In a study investigating the effect of rubella infections on childbirth, a total of 578 pregnancies were classified in retrospect as having been either "normal" or "abnormal," the latter group including abortions, stillbirths, birth defects, and all infant deaths within two years. Altogether, there were 86 abnormal pregnancies. The second variable looked at was when the rubella infection occurred during the first trimester or after the first trimester. It was found that 59 of the 86 abnormal births were among the 202 pregnancies complicated during the first trimester; the remaining 27 were born to mothers who contracted the virus after the first trimester. Is the risk of an abnormal birth dependent on when during the pregnancy the virus is contracted?

Let = .01.