between them are in different developmental
stages for most of their childhood years, requiring
different kinds of attention. Providing adequate
attention to each child is more difficult when their
ages are so close together that their needs are sim-
ilar. Birth spacing requires either abstinence or
some form of contraception between pregnancies
to prevent unintended pregnancy.
People may choose adoption (acquiring legal
responsibility for a nonbiologic child) as an option
for resolving INFERTILITYor because they feel it is a
personally desirable or socially responsible
approach to creating a family. Other people may
choose to have no children, opting instead to
define family in other ways.
See also ABORTION; GESTATIONAL SURROGACY.
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 MENOPAUSEand are
fertile on a cyclic, monthly basis.
Female Fertility: Ovulation,
Conception, and PregnancyWithin a narrower context, fertility is the period
of time within a woman’s MENSTRUAL CYCLEwhen
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 fertiliza-
tion during the time it travels through the fallo-
pian tube on its way to the UTERUS. SPERMcan
survive 48 to 72 hours after entering the woman’s
reproductive tract (such as with SEXUAL INTER-
COURSE). A woman can conceive when viable
sperm are present in her body when she ovulates.
Knowing the precise timing of ovulation is dif-
ficult because it varies somewhat from one men-
strual cycle to another. As well, physical illness,
trauma, or surgery can affect ovulation and fertil-
ity. 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 fer-
tility is most likely are 12, 14, and 16 days before
the onset of menstruation. This method is impre-
cise 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 esti-
mate a woman’s fertile time is basal body temper-
ature. 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 ovula-
tion. Either a regular oral thermometer or a basal
body thermometer (which registers only between
96ºF and 100ºF) works for this purpose. Combin-
ing 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 PITU-
ITARY GLANDreleases LH to stimulate the luteal, or
secretory, phase of the menstrual cycle and the
ultimate release of the ovum. The LH test is simi-
lar 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 ESTROGENSthat
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 preg-
nancies spontaneously abort (miscarry) within the
first eight weeks. Spontaneous ABORTIONbecomes
less common after the 14th week.282 The Reproductive System