Research on medical abortion was initiated in the year 1972 with introduction of prostaglandins followed by introduction ofmifepristone in 1982 and sequential regimen in 985. Comparative study of sulprostone, gemeprost and meteneprost for termination of early pregnancy by PGs in 1983 in patients undergoing medical abortion showed complete abortion rate of 94%, 92% and 93%; incomplete abortion rate of 3%, 5% and 7%; and
continuing pregnancy rate as 3%, 3% and 0% respectively (Bygdeman et al 1983). Randomized study comparing sulprostone versus vacuum aspiration had a success rate of 91.1% and 94%, incomplete abortion rate of 7.4% and 2.8% and continuing pregnancy in 1.5% and 3.2% respectively.

The most common side-effects of prostaglandins noticed were pain (ranging from 30% to 100%), nausea and vomiting (20-30%) and diarrhoea (20-60%). All of the side-effects were dose-dependent.

Subsequently, Mifepristone was dentified to have several actions on Reproductive System.

It acts on the progesterone receptors in the myometrium, endometrium and decidual cells following which there is local withdrawal of progesterone.

The affinity of mifepristone to the progesterone receptor is five times higher than progesterone. It mainly causes choriodecidual separation by initiating breakdown of endometrium and detachment of embryo. This leads to decline in beta HCG and atrophy of corpus luteum, thus declining the serum progesterone levels. This initiates myometrial contractility and ripening of cervix and even expulsion of the embryo. Mifepristone has been used for preabortion cervical ripening and as an abortifacient alone or with prostaglandins. Mifepristone when used alone is not very effective. It is successful in terminating early pregnancy in 75% of cases. To make this method more successful, a small dose of prostaglandin is necessary, thus increasing the chance of successful expulsion in 95–98%. Mifepristone also increases uterine sensitivity to PGs, thus increasing its release.

In a study comparing mifepristone alone (600 mg single dose at gestation < 42 days) with mifepristone and PG combination at gestation < 49 days, the efficacy rates were 80% and 95%, blood transfusion rates 0.4% and 0.2% and haemostatic evacuation in 1.1% and 0.9% of patients.

The need for ideal technology development in medical abortion is still under research. Issues that need to be considered are the dose of mifepristone, dose and route of misoprostol administration, interval between mifepristone and misoprostol, length of gestation, misoprostol alone regimen and acceptability of medical abortion. Whether misoprostol should be routinely used as a cervical priming agent, prior to surgical abortion also needs concern.

A study comparing three mifepristone doses (200 mg, 400 mg, 600 mg) followed by gemeprost for early pregnancy termination revealed a complete abortion rate of 93.8%, 94.1% and 94.3% respectively (WHO, 1993). Earlier, only a few countries had mifepristone registration. It was registered in France in 1988, UK in 1991, Sweden 1992, USA and China in 2000 and India in 2002.

Misoprostol is a synthetic analogue of naturally occurring prostaglandin E1. It has been approved in more than 90 countries for prevention and treatment of gastric and duodenal ulcers. Very few countries have misoprostol registered as an abortion pill. It is safe and well tolerated, and can be kept at room temperature when packed in aluminium blisters.

Outcome of treatment with misoprostol when used orally or vaginally has shown a complete abortion rate of 87% and 95%, incomplete abortion 3% and 4%, missed abortion 3% and 1% and continuing pregnancy in 7% and 1% respectively (El Refaey et al 1995).

Misoprostol is rapidly absorbed after oral administration and converted to its pharmacologically active metabolite, misoprostol acid. Plasma concentrations of misoprostol acid peak in approximately 30 minutes and decline rapidly thereafter.

The effects of misoprostol on the reproductive tract are increased, and gastrointestinal adverse effects are decreased, if this is administered vaginally. On vaginal administration, the plasma concentrations of misoprostol acid peaks in 1-2 hours and then declinesslowly. Vaginal application results in slower increase and lower peak plasma concentration of misoprostol acid than does oral administration. Uterine contractility increases and then plateaus one hour after oral administration, whereas, contractility continues for four hours after vaginal route.

Intrauterine pressure begins to increase 8 minutes and 21 minutes and reaches maximal 25 minutes and 46 minutes after oral and vaginal administration respectively. Maximal uterine contractility is significantly higher after vaginal administration.

Studies of mifepristone in combination with oral misoprostol (0.4 mg) have shown that as gestational age increases, failure rate increases. In one such study, it was found that at 6 and 9 weeks of gestation, failure rate was 7.8% and 19.7% respectively.

WHO multicentric randomized controlled trialcomparing three misoprostol regimens (oral/oral, vaginal/oral, vaginal only) after priming with mifepristone 200 mg have shown a success rate of 94- 96% and continuing pregnancy rate of 0.1–1% (1998- 2000). Vaginal misoprostol was more effective than oral misoprostol.

The preferred regimen now is 200 mg mifepristone (one tablet) on day 1 followed by 2-4 tablets of 200 µg vaginal misoprostol on day 2.Advantages of medical abortion are that it does not involve any risk of surgery or anaesthesia, does not require an operating room and is more natural, whereas drawbacks are that it takes a longer time to abort and is associated with a longer duration of bleeding postabortion.

Advantages of surgical abortion are that it is a one step and quicker procedure and some clients prefer not to know what happens, whereas drawbacks include requirement of more trained personnel and the risks of surgery or anaesthesia complications.