The three trimesters of canine pregnancy
A dog's nine weeks of pregnancy divide neatly into three 21-day trimesters. In thefirst trimester (days 1–21) there is little to see from the outside: the fertilized eggs travel to the uterus and implant around day 16–18. Some dogs have a brief spell of nausea or appetite dips, but most act completely normal. Don't change her food or exercise yet — a normal adult diet is exactly right at this stage.
The second trimester (days 22–42) is when pregnancy becomes confirmable and then visible. An ultrasound from about day 25 can show heartbeats, and by day 35 the fetuses enter their fastest growth phase. Her appetite climbs, nipples enlarge and pink up, and her waistline starts to thicken. From roughly week 5–6, vets commonly recommend gradually switching to a high-quality puppy or performance food to support fetal growth.
In the third trimester (days 43–63) the puppies gain most of their birth weight and their skeletons calcify — which is why an X-ray from day 45 onward can give an accurate puppy count, invaluable for knowing when whelping is actually finished. Feed smaller, more frequent meals as the crowded abdomen leaves less room for the stomach, and set up the whelping box by day 56 so she has a week to get comfortable in it.
| Milestone | Days after mating |
|---|---|
| Implantation in the uterus | Day 16–18 |
| Ultrasound / relaxin test can confirm | Day 25–30 |
| Vet can palpate abdomen | Day 28–35 |
| Switch gradually to puppy food | Day 35–42 |
| X-ray shows puppy skeletons (count) | Day 45+ |
| Whelping box ready | Day 56 |
| Temperature drop below 99°F | 12–24h before labor |
| Whelping | Day 58–71 (avg. 63); past day 70 = call the vet |
Signs labor is starting
Start taking her rectal temperature twice a day from around day 58. Normal is 100–102.5°F; a drop below 99°F is the classic signal that labor will begin within about 24 hours. In the final day she'll typically become restless, pant, shiver, dig at her bedding ("nesting"), refuse food and may vomit once. Stage-one labor — uterine contractions without visible straining — can last 6–12 hours before the first puppy appears.
When to call the vet during whelping
Most dogs whelp without help, but some situations shouldn't wait. Per the Merck Veterinary Manual's dystocia criteria, call your vet immediately if she strains strongly formore than 30 minutes without producing a puppy, if active labor passes4 hours with no puppy at all or more than 2 hours between puppies, or if you see green or black discharge before the first puppy — after a puppy it's normal (placental separation), before one it can mean a puppy in distress. Also call for heavy bleeding, extreme lethargy, or if the temperature drop happened more than 24 hours ago with no labor. Know your nearest emergency clinic's number before day 58, not during a 2 a.m. crisis.
Frequently asked questions
How long are dogs pregnant?
Canine pregnancy lasts about 63 days (9 weeks) from ovulation — Merck gives 62-64 days. Counted from a mating date the realistic window is 58 to 71 days, because sperm survive several days in the reproductive tract and mating rarely lines up exactly with ovulation. Beyond day 70 from breeding, veterinarians treat the pregnancy as prolonged — call your vet.
How soon can a vet confirm my dog is pregnant?
Ultrasound can reliably confirm pregnancy around day 25-30 after mating. A blood test for relaxin works from about day 25-30 as well. Abdominal palpation by a vet is possible around day 28-35, and an X-ray from day 45 onward can count puppies once their skeletons mineralize.
How do I know labor is close?
The most reliable sign is a drop in rectal temperature below 99°F (37.2°C), which typically happens 12-24 hours before whelping. Take her temperature twice daily in the final week. Restlessness, nesting, panting and refusing food are also common in the last 24 hours.
When should I call the vet during whelping?
Per the Merck Veterinary Manual: call immediately if strong straining lasts more than 30 minutes without a puppy, active labor passes 4 hours with no puppy at all, more than 2 hours pass between puppies, green discharge appears before the first puppy, or she seems weak or in distress.