Health & Testing

Canine Pregnancy Week by Week: A Complete Guide for Breeders

From fertilization to whelping is approximately 63 days — but each week brings dramatic developmental changes. Here's the complete week-by-week guide to canine pregnancy.

April 30, 2024 · 7 min read

Week 1 (Days 1–7): Fertilization and Early Cell Division

After breeding, eggs are fertilized as they travel down the fallopian tubes. The fertilized eggs (zygotes) undergo rapid cell division, forming morulas (compact cell clusters) and then blastocysts. No external signs are visible. The dam's routine need not change.

Week 2–3 (Days 8–21): Implantation

Blastocysts travel to the uterine horns and implant into the uterine wall around day 18–21. After implantation, embryonic development begins in earnest. The dam may show mild behavioral changes. Progesterone levels rise significantly. Ultrasound can detect pregnancy as early as day 21–25 in some cases, though day 28 is more reliable for early confirmation.

Week 4 (Days 22–28): Organ Development Begins

This is the most critical developmental week. Major organ systems begin forming. Limb buds, the spinal cord, the heart, and the digestive tract begin to develop. The embryos are approximately 1.5 cm long by day 28. Ultrasound now reliably confirms pregnancy and gives approximate count (though movement makes exact count difficult).

Weeks 5–6 (Days 29–42): Rapid Fetal Growth

Fetuses grow dramatically. Toe pads, facial features, and sex organs differentiate. The dam's abdomen becomes noticeably enlarged. Appetite increases. By day 40, a skilled ultrasound can sometimes detect heartbeats. X-ray at day 45+ gives an accurate skull/spine count.

Weeks 7–9 (Days 43–63): Final Development and Whelping Prep

The final weeks involve continued growth, fur development, and positioning for birth. The dam's temperature drops below 99°F (from normal 101°F) 12–24 hours before labor begins — the most reliable sign of imminent whelping. Prepare the whelping box by week 7. X-rays at days 55–58 give accurate skeletal count. After day 63, consider veterinary evaluation if whelping has not begun.