I got naturally pregnant.i didn't have miscarriages or bleeding, but my gyn said that i should take utrogestan until the end of the pregnancy.why?

Have to ask OB why: Normally this would be given to a women during assisted reproductive assisted pregnancies or for someone who has had recurrent miscarriage. I can not say a reason now why you would need it with the history you have given or for the entire pregnancy.

Probable precaution: Progesterones are often prescribed in some high risk pregnancies when there is a fear of a (repeat) miscarriage or of (another) preterm delivery. In the USA, there is no strong scientific evidence that progestins improve the outcomes of first pregnancies. You may want to seek the opinion of an obstetrician familiar with Utrogestran and experienced in managing threatened abortions,preterm labor