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Oral Contraception Abortion-Rate Calculations

Let us briefly review the data to do justice to this argument.  What is the miscarriage rate of women of child-bearing age who are not on oral contraceptives?  There is considerable disagreement in various studies and articles.  In a September 1995 bulletin, the American College of Gynecology stated, "Approximately 50-70 % of pregnancies end in spontaneous abortion.”  (A spontaneous abortion is the term for a miscarriage in the medical literature.)  That is the highest estimate I have found.  More conservative estimates are more common.  One article stated, “As many as 30 % of all pregnancies end in miscarriage, half of them before the woman even realizes she is pregnant.”  There are smaller estimates, but those estimates probably limit their definition of miscarriage to those pregnancies that attach to the endometrium and then later miscarry; they don’t take into account pregnancies that miscarry before implantation.  Most researchers agree that about 20% of all pregnancies end up as miscarriages after implantation and cause symptoms like cramping, bleeding, and the passage of a clot or tissue from the vagina, while about an equal number cause "silent" miscarriages of pregnancies that have not implanted or that implanted only for a brief period of time.  (D. Ashley Hill, MD, The Medical Reporter, 3-1-97.) 


It is generally agreed in the medical literature that normal fertile couples of child-bearing age will measurably conceive about 25 % of the time over one cycle.  This number excludes those silent miscarriages that do not result in elevated HCG levels or symptoms of a miscarriage.  So if we took 1,000 sexually-active women of child-bearing age not on contraceptives, 250 of them would knowingly conceive within a single cycle, and 20%, or 50 of those pregnancies would miscarry.  Another 50 of the 1000 women would have a “silent” miscarriage.  With a symptomatic miscarriage rate of about 20 % and an asymptomatic miscarriage rate of about 20 %, 1,000 women of child-bearing age would experience a total miscarriage of about 40%, which would amount to a miscarriage of 100 of their children conceived in that first month.


Let’s compare this estimate to an approximate number of miscarriages in the same amount of time among 1,000 women on OCs.  The breakthrough ovulation rate on the commonly-used low-dose OCs is anywhere from 2 – 10 %.  Let us use the liberal rate of 10 % breakthrough ovulations for our calculation: of those 1,000 women on OC’s, 100 of them will ovulate in one month.  Of those ovulations, let us assume that the 25 % pregnancy rate over one cycle holds true for ovulating women on OCs as it does for ovulating women who are not on OCs.  Of those breakthrough ovulations, there will be 25 conceptions. 


Let us pause here to reflect: even if all 25 of those babies miscarry, it is four times less than the number of miscarriages in the equal number of women who are not on OCs.  Put in other terms, it could be said that the OC prevented 75 % of miscarriages. 


In reality, the miscarriage rate of women on OCs cannot be that high, because the accepted rate for “pill pregnancies” is 3-5 per 100 women years.  That is, if 100 women take the OC for one year, they will have 3-5 healthy pregnancies in spite of the OC.  Thus, if 1,000 women took the OC for one year, they would have 30 to 50 healthy pregnancies over that year, or 2.5 to 4.2 healthy pregnancies per month.  Thus, of those 25 conceptions that result from breakthrough ovulations in women on OCs, 2 to 4 (10 – 20%) of them will survive, resulting in a total miscarriage rate that is around one-fifth of that of women who are not on OCs. 


Different physicians have calculated different possible OC-induced abortion statistics for the 10 million women on OCs in the U.S.  Dr. Murphy Goodwin arrived at OC-induced abortions totals between 104,100 and 1,561,500 per year.  Dr. Don Gambrell calculated the possible abortion rate induced by OCs to be 1,894,620 per year.


Compare those figures to the number of accidental miscarriages of the 30 million sexually-active American women of child-bearing age who are not on OCs.  There were 4,021,726 births in 2002.  At a 40 % miscarriage rate, 2,681,150 babies died via miscarriage to women who are not on OCs, much more than the most liberal estimates of miscarriage rates of women on OCs. 


Add to that the 1,328,000 estimated to have been aborted in 2002, the vast majority of their mothers not being on oral contraceptives, and you have four million deaths of children conceived by mothers not on oral contraceptives.  By these calculations, there are considerably less deaths of preborn children whose mothers are on OCs compared to mothers who are not.

As stated in the body of the main article, for a drug to be classified as abortifacient, the conception loss must exceed the base-line loss for populations not using the drug, or be shown to occur solely due to the drug.  Thus, it is erroneous to classify OCs as abortifacient, and unnecessary divisive.



Copyright © 2004 Victor Claveau. All Rights Reserved