I am 5'3", 88lbs at age 28.Is underweight increases the chance for miscarriage?I want to become pregnant.?

I am from Bangladesh.I am married for 2.5 years.Every ones says me i am underweight and i am waiting more after marriage for a child.Thats why it will be hamper for becoming pregnant.I am trying my best to gain my weight and for conceive also. But i don't know why it doesn't work.I am so afraid. Can anybody tells me is that true?