Contraception - Chemical Methods / Hormonal Contraception / Emergency / Morning After Pill

Oral Contraceptives: Mechanism of Action (Feb 2005: Birth Control)

Scientists Refute Study Touting The Pill's Benefits

Mechanism of Action for Oral Contraceptives Described



SCIENTISTS REFUTE STUDY TOUTING PILL'S BENEFITS — A recent study touting a list of unexpected health benefits for the birth-control pill was wrong and should be discounted, say scientists with the landmark Women's Health Initiative, whose database was used for the study. Researchers at Wayne State University in Detroit were using Women's Health Initiative data to overturn the common wisdom on the pill. Epidemiologist Ross Prentice is the chief statistician for the health initiative. Dr. Rahi Victory and co-authors at Wayne State, Dr. Susan Hendrix & Dr. Michael Diamond, did not get authorization or input from the health initiative, as is customary, before presenting their data at the annual meeting of the American Society for Reproductive Medicine on Oct. 20. Women are urged to disregard the Wayne State findings. A separate survey by the CDC in 12/04 found that 82% of women aged 15-44 had used the pill at some point. Past studies have produced cautions about the birth-control pill (increases the risk of heart attack, stroke, blood clots and certain types of cancer). Those warnings still stand. [AP report in The Seattle Times; 11Dec04.Julia Sommerfeld: 206-464-2708 or [email protected]]

MECHANISM OF ACTION — This information is from Dr. Hanna Klaus M.D., FACOG [Natural Family Planning Center of Washington, D.C. and Teen STAR Program]: “While .75 mg of levonorgestrel (LNG) x 2 induces far less nausea and vomiting than Preven, not to speak of trying to swallow 40 oral contraceptive tablets, fewer pregnancies are putatively prevented, as not many women repeat the dose of pills lost in emesis. When .75 mg of LNG x 2 is given earlier than 48 hours prior to the LH surge, ovulation is delayed; but if given within the 48 hour window before the surge, the result is ovulation and a blunted corpus luteum leading to implantation failure, in other words, early abortion. [Marta Durand, Ma.del Carment Cravioto, Elizabeth G. Rayond, Ofelia Duran-Sanchez, Ma.De la Luz Cruz-Hinojosa, Andres Castell-Rodrigues, Raffaela Schiavon, Fernano Larrea, On the mechanism of action of short term levonorgestrel administration in emergency contraception, Contraception  64 (2002) 227-234.]  Thus, to be correct,…once implantation is established, EC cannot interfere with it. But when Preven or ordinary OCs which also contain synthetic estrogens are used, they will alter the endometrium disrupting implantation. Plan B will coagulate spermatozoa 48 hours after ingestion.  But,  when coitus occurs within the 48 hour window prior to the LH surge,  even though the first wave of sperm would not be capable of fertilization because they had not stayed in the cervix long enough to be capacitated,  subsequent waves could easily reach the freshly ovulated ovum.  If this occurs prior to the LH surge, the blunting of the LH surge mentioned above will occur.  If it occurs after the surge, conception could proceed normally, this negating the statement that EC prevents sperm from reaching the ovum. [Hanna Klaus, M.D., FACOG, Natural Family Planning Ctr of Wash, D.C. & Teen STAR Program, [email protected],, writing to Dr. Camacho regarding the wording of the PAHO Fact sheet on E.C. in the Americas]