Most U.S. doctors believe pregnancy starts when the sperm fertilizes the egg, a survey shows, contradicting the position of a key medical group with a view that could potentially affect U.S. policy and laws regarding contraception and research.
The American College of Obstetrics and Gynecology (ACOG), the leading organization for this field of medicine, defines pregnancy as beginning when the fertilized egg implants in the uterus, roughly a week after fertilization.
"People say that the medical profession has settled on this," said Farr Curlin, senior author of the study, which appeared in the American Journal of Obstetrics and Gynecology, and a professor at the University of Chicago.
"What our data show rather clearly is that it is not at all settled among the medical profession."
Physicians who responded that they were religious or opposed to abortion or contraceptives that prevent implantation were more likely to believe that conception is the start of pregnancy, the study said.
Embryonic stem cells, used in scientific research, are often derived from surplus embryos that aren't transferred to a woman after in vitro fertilization, and some contraceptive devices, such as intrauterine devices, prevent implantation.
"Then you see why any technology that prevents implantation would be problematic," Curlin said.
For the survey, Curlin and his colleagues sent questionnaires to more than 1,000 obstetrician-gynecologists. The questions asked whether pregnancy begins at conception, at implantation, or if the doctor was unsure.
Most of the doctors, 57 out of every 100, said that pregnancy begins at conception, while 28 out of every 100 said it begins at implantation. The rest, 15 out of every 100, said they were unsure.
Implantation takes place about a week after fertilization, when the blastocyst, a tiny group of cells that will later become the fetus, embeds itself into the wall of the uterus.
Curlin said he was surprised that a majority of doctors in his study disagreed with the ACOG, which did not respond to requests for comment.
"In this case, the science shows exactly what happens, but what you define as pregnancy is not what science can settle," Curling told Reuters Health.
He added that one of the weaknesses in the survey is the use of the word "conception" instead of fertilization. While conception is usually defined as fertilization, others interchange it with implantation.