MUSIC
Professional musician Hank Wankford there but when he's not singing country and western he's Dr Sam Hutt, a specialist in contraception and reproductive healthcare at the Margaret Pyke Clinic in London and in his time he's fitted hundreds of Mirenas.
HUTT
It has a little what is called silastic membrane which is filled with progestogen which is the synthetic copy of progesterone. And the silastic membrane is very clever because it'll deliver a metered dose of so many micrograms every day to the lining of the womb.
HAMMOND
How does it actually prevent pregnancy - is it the hormones that are preventing that?
HUTT
Well it's the hormone that affects the endometrium, which is the medical word for the lining of the womb, and it makes it thinner. The other effect is that the progestogen actually affects the little plug of mucus that you have in the canal of your cervix. With the Merina in that little plug stays very, very thick and sort of impenetrable to the sperm. So in a funny way it's like having a biological cap preventing the sperms getting in in the first place but if they do get in and they do get to the egg, the egg has not got a lot of chance of implanting.
