By: Carlos Daniel Caicedo &
Carlos Eduardo Calle
What is Gestation?
 Gestation is when a female viviparous* animal carries
an embryo* or fetus.
 The interval time of a gestation plus two weeks is
called gestation period*.
 The length of time plus two weeks that the offspring
have spent developing in the uterus is
called gestational age*.
What is gestation period?
 In mammals the gestation
period is the period in which
the fetus develops, this starts
with the fertilization and
ends on the birth.
 Smaller species normally have
a shorter gestation period
than larger animals:
 An example is the gestation
period of a cat it normally
takes 58–65 days while an
Elephant's gestation period
lasts 645 days.
 In humans the gestation
period is normally of
nine months.
 Factor such as gender
can affect the duration
of the gestation period,
for us humans a male
fetus tends to gestate
longer than female
fetuses and multiple
pregnancies, tend to
take a shorter time.
 The ethnicity (race)
make the gestation
period longer or shorter.
Gestational age
 Gestational age is the time measured from the first day
of the woman's last menstrual cycle to the date were
the baby is born, it is measured in weeks. A normal
pregnancy can range from 38 to 42 weeks.
 Infants born before 37 weeks are considered
premature. Infants born after 42 weeks are considered
post mature.
 You can determine the gestation age in two ways,
before or after the baby is born:
 Before birth, growth is determined with ultrasound by
measuring the size of the head, and abdomen.
 After the birth, it can be
determined by measuring
the babys head
circumference, the babys
height, condition of skin and
hair, reflexes, muscle tone,
posture, and vital signs.
 Finding the gestational age
is really important because
with this doctors can gather
valuable information of
expected or potential
problems that the baby
could have.
Whats a zygote?
 After a female egg is
fertilized, the resulting one
celled organism is called
zygote. Once the egg is
fertilized, the zygote begins a
two week period of rapid cell
division and becomes to be a
 The zygote divides with the
process of mitosis, in witch
each cell doubles by dividing
in two cells.
 This two week period is
called the germinal period of
 A zygote is a single diploid cell(a
diploid cell is cell with two
chromosomes), created through
the merging of two haploid cells
(a cell that contains a complete
set of chromosomes).
 The period of the zygote lasts for
about four days. Around the fifth
day, the mass of cells becomes
known as a blastocyst
(the blastocyst is a structure
formed in the
early embryogenesis of
mals). The germinal period will
last for fourteen days, after this
the embryonic period begins.
Whats a embryo?
 An embryo is an organism
in the early stages of
development which cannot
survive on its own.
 The precise definition of
an embryo varies; in
humans, for example, a
fertilized egg may be
considered an embryo until
around the eighth week of
pregnancy, as
the embryo mature it starts
to turn into a recognizable
form to the point when
people start referring to it
as a fetus, especially in
 The term “embryo” is
only used to refer
to eukaryote (or
organisms) organisms.
 The formation of
an embryo starts
at fertilization, when
eggs and sperm meet,
they form what is
known as a zygote.
After fertilization, the
zygote starts to divide,
when division begins
the zygote turns into
an embryo.
Multiple gestations
 Occurs when two or more fetuses are conceived at the
same time in the same woman.
 With multiple gestation, the fetuses are either
monozygotic* or dizygotic*.
 There is a higher rate of occurrence with use of fertility
drugs or treatments, such as in vitro fertilization.
 Monozygotic: during conception, the sperm fertilizes
one egg, which will later split into two or more
developing embryos.
 Dizygotic multiples: occur when a woman’s body
releases several eggs, and those eggs are each fertilized
by different sperm. The resulting fetuses are fraternal
siblings, and are not identical.
Social factors which affect
 Medications and drugs can also impact embryonic growth.
This 8,000 babies were born with birth defects because
their mothers had taken the tranquilizer Thalidomide.
 Some races are more prone to teen pregnancy, data taken
by “The Guttmacher Institute ” show that:
 blacks typically have 126 teen girls become pregnant in every
1,000 girls.
 Hispanic have 127 teen girls become pregnant in every 1,000
 Non-Hispanic whites average 44 pregnancies per 1,000 girls.
 Today researches show that a girl who lives in poverty
is more likely to become pregnant because of
teachings and attitudes on sex, as well as access to
Enviromental factors which affect
 Researchers found that the air quality of the area was worse
during the winter months, and the infants conceived during
those winter months saw the most intrauterine growth
 Smoking during gestation cause aproximately 20 to 30 percent of
low-birth weight babies.
 Reaserches states that up to 14 percent of preterm deliveries are
due to smoking.
 What is the difference between a pregnancy and
Pregnancy is the fertilization and development of the
offspring in womans uterus, while gestation is the
carrying of the embryo .
 Why do all animals have a different gestation period?
For most species, the amount a fetus grows before birth
determines the length of the gestation period. Smaller
species normally have a shorter gestation period than
larger animals.