Studies on low dose oral contraceptives: plasma hormone changes in relation to deliberate pill ('Microgynon 30') omission

Pharmacodynamics of combined estrogen-progestin oral contraceptives 3. Inhibition of ovulation

INTRODUCTION

Following a historical overview, the ovulation-inhibiting effect of various orally administered estrogen-progestin combinations (combined oral contraceptives [COCs]) are examined for their components alone or in the various combined formulations. Special emphasis is given to products containing natural estrogens. Areas covered: Inhibition of ovulation with progestins alone; estrogens alone; various progestins in combination with ethinyl estradiol; various progestins in combination with natural estrogens (estradiol, estradiol valerate, and estetrol). Expert commentary: The original idea to achieve ovulation blockage through the administration of steroid hormones involved the use a progestogen (both progesterone and its synthetic homologous). The ability of a progestin to inhibit ovulation depends on the type of compound and on its dosage and a difference of more than 20-fold in activity exists between compounds utilized today in COCs. Initially, the estrogenic component was present only because it contaminated the first progestin utilized. It was soon found that an estrogen is necessary for proper cycle control. It was also found that the estrogen acts synergistically in inhibiting ovulation. For almost half a century, most COCs contained ethinyl estradiol. Today, also natural estrogens are being employed. Inhibition of ovulation was complete with all early high dose preparations. Decreasing dosage allowed some ovarian activity to occur, occasionally leading to a mature follicle. Even in this situation, defective corpus luteum formation assured contraceptive protection.

Effect of missed combined hormonal contraceptives on contraceptive effectiveness: a systematic review

BACKGROUND

Combined hormonal contraceptives (CHCs) are popular methods of reversible contraception in the United States, but adherence remains an issue as reflected in their lower rates of typical use effectiveness. The objective of this systematic review was to evaluate evidence on the effect of missed CHCs on pregnancy rates as well as surrogate measures of contraceptive effectiveness (e.g., ovulation, follicular development, changes in hormone levels, cervical mucus quality).

STUDY DESIGN

We searched the PubMed database for peer-reviewed articles published in any language from database inception through April 2012. We included studies that examined measures of contraceptive effectiveness during cycles with extended hormone-free intervals or nonadherence (e.g., omission of pills, delayed patch replacement) on days not adjacent to the hormone-free interval. We used standard abstract forms and grading systems to summarize and assess the quality of the evidence.

RESULTS

The search strategy identified 1387 articles, of which 26 met our study selection criteria. There is wide variability in the amount of follicular development and risk of ovulation among women who extended the pill-free interval to 8-14 days; in general, the risk of ovulation was low, and among women who did ovulate, cycles were usually abnormal (i.e., low progesterone levels, small follicles and/or poor cervical mucus) (Level I, good, indirect to Level II-3, fair, indirect). Studies of women who missed one to four consecutive pills or 1-3 consecutive days of delay before patch replacement at times other than adjacent to the hormone-free interval reported little follicular activity and low risk of ovulation (Level I, fair, indirect to Level II-3, poor, indirect). Studies comparing 30 mcg versus 20 mcg mc ethinyl estradiol pills showed more follicular activity when 20 mcg ethinyl estradiol pills were missed (Level I, good, indirect).

CONCLUSION

Most of the studies in this evidence base relied on surrogate measures of pregnancy risk and ranged in quality. For studies providing indirect evidence on the effects of missed CHCs, it is unclear how differences in surrogate measures correspond to pregnancy risk. Fewer studies examined the transdermal patch and vaginal ring than combined oral contraceptives.

Missed hormonal contraceptives: new recommendations

OBJECTIVE

To provide evidence-based guidance for women and their health care providers on the management of missed or delayed hormonal contraceptive doses in order to prevent unintended pregnancy.

EVIDENCE

Medline, PubMed, and the Cochrane Database were searched for articles published in English, from 1974 to 2007, about hormonal contraceptive methods that are available in Canada and that may be missed or delayed. Relevant publications and position papers from appropriate reproductive health and family planning organizations were also reviewed. The quality of evidence is rated using the criteria developed by the Canadian Task Force on Preventive Health Care.

BENEFITS, HARMS, AND COSTS

This committee opinion will help health care providers offer clear information to women who have not been adherent in using hormonal contraception with the purpose of preventing unintended pregnancy.

SPONSORS

The Society of Obstetricians and Gynaecologists of Canada. SUMMARY STATEMENTS: 1. Instructions for what women should do when they miss hormonal contraception have been complex and women do not understand them correctly. (I) 2. The highest risk of ovulation occurs when the hormone-free interval is prolonged for more than seven days, either by delaying the start of combined hormonal contraceptives or by missing active hormone doses during the first or third weeks of combined oral contraceptives. (II) Ovulation rarely occurs after seven consecutive days of combined oral contraceptive use. (II) RECOMMENDATIONS: 1. Health care providers should give clear, simple instructions, both written and oral, on missed hormonal contraceptive pills as part of contraceptive counselling. (III-A) 2. Health care providers should provide women with telephone/electronic resources for reference in the event of missed or delayed hormonal contraceptives. (III-A) 3. In order to avoid an increased risk of unintended pregnancy, the hormone-free interval should not exceed seven days in combined hormonal contraceptive users. (II-A) 4. Back-up contraception should be used after one missed dose in the first week of hormones until seven consecutive days of correct hormone use are established. In the case of missed combined hormonal contraceptives in the second or third week of hormones, the hormone-free interval should be eliminated for that cycle. (III-A) 5. Emergency contraception and back-up contraception may be required in some instances of missed hormonal contraceptives, in particular when the hormone-free interval has been extended for more than seven days. (III-A) 6. Back-up contraception should be used when three or more consecutive doses/days of combined hormonal contraceptives are missed in the second and third week until seven consecutive days of correct hormone use are established. For practical reasons, the scheduled hormone-free interval should be eliminated in these cases. (II-A) 7. Emergency contraception is rarely indicated for missed combined hormonal contraceptives in the second or third week of the cycle unless there are repeated omissions or failure to institute back-up contraception after the missed doses. In cases of repeated omissions of combined hormonal contraceptives, emergency contraception may be required, and back-up contraception should be used. Health care professionals should counsel women in these situations on alternative methods of contraception that do not demand such stringent compliance. (III-A).

Effects of oral contraceptives administered at defined stages of ovarian follicular development

OBJECTIVE

To elucidate the effects of initiating oral contraceptives (OC) at defined stages of ovarian follicle development.

DESIGN

Prospective longitudinal study.

SETTING

Healthy volunteers in an academic research environment.

PATIENT(S)

Forty-five healthy women between the ages of 18 and 35 years, randomized to initiate OC when a follicle diameter of 10, 14, or 18 mm was first detected.

INTERVENTION(S)

The OC administration at defined stages of dominant follicle development.

MAIN OUTCOME MEASURE(S)

Fates of all dominant follicles and serum concentrations of E(2)-17beta, LH, and P before and after initiating OC.

RESULT(S)

No ovulations (0/16) were observed when OC use was initiated at a follicle diameter of 10 mm, 4/14 (29%) follicles ovulated when OC were initiated at 14 mm, and 14/15 (93%) ovulated when OC were initiated at 18 mm. When ovulation did not occur, follicles regressed or became anovulatory cysts. Peak LH and E(2) levels were lowest in the 10-mm group, moderate in the 14-mm group, and greatest in the 18-mm group. Peak endocrine levels in all treatment groups were lower than the historic reference group.

CONCLUSION(S)

Follicular development, ovulation, and endocrine concentrations were not suppressed effectively when OC were initiated at late stages of dominant follicle development.

Effective use of hormonal contraceptives

This systematic review examines evidence regarding when during the menstrual cycle a woman can initiate combined oral contraceptive (COC) use and what can be done if a woman misses COCs. We searched the MEDLINE and EMBASE databases for articles published from 1966 to March 2005 related to COC initiation and to the effects of late or missed COCs. We identified 11 studies related to COC initiation and 25 studies related to the effects of missed pills. Evidence from these studies suggested that taking hormonally active pills for 7 consecutive days prevents normal ovulation and that initiating COCs through Day 5 of the menstrual cycle suppresses follicular activity. Studies on the effects of missed COCs generally showed that the risk of ovulation is greatest when the pill-free interval lasts >7 days. Limitations of this body of evidence include small sample sizes that may not reflect variation in larger populations, lack of a standard measurement of ovulation and difficulty in discerning how ovulation resulting from late or missed COCs corresponds to the risk of conception.

Modeling and simulation of adherence: approaches and applications in therapeutics

Partial adherence with a prescribed or randomly assigned dose gives rise to unintended variability in actual drug exposure in clinical practice and during clinical trials. There are tremendous costs associated with incomplete and/or improper drug intake-to both individual patients and society as a whole. Methodology for quantifying the relation between adherence, exposure and drug response is an area of active research. Modeling and statistical approaches have been useful in evaluating the impact of adherence on therapeutics and in addressing the challenges of confounding and measurement error which arise in this context. This paper reviews quantitative approaches to using adherence information in improving therapeutics. It draws heavily on applications in the area of HIV pharmacology.

Faculty Statement from the CEU on a New Publication: WHO Selected Practice Recommendations for Contraceptive Use Update Missed pills: new recommendations

The World Health Organisation Selected Practice Recommendations for Contraceptive Use (WHOSPR) was first published in 2002 and provides evidence-based recommendations on how to use contraception effectively. The WHOSPR was adapted for UK use by the Faculty of Family Planning and Reproductive Heath Care (FFPRHC). The UK version is available on the FFPRHC website (www.ffprhc.org). Extensive field experience with the first edition of the WHOSPR highlighted to the WHO the need for revised recommendations for missed combined oral contraceptive pills (COCs). The WHOSPR was updated in 2004 and revised guidance on missed pills published. This guidance is now available on the WHO website (www.who.int/reproductive-health). The FFPRHC endorses the new recommendations from WHO on missed COCs for the following reasons: There is new evidence on which to base guidance. The WHOSPR follow a published and rigorous process for assessing the available evidence. The recommendations were developed by an international expert panel, with UK representation. Field experience shows a need for simple, harmonised guidance. This Statement summarises the revised WHOSPR evidence-based 'missed pill rules' in formats which we hope clinicians will find useful. We recognise that different individuals favour different styles for the presentation of information. Thus, both tabular and flow chart styles of summary are provided; these convey the same information but in different ways. The FFPRHC considers that the following statements may also serve as useful aides memoir for the 'missed pill rules': Whenever a woman realises that she has missed pills, the essential advice is 'just keep going'. She should take a pill as soon as possible and then resume her usual pill-taking schedule. Also, if the missed pills are in week three, she should omit the pill-free interval. Also, a back-up method (usually condoms) or abstinence should be used for 7 days if the following numbers of pills are missed: 'Two for twenty' (ie if two or more 20 microgram ethinylestradiol pills are missed). 'Three for thirty' (ie if three or more 30-35 microgram ethinylestradiol pills are missed). The fpa (Family Planning Association) has produced a revised COC user information sheet to reflect these changes; available from April 2005.

Plasma concentrations of endogenous hormones during one regular treatment cycle with a low-dose oral contraceptive and during two cycles with deliberate omission of two tablets

In this open, prospective, phase-I study we closely monitored levels of endogenous progesterone, 17beta-estradiol, luteinizing hormone (LH) and follicle stimulating hormone in six healthy women. We determined plasma concentrations every 1-3 days during one untreated baseline cycle and during the first treatment cycle with regular pill intake of an oral contraceptive containing 30 microg ethinylestradiol plus 75 microg gestodene. During the following two treatment cycles, two tablets were deliberately omitted (in cycle 2 on days 6/7 and in cycle 3 on days 11/12). All but possibly one volunteer ovulated in the untreated pre-cycle, as concluded from LH peaks followed by marked increases of progesterone. During the regular first treatment cycle and even after deliberate omission of two tables in treatment cycles 2 and 3, the progesterone and estradiol levels remained low, so that we concluded that no ovulation took place. However, two volunteers showed some sort of LH peak in the first regular treatment cycle and all women showed LH increases of > 40 microg/ml in at least one omission cycle. In ten out of 12 cycles, omissions of pill intake were followed by an episode of intermenstrual bleeding. In conclusion, we have shown that, after omission of two consecutive oral contraceptive tables, the endogenous hormone parameters did not provide evidence for ovulation. Although this provides confirmation of the robustness of this oral contraceptive towards non-compliance, the widely published practical recommendations should be followed.

Ovarian follicular development during the use of oral contraception: a review

Over the past 40 years, alterations to the composition of oral contraceptives (OCs) have been made in attempts to reduce adverse effects and to improve patient compliance while maintaining contraceptive efficacy. However, there is growing evidence to indicate that reducing the estrogen dose to minimize adverse effects may have compromised the degree of hypothalamo-pituitary-ovarian suppression, particularly during the hormone-free interval (HFI) or following missed doses. Follicle development during OC use appears to occur in association with a loss of endocrine suppression during the HFI. This information provides a rationale for reducing or eliminating the HFI in OC regimens. There is also evidence for an increased risk of follicle development and ovulation in women who use delayed OC initiation schemes, such as the "Sunday Start" method. It is not currently known why some follicles ovulate during OC use while others regress or form anovulatory follicle cysts. Continued research about follicle development during OC use would provide insight into understanding the precise mechanisms of action underlying combined OCs, as well as those of continuous OC formulations and emergency contraceptive regimens.

Activity of the pituitary-ovarian axis in the pill-free interval during use of low-dose combined oral contraceptives

This study was performed to evaluate pituitary-ovarian recovery in the pill-free interval during use of three low-dose combined oral contraceptives (COC). Either the estrogen component or the progestin component was comparable in the study groups, to evaluate their relative influence. Serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol (E2) levels were measured and follicle number and size estimated by transvaginal sonography daily during the 7-day pill-free interval in 44 healthy volunteers using three different low-dose oral contraceptives. Healthy volunteers were enrolled using 20 micrograms ethinyl estradiol (EE) + 75 micrograms gestodene (GSD) (Harmonet, Wyeth-Lederle; n = 15), 20 micrograms EE + 150 micrograms desogestrel (DSG) (Mercilon, Organon n = 17), or 30 micrograms EE + 150 micrograms DSG (Marvelon, Organon, n = 12) given according to the usual regimen of one tablet daily during 3 weeks and 1 week pill-free interval. No ovulations were observed. Pituitary hormones were not statistically significantly different at the beginning of the pill-free interval between the study groups. FSH concentrations were significantly higher at the end of the pill-free interval in the 30 micrograms EE group compared with both 20 micrograms EE groups (7.0 [0.6-12.4] IU/L vs 4.9 [1.4-6.1] IU/L and 4.5 [2.4-7.4] IU/L; p = 0.001). In both 20 micrograms EE groups, a single persistent follicle (24 and 28 mm) was present in one subject. Follicle diameters were statistically significantly smaller at the beginning and at the end of the pill-free period in the 30 micrograms EE group compared with both 20 micrograms EE study groups. Dominant follicles (defined as follicle diameter > or = 10 mm) were observed at the end of the pill-free interval in both 20 micrograms EE groups (in 27% and 18% of women, respectively) but not in the 30 micrograms EE group. Finally, the area-under-the-curve for E2 was statistically significantly lower in the 30 micrograms EE group compared with both 20 micrograms EE groups. In conclusion, the EE content rather than the progestin component in the studied COC determined the extent of residual ovarian activity at the beginning of the pill-free interval. Dominant follicles were encountered only in the 20 micrograms EE study groups.

Dimeric inhibin serum values as markers of ovarian activity in pill-free intervals

Levels of inhibin A and B as well as other hormones in serum samples obtained during the pill-free interval in women taking combined oral contraceptives (OC) were measured to asses the extent of ovarian activity during that period. Type of pill and day of pill-free interval were recorded during routine gynecologic check-ups, if patients were in the pill-free period and had taken their pills regularly in the previous cycle. In addition to inhibin A and B, serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E2), and progesterone were also quantified. Inhibin B levels rise significantly in parallel with rising levels of FSH, LH, and E2. Progesterone levels were completely suppressed and inhibin A levels rose slightly but insignificantly. Inhibins are sensitive biochemical markers of ovarian activity in pill-free intervals.

Modulation of ovarian function by an oral contraceptive containing 30 micrograms ethinyl estradiol in combination with 2.00 mg dienogest

Twenty-two healthy female volunteers with normal ovulatory cycles, aged between 20 and 34 years (27.3 +/- 4.1), were included in a single-center, noncomparative study to investigate the modulation of ovarian function by an oral contraceptive containing 30 micrograms ethinyl estradiol in combination with 2.00 mg dienogest. At baseline, during three treatment cycles and post-treatment, serum levels of luteinizing hormone, follicle-stimulating hormone, 17 beta-estradiol, and progesterone were assayed and ultrasonography was used to measure follicular size and the thickness of the endometrium. The primary efficacy variable was inhibition of ovulation as measured by ovarian activity grading. All volunteers ovulated during the pretreatment cycle. During treatment, none of the subjects had ovulatory cycles, although there was still some ovarian activity in several subjects. During the first treatment cycle, only 4% (1 subject) of cycles showed active follicle-like structures. The frequency of follicle-like structures increased to 33% and 35% during treatment cycles 2 and 3. The frequency of presumptive luteinized unruptured follicle-like structures was 5% (1 subject) and 15% (3 subjects) in treatment cycles 2 and 3. The serum hormone concentrations were effectively suppressed in comparison to baseline. The ovarian activity returned to baseline during the post-treatment period. One subject was excluded from further study because of a medical problem believed unrelated to use of the oral contraceptive. No serious adverse events were recorded during the course of the study. The results of the present investigation indicate that the modulatory effects on ovarian function of the monophasic oral-contraceptive containing 30 micrograms ethinyl estradiol combined with 2.00 mg dienogest lead to adequate suppression of ovarian activity and effective inhibition of ovulation.

Ovarian activity during regular oral contraceptive use

The aim of this study was to assess whether during regular OC use ovarian activity might lead to ovulation, as assessed by ultrasound (US) evaluation of follicular growth and blood levels of 17-beta-estradiol and progesterone. A total of 51 healthy women with normal menstrual cycles (28 +/- 3 days) and no gynecological symptoms were recruited. A total of 22 patients were given a triphasic OC pill containing 35 mg ethinyl estradiol (EE) and 50 mg desogestrel (DSG) in the first seven tablets; 30 mg EE and 100 mg DSG in tablets 8 to 14, and 30 mg EE and 150 mg DSG in tablets 15 to 21; 29 patients received one of two OC pills, both containing 20 mg EE plus 150 mg DSG (15 patients) or 75 mg of gestodene (14 patients). A total of 86 cycles were monitored: 51 during the 3rd-4th cycle and 35 during the 6th-8th cycle of OC treatment. Follicular-like structures were observed in nine patients. The frequency of follicular-like structures was similar during the 3rd-4th cycle (9%) and during the 6th-8th cycle (11%). There was no relationship between follicular growth and blood levels of E2 and progesterone, which always appeared suppressed. In conclusion, the results of this study suggest that during OC use (even with low dose of ethinyl estradiol), a little ovarian activity may be present without ovulation.

Shorter pill-free interval in combined oral contraceptives decreases follicular development

The objective of the study was to determine the suppressive effect on ovarian activity of 20 micrograms ethinylestradiol plus 75 micrograms gestodene administered for 21 or 23 days. The study was designed as a double-blind, randomized, multicenter trial in 60 women. A pre-treatment cycle, three treatment cycles and a post-treatment period were monitored by ovarian ultrasound and by LH, FSH, 17 beta-estradiol and progesterone measurements every other day. No ovulation and no luteinized, unruptured follicle were observed. Suppression of ovarian activity was more pronounced by the 23-day regimen. 17 beta-Estradiol serum levels during the last six days of a cycle and during the first six days of the next cycle were significantly less (p < 0.05) in the 23-day regimen. The superiority of the 23-day regimen in comparison to the 21-day regimen with regard to the suppression of ovarian activity was shown in this study. The observed differences in the 17 beta-estradiol levels and follicular development between a 21-day and 23-day preparation combine to suggest that shortening the pill-free interval in combined oral contraceptives may increase the contraceptive safety margin in women on low-dose formulations.

Role of patient compliance in clinical pharmacokinetics. A review of recent research

Until 1986 to 1987, the estimation of patient compliance with prescribed drug regimens in ambulatory care relied on methods that were biased either by their subjectivity or by the improvement in compliance that commonly occurs during the day or two prior to a scheduled examination, so called 'white-coat compliance'. In 1986 to 1987, 2 objective methods were developed: electronic monitoring and low-dose, slow-turnover chemical markers (digoxin or phenobarbital [phenobarbitone]) incorporated into dosage forms. While neither method is without limitations, both have enabled major advances in the understanding of patients' compliance with dosage regimens and, thus, the spectrum of drug exposure in ambulatory care. The new methods have also triggered not only a revival of interest in patient compliance and its determinants, but also new statistical approaches to interpreting the clinical correlates of widely variable drug administration, and thus drug exposure, in drug trials. The marker methods prove dose ingestion during the 3 to 7 days prior to blood sampling, but do not reveal the timing of doses. The electronic monitoring methods, i.e. time and date-stamping microcircuitry incorporated into drug packages, provide a continuous record of timing of presumptive doses throughout periods of many months, but do not prove dose ingestion. The electronic record has been judged robust enough to detect certain types of investigator fraud, and to support modelling projections of the complete time course of the plasma drug concentration during a trial. Both marker and electronic methods show that the predominant errors are those of omission, i.e. delays or omissions of scheduled doses. Patient interviews, diaries, and counts of returned, untaken doses have been shown by both marker and electronic monitoring methods to consistently and substantially to overestimate compliance. Monitoring of plasma drug concentrations also overestimates compliance, because white-coat compliance is prevalent, and the pharmacokinetic turnover of most drugs is rapid enough that measured concentrations of drug in plasma reflect only drug administration during the period of white-coat compliance. Thus, compliance is a great deal poorer in clinical trials than has been revealed by the older methods. The long-standing underestimation of poor compliance in drug trials has many implications for the interpretation of drug trials, for optimal dose estimation, for the interpretation of failed drug therapy, and for accurate labelling of prescription drugs.

Gonadotropin and estradiol secretion during the week of placebo therapy in oral contraceptive pill users

The changes in the hypothalamic-pituitary-ovarian axis during the placebo week in oral contraceptive pill users were assessed. Fifteen women using the combined oral contraceptive pill were studied for eight hours at the start and at the end of the placebo week and gonadotropin secretion and estradiol concentrations were compared with those in control women in the follicular phase of an unmedicated menstrual cycle. Both gonadotropin and estradiol concentrations were suppressed at the start of the placebo week. By day 7 of placebo, gonadotropin concentrations and pulse patterns were indistinguishable from those of the control subjects although estradiol concentrations were still significantly lower.

Ovarian follicular development in oral contraceptive cycles

The cyclic changes in serum hormone concentrations, ovarian follicular development, uterine size, and endometrial appearance have been observed in 58 spontaneous ovulatory cycles and compared with 22 initial cycles of oral contraceptive (OC) therapy. A far greater inhibitory effect on the ovary was achieved by starting contraception on day 1 of the cycle rather than on day 5. The relevance of these findings with regard to OC failures is discussed.

The effect of deliberate omission of Trinordiol or Microgynon on the hypothalamo-pituitary-ovarian axis

The effect of deliberate omission of a phased formulation pill, Trinordiol (ethinyl estradiol 30 micrograms + levonorgestrel 50 micrograms: 6 tablets; ethinyl estradiol 40 micrograms + levonorgestrel 75 micrograms: 5 tablets; ethinyl estradiol 30 micrograms + levonorgestrel 125 micrograms: 10 tablets) or a low-dose, combined, oral contraceptive pill, Microgynon (ethinyl estradiol 30 micrograms + levonorgestrel 150 micrograms: 21 tablets) on the hypothalamo-pituitary-ovarian axis were studied. Thirty-six women were recruited to the study and divided equally between the two types of pill. Medication was begun on the 8th pill-free day of the cycle and continued for 7 days (Group 1), 14 days (Group 2) or 21 days (Group 3). Levels of FSH, LH, estradiol (E2) and progesterone (P) were measured in plasma on alternate days during the final week of pill therapy, and daily for the 7 days after stopping the pill. For the first 2 weeks of pill therapy, follicular activity, as judged by plasma levels of E2, was greater in women taking Trinordiol than in those taking Microgynon, but was similar in both groups by the third week of pill treatment. Five women taking Trinordiol (2 in Group 1 and 3 in Group 2) had plasma levels of E2 in excess of 500 pmol/l whilst taking the pills, and only 1 patient achieved this degree of follicular activity after stopping the tablets. One woman who had taken 7 days of Trinordiol (Group 1) showed a rise of plasma levels of P to 6.8 nmol/l, but luteinization did not occur in any of the remaining 35 women who took Trinordiol or Microgynon. These findings suggest that follicular activity is less completely suppressed by Trinordiol than Microgynon, at least in the first 2 weeks of pill therapy, but that normal ovulation is still a rare event in the week after cessation of either of these pills, even if only 7 days of medication have been taken.

Hormonal consequences of missing the pill during the first two days of three consecutive artificial cycles

The hormonal effects of the deliberate omission of a low-dose combined oral contraceptive pill (30 micrograms ethinyl estradiol + 150 micrograms levonorgestrel) during the first two days of three consecutive artificial cycles were studied in 10 women. The plasma levels of estradiol, progesterone, levonorgestrel and--whenever justified--of LH were measured three times weekly (Mondays, Wednesdays and Fridays) throughout a 90-day period, and the ovarian reaction to the prolongation of the pill-free period from 7 to 9 days was assessed. One subject (with a premature LH surge) showed a marked follicular and an inadequate luteal activity in 2 of 3 cycles. The remaining cycles were characterized by a varying degree of follicular activity associated with the absence of any luteal function. None of the subjects exhibited peripheral steroid levels indicating a normal ovulatory cycle. The results are interpreted as suggesting that repeated prolongation of the pill-free period from 7 to 9 days might result in a gradual increase in ovarian activity.

Why do inadvertent pregnancies occur in oral contraceptive users? Effectiveness of oral contraceptive regimens and interfering factors

Inadvertent pregnancies in combined pill users are not uncommon, and are usually due to errors of tablet taking. However, many factors may contribute to 'pill failure'. In this review the endocrine pharmacology of pill use and the changes reported with missed pills have been considered in detail. The influences of other factors including drug interactions have been reviewed and a series of recommendations made for reducing the risk of pregnancy in each of these circumstances.

The effect of ethinyl estradiol 20 mcg and levonorgestrel 250 mcg on the pituitary-ovarian function during normal tablet-taking and when tablets are missed

A new combined pill containing 20 micrograms of ethinyl estradiol and 250 micrograms of levonorgestrel has been developed. The safety margin of this type of low-dose preparation needed to be assessed and this was done by evaluating daily levels of LH, FSH, estradiol, progesterone, 1-NG and EE2 as well as cervical mucus characteristics in six patients when one and then two consecutive pills were deliberately omitted mid-way through the cycle. Results demonstrated that there was no evidence of breakthrough ovulation, although there was some continued ovarian steroidogenesis, a feature consistent with previous studies using combined preparations. Existing instructions to patients regarding missed pills should continue in order to ensure maximal contraceptive safety.