Definition of Fertility

The ability to conceive a pregnancy, and in women to also carry the pregnancy to term. Men and women both become fertile during puberty, when sexual maturity results in the development of secondary sexual characteristics.

Men remain fertile all of their lives and are fertile on a continuous basis; women remain fertile through their late 40s or until menopause and are fertile on a cyclic, monthly basis.

Female Fertility: Ovulation, Conception, and Pregnancy

Within a narrower context, fertility is the period of time within a woman’s menstrual cycle when she is physiologically capable of conception. This period of time is the approximately 48 hours before and 24 hours after ovulation (release of an ovum). The ovum remains receptive to fertilization during the time it travels through the fallopian tube on its way to the uterus.

Sperm can survive 48 to 72 hours after entering the woman’s reproductive tract (such as with sexual intercourse). A woman can conceive when viable sperm are present in her body when she ovulates.

Knowing the precise timing of ovulation is difficult because it varies somewhat from one menstrual cycle to another. As well, physical illness, trauma, or surgery can affect ovulation and fertility. Several methods may help a woman estimate when she is ovulating.

The easiest, though the least precise, is counting 14 days back from the anticipated first day of menstruation. The days fertility is most likely are 12, 14, and 16 days before the onset of menstruation. This method is imprecise because many women ovulate earlier or later than 14 days and experience variation from one menstrual cycle to another. Other methods may detect when ovulation occurs but cannot predict it before the fact.

The simplest device-oriented measure to estimate a woman’s fertile time is basal body temperature. This is the first temperature of the day, taken before getting out of bed and with minimal movement. A woman’s body temperature is up to one degree higher after ovulation than before ovulation. The beginning of the rise marks ovulation. Either a regular oral thermometer or a basal body thermometer (which registers only between 96ºF and 100ºF) works for this purpose. Combining basal body temperature with calendar timing is more accurate than either method alone.

Home ovulation tests may examine saliva or urine. The urine test, which has been available since the mid-1980s, detects the presence of luteinizing hormone (lh) in the urine. The pituitary gland releases LH to stimulate the luteal, or secretory, phase of the menstrual cycle and the ultimate release of the ovum.

The LH test is similar to a home pregnancy test in that the sample of urine causes a change in the indicator when LH is present in the urine. The saliva test, which became available in 2002, allows examination of the saliva for changes in the concentration of potassium chloride.

The amount of potassium chloride in the saliva increases during the luteal phase, a reaction to the surge of estrogens that precedes ovulation. The saliva test uses a small microscope, which comes with the test kit, to examine a drop of saliva on a slide for the pattern of potassium chloride. Small spots are normal; fernlike patterns suggest ovulation.

The final element of fertility in women is the ability to sustain pregnancy through birth. Some conceptions are unable to implant, perhaps because of extensive uterine fibroids, excessively tipped uterus, malformation of the uterus, and other circumstances in which the uterus cannot support the blastocyst. As many as a third of pregnancies spontaneously abort (miscarry) within the first eight weeks. Spontaneous abortion becomes less common after the 14th week.

Though a woman retains fertility for as long as she ovulates and has menstrual cycles (even if irregular), her fertility diminishes as she approaches menopause. Menstrual cycles and ovulation often become irregular in timing, and anovulatory cycles (menstrual cycles without ovulation) become more common. Other factors that influence fertility in women include

Male Fertility and Conception

Male fertility relies on the motility (movement and thrust), morphology (physiologic form), and volume of sperm present in the ejaculate (semen that leaves the man’s penis with ejaculation). Laboratory examination of a sperm sample measures these and other factors; there are no home tests for sperm viability.

Sperm can live about 72 hours in the woman’s reproductive tract, though the environment of the vagina is particularly hostile, and about half of the 500 million or so sperm typically present in a fertile man’s ejaculate die during their passage through the it.

However, dead and dying sperm are important to fertility because they provide protection and support for living, motile sperm. Dead sperm help form a protective barrier around surviving sperm. The movement of dying sperm helps propel onward the cluster of sperm that remain viable.

One healthy, functioning testicle is adequate to produce enough sperm for fertility. Though a man remains fertile all his life the quality of his sperm (motility, morphology, and other characteristics) tends to decline in his later years (age 70 and older). This may become an issue in regard to fertility if the woman’s fertility is marginal. Other factors that influence male fertility include

Body temperature also affects male fertility. Normally the scrotum (saclike structure that contains the testicles) rises and lowers to maintain ideal temperature for spermatogenesis (production of new sperm).

Fever, sitting in a hot tub, and wearing clothing that holds the scrotum tight against the body are factors that can raise the temperature in the testicles to one at which sperm cannot survive. Though these often are temporary factors, they may be permanent.

See also AGING, REPRODUCTIVE AND SEXUAL CHANGES THAT OCCUR WITHASSISTED REPRODUCTIVE TECHNOLOGY (ART)STILLBIRTH.

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