Emergency contraception (EC) is defined as the use of any drug or device after unprotected intercourse to prevent an unintended pregnancy. It is an ‘after-sex’ or ‘back-up’ contraception solution. It is also commonly known as ‘morning-after pill’ or ‘day-after pill’.
Emergency contraception can best prevent pregnancies when used soon (within 24h) after intercourse. It provides an important back-up in cases of unprotected intercourse or contraceptive accident and also after forced sex.
Unprotected sexual intercourse can result from a couple not using any contraception, including ‘withdrawal’. It can also happen when they consciously try to prevent it. For example UPSI can happen as a result of accidental condom problem (breakage, slippage, not on in time); oral contraceptive (OC) problems e.g. forgotten pill; a temporary break from the usual contraceptive; forgetting to apply a patch or insert a vaginal ring. UPSI can also happen as a result of non consensual intercourse (rape).
Unprotected sexual intercourse (UPSI) is quite common. Approximately 30% sexually active women aged 16.45 report having at least one unprotected sex in the last 12 months. These frequent acts of unprotected sexual intercourse are not happening in a distinct sub-population, but happen irrespective of age, income, education level and marital status.
Following UPSI, emergency contraception can help women to reduce risk of getting pregnant. Although the risk of pregnancy exists most of the time, women may underestimate the risk of pregnancy. Not recognizing pregnancy risk may be the most important barrier to EC use. A study has demonstrated that 61% of women terminating unplanned pregnancy in artificial abortion were not at all aware of the pregnancy risk - they didn't know that they have had unprotected, "risky" sexual intercourse.
Among those biomedical fields in which a virtual explosion of new knowledge and understanding has occurred over the past decades, the physiology and pathophysiology of reproductive processes are prime examples. It is of the utmost importance to transfer new knowledge towards general population in order to improve their reproductive health competencies and to achieve more favourable population outcomes.
Menstrual cycle theory
The follicular phase starts on the first day of menstruation and ends with ovulation. Prompted by the hypothalamus, the pituitary gland releases follicle stimulating hormone (FSH). This hormone stimulates the ovary to produce several follicles (tiny nodules or cysts), on the surface. Each follicle houses an immature egg. Usually, only one follicle will deliver an egg, while the others die. The growth of the follicles stimulates the endometrium to thicken in preparation for possible pregnancy.
The ovulatory phase relates to ovulation - the release of a mature egg from the ovary’s surface in response to rising levels of luteinising hormone (LH) and FSH. When the LH reaches a peak it triggers the rupture of the developing follicle to release the mature egg: ovulation; with no LH surge, ovulation does not occur. The released egg is funnelled into the fallopian tube and towards the uterus by waves of small, hair-like projections. The life span of the typical egg is only around 24 hours. Unless it meets a sperm during this time, it will die.
The luteal phase follows the release of the ovum, when ruptured follicle stays on the surface of the ovary. The follicle transforms into a structure known as the corpus luteum, which releases progesterone and small amounts of oestrogen. The thickened lining of the uterus is maintained and waits for a fertilised ovum to implant. If this happens the implanted ovum will start to produce human chorionic gonadotropin, detectable in a urine test for pregnancy. If pregnancy doesn’t happen, the corpus luteum regresses, usually around day 22 in a 28-day cycle. The drop in progesterone levels causes the endometrium to break down and menstruation begins again.
Current evidence challenges the simplified ‘text book’ understanding of the fertile window and overall menstrual cycle: we know today that only about 12% of ovulations happen on day 14 of the menstrual cycle. The variability of ovulation is large – it can happen from day 11 to day 21 in women with regular cycles. In women with irregular cycles, it is even harder to predict. Furthermore, ovulation also varies from cycle to cycle.
Having in mind the variability of the ovulation and 5 days sperm survival following UPSI, it can be concluded that there are no risk free days of the cycle.