The interview is given a fairly low weight relative to much more important factors such as GPA, academic rigor, and recommendations. The importance of the interview and other factors are found in the Common Data Set, such as listed here:
http://www.collegedata.com/cs/data/college/college_pg02_tmpl.jhtml?schoolId=195
For international students, the interview is not required and won’t hurt your chances if you didn’t have one. For U.S. students, the interview is strongly recommended though not required.
http://www.wellesley.edu/admission/visitus/interviews#4S49Mf7TKcjKwzDx.97
Good luck!