Fishel S B, Edwards R G, Evans C J
Science. 1984 Feb 24;223(4638):816-8. doi: 10.1126/science.6546453.
Human oocytes were collected by laparoscopy and fertilized and cultured in vitro. Human chorionic gonadotropin was detected in the medium surrounding two embryos cultured for more than 7 days after fertilization.