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Home pregnancy test, negative result. Test stick used to test urine for a hormone produced during a pregnancy. An absorbent tip (centre right) is dipped in a urine sample. Lines (blue) in the result windows show the results. The round window displays a reference line that shows that the test has worked. The absence of a line in the square window shows that human chorionic gonadotrophin (HCG) hormone has not been detected. The HCG hormone is produced by the placenta, the organ that attaches an embryo to the wall of the uterus. (KEYSTONE/SCIENCE PHOTO LIBRARY/CORDELIA MOLLOY)