J.C. Willke MD
Contraceptive pills contain,
in differing dosages to be taken in different combinations
during the month, two synthetic female hormones. They contain
estrogen and the second hormone, progesterone. Sometimes
that's called the "pregnancy hormone." This hormone is normally
formed in a woman's body in the second half of her monthly
cycle. Its function is to prepare the lining of the womb
for the nesting of the new human, if fertilization has occurred
that month, and it is the withdrawal of this second hormone
at the end of the month, if there is no pregnancy, that produces
the sloughing of the lining of the womb and its passage from
her body, a process called "menstruation." Contraceptive
pills used today contain varying percentages and dosages of
these two hormones. The pills are usually taken three weeks
out of a four-week month.
How do these pills work? They basically
have three effects. The first effect is the thickening of
the mucous plug at the opening of the cervix, the mouth of
the womb. This provides something of a natural barrier to
the passage of sperm into the womb. This is a contraceptive
function, as it prevents the union of sperm and egg.
There's a second effect, which usually
is the primary effect, and that is the suppression of ovulation.
A projected ovulation is simply blocked and does not occur.
The sperm may well be deposited in her female tract; they
may swim through her tubes and out to the ovaries, but if
there is no egg to fertilize, then we have a primary effect,
an action technically called "temporary sterilization"-or,
in more common, but less accurate language, "contraception."
There is a third effect of the contraceptive
pill. This effect is on the lining of the womb. What this
does is to harden the lining of the womb-we say, make it hostile
to implantation to this one-week-old embryo. If this is the
function that prevents "pregnancy" that month, then it is
implantation that is prevented. And this implantation, if
prevented, kills a tiny one-week-old baby.
So the widely used contraceptive pills
have three functions, any one of which is said to "prevent"
pregnancy. Only two of the functions, however, actually do
prevent pregnancy: (1) the barrier mechanism of the mucous
plug at the cervix, (2) the suppression of ovulation. The
third function, however, does not really prevent pregnancy,
but rather produces a micro-abortion at one week of life.
The original contraceptive pills, 30 years
ago, contained a high dose of the hormone estrogen. Because
of this, almost 100% of their effect was to suppress ovulation.
But there were side effects from this high estrogen content,
and that was primarily the substantial risk of blood clots.
If these broke loose and went to the heart, lung or brain,
they were very dangerous, and sometimes fatal, even for young
During the years since that time, the
drug companies have progressively reduced the amount of estrogen
in the pill so that now, depending on the pill, it is only
1/20th, or even 1/30th as much as it
was when the pill was first introduced. With this reduction
in estrogen, there has been a drop in the complication of
blood clots, but, with the reduced estrogen, there has been
an increase in what we call "breakthrough ovulation." The
estrogen level is so low that it doesn't suppress ovulation
all of the time anymore, and sometimes there is what we call
a breakthrough ovulation-ovulation which breaks through the
effect of the drug and is simply a plain old ovulation. It
just happens. Fertilization, then, can occur. But if fertilization
occurs, implantation within the nutrient lining of the womb
is prevented by another action of the same pill. That action
is a hardening of the lining of the womb. What occurs, then,
is an induced micro-abortion at one week of life.
How frequent is breakthrough ovulation
in a woman taking a low-estrogen contraceptive pill? Well,
let's take a high estimate-20%. Probably lower than that.
How frequently does pregnancy occur when there is an egg or
an ovum waiting? Probably not much more than two or three
times out of the twenty.
So if we use a high figure, a 20% breakthrough
ovulation, that would mean a two or three percent fertilization
rate. But, as a matter of fact, pregnancy occurs only about
1% or less of the time, so, in the other 1 or 2%, fertilization
does occur, implantation cannot occur, and the little embryonic
The bottom line, then, for the commonly
used contraceptive pill is this: In 97 or 98% of the time,
the effect is one of preventing pregnancy. But, in perhaps
two or more percent of the time, the effect is abortifacient.
There is no way in the normal clinical practice of obstetrics
of knowing which is happening, or when.