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Belief That Emergency Contraception Blocks Implantation Not Supported by Science, Investigation Finds

Belief That Emergency Contraception Blocks Implantation Not Supported by Science, Investigation Finds

June 6, 2012 — Scientific studies do not support claims on federally approved labels and medical websites that emergency contraceptives, including Plan B and Ella, could prevent fertilized eggs from implanting in the womb, a New York Times investigation has found.

According to the Times, studies indicate that EC mainly works by delaying ovulation -- the release of eggs from ovaries -- which occurs prior to fertilization. The pills also can thicken cervical mucus to make it more difficult for sperm to swim. However, studies have not proven that the pills can prevent an egg that is already fertilized from implanting in the womb.

Abortion-rights opponents, based on the belief that life begins at fertilization, have argued that using the drugs after sex is equivalent to an abortion because the medication was believed to prevent implantation. Some abortion-rights opponents remain unconvinced by the studies, and both sides noted that is it difficult to create a study that could definitively rule out the possibility.

"You can never prove the negative," said James Trussell, an EC researcher at Princeton University, who added that the current evidence was sufficiently convincing that the pills do not block implantation.

Misleading Information Rooted in FDA-Approved Labels

The idea that the pills could affect implantation likely came from an FDA decision during the drug-approval process to include that information on the label, despite objections by the manufacturer of Plan B and a lack of scientific evidence. The Times' review of the application documents found no mention of evidence supporting the implantation claim.

Some experts said implantation likely was included on the label because certain daily contraceptives that contain Plan B's active ingredient can alter the endometrium -- the lining of the uterus. However, altering the endometrium is not proven to prevent implantation.

Experts familiar with the FDA decision said the implantation statement was uncontroversial at the time and not at the forefront of the approval decision. Kristina Gemzell-Danielsson -- an obstetrics and gynecology professor at the Karolinska Institute in Sweden and a contributor to World Health Organization studies that led to FDA approval -- noted that research at the time was focused on whether the drugs were safe and effective, not how they worked.

Responses to Investigation

FDA declined to discuss decisions regarding the implantation information or whether it would consider changing the labels, the Times reports. Erica Jefferson, an FDA spokesperson, said, "The emerging data on Plan B suggest that it does not inhibit implantation. Less is known about Ella. However, some data suggest it also does not inhibit implantation."

Although scientific and political disputes over the drugs likely will continue even if the labels change, both sides said wording on labels is important because it summarizes the scientific consensus and influences medical authorities, according to the Times.

For example, the statements about implantation have long been included on many authoritative websites, including those of NIH and the Mayo Clinic, based on the information on the labels. Roger Harms, medical editor in chief of the Mayo Clinic's site, said he is eager to remove the reference but is waiting for FDA to change the label or for other agencies to make official statements (Belluck [1], New York Times, 6/5).

'Morning-After Pill' Nickname Might Contribute to Controversy

Some scientists said the nickname "morning-after pills" has helped perpetuate misconceptions about how EC prevents pregnancy, according to the Times. It typically takes one or two days after intercourse for fertilization to occur, but it can take up to five days.

The nickname does not refer to "the morning after fertilization -- it's the morning after intercourse," said Diana Blithe, program director for contraceptive development for NIH's National Institute on Child Health and Human Development. "People think that the act of intercourse results in pregnancy immediately, within a minute after you have sex," she said, adding, "They don't understand how long it takes sperm to get ready to fertilize" (Belluck [2], New York Times, 6/5).