Psychology2016

Development across the Life Span 321

affect the physical functioning (physiology) of the organs rather than their structure.
The functioning of the central nervous system, for example, is vulnerable throughout
the fetal period, as are the eyes and the external sexual organs.
The last few months continue the development of fat and the growth of the body,
until about the end of the 38th week. At 38 weeks, the fetus is considered full term. Most
babies are born between 38 and 40 weeks. Babies born before 38 weeks are called preterm
and may need life support to survive. If they are very premature, they may also experi-
ence problems later in life. This is especially true if the baby weighs less than 5½ pounds
at birth. How early can an infant be born and still survive? The age of viability (the point
at which it is possible for an infant to survive outside the womb) is between 22 and
26  weeks, with the odds of survival increasing from 10 percent at 22 weeks up to about
85 percent at 26 weeks (National Commission for the Protection of Human Subjects of
Biomedical and Behavioral Research, 2006). Those odds will also increase if the infant is
in a facility with advanced neonatal health care (Rysavy et al., 2015).
The most likely time for a miscarriage, or spontaneous abortion, is in the first 3 months,
as the organs are forming and first becoming functional (Katz, 2007; Speroff et al., 1999).
Some 15 to 20 percent of all pregnancies end in miscarriage, many so early that the
mother may not have even known she was pregnant (Doubilet et al., 2013; Hill, 1998;
Medical Economics Staff, 1994; Nelson et al., 2015). When a miscarriage occurs, it is most
likely caused by a genetic defect in the way the embryo or fetus is developing that will
not allow the infant to survive. In other words, there isn’t anything that the mother did
wrong or that could have been done to prevent the miscarriage.

This pregnant woman is getting an

ultrasound. Ultrasounds use high-frequency

sound waves to create a picture, or

sonogram, that allows doctors to see any

physical deformities and make accurate

measurements of gestational age without

risk to the mother or the fetus.

once attached to the uterus,

developing organism is called an

embryo

embryonic period

(2 weeks after conception

to 8 weeks)

cell differentiation is the process

that results in specialized cells for

all of the various parts of the body

germinal period

(2-week period

following fertilization)

fetal period

(from about 8 weeks to birth)

egg and sperm unite through

process of fertilization, resulting

in a single cell (zygote) that has 46

chromosomes

through mitosis, zygote begins to

divide, into two cells, then four, etc.,

until baby is formed

zygote continues dividing and

moving toward the uterus; the

placenta and umbilical cord also

develop during this time cell specialization continues to

occur, resulting in the preliminary

versions of various organs

embryo is vulnerable to hazards

such as diseases and substances

ingested by the mother as it

receives nourishment through the

placenta

developing organism now called

a fetus; time of tremendous

growth and development

organs continue to develop

and become fully functional

miscarriages (spontaneous

abortions) are most likely

to occur in the first 3 months

full-term birth occurs around

end of 38th week

alterations in mitosis can result in

twins or multiples

fertilization, the zygote,

and twinning

Prenatal Stages

Prenatal Development

from conception to birth of the baby is approximately 9 months in humans

Concept Map L.O. 8.4, 8.5

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