You can't be a little bit pregnat.

That is as true today as it ever was, but people are just a little bit less honest about what that means.

It used to be that “pregnancy” began when human life began. That is, when a human egg was fertilized by a human sperm somewhere in the vicinity of the ovary, before the tiny growing embryo began the weeklong journey through the fallopian tube and into the uterus to burrow into the endometrium, a nourishing temporary home.

But the IUD changed all that. Not the process, of course, but the definition. Promoters of intrauterine devices in the 1960s lobbied successfully to push the start of pregnancy forward 10 days to the point of implantation so that the IUD, which works post-fertilization, could still be labeled a “contraceptive.” (Embryology textbooks still mark the start of human life at fertilization — they have skirted the shakedown, so far.)

Thus, while new human life begins when it always began, “pregnancy” can sometimes begin a week and a half later, depending on what you're reading.

The “morning-after” pill pushers are taking this confusion to the bank. Literally.

One morning-after pill known as Plan B is being marketed and advertised as a contraceptive even though it works before and after conception. It works before conception to delay ovulation or interfere with sperm capacitation, and it works after conception by impeding the movement of the new embryo through the fallopian tube and by interfering with the process of implantation. In fact, an extensive review of the literature on Plan B suggests up to 11 possible modes of action for the drug, seven of which work after conception. (See H. Croxatto, et al., Mechanism of action of hormonal preparations used for emergency contraception: a review of the literature, 63 Contraception 111-21, 2001).

Recently the distributor of Plan B, a for-profit drug company, petitioned the FDA to allow its drug to be sold over the counter without a prescription. Two FDA advisory committees (Nonprescription Drugs Advisory Committee and the Advisory Committee for Reproductive Health Drugs) voted 24-3 in favor of the switch. The final decision, expected this month, rests with the commissioner of the FDA, Mark McClellan.

Putting Plan B on the shelves of drug stores is a very bad idea.

First, there is the enormous problem that women are being misled about what this drug does. It's marketed, advertised and promoted as a contraceptive, so it is surely reasonable to assume that many women who take Plan B think they are simply using a new kind of contraception. Indeed, Plan B's appearance on the shelf next to the condoms will only exacerbate this problem.

Women deserve to know the truth about drugs that are marketed to them. Plan B's distributor might argue that it's all the same (remember, they want to sell more drugs to women), but preventing human life from its beginning is not the same thing as destroying life that has already begun. And to many, many women it is a distinction that makes all the difference.

Second, this powerful drug has been associated with a heightened risk of ectopic pregnancy, a potentially fatal condition. (Note to pregnancy deconstructionists: Ectopic pregnancy occurs before implantation. Must change this definition, too!) There is no mystery why this should be so. Remember, one of the ways Plan B works after conception is to slow the transport of the new embryo through the fallopian tube.

While initial clinical trials did not show a risk, experience with the drug in the United Kingdom and New Zealand has revealed the danger and prompted medical authorities to issue warnings. The U.K.'s Committee on Safety of Medicines recently found 12 ectopic pregnancies out of 201 pregnancies following use of the drug.

What's more, the common side effects of the morning-after pill — nausea and abdominal pain — are also the symptoms of an ectopic pregnancy! A switch to over-the-counter Plan B would leave countless women vulnerable to a potentially “hidden,” potentially fatal medical complication with no clinical supervision. This is bad policy and bad medicine.

Plan B's distributor has been joined by pro-abortion groups who claim that switching the status of the drug will reduce abortion numbers by as many as half. Putting aside for a moment the obvious rejoinder that an abortion drug won't reduce abortions, there simply is no evidence to support this claim.

In fact, abortion numbers have not been significantly affected in areas of the country where the drugs have already been made more widely available. Washington state, for example, removed the need for a prescription in 1998 but its abortion numbers kept pace with prior state and national rates (all of which were falling marginally year by year).

The Food and Drug Administration is about to make a big mistake. If it follows the recommendation of its advisory committees and approves Plan B for over-the-counter use, it will begin a reckless experiment on the lives of women and children. This drug, with its serious risk of life-threatening consequences — for the woman taking it and for her developing child — does not belong on the shelf of a drug store. Or at the reach of a frightened teen-ager.

Cathy Cleaver Ruse, Esq., is director of the Planning and Information Secretariat for Pro-Life Activities of the U.S. Conference of Catholic Bishops.