Pregnancy Starts Before Conception? Here's Why Some Physicians Agree

Last week, the Arizona legislature passed a bill, which was signed by the governor, banning abortion at 20 weeks or more of gestation. Here's the kicker though: the bill's language places pregnancy as beginning before the child is even conceived.

How does this make sense? The bill defines gestation as "the age of the unborn child as calculated from the first day of the last menstrual period of the pregnant woman." New Scientist explains this would mean the "fetal clock" would start ticking about two weeks before conception would even take place:

The purpose of a menstrual period is to get rid of an unfertilised egg, plus all the tissue that has built up in the womb to support it. A new egg typically reaches the uterus two weeks later. In practice, the law therefore bans abortions as early as 18 weeks into the fetus's development.

Some consider this measurement "disputable biology", but New Scientist explains many physicians calculate how far along a woman is in pregnancy based on the timing of her last period. In the medical community, New Scientist reports, when pregnancy actually begins is still a debated topic. Some physicians see it beginning at conception, while others state it doesn't begin until implantation. Farr Curlin, a medical ethicist at the University of Chicago, conducted a survey that found 57 percent of obstetricians and gynecologists believe pregnancy begins at fertilization.

Some physicians measure timing of gestation based on the woman's last period because it can be difficult to estimate when exactly fertilization occurred, but the last period is more easily remembered.

So, what evidence is the Arizona law based on? New Scientist states:

The idea behind banning late-term abortions is to avoid terminating a fetus that could survive outside the womb – a so-called viable fetus. A 2001 study found that 75 percent of fetuses could survive at 25 weeks, but none survived at 21 weeks, counting from the last menstrual period.

"No baby born at 20 weeks gestation has ever survived anywhere in the world," says John Lantos of the Children's Mercy Hospital in Kansas City, Missouri.

The Arizona law also states that, based on "strong medical evidence", an unborn foetus can feel pain during an abortion at 20 weeks. The issue of when a fetus can feel pain has been hotly contested. However, it is widely considered that brain pathways responsible for the perception of pain are not thought to be complete until 26 to 29 weeks.

New Scientist points out that six other states ban abortions after 20 weeks as well, except in cases of medical emergency, but they cite pregnancy as beginning at actual conception.

As for the Arizona law itself, supporters state it was created in the interest of women's health. The Arizona Republic has more:

"This bill is intended to protect women," said Center for Arizona Policy President Cathi Herrod. "The safety risks to the mother and the pain endured by the child after 20 weeks is just too high."

[...]

Rep. Kimberly Yee, R-Phoenix, who sponsored the bill, said the goal was to protect both the health of women and that of the fetus.

"The state has a compelling interest to protect women from the serious health and safety risks of abortion," Yee said.

The Arizona Republic reports Planned Parenthood of Arizona lobbyist Michelle Steinberg saying it was the "most extreme piece of anti-abortion legislation" in the country.

Read more about the new law here.