The document details the gestation period in humans, explaining it as the time from conception to birth, averaging about 40 weeks. It outlines the three trimesters of pregnancy, detailing developmental milestones of the fetus during each stage. Additionally, it compares gestation periods across various mammals, highlighting differences according to species.

1. Gestation period in Humans
Samarth Patel | BIOLOGY | 12 Science

2. PAGE 1
INDEX
Srno Topic Page
1 What is gestation period? 2-3
2 Gestation period in humans 4-5
3 Phrases of human gestation
period
1. First trimester
2. Second trimester
3. Third trimester
6-12
4 Gestation period of different
mammals (table)
13-15
7 Summary and observation 16
8 References 17

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What is Gestation Period?

4. PAGE 3
 We have studied that gestation is period of embryonic
development.
 In broad, Gestation is the carrying of an embryo or fetus
inside female viviparous animals. It occur in in mammals, but
also occurs for some non-mammals. Mammals during
pregnancy can have one or more gestations at the same
time (multiple gestations).
 The time interval of a gestation is called the gestation period.
In human obstetrics, gestational age refers to the embryonic
or fetal age plus two weeks.

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Gestation Period in
Humans

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 In mammals, pregnancy begins when a zygote implants in
the female's uterus and ends once the fetus leaves the
uterus.
 In Humans, Pregnancy begins at conception when the sperm
from the man fertilizes the egg, or ovum, of the woman. The
gestation period for humans continues until the child is born.
The “normal” gestation period is about 40 weeks, but may
range from 37 to 42 weeks and still be considered a normal
pregnancy.

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Phrases of human gestation period
 Human pregnancy can be divided roughly into three
trimesters, each approximately three months long.
 The first trimester is from the last period to the 13th week.
 The second trimester is from the 14th to 27th week.
 The third trimester is from the 28th week to the 42nd week.

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First Trimester
 During this trimester, the fetus implants into the womb of
the woman.
 During the first month the lungs are formed, the heart
starts beating and the spinal cord is growing.
 The placenta also develops at this point in the first
trimester.

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 In the second month head and facial features are shaping,
including eyes and mouth. Hands and feet are also
forming.
 At the beginning of the third month fetus is around 3 cm
long, fingers and toes are formed as well as sexual
organs.
 At the end of third month, fetus is approximately 8 cm long
and develops immunity towards infections thus the risk of
miscarriage is lower.

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Second Trimester
 During the 2nd trimester, the baby begins to grow rapidly.
 At the start of the fourth month, the baby has fine hair
covering the body and can curl the fingers.
 By about the 20th week (5 month) of the gestation period,
most women will begin to feel movement of the fetus.

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 In the fifth month, senses are developed and the skin is
protected by a layer of a waxy secretion.
 By the end of 24 weeks (6 month)-
1.Body is covered with fine hairs.
2.Eye lids separate.
3.Eye lashes are formed.
4.Strong digestive and immune system.

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Third Trimester
 During this period, the fetus increases in size and stretches
the uterus and abdomen of the woman. In the first part of
the 3rd trimester, the fetus will be at its most active and
movement will be very obvious. As the child fills up the
available space, movement will become less but stronger
and the woman will become more uncomfortable.
 At the beginning of the last three months, almost every
organ, except for the lungs, begins to function.

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 During the seventh month the brain starts to develop.
 The movements decrease because of the baby’s large size.
The baby is positioned for the birth, with its head down.
 By the end of 9 months the baby is fully developed and
ready for delivery.

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Gestation Period of different
mammals

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Mammal
Species
Gestation period
(Days)
Opossum 12
Hamster 16
Mouse/ Rat 21
Rabbit 31
Skunk 31
Squirrel 44
Eagle, Golden 44
Bobcat 60
Dog 61
Cat 63
Scorpion 90 - 540
Lion 108
Pig 114

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Goat 145
Sheep 150
Bear, Grizzly 220
Human baby 266
Cow 284
Horse 336
Sea Lion 360
Whale 360
Donkey 374
Camel 400
Giraffe 425
Rhino, Grey 480
Rhino, Black 540
Elephant, Asia 610
Elephant, African. 660

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Summary
 Gestation period is the time period in which the fetus gets
develops inside the mother womb.
 It occurs in all the mammals.
 Every mammal have different time period of gestation
period.
 Gestation period may depend on the size of organisms.
Observation
 From the research I have learnt that there are many
aspects in field of biology.
 I am able to study the intermediate aspect of reproduction.
 We can now say that gestation period is very important
time period when it comes to childcare.

18. PAGE 17
References
1. NCERT Class 12 biology
2. Pradeep Class 12 biology guide
3. Wikipedia.com
4. steadyhealth.com
5. youtube.com
6. Notes by nithya madem
Thank you!