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Biology Summaries
Pregnancy Length

Gestation Periods Chart

by Vaughn Aubuchon

Here is a pregnancy period comparison chart of human babies, selected pets and other mammals.
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The length of a human pregnancy is usually referred to as "9 months" for a baby, which is not completely accurate. It's 14 days less, if measured from conception.

The length of time in the womb for humans and other mammals varies considerably, based mostly upon size. Note that the length of a mammal's life expectancy is also closely related to its physical size.
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      Human Pregnancy Length
         vs.
      Some Pets and Animals

Time
Groups

Mammal
Species
Preg.
# of
Days

Life
Expect.
Years

   Notes


Group

1

Opossom

12

-

 small size
 rapid heart rate
 short life

Hamster

16
17

 

 -

-

Mouse/ Rat

21
3

Rabbit

31
8

Skunk

31

-

(gap)

Group

2

Squirrel

44
9

 (years)

Eagle, Golden

44

-

 -

Bobcat

60

-

 -

Dog

61
12

 50-70 days- species dependent

Cat

63
12

 58 - 65 days

Scorpion

90 - 540

-

 highly species dependent

Lion

108
10

 -

Pig

114
10

 -

Goat

145

-

 -

Sheep

150
12

 -

(gap)

Group

3

Bear, Grizzly

220
30

  (tens of years)

Human baby*

266*
76

 (40 weeks = 280 days)*

Cow

284
12

 -

 -

 (gap)

 -

 -

Horse

336
25

 -

Sea Lion

360

-

 -

Wha|e

360
80

 -

Donkey

374
20

 

(gap)

Group

4

Camel

400
40

 large size
 slow heart rate
 long life

Giraffe

425
25

Rhino, Grey

480

-

 

  (gap)

 -

Rhino, Black

540

-

Elephant, Asia

610
40

Elephant, Afr.

660
40

 
   Average human baby pregnancy time vs. other mammals.
   In general,
   the larger the animal, the longer the gestation period.
   In general, the larger the animal, the longer the life.

* = 280 days, from the first day of a woman's last menstrual period.
    = 266 days, if measured from the sperm joining the ovum.

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50

100

50

50

200 - 450

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This Vaughns Summaries Gestation Period
Summary was last updated on 2019-10-01.