Gestation Periods - Humans & Mammals
We offer the best Condoms at Wholesale and Bulk Quantities
help prevent gestation. Their major role is to block the
union of the sperm and female egg so that no fertilization
takes place thereby preventing a woman from getting pregnant.
For this reason, condoms are considered
very effective in preventing pregnancy and the spread of sexually
transmitted diseases notably in humans. Many users can attest to this
and various non-profit organizations worldwide have actually been
urging people, from teenagers to sexually active adults, to use condoms
for the same reasons. Countries with large populations have also turned
to this birth control method to minimize the increase in birth rates.
While humans can have as many children as they want, it is not ideal
for women in poverty-stricken areas to do this. One reason is that
poor families are not capable of feeding their children and giving
them the proper education as they grow. And in countries that have
huge population, there’s a tendency that a nation’s wealth
will not be equally shared. As a result, various non-profit organizations
around the world have been strongly advocating birth control programs
including the use of condoms and other contraceptives to curb the
increase in birth rate.
Mammals, on the other hand, differ from humans as they can
freely produce as many offspring as they want. They need
to do this to save their species from extinction and their continued
existence is highly important in ecology. Condoms are not their thing.
They don’t have the intelligence to use condoms like humans.
Humans and animals also differ in their gestation period.
While humans have a fixed length of pregnancy, mammals in particular
vary in the length of time they carry their babies in their womb.
Another major difference that’s noteworthy is in the number
of babies they produce. While most pregnant women give birth to only
one baby, medium-sized mammals give birth to a litter or multiple
offspring. Only the large mammals normally deliver a single baby.
Gestation In Humans
Gestation simply refers to the carrying of a fetus in a woman’s
womb or uterus. This is also referred to as pregnancy which normally
takes nine months or specifically from 37 to 42 weeks. The average
length of gestation, though, is estimated at 40 weeks. The reason
for this is that pregnancy begins from the first day of a woman’s
last menstrual period and not from the date of conception. In truth,
the date of conception takes place two weeks after pregnancy begins.
Sometimes, though, there are women who failed to keep track of their
last menstruation notably those with irregular periods. What medical
experts do then is consider a pregnancy in its full term if the expected
due date falls between 37 and 42 weeks. In medical terminology, the
due date is called estimated date of confinement (EDC). Not all pregnant
women, though, deliver their baby on the exact EDC given.
There are various ways to calculate the due date. With the advent
of the internet, this has become very convenient. There are now many
online pregnancy calculators on the web.
The simplest way to determine the due date is to just add seven days
to the date of the first day of your last menstrual period and then
add nine months. So, for instance, if the first day of your last period
is March 10, add seven days (that’s March 17) and add nine months
which results in December 17.
But then, not all women have regular periods and
those with irregular menstruation often find it hard to determine
the date they started conception. And so, there are other ways that
obstetrician-gynecologists (OB-Gyn), or doctors specializing in childbirth
and the treatment of disorders in women’s reproductive system,
use that enable them to estimate the length of gestation. One way
is through an ultrasound examination done between six and 12 weeks.
Other ways include determining the size of the uterus during vaginal
or abdominal examination and the time when the first fetal movements
A pregnancy ultrasound is a non-invasive test that uses high frequency
sound waves to scan the fetus and the mother’s reproductive
organs. It is used to estimate the baby’s due date as well as
diagnose other conditions such as the presence of multiple fetuses,
health problems of the baby, ectopic pregnancy, abnormalities of the
placenta and the reproductive organs of the mother.
The three trimesters
The gestation period starts when a female egg is fertilized
by a sperm inside the fallopian tubes. This important period
in humans is divided into three trimesters with each trimester taking
three months for a total of nine months of pregnancy.
The first three months are critical and involve a lot of adjustment
on the part of the mother. Some first time mothers have mixed emotions
from fear to anxiety to hope for the baby’s future. Sometimes,
the father also experiences unusual feelings as if he’s conceiving
himself. Sexual activity among couples may even be reduced for fear
it could affect the baby inside the womb. Physical changes start to
show during this stage sometimes causing much discomfort. These include
a feeling of bloated breasts, nausea and vomiting causing loss of
appetite at times, frequent urination, fatigue, weight gain and increased
First month – embryo implants on the uterine wall, heartbeat
starts on the 25th day, arm buds show on the 26th day, leg buds show
on the 28th day, embryo is 1/5th inch long.
Second month – the face forms, ears, spine, brain, liver, kidneys,
digestive system start developing, arms and legs developed, fetus
measures 1 and 1/18th inches.
Third month – facial features present, nose and outer ears
formed, head movement and sucking starts, teeth buds form, hair appears
on head, all internal organs formed, swallows amniotic fluid, fetus
about three inches long and weighs one ounce, placenta fully developed.
Fourth month – fetus is complete with strong heartbeat, can
move, kick, sleep and swallow, skin is pale and transparent, measures
6-7 inches and weighs about five ounces.
Fifth month – fetus grows and moves from side to side or somersaults,
may suck its thumb, is about 8-12 inches and weighs ½ to 1
Sixth month – fetus is covered with soft hair known as lanugo,
skin is thin, wrinkled and red, eyes start to open, 11 to 14 inches
in length and weighs 1-1 ½ pounds.
Seventh month – fetus grows and gains weight rapidly, kicks
and stretches, sucks its thumb, opens and closes eyes, 15 inches long
and about three pounds.
Eighth month – less fetal movement due to big size, stronger
kicks, head bones still soft and flexible, about 18 inches long and
Ninth month – fetus gains ½ pound every week, has mature
lungs, settles in good position for birth with its head down and knees
curled up high against the chest.
Phases of human development
There are four phases in the early development of humans. These are
the fertilization stage, implantation, gastrulation and embryogenesis.
The first stage is fertilization which refers to the union of a sperm
and the female’s egg or ova. This is followed by the egg’s
second division that takes place in the fallopian tube or the oviduct.
After this, the egg is now scientifically called a zygote and continues
to travel down the fallopian tube to the uterus.
The second stage is known as implantation. This is when the fertilized
egg gets implanted on the uterine wall and cells are divided and organized
into a two-layered disc. After implantation, the placenta, a rich
mass of tissue filled with blood vessels, is formed. While this takes
place, another group of cells separates from the developing embryo
and develop into the membrane that will surround the fetus or the
embryonic sac. This sac is filled with fluid and helps protect the
fetus as it develops into the later stages. This phase starts during
the second week of development.
Gastrulation is the third phase and occurs during the third week
of fetus development. During this time, the embryo forms a three-layered
disc. Three germ layers are then established – the endoderm,
ectoderm and the central mesoderm. These three later develop into
the different organ systems. It is the mesoderm that forms the umbilical
cord which is crucial in delivering nutrients and wastes between the
fetus and the placenta.
Finally, the last stage is called embryogenesis. This refers to the
real embryonic phase which takes place from the third week through
the eighth week after conception. The organs are developing during
this phase. At the end of this stage, the circulatory system which
involves the heart or the largest organ is already functional. The
nervous system is still in a stag of cell division.
After the embryogenesis, the last stage of human development is called
fetal period taking place from nine weeks to the 38th week. It is
during stage when the fetus forms its appearance.
Two processes are involved here. The first is known as rapid growth
or an increase in the fetus’ size and cell number. The second
process is the differentiation of tissues and organs to be able to
perform their distinct functions.
During rapid growth, the growth rate of the fetus is at its peak
and this occurs until the 16th week. At this time, the weight of the
fetus increases 25 times. However, the biggest rise in weight gain
happens during the last month of gestation. During the last four weeks,
the baby gains as much as 500 grams which is the average weight it
gains during the first 20 weeks of development.
Full term babies normally weigh an average of 7.7 pounds or 3,500
grams. Infants weighing around 2.2 pounds are called immature while
those weighing about 5.5 pounds are premature. Those weighing less
than 500 grams or less do not often survive. Weight is just one way
of gauging the age of a fetus. Length is another way to estimate a
baby’s age and its chances for survival.
Fetal growth is influenced by various factors. These include the
mother’s nutrition, social habits, condition of the placenta
and the genetic makeup of the fetus.
There’s actually a medical sub-specialization known as perinatology
which deals with the mother and fetus during the third trimester or
last three months of pregnancy to about one month after birth. A perinatologist
analyzes the fetus in a variety of ways. One technique is called amniocentesis
which enables the examination of amniotic fluid taken from the mother’s
amniotic sac for metabolites and fetal cells.
As for the fetus, it can be examined via the ultrasound and fetoscopy.
Ultra sonography is non-invasive and makes use of ultrasonic waves.
Fetoscopy is an invasive method which involves the insertion of a
needle into the amnion. This technique is used not only the find out
the fetus’ condition but even to take a sample of fetal issues
The second process involves the development of tissues and organs.
During the earliest stage of fetal development notably in the first
trimester, the head is the most dominant part of the body that can
be seen and accounts for almost half of the fetus’ length. The
face is still flat with eyes wide apart and ears low. At this time,
the intestines protrude temporarily through the abdominal wall and
the external genitalia appear the same between the sexes. The fetus
also excretes urine into the amniotic cavity.
The rest of the body development occurs after the fourth month when
the limbs start to grow. The first movements of the baby inside the
womb or quickening can be felt by the fifth month. Fine hair also
begins to develop. By the sixth month, the fetus can breathe through
its lungs. This, however, depends on the protein-lipid complex called
surfactant secreted from lung cells. If the surfactant is insufficient,
babies born prematurely may like suffer from respiratory distress
The nervous system of a fetus develops reflex responses as it moves
into its seventh month. At this stage, the fetus reacts to light by
constricting its pupils, it can control its breathing and swallowing.
As for the cardiovascular system, it normally experiences major changes
during the time of delivery.
As the fetus is nearing its full term, fat tissue is deposited in
its body. The stomach’s circumference becomes slightly bigger
than the head. What some people find it incredible and hard to comprehend
sometimes is how the baby passes through the birth canal which may
not be as big as the baby. The reason is that the fetus’ skull
still has flat bones separated by the connective tissue known as fontanelles.
This enables compression of the head during delivery or the process
called molding. There’s actually no need to worry when the head
appears misshapen after birth as it will quickly go back to its normal
The process of giving birth is also referred to as labor and has
three stages. The dilation of the cervix is the first stage, then
the actual delivery of the baby and finally, the expulsion of the
Premature and overdue
If a woman gives birth before reaching her 37th week, her baby is
called premature or preterm. Most often, a baby’s chances to
survive is higher if it is closer to the estimated date of confinement
or due date. Most babies born after 34 weeks of gestation and given
great pediatric care will most likely survive.
Preterm babies including those with low birth weights account for
the second leading cause of infant death or 17 percent. These premature
babies are prone to health problems because of their immature internal
organs. The most common problems they encounter include difficulty
in the respiratory system and higher susceptibility to infection.
On the other hand, a baby that has not been born way past the due
date is called overdue. When this happens notably after two weeks
past its expected date, labor is usually induced. Pregnant women who
are one week past their due date without showing any signs of labor
are closely monitored by their doctor. More tests may be conducted
such as the monitoring of the baby’s heart rate using a cardiotocograph
machine and ultrasound scans.
The placenta usually begins to deteriorate after an average of 38
weeks of gestation. In this case, the baby inside may not have sufficient
oxygen supply. Another possibility is that the fetus could grow too
big for vaginal delivery. When this happens, a caesarian section delivery
is the most likely option.
A new research by the Hamilton Health Sciences has found that the
brains of babies born very prematurely do not develop well compared
to full term babies born. Specifically, an ultrasound examination
of the brains of babies born around only 26 weeks of gestation showed
that certain aspects of brain development were affected.
Dr. Sandra Witelson, a professor of psychiatry and behavioral neurosciences
at the Michael G. DeGroote School of Medicine at McMaster University
and chief investigator said in very premature babies, a part of the
brain does not grow in a normal way after birth. Their study also
found that some parts of the brain did not show any changes from the
day the babies were delivered until they reached their supposedly
full term birth date.
The study involved 80 premature boys and girls weighing less than
2.2 pounds and born 26 weeks. The babies’ brains underwent ultrasounds
at birth and before they were discharged from the hospital at already
around 36 weeks. Their ultrasound results were then compared with
those of 38 full term babies also at about 26 weeks gestation and
The study’s results are considered relevant in how premature
babies are cared for. They point out that the early brain may be affected
when subjected to complex stimulation at a very early stage.
Gestation in mammals
Approximately 4,500 species of mammals exists in the world. Mammals
are said to be the best-developed vertebrates and posses highly developed
nervous systems compared to other animals. The largest is the blue
whale with a length of 30 meters and a weight of up to 190 tons. The
African elephant is the biggest mammal living on dry land weighing
up to 5.7 tons.
The common characteristics that mammals share with humans include
the ability to nourish their young with milk from their mammary glands,
the presence of hair as body covering and the existence of a muscular
diaphragm. All mammals produce live offspring that go through the
early stages of development in the womb of the mother. At birth, some
mammals are helpless while the others are able to walk and run right
away with eyes and ears open.
Mammals are bisexual and fertilization takes place internally. This
only means that embryo develops inside the mother’s body similar
to humans. How long the gestation takes place, however, varies among
mammals. Smaller animals like rodents have shorter gestation periods
and they can reproduce as often as six to eight times each year. In
bigger animals, gestation takes longer and they can deliver their
young once in several years. The number of their offspring also differs
usually depending on the size. Smaller animals tend to have a lot
of newborns while big animals often have only one.
Mammals conceive immediately after mating. The period of gestation
may take as short as 12 days to more than 20 months in the case of
the African elephant. In a few species such as bats, rodents and kangaroos,
embryo development can temporarily be stopped at a very early stage.
This is known as delayed implantation or embryonic diapause which
enables the adjustment of the time of birth. In rodents, this system
helps to ensure the proper spacing of successive litters. In kangaroos,
it enables the birth of a young joey to be put on hold until rain
produces enough food for them.
In mammals, gestation begins when a fertilized zygote implants in
the uterus of a female. Did you know that mammals can actually have
one or more gestations at the same time during their pregnancy?
The shortest gestation period is estimated at only 12 days. The mammals
that fall under this category are the American or Virginian opossum,
the rare water opossum and Australia’s eastern native cat. These
three animals give birth to their babies even while still at the embryonic
stage. The young then develop into maturity for about two months inside
a small pouch similar to a kangaroo. From there, they continue to
stay close to their mothers normally holding tight on the back for
If the shortest takes only a few days, the longest gestation in mammals
takes almost two years. The record holder is the African elephant
which carries its baby for approximately 660 days or about 22 months.
Elephants are the biggest land animals that still exist today. Only
three species of elephants are living – the African Bush elephant,
African Forest and the Asian elephant. A newly born elephant would
normally weight 120 kilograms while its lifespan may reach 70 years
or even longer. Also, the infants are weaned only after their first
year of life.
Next in line for having long gestation periods are killer whales,
517 days, followed by the giraffes and camels which carry their babies
in their wombs for 400 days. Baby killer whales or commonly known
as the orca, the largest member of the dolphin family, are born in
the autumn although mating takes place all year round. Female orcas
give birth to only one baby killer whale at a time. After birth, the
baby whale stays close beside its mother for another year before it
Mammals with gestation periods almost similar to humans are the dolphins
(276 days), chimpanzees (237 days) and cattle (280 days).
Other mammals and their gestation periods are bats 5-34 depending
on species, hamster – 16, rat – 21, bear – 31, rabbits
– 33, kangaroo – 40, fox – 42, squirrel –
44, cats and skunk – 62, dogs – 65, guinea pig –
68, lions – 108, pigs – 115, sheep – 150, goats
– 165, baoon – 187, black bear – 210, grizzly bear
– 225, polar bear – 240, reindeer – 215-245, cows
– 280, horses – 336, giraffe – 395-425, camel -
In dogs, the period of gestation may vary depending on whether the
bitch has been bred two or three times or whether the eggs are fertilized
after a day or two days following the mating stage. Eggs can also
remain fertile for about two days and the sperm can stay in the vaginal
tract for several days.
Small sized cats carry their babies for about two months while the
bigger ones for about four months. Each litter consists of one to
six kittens. Breeding happens in the later part of winter or early
part of spring. However, some members of the cat family such as the
lions, tigers and leopards can breed during any part of the year.
Canines give birth to about four to six young after 51 to 80 days
of gestation. Among the carnivores, the Arctic fox produces the biggest
litter, about 11 on average but other times, they can be 20 or more.
As for orangutans, they usually carry their young in the womb for
about eight months. They give birth once every eight years. Wild females
first give birth when they reach the age of 15 or 16. Those in captivity
can, however, give birth at a young age of seven.
Where bats are concerned, everything in their sexual cycle is synchronized
– from the gestation, birth, lactation and weaning. It’s
only in the gestation period where they differ depending on the species.
Black bears mate in June and July but implantation of the fertilized
egg is delayed and takes place in November or December. Gestation
takes from 60 to 70 days and by January or February, four cubs are
born. The cubs come out as blind, with hair and no tooth and they
stay with their mother for 16 months.
The brown bears deliver their babies during the winter season. The
cubs are usually twins and were developed in their mother’s
womb for about six to eight months. A cub weighs less than one kilogram
Camels have a gestation period of about 14 months and they give birth
to their young during the rainy season.
Wolves breed between the months of February and April and give birth
to about six puppies in the spring. Gestation lasts for about two
months. Their favorite place of delivery is the den notably a natural
hole in a hillside. Otherwise, a hollow log or abandoned beaver lodge
Not all mammals breed all year round. Most of them, though, have
specific breeding seasons that allow their date of delivery to coincide
with times when food is abundant. In some species, females show signs
when they are ready to mate. In most mammals, however, males know
when females are fertile by sensing the pheromones or the airborne
chemicals. There are some mammals such as cats and horses that can
sense these pheromones with their Jacobson’s organ found on
the roof of their mouth.
All mammals reproduce through sexual contact which involves two types.
In the egg-laying mammals, their excretory and genital organs open
into a common orifice known as the cloaca. The sex cells are normally
transferred from the male to the female by bringing the cloacae into
In other mammals, the male sex cells are transferred during copulation.
After fertilization takes place, the offspring develops inside the
mother’s body. However, for the monotremes, they produce eggs
with large yolks and leathery shells. In many marsupials, gestation
occurs only from 10 to 15 days with the young developing in the mother’s
pouch after birth. All the other mammals stay close to their mother
after birth for some time before they can continue an independent
Milk from the mother’s mammary glands nourishes the newborn
mammals with water and other vital nutrients. Mammals have a strong
sucking instinct that enables them to feed immediately after birth.
In marsupials and placental mammals, milk is released by a set of
nipples also known as teats. They feed differently, though. While
the young placental mammals normally leave their mother’s nipples
between feedings, the newborn marsupials are stuck firmly to their
mother’s nipples via their mouth and cannot be moved.
If mammals differ in the way they breed, the length of their gestation
and how they feed their young, they also differ in the age they achieve
sexual maturity. Rhinoceros, for instance, are considered sexually
mature at the age of 20.
Fertilization of the egg or ovum in most mammals occurs high up in
the fallopian tubes. It is when the fertilized egg moves down the
fallopian tubes when the cell undergoes its initial division. The
egg initially turns into a ball of cells known as morula. The next
process involves the separation of the egg into an inner cell mass
and an outer layer of cells and this is known as blastula. Separately,
the inner cell mass is called the zygote while the outer layer of
cells is called the chorion.
While the cell growth moves down the fallopian tube, it gets nourished
by the stored food in the egg. However, nutrition is in short supply
in mammals and the zygote will eventually need an additional source
of food. From the fallopian tubes, the fertilized egg then enters
the uterus or the uterine cavity.
Once inside the uterus, the egg connects with the endometrium of
the uterine wall in different ways depending on the species of mammal.
From here, embryonic tissues and a host of maternal material are then
developed by the placenta. The placenta can actually take five various
forms depending on the degree of contact and the number of tissue
layers between the maternal and the embryo’s blood supply.
The layers of tissue that develop on the maternal side are known
as the endometrial epithelium, connective tissues and the blood vessels’
endothelium. On the part of the embryo, the tissues involved are the
blood vessels’ endothelium, the mesenchymal tissues and the
chorion. Experts point to the varying lifestyles of the different
species of mammals as a major factor in the differences in placenta
forms that take place.
Most mammals are known to be placental mammals including rabbits,
cows, yaks, hippopotamuses, bats and humans. In other words, they
are developed inside a placenta in a longer gestation period. The
placenta here plays a vital role in allowing a longer gestation period.
It is the placenta which enables nutrients from the mother to travel
to the embryo. It also enables waste products to leave the embryo
so they can be discharged by the mother.
The placenta is made up of several layers of material. It is comprised
with blood vessels which serve as a courier of nutrients originating
from the mother’s system to the embryo. While the white blood
cells and other components of the immune system including blood are
maintained within their own areas, the nutrients from sugar and fats
to the minerals are passed into the embryo and the waste products
discharged. This biological fact enables young mammals to stay longer
in their mother’s womb and after they are brought out into the
world, are already able to run along with their parents after only
a few hours or days.
It is worth noting that the gestation period of a mammal sometimes
depends on its size. In other words, the bigger the animal, the longer
is its gestation period. And that’s why the largest animal on
earth, which is the elephant, carries its baby inside its womb for
approximately 22 months.
Out in the world
Most mammals give birth to their young on their own. However, there
are some species such as the dolphins and elephants that get help
from non-breeding females during their birthing process. Placental
mammals that gather around the animal giving birth often lick the
embryonic membranes off the newly born young and nudge them to the
mammary glands of the mother for their very first milk. This the complete
opposite showed by female marsupials in that they just leave their
young to find their own way into the pouch without any help from the
Not all mammals, however, are the same especially when it concerns
their newly born young. Did you know that herbivores or the plant-eating
mammals are actually more capable of standing and moving on their
own just a few minutes after they are born compared to the carnivores
or meat-eating mammals?
Another interesting to note is that even mammals belonging to a single
order differ greatly. For instance, newly born rats have their eyes
closed are naked and helpless after a gestation period of 21 days.
On the other hand, a baby guinea pig is born with open eyes, covered
hair and is almost capable of feeding itself after a 67 day gestation
period. Another example is the rabbit born with eyes closed while
its relative, the hare is born with open eyes.
From all this information we have detailed, one thing that can be
deduced is the fact that gestation happens only when the sperm meets
the female egg and that only humans can make use of the condom as
a way of controlling
birth. It also serves a vital function in the proper spacing of children
and preventing the spread of infectious diseases that can be transmitted
through sexual contact. Condoms now come in different forms, in various
scents and flavors and manufactured for use by men and women.
Yes, humans may be part of the mammal family but, unlike animals,
they cannot just go on having children frequently. Men have to remember
that there is a limit to the capacity of a woman’s reproductive
system, notably the uterus where the baby develops. While sure, the
more children, the merrier the family, a couple should put a limit
to the number of children that they want to raise. Times are hard
and education is becoming more expensive these days.