Recombinant DNA technology - or gene engineering - has progressed dramatically in the past decade to the point where it now represents 98 per cent of all fertility drugs prescribed in the US.

The technique involves reprogramming cells to produce more female hormones, or gonadotropins. These modified cells, called recombinants, begin transmitting new characteristics to other cells that, in turn, secrete the proteins needed for conception, such as human follicle-stimulating hormone (hFSH), human luteinising hormone (hLH) and human chorionic gonadoptropin (hCG).

The new generation of fertility drugs still come with side-effects and dangers. All of them can cause headaches, nausea and abdominal pain, but recombinant gonadotropins can also cause injection site reactions (pain, swelling or irritation), and ‘ovarian hyperstimulation syndrome’, which leads to enlargement of the ovaries, causing serious discomfort in 4 per cent of women, while 1 per cent of sufferers also need hospital care (Hum Reprod, 1999; 14: 294-7). Thromboembolic (blood-clotting) events can also arise, including thrombophlebitis (inflammation and clots in veins), pulmonary embolism, stroke and arterial occlusion, some of which have been fatal, as well as vomiting, diarrhoea, fever, bloating, breast tenderness, ovarian cysts or allergic reactions (such as fever, chills, joint pain, headache and fatigue).

Again, the possibility of a link between these new fertility treatments and ovarian cancer, first uncovered by Dr Alice Whittemore of Stanford University, has never been satisfactorily laid to rest (Am J Epidemiol, 1992; 136: 1212-20).