In-Utero Puppy Development & Placental Health: A Complete Guide for Dog Breeders
fetal development of puppies
How puppies attach and connect in utero
1. Implantation process
Around 18β20 days after the LH surge, blastocysts attach centrally on the uterine wall (antimesometrial side) and begin implantation.
The trophoblast (outer layer of embryonic cells) produces enzymes that erode the maternal endometrium, letting it embed close to maternal blood vessels.
2. Zonary, endotheliochorial placenta
Dogs develop a zonary placenta, shaped like a band encircling each fetus within the uterine horn.
Itβs endotheliochorial: fetal chorionic cells contact maternal endothelial cells (vessel lining) beneath the uterine epithelium.
3. Formation and structure
As the placenta forms, youβll see a green-brown βmarginal hematomaββa blood-rich zone at the edge of the placental band.
Inside the placenta, a labyrinth of fetal vessels within the chorioallantoic membrane develops, through which nutrient, gas, and waste exchange occurs.
4. Umbilical cord connection
An umbilical cord forms, connecting the fetus (inside its amniotic sac) to the placenta, transferring nutrients and oxygen from the motherβs blood.
5. At birth
The placenta detaches across the junctional zone and is delivered after each puppy β the mother often removes the sac and chews the cord.
Summary
Blastocyst implants ~dayβ―18β20.
Trophoblast erodes the uterine lining to form the zonary placenta.
The placenta surrounds the fetus with a vascularized interface and a hematoma.
The fetus connects via the umbilical cord to the placenta.
At parturition, the placenta detaches and is expelled.
Puppy Fetal Development (Week by Week)
Developmental Stage | Timeline | Key Milestones |
---|---|---|
Fertilization & Zygote Formation | Days 0β3 | Ovulation occurs; sperm meets egg in oviduct; zygote begins rapid cell division |
Blastocyst Migration | Days 5β15 | Embryos travel through uterine horns, forming protective outer layer |
Implantation | Days 17β21 | Blastocysts embed into uterine lining; early placenta begins forming |
Placental Development | Days 21β28 | Zonary placenta forms; nutrient exchange begins; basic body systems emerge |
Organogenesis | Weeks 3β4 | Major organs develop; spine, head, limbs, and facial structures become visible |
Mid-Gestation Growth | Weeks 5β6 | Skeleton begins ossifying; gender becomes visible via ultrasound; puppies grow rapidly in length |
Late Gestation & Whelping Readiness | Weeks 7β9 | Hair and pigmentation develop; puppies crowd the uterus; lungs mature; birth is imminent |
Understanding the prenatal journey of puppies helps breeders support healthy pregnancies and anticipate key milestones. Below is an overview based on first breeding (Dayβ―0) toward the average 63-day gestation (range: 59β70 days).
Week 1 (Days 1β7)
Whatβs happening: Fertilization occurs; embryos are 2β4 cells deep, moving through the oviduct.
Damβs signs: Subtleβpossibly mild fatigue, no overt pregnancy changes; heat cycle continues for another 4β14 days.
Week 2 (Days 8β14)
Embryo development: Cell division continuesβembryos reach the 64-cell stage and enter the uterine horns.
Damβs signs: Behavior and appetite likely unchanged; breeders should still manage male access and maintain her normal routine.
Week 3 (Days 15β21)
Implantation: Embryos embed into the uterine lining around Days 17β22; the placenta begins forming (~Dayβ―18).
Embryo becomes complex: By the end of week, head, spine, and early organ systems begin to develop.
Damβs signs: May show slight appetite changes or mood shifts, though often still unremarkable.
Week 4 (Days 22β28)
Fetal milestones (5β17β―mm): Head shifts forward, brain and facial features begin, spinal cord forms, initial eyes appear, limb buds emerge.
Diagnostics: Ultrasound can often detect a heartbeat from Day 25 onward; palpation may also be possible in experienced hands.
Damβs signs: Slight appetite loss (βmorning sicknessβ), nipple enlargement, potential mild discharge.
Weeks 5β6 (Days 29β42)
Puppy features: By Dayβ―35, embryos transition to recognizable fetusesβclaws, whisker buds, digit formation, eyelids closed by Dayβ―32β35; fetal length ~30β45β―mm, weight ~2β6β―g
Fetal heartbeats are detectable with a stethoscope; skeletal ossification begins
Dam care: Nutritional needs riseβstart gradual food increase and transition to growth diet; abdomen visibly expanding; nipples darken, mammary gland secretions may begin.
Weeks 7β8 (Days 43β56)
Rapid growth: Skeleton fully ossified by Dayβ―50βpuppy bone structure visible on X-ray; coat beginnings, pigmentation, proportional development continue; fetal movement can be felt.
Dam signs: Reduced appetite, heavier abdomen, nesting behavior; milk production (βfirst milkβ) may appear.
Breeder tasks: Perform X-ray to confirm litter size; finalize whelping area and gather supplies.
Week 9 (Days 57β63+)
Final prep: Puppies gain last ounces; full-term between Daysβ―58β65, though larger litters may come early; some may extend to Dayβ―70 from breeding due to ovulation timing.
Dam signs: Nesting intensifies, restlessness rises, and appetite may drop. Monitor temperature for drop to ~100β―Β°F (37.8β―Β°C) β whelping likely within 24 hours.
Outcome: Puppies born blind and deafβtheir senses, eyes, and ears develop postnatally.
REFERNCES
Elanco Animal Health. (n.d.). Week by week guide to dog pregnancy. Retrieved June 24, 2025, from https://www.elanco.com
Baldivis Vet Hospital. (2022). Gestation in dogs β week by week. Retrieved June 24, 2025, from https://www.baldivisvet.com.au
American Kennel Club. (2021, April 5). Dog pregnancy: Signs, care, and preparing for puppies. Retrieved June 24, 2025, from https://www.akc.org/expert-advice/health/dog-pregnancy-signs-care/
Luv-N-Care Animal Hospital. (2020). Fetal development of a puppy. Retrieved June 24, 2025, from https://www.luvncare.net/fetal-development-of-a-puppy.pml
Veterinary Partner (VIN). (2020). Pregnancy and parturition in dogs. Retrieved June 24, 2025, from https://veterinarypartner.vin.com
Royal Veterinary College. (n.d.). Prenatal development in the dog. eMedia Unit. Retrieved June 24, 2025, from https://emedia.rvc.ac.uk
Puppy Midwife. (2023). Dog pregnancy calendar. Retrieved June 24, 2025, from https://www.puppymidwife.com/dog-pregnancy-calendar
Concannon, P. W. (2011). Reproductive cycles of the domestic bitch. Animal Reproduction Science, 124(3β4), 200β210. https://doi.org/10.1016/j.anireprosci.2010.08.028