERED

Mechanisms involved in the progestin-induced endometrium desynchronization are individually reviewed for each of the routes of administration and, whenever possible, by individual members of the various families of synthetic progestin derivatives.

EXPERT OPINION

For contraceptive purposes, progestins are today administered through several routes: orally, as injections, subdermally and via the vagina or the uterine cavity. Given this variety of modalities, their effects may differ, depending on the route of administration, concentration reached at the level of the endometrium and the duration of use. These are characterized by inactivation of the endometrium. Progestin-only contraception provides a safe and effective control of fertility regulation, although, they are associated with the problem of endometrial break through bleeding that may lead to discontinuation. Unfortunately, in spite of a major research effort over two decades, there is not, as yet, an established long-term intervention available to manage bleeding irregularities, making mandatory a deeper understanding of the mechanisms involved is required.

Clinical profile of contraceptive progestins

The term progestogen has been widely utilized to indicate the general class of agents that includes both progesterone and its synthetic analogs, whereas the term progestin refers only to synthetic progestational steroids. The development of progestins has been influenced in a major way by the search for orally active hormonal contraceptives, since it is likely that hormonal contraceptives will continue to utilize a progestin, the only possible alternative being represented by the utilization of antiprogestins. Synthetic progestogens in clinical use today belong to three main chemical families: progesterone derivatives (progesterone, retro-progesterone, 19-norprogesterone and 17alpha-hydroxyprogesterone); gonane and 19-nortestosterone derivatives (norethisterone, levonorgestrel, desogestrel, gestodene, norgestimate); a spironolactone derivative. Biological potency of progestogens varies depending on the end-point measured, usually ovulation inhibition and endometrial transformation; with both these tests, the most active compounds are all gonane derivatives, with a potency over a 100 times that of the natural hormone. When administered in adequate doses, a progestin inhibits fertility by inhibiting ovulation. This action is mainly exerted at the hypothalamic level where, physiologically, progesterone decreases the number of LH pulses. When progestogens are delivered directly to the uterine cavity, their action seems to be purely local. It has been amply proven that--even when administered in doses that do not constantly inhibit ovulation--a progestin can still remain effective as a contraceptive by acting at the level of the cervical mucus and, at least in part, of the endometrium. Progestogens utilized today differ largely in their pharmacokinetics. In general, after intake, these compounds are rapidly absorbed and distributed so that peak serum concentrations are reached between 1 and 4 h. Third-generation progestins (desogestrel, gestodene, norgestimate) have common characteristics: a higher affinity for progesterone receptors than their predecessors, a lower affinity for androgen receptors, a higher selectivity of action, a higher central inhibitory activity, a higher potency at the level of the endometrium, and an overall metabolic neutrality, in terms of effects on lipid and carbohydrate metabolism. In general, progestins can induce two types of adverse effects: changes in lipid metabolism and bleeding irregularities. Whereas the newer compounds seem to have overcome the first of these adverse effects, the second remains untouched: to this day, proper cycle control can only be achieved with combined hormonal contraceptives.

Role of progestins in contraception

Progestins have been used for contraception for more than 30 years. The main goal was to develop a contraceptive method devoid of the metabolic or clinical side-effects associated with the use of estrogens. The development of new contraceptive methods and formulations is time-consuming and requires devotion, belief, and also strong economical basis. As a result of this endeavor new methods have been developed: oral progestins, implants, injectables, intrauterine hormonal systems, and vaginal rings. Progestin-only contraceptives may be preferable in some situations, which have absolute or relative contraindications to estrogen, side-effects to estrogen containing hormonal contraception, lactation, and comfort and feasibility of formulations for long-term use. At present, emergency contraception is also performed with progestin.

Seventy-Five Microgram Desogestrel Minipill, A New Perspective in Estrogen-Free Contraception

Progestin-only minipills have been available for over three decades, yet their use has been limited, because of a documented lower efficacy when compared to pills that combine estrogen and progestin. The availability of a new low-dose progestin-only minipill containing 75 microg desogestrel (DSG) offers a new perspective, since, in a large multicenter study, this minipill gave a crude Pearl index of 0.41 and an adjusted one of 0.14, which is comparable to indices found in clinical trials of oral contraceptives. This minipill also allows for a 12-hour tolerance time in taking the pill. The high effectiveness of the DSG minipill is attributable to an almost constant inhibition of ovulation, as shown by the absence of elevated progesterone circulating levels and inhibition of follicular growth in the vast majority of cycles studied. Since irregular bleeding patterns are observed with all minipills, patterns experienced with DSG 75 microg have been compared to those obtained with levonogestrel 30 microg. As expected, the more pronounced ovarian inhibition produced wider bleeding variability with DSG, but also less bleeding overall. The DSG minipill is suitable for lactating women and represents a valuable addition to oral contraception.

Progestogens with antiandrogenic properties

Chlormadinone acetate, cyproterone acetate and dienogest are potent, orally active progestogens, which have antiandrogenic instead of partial androgenic activity. They act mainly by blocking androgen receptors in target organs, but also reduce the activity of skin 5alpha-reductase, the enzyme responsible for converting testosterone to the more potent androgen, 5alpha-dihydrotestosterone, in sebaceous glands and hair follicles. Chlormadinone acetate and cyproterone acetate also suppress gonadotropin secretion, thereby reducing ovarian and adrenal androgen production. Combined oral contraceptives (COCs) containing antiandrogenic progestogens provide highly effective contraception (gross and adjusted Pearl indices: 0-0.7 and 0-0.3, respectively) with excellent cycle control. Furthermore, COCs containing 2mg of chlormadinone acetate or cyproterone acetate plus 30 or 35 microg of ethinylestradiol produced improvement or resolution of seborrhoea in 80% of users, acne in 59-70%, hirsutism in 36% and androgen-related alopecia in up to 86%. These COCs are generally well tolerated, the main adverse effects being nonspecific or as expected for a COC (headache, breast tenderness and nausea). They have no clinically relevant effects on metabolic or liver functions or on bodyweight. Effects on mood and libido are uncommon (<3.5% and <6% of women, respectively). COCs containing antiandrogenic progestogens are likely to be particularly valuable in women with pre-existing androgen-related disorders who require contraception. They also increase the choice of products available for women with normal skin and hair who are concerned about the possibility of developing seborrhoea or acne with other COCs.

Timing of onset of contraceptive effectiveness in Norplant implant users. Part I. Changes in cervical mucus

OBJECTIVE

To provide scientific data regarding the changes in cervical mucus within the first hours to days after Norplant implant insertion and to estimate when the cervical mucus is hostile enough to suggest a contraceptive effect.

DESIGN

Multicenter, clinical descriptive study.

SETTING

Family planning clinics.

PATIENT(S)

Forty-two women who were between days 8 and 13 of their menstrual cycle and who had requested Norplant implants were admitted to the study.

INTERVENTION(S)

Cervical mucus and blood samples were obtained.

MAIN OUTCOME MEASURE(S)

Cervical mucus scores, sperm penetration distances, and serum levels of progesterone, estradiol, and levonorgestrel.

RESULT(S)

The median cervical mucus score observed at baseline was 6 ("fair"), indicating that the mucus was already somewhat hostile before insertion of the Norplant implants. The median scores declined to 5 at 12 and 24 hours and continued to decrease through day 7 to 2 ("poor"), a score that is judged as hostile to sperm penetration. Overall, 73% of all subjects had a poor cervical mucus score by 3 days after insertion; at 7 days after insertion, 90% exhibited poor mucus and none had a good score. There was a substantial drop in the overall median distance traveled by the vanguard sperm after 12 hours for each cervical mucus score grouping. The distance traveled decreased rapidly between 12 and 24 hours to < 0.5 cm in subjects with fair and poor mucus, and by day 3, 91% of the subjects exhibited poor sperm penetration.

CONCLUSION(S)

On the basis of our findings, deterioration of the quality of the cervical mucus and sperm penetration is evident by 24 hours after insertion, although not to a level that would suggest adequate protection until 72 hours after insertion. Therefore, we are confident in recommending that backup methods of contraception (e.g, condoms) need not be used for more than 3 days after insertion, even when the implants are inserted close to ovulation. These findings provide policy makers, clinic managers, and clinicians with important information about how they can improve client access to Norplant implants.

Ethinylestradiol from contraceptive formulations and the ovarian response: an estrogen dose-dependency on natural estradiol concentrations

To evaluate the competitive molecular phenomenon of ethinylestradiol from contraceptive formulations vs. endogenous 17 beta-estradiol in the intra- and extracellular compartments, a descriptive analysis was performed. Plasma and endometrial samples were simultaneously obtained on different days of the pseudomenstrual cycle from oral contraceptive users taking ethinylestradiol/norgestrel (30 micrograms/500 micrograms; n = 13) and ethinylestradiol/norethindrone (50 micrograms/1.0 mg; n = 14) in order to quantify the 17 beta-estradiol concentrations. From our results the chronic administration of these combined oral contraceptives demonstrated that the lower component ethinyl-estradiol (30 micrograms) does not compete substantially at the circulating level, permitting concentrations of natural estradiol such as those seen during follicular maturation in the ovulatory cycle. However, in the endometrium such a cyclicity is not seen, thus the possibility of a local infertility effect should be reconsidered to enable the investigation of a different approach in future methods of contraception.

Mechanism of action of gestagens

In the mid-1950s it was shown that ovulation can be inhibited by oral administration of progesterone or of synthetic progestogens such as norethynodrel. The idea that progestogens may interfere with fertility even when administered in doses so small, that they do not invariably inhibit ovulation was launched in the mid-1960s by a group of Mexican investigators. Since then a large number of studies have been conducted on the mechanism of action of gestagens when used as contraceptives. The objective of this communication is to review the information collected so far on this topic.

Demonstration of an early abortifacient effect of norethisterone (NET) in the primate (baboon)

A long-acting injectable contraceptive which provides continuous controlled release of norethisterone (NET) for three months following a single intramuscular injection was tested for antifertility effects in baboons using a low dose of microcapsules (total NET dose 2.5 mg; daily dose approximately 0.03 mg/day) which has no effect on ovarian function or ovulation. The continuous administration of NET during the cycle of conception had no effect on ovulation, fertilization or implantation as evidenced by the occurrence of nine pregnancies following 23 test matings. Pregnancy was diagnosed by the measurement of baboon chorionic gonadotropin hormone and the maintenance of elevated serum progesterone levels past the normal time of menstruation. Six of the nine pregnancies, however, ended in abortion between days 27 and 35 of pregnancy. The remaining three pregnancies continued to term and normal, healthy babies were delivered. Five control baboons included in this study became pregnant and all delivered normal, healthy infants. The results of this study demonstrate that early abortion should be considered as a mechanism of antifertility action of NET when administered continuously in low doses. These findings are contrary to the generally accepted explanation that low-dose synthetic progestins exert their contraceptive effect by inhibiting sperm transport and/or preventing implantation.

Low-level, progestogen-releasing vaginal contraceptive devices

Silicone rubber vaginal contraceptive devices of four different formulations, which release predetermined, controlled doses of three progestogens at four distinct levels, were designed and fabricated, and tested in 90-day clinical trials. Data obtained with 70 of the devices indicated that in vivo release rates (microgram/day +/- S.D.) for the formulations were: progesterone, 1400 +/- 30; norethindrone (two levels), 49.4 +/- 2.4, 196 +/- 21; d-norgestrel, 21.6 +/- 1.4. Clinical studies with these devices indicate that the women usually ovulate (with the exception of the high-dose norethindrone-releasing devices) while sperm penetration of the cervix was inhibited by all four fromulations, most consistently by the norgestrel-releasing devices.

'Patient failure' as a reliability model for the 'minipill': a clinical study

A trial was carried out in 10 healthy women to study the effects of withdrawal of treatment with 0.5 mg lynestrenol per day, for 3 successive days during the pre-ovulatory phase, on the physiological properties of the cervical mucus, vaginal cytology and pituitary and ovarian functions. In most cases, the amount, Spinnbarkeit and ferning of the cervical mucus and sperm penetration remained the same as that before interruption of treatment. In 2 women, the ferning altered to 'good' for 2 to 3 days as the amount of mucus increased slightly. Spinnbarkeit increased at the same time and sperm penetration was good. The changes in LH and FSH excretion suggested that ovulation possibly took place in 1 of the women studied. A mid-cycle oestrogen peak was seen in 2 women. No side-effects were reported during the study apart from irregular intermenstrual bleeding in 1 woman.

A review of recent developments in human fertility control

Recent and significant developments in the field of fertility control are reviewed. Consideration is given to new aspects of existing methods, recent modifications to steroidal formulations and Intrauterine devices, increased utilization of older methods (abortion and sterilization) and evaluation of new fields (postcoital contraception, prostaglandins and immunological techniques). There is an increasing demand for better application of newly developed methods and a rational decision in the selection of appropriate methods.

Clinical and laboratory findings in a trial of norgestrel, a low-dose progestogen-only contraceptive

Norgestrel, a progestogen-only oral contraceptive, was given continually at a dose of 75 mug/day to 144 women of proved fertility. It was an efficient contraceptive with a failure rate of 2.1% (assessed by the "life-table" method) within the first 12 cycles and 3.6% within the first 30 cycles (or 2.0 conceptions per 100 woman-years when assessed by the Pearl index). The overall conception rate for the entire trial period was 2.1% and 1.3 pregnancies per 100 woman-years respectively. Norgestrel caused a high proportion of irregular and generally short bleeding intervals, about one-fifth of the cycles lasting less than 17 days. This irregularity appeared to be due to individual variance in cycle length between women rather than that between their successive cycles. No confirmed instances of thromboembolism were observed. Norgestrel apparently exerts its contraceptive action by several mechanisms: reduction in the sperm penetrability of the cervical mucus and an impairment of luteal function appear important. The serum concentrations of cholesterol and globulin were significantly reduced in women taking norgestrel. Preliminary observations suggest that on discontinuing the medication fertility is promptly restored. Of the 144 women originally enrolled 57 (40%) withdrew for reasons connected with the method before completing 30 months on trial, over half of them because of the irregular menstrual pattern. Nonetheless, in view of its main clinical and laboratory characteristics and simple mode of administration, norgestrel appears to be a useful alternative to the combined type of pill for women unsuitable for, or unable to tolerate, oestrogen-containing preparations.