A survey taking the opinions of various scientists was conducted and the results have revealed several and mixed responses. This comes prior to a controversial constitutional amendment next week in Colorado, which will confer legal rights on embryos at the point of fertilization.
Out of the 650 votes polled in, only 22.7pct of voters selected fertilization as the point when human life begins.
But, detection of fetal heartbeat scored the highest, with 23.5 pct vote in its favor, and at the third position was implantation of the embryo in the womb lining with 15pct.
Jaclyn Friedman of Reproductive Biology Associates, the IVF clinic in Atlanta, Georgia, which commissioned the poll, said that the poll question asked respondents when human life began in a biological sense of being an original entity.
"We didn't ask when it's a person. There's a distinction between when a group of cells is considered living, and when it deserves human rights, and that's what comes into play with this amendment," New Scientist quoted her, as saying.
However, the amendment has proposed that fertilization is not only when human life begins, but also that this is when someone becomes a person, deserving the same legal rights and protection under the American Constitution as any baby, child or adult citizen.
"People might say this or that is when life begins, but it doesn't necessarily confer legal rights on that entity," said Thomas Elliott of Reproductive Biology Associates.
There's a clear divide of opinion based on religion and geography when it comes to the question of when biological life begins.
Roman Catholics were found to have the highest proportion voting for "sperm-egg" fusion, with 31pct. On the other hand, a total of 29 pct Jewish respondents voted for agnostics and 27pct of Muslims opted for fetal heartbeat and the same was seen with 38pct of IVF patients.
Geographically, just 13pct of UK respondents opted for "sperm-fusion", with 43pct choosing "fetal heartbeat" as compared to 47pct of Australasians, who voted for "sperm-egg." Only 7pct voted for "fetal heartbeat".
The figures in North America was more even, with 27pct opting for "sperm-egg", 24pct "fetal heartbeat" and 18pct "implantation".
The results of the study will be presented in San Francisco at the Annual meeting of the American Society for Reproductive Medicine.