Day 1
First mating occurs. Millions of sperm are released and begin travelling through the reproductive tract toward the eggs. Ovulation may already be occurring or may happen shortly after.
Day 2
Sperm continue maturing and moving through the reproductive tract in search of eggs to fertilise.
Day 3
Fertilisation may begin. A second mating can still successfully occur around this time.
Day 4
Eggs are fertilised. Early pregnancy has begun, although there are no visible physical changes yet.
Days 5–11
Fertilised eggs travel down the fallopian tubes toward the uterus where implantation will later occur.
Day 12
Tiny embryos shed their outer membranes and float freely within the uterus while searching for implantation sites. Embryos are approximately 0.6 mm long.
Day 13
Embryos continue searching for suitable implantation areas within the uterine lining.
Day 14
Embryos spread evenly through the uterine horns in preparation for implantation.
Day 15
Major organ development begins. This is a very sensitive stage of pregnancy where medications, stress, illness or toxins may affect development.
Day 16
The dam’s nipples may become slightly enlarged and pinker. Embryos measure about 1 mm.
Day 17
Embryos implant into the uterine wall. Early nervous system development begins.
Day 18
Placenta formation begins. Development of the nervous system continues. Embryos are about 2 mm long.
Day 19
Internal organs begin forming rapidly.
Day 20
Placental development continues. Embryos measure approximately 4 mm. Pregnancy may sometimes be detected by experienced palpation or ultrasound.
Day 21
The placenta is more established and early heart development begins. Fluid-filled gestational sacs may be visible on ultrasound. Embryos are around 5 mm long.
Day 22
Some dams develop mild morning sickness, reduced appetite or lethargy due to hormonal changes.
Day 23
Eyes, ears, nose, jaws and liver begin developing. Embryos are approximately 10 mm long.
Day 24
Rapid organ development continues while overall growth remains slow.
Day 25
Heartbeat may now be visible on ultrasound. Teeth buds, spine and limbs begin forming. Embryos measure around 14 mm.
Day 26
Embryos are roughly walnut-sized and may sometimes be felt by an experienced veterinarian. Limb and skeletal development progresses.
Day 27
Pregnancy is commonly confirmed by ultrasound during this stage.
Day 28
Jaw and skull bones begin ossifying (hardening). Puppies change from an oval to a more rounded shape. Approximately 17 mm long.
Day 29
Foetuses now resemble miniature puppies. Food intake may gradually increase.
Day 30
Skull and jaw ossification continue. Puppies are about 2 cm long.
Day 31
Sensory whiskers begin growing on the muzzle, chin and eyebrows.
Day 32
Foetuses reach roughly 20% of their eventual birth size.
Day 33
Toes form and ribs, nose and leg bones continue ossifying. Major organ development is nearly complete. Puppies measure about 27 mm.
Day 34
The dam may appear calmer and more affectionate. Abdomen and vulva may begin enlarging slightly.
Day 35
Major organ development is complete. Puppies are about 35 mm long. Appetite usually increases noticeably.
Day 36
Rapid foetal growth phase begins. Reproductive organs and skeletal structures continue developing.
Day 37
The fastest stage of puppy growth begins.
Day 38
The dam’s abdomen starts visibly enlarging as the uterus expands. Mammary glands may become more prominent.
Day 39
Foetal growth accelerates further while skeletal development continues.
Day 40
Most internal organs are fully formed. Early hair growth begins. Puppies are approximately 6.5 cm long.
Day 41
Foetuses reach roughly 30% of birth size. Spine and toes continue ossifying.
Days 42–43
Rapid growth continues. Spinal column and toes harden further.
Day 44
The uterus occupies much of the abdomen. Puppies may be easier to feel through the abdominal wall.
Day 45
Pelvic bones ossify and coat growth becomes more noticeable. Puppy skeletons are usually visible on X-ray from this stage onward.
Days 46–47
Bone development and coat growth continue rapidly.
Day 48
The dam becomes visibly pregnant. Appetite may fluctuate as puppies crowd abdominal organs.
Day 49
Puppies reach approximately 75% of birth size. This is a good time to introduce the whelping box.
Day 50
Puppies are well developed and movement may sometimes be visible externally. Food intake usually increases further.
Day 51
The dam may begin nesting behaviour and seek quiet places to give birth.
Day 52
Some dams begin producing or leaking milk. Resting periods increase significantly.
Day 53
The dam’s abdomen is very enlarged and puppy movements are often clearly visible. Appetite may decrease as space in the abdomen becomes limited.
Day 54
Puppies continue gaining weight rapidly. The dam may become restless, pant more easily and seek increased comfort or attention.
Day 55
Puppies are now fully furred. X-rays taken at this stage can provide a more accurate puppy count. The dam may begin spending more time in her whelping area.
Day 56
Puppies are almost fully developed and continue maturing in preparation for birth. The dam may show stronger nesting behaviour and reduced appetite.
Day 57
Puppies are considered full term from this point onward, although birth may still be several days away. Lung maturation continues.
Day 58
The dam may become increasingly restless and clingy or alternatively seek solitude. Clear vaginal discharge may sometimes be seen.
Day 59
The cervix begins softening and dilating in preparation for labour. Milk may be easily expressed from the nipples.
Day 60
The dam’s temperature may begin dropping below normal as labour approaches. Puppies are fully developed and positioned for birth.
Day 61
Stage one labour may begin. Signs include panting, pacing, shivering, nesting, digging and refusing food.
Day 62
Active labour and delivery may occur. Contractions become stronger and visible. Puppies are born enclosed in their amniotic sacs.
Day 63
Average due date. Most puppies are born between days 58–63 after ovulation, though some variation is normal.
Days 64–65
Some litters, especially smaller litters, may naturally arrive slightly later. Veterinary advice should be sought if there are no signs of labour by this stage.
Video, pictures, and content of this page are the property of National Geographics “In the Womb Series” (2009).