**2. Ovulation induction**

Ovulation induction involves stimulating the ovary with the aim to induce mono-follicularovulation in a sub-fertile woman who is anovulatory. A trigger injection, to mimic the midcycle luteinising hormone (LH) surge, is given to initiate release of the ovum and timed intercourse is advised.

Multiple pregnancy may occur with ovulation induction secondary to unintended overstimulation of the ovary and the development of more than one follicle and the release and subsequent fertilisation of more than one oocyte. Rates of multiple pregnancy with ovarian stimulation depend greatly on the treatment protocol used, but for all methods has been approximated at up to 9 times the rate of natural conception in fertile women [3].

A recent 5-year review of multiple pregnancy rates in the United States revealed 22% of the nation's twin pregnancies were due to ovulation induction and 40% of triplet pregnancies were as a result of ovulation induction treatment [4]. The rates of multiple pregnancy secondary to ovulation induction are falling as better techniques and practices are introduced however, not as quickly as is being seen with more invasive ART techniques such as IVF. Stricter controls and more stringent regulations are being enforced in many countries towards IVF treatments in the hope of stalling the multiple pregnancy rate, however this has not been replicated in the field of ovulation induction, as this is often performed outside of large fertility clinics, or without strict tracking protocols. Hence it is believed that ovulation induction accounts for up to 65% of the world's higher order multiple pregnancies [5].

Ovulation induction agents are usually divided into oral and injectable agents with the historical belief being that injectable agents, usually recombinant or urinary derived follicular stimulating hormone (FSH), being associated with higher rates of both multiple pregnancy and ovarian hyper-stimulation syndrome.
