Report: Morning-after pills don't stop implantation

"These medications are there to prevent or delay ovulation," Dr. Petra M. Casey, an obstetrician-gynecologist at the Mayo Clinic, told the paper.

"They don’t act after fertilization."

Birth control has become a hot political topic since the Obama administration announced this spring that under its 2010 healthcare law, insurance plans will need to provide birth control coverage to women without a co-pay.

Religious organizations loudly objected and have sued, arguing that the new coverage rule forces employers to tacitly endorse the use of birth control in all its forms — including emergency contraception (EC).

But scientists told the Times that studies have not established that EC affects implantation. Instead, the pills delay the ovulation that tends to precede fertilization. Some also prevent sperm from swimming freely.

"The implantation idea stems from the Food and Drug Administration’s (FDA) decision during the drug-approval process to mention that possibility on the label — despite lack of scientific proof and objections by the manufacturer of Plan B, the pill on the market the longest," the report stated.

A spokeswoman for the FDA acknowledged that "emerging data" suggest Plan B, the leading morning-after pill, "does not inhibit implantation."

"Less is known about ella. However, some data suggest it also does not inhibit implantation," Erica Jefferson said.