First, I think you misspelled the first word. Should be "religion," right?
Second, "reasons" do not "cause" anything. So you shouldn't say "one of the reason that causes...." You might contend that "Religion is one of the reasons for population growth" or you might say "Reglion is one of the causes of population growth."
The last few words should either be "... use a birth contol method" (which is correct, but awkard) or "... use birth control." [The article in the first instance is indefinite, as there are several methods of birth control.]
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