First, your statement that abortions have decreased crime in the US is based on one of the most flawed and controversial studies in the scientific community [1]. Correlation does not imply causation.
Second, Utilitarianism roughly translates to "the greatest good for the greatest number." If a pregnant, utilitarian woman was granted with the power of foresight, she would abort her child only if he/her was to provide a negative net utility to society. If the child was to provide a net benefit to humankind, she would not abort.
Third, your assumption that unborn (and born) children are a burden to society is correct, but that initial investment is small with regards to the average net "benefit" a grown human creates. It must also be noted that the vast majority of humans benefit humankind through their work (although some have greater impact than others).
No person can see the future, however, so most utilitarians would never abort their children, as the probability their offspring benefit humanity as a whole is greater than the chance that they destroy value.
Frankly, I doubt any woman considers the ethical implications of abortion when they undergo one, and are primarily concerned with family, relationship, and personal problems. If one thinks beyond personal convenience, and look at the bigger picture, abortions are morally unjust from almost every popular ethical system.
Think hard about the choice your parents made by not aborting you. Do you think they made the right decision? Whether you're old, young, rich, poor, hopeful or hopeless, I imagine you'll answer yes.
1. https://en.wikipedia.org/wiki/Legalized_abortion_and_crime_e...