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"NO MORE CHRISTIAN DOCTORS"

Appendix "E"

 Human Fertility Cycles


Introduction

What is provided here is not exhaustive.  It is intended only to provide the reader with sufficient information to understand the factors and issues likely to be involved when health care workers decline to provide contraception services for reasons of conscience.

Contents

E1.  Male fertility

E2.  Female fertility

E3.  Combined fertility

E4.  Comparing Male, Female and Combined Fertility Patterns


E1.  Male fertility
Sperm production

Sperm production begins during puberty, generally between the ages of 10 and 15.  For present purposes an approximate age of 14 is a satisfactory estimate.1 From that point until death, sperm production is continuous.

Sperm lifespan

Sperm that is not ejaculated is reabsorbed by the body.2  Outside the body, the lifespan of sperm depends upon the environment.  In a hostile environment, sperm will die rapidly, though it may live a few hours in seminal fluid.3  In a supportive environment, sperm can live five to seven days, though five days seems to be the commonly accepted upper limit.4

Male fertility during reproductive lifespan

Since sperm production is continuous from puberty until death, fertility during a man's reproductive lifespan can be represented by a pie chart illustrating fertility for 100% of that period (Chart E1.1).  Male fertility can also be represented by a pie chart illustrating fertility as a percentage of the average male lifespan (Chart E1.2).

Chart E1.1(click to enlarge)
Male fertility 01
Chart E1.2 (click to enlarge)
Male Lifetime Fertility
E2.  Female fertility
Ovulation

A woman actually begins the production of oocytes during her development as a foetus.  By puberty she has about 400,000 primary oocytes in her ovaries.  The popular term for an oocyte (primary or secondary) is "egg," so that term is used here.5  Ovulation - release of the egg from the ovary- occurs during each menstrual cycle.  The age at which the first and last menstrual cycles occurs is quite variable.  For present purposes we assume they begin at about age 12, and end at about age 50. 

Egg lifespan

After ovulation an egg must be fertilized within 12 to 24 hours, or fertilization cannot take place and it will die.  Thus, for reproductive purposes, the lifespan of an egg can be said to be 12 to 24 hours.6

Female fertility during reproductive lifespan

From the beginning of sperm production at puberty until death, a man has the capacity to cause a pregnancy 24 hours a day, 365 days a year.  In contrast, a woman can become pregnant only for a 12 to 24 hour period following ovulation during each menstrual cycle.  The enormous difference between the male and female fertility pattern becomes more readily apparent when the female pattern is illustrated by a pie chart. 

Calculations to produce the chart begin by calculating an approximate reproductive lifespan, assuming that ovulation begins at about age 12, and ends at about age 50.

50-12 = 38 years

Assume 13 cycles per year.

38 X 13 = 494 cycles in a lifetime.

IN EACH CYCLE

Assume egg present one day

494 cycles X 1 = 494 days

Expressed as years

494 days / 365 days = about 1.4 years.

Expressed as a percentage of average reproductive lifespan (38 years)

= about 4% (Chart E2.1)

Expressed as a percentage of women's average lifespan (83 years)

= about 2% (Chart E2.2)

Chart E.2.1 (click to enlarge)                              Chart E2.2 Female Reproductive Lifetime Fertility Female Lifetime Fertility(click to enlarge)

 

E3.  Combined fertility
Effect of cervical mucus

While fertilization can occur during only a 12-24 hour time-span during each menstrual cycle, or about 4% of a woman's reproductive lifespan, this does not mean that she can become pregnant only if sexual intercourse occurs while the egg is available for fertilization.

The reason for this is that the lifespan of sperm in the female reproductive tract increases dramatically in the presence of a specific kind of cervical mucus produced in the days leading up to ovulation.  This mucus will sustain viable sperm for three to five or even seven days.4  It is, in fact, essential if fertilization is to occur.  In the presence of this sperm-supportive mucus, sexual intercourse on a Wednesday (before ovulation) can result in a pregnancy after ovulation on Saturday.

We can illustrate the combined fertility pattern using a pie chart.  We begin the calculations as we did above, assuming a 38 year reproductive lifespan with 13 reproductive cycles per year, yielding 494 cycles in a lifetime.

IN EACH CYCLE

Assume seven days combined fertility

494 cycles X 7= 3,458 days

Expressed as years

3,458 days / 365 days = about 9.5 years

Expressed as percentage

= about 25% (Chart E3.1


E4.  Comparing Male, Female and Combined Fertility Patterns

Male fertilityFemale FertilityCombined Fertility











Notes

1.  Kuhn HE,  Frontera MA, Demers LM, Bartholomew MJ, Lloyd TA. The Onset of Sperm Production in Pubertal Boys:  Relationship to Gonadotropin Excretion.  Am J Dis Child. 1989;143(2):190-193. doi:10.1001/archpedi.1989.02150140080024

2.  WEBMD, Birth Control Health Center: Vasectomy.  (Accessed 2014-02-13)

3.  Harms RW, Sperm: How long do they live after ejaculation?  Mayo Clinic, 5 May, 2012 (Accessed 2014-02-14)

 4.  "[Our] finding. . . indicates that sperm retain their ability to fertilize an ovum for up to five days in the female reproductive tract . . . Motile sperm have been found in the cervical mucus for seven or more days after insemination . . .". . Wilcox, A.J Clarice R. et al, "Timing of Sexual Intercourse in Relation to Ovulation." N Eng J Med 1995; Vol. 333 No. 23: 1320, citing Perloff WH, Steinberger E., In vivo survival of spermatozoa in cervical mucus. Am J Obstet Gynecol 1964; 88:439-42; and Glezerman, M. Artificial Insemination. In Insler, V. Lunenfeld, B. eds. Infertility: male and female. 2nd ed. New York: Churchill Livingstone, 1993.

5.  O'Rahilly R.  and Muller F. Human Embryology & Teratology. New York: Wiley-Liss, 2001, p. 87. Quoted in Irving D. "When do Human Beings Begin? 'Scientific' Myths and Scientific Facts.International Journal of Sociology and Social Policy 1999, 19:3/4:22-47

6.  University of California San Francisco, Center for Reproductive Health.  Conception: How it Works. (Accessed 2014-02-13

 

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