Most discussion of progesterone in breeding programs stops at the moment of insemination. That is understandable, since timing is where the tool earns its keep. But progesterone has two further jobs after the breeding, and one very prominent job it cannot do at all. The first is the progesterone whelping date: the most accurate due-date prediction available in dogs.
- The LH surge is the most accurate whelping anchor: about 65 days. Ovulation gives 63 days and fertilization 61 days, both less accurate.
- Prediction from the first rise past ~2 ng/mL lands within ±1 day 67% of the time, ±2 days 90%, ±3 days 100%.
- Below 2.8 ng/mL there is a 99% probability of whelping within 48 hours; below 1.0 ng/mL, 100%.
- Progesterone cannot diagnose pregnancy in dogs. Use relaxin, ultrasound, or radiography instead.
If you run a Finecare Vet or Pro-DX
The figures above come from laboratory and reference-method literature. This analyzer reads on its own scale and sits systematically higher: independent testing puts the regression at Finecare = 5.87 + 1.28 × reference, so on the Finecare chart estimated ovulation falls at 8–15 ng/mL and the fertile range at 15–40 ng/mL. Time from the chart supplied with your kit lot, not from the numbers in this article. Why thresholds belong to the assay that produced them →
The progesterone whelping date: the best due date you will get
Canine gestation is often quoted as 58 to 68 days, which sounds imprecise enough to be nearly useless for planning. That range exists almost entirely because it is measured from the breeding date, and breeding dates are a poor anchor. Fresh sperm can wait several days in the reproductive tract, so a bitch bred on the same calendar day as another may fertilize two or three days later.
Measured from a hormonal event instead, gestation is far more consistent. Kurt De Cramer sets out the three anchors and, importantly, ranks them: pregnancy lengths based on the LH surge, ovulation and fertilization are respectively 65, 63 and 61 days, with the latter two less accurate than the former. The order surprises people, because ovulation feels like the more concrete event.
| Anchor point | Days to whelping | Relative accuracy |
|---|---|---|
| LH surge / Day 0 (progesterone around 2 ng/mL) | 65 | The most accurate of the three |
| Ovulation (progesterone 5 to 8 ng/mL) | 63 | Less accurate than the LH surge |
| Fertilization (progesterone around 10 ng/mL) | 61 | Least accurate of the three |
| Date of breeding | 58 to 68 | Poor |
The LH surge, not the breeding date, is the best predictor of whelping. If you recorded nothing else during the cycle, record Day 0.
How accurate is “accurate”?
It is worth being precise about this, because “progesterone predicts the due date to the day” is an overstatement that gets repeated a lot. Kutzler, Mohammed, Lamb and Meyers-Wallen, publishing in Theriogenology in 2003, measured the accuracy of canine parturition date prediction from the initial rise in preovulatory progesterone. Using the date on which progesterone first exceeded 1.8 ng/mL, they found:
So plan the whelping window, not the whelping day. A one-in-three chance of being off by more than 24 hours is exactly the margin that catches breeders who booked travel for the calculated date.
The two curves that look almost the same
Before going further, it helps to see what progesterone actually does across the eight or nine weeks after ovulation — and, crucially, what it does in a bitch who did not conceive.
The prepartum drop
In the bitch, labor is preceded by a sharp collapse in progesterone as the corpora lutea are actively broken down. De Cramer and Nöthling quantified how tightly this tracks parturition in Theriogenology in 2018, and their thresholds are what turn the number into a usable countdown.
| Progesterone | What it means | What to do |
|---|---|---|
| 5 ng/mL or above | Under 2% chance of spontaneous whelping in the next 12 hours | Low risk. Overnight observation is probably not needed tonight |
| Below 2.8 ng/mL | 99% probability of whelping within 48 hours | Prepare |
| Below 2 ng/mL | Most are within 48 hours of onset of parturition | High alert for 48 hours |
| Below 1 ng/mL | 100% probability of whelping within 48 hours; very likely within 24 | High alert for 24 hours |
That top row is the underrated one. Knowing a bitch is not going to whelp tonight is worth as much to a tired breeder as knowing that she is.
An important limitation on cesarean timing
De Cramer and Nöthling state directly, in the same work that produced these thresholds, that controlled studies large enough to be convincing are still required before it can be considered safe to routinely perform a cesarean section once progesterone has decreased below a defined threshold. Use these numbers as one input to a conversation with your veterinarian, not as a surgical decision rule. This is covered in more depth in timing an elective C-section.
Temperature monitoring at home remains valuable, but it is noisy. It is easily confounded by ambient conditions, activity, and inconsistent technique, and a single reading is difficult to interpret. Progesterone measures the underlying event directly, which is why in-clinic and in-house analyzers that return a quantitative result the same day — such as the PETlife Pro-DX, which runs a canine progesterone (cProg) test on 75 µL of whole blood, serum, or plasma in about 15 minutes — are useful in the final week.
What progesterone will never tell you
This surprises people
Progesterone cannot diagnose pregnancy in dogs. Not with a better assay, not with more frequent sampling. As De Cramer puts it: the progesterone profiles of pregnant and non-pregnant bitches do not differ significantly, therefore progesterone cannot be used for pregnancy diagnosis.
The reason is a genuine peculiarity of canine reproductive physiology. In dogs, the corpus luteum forms and persists after every ovulation, whether or not conception occurs, and it produces progesterone on essentially the same schedule either way. Dogs lack the maternal recognition of pregnancy signal that most species use to rescue the corpus luteum. There is nothing to rescue, because it was never going to regress on schedule in the first place.
The consequence is the pair of curves in Figure 1 above: profiles that run nearly in parallel through most of diestrus, diverging only at the very end. A non-pregnant bitch spends roughly two months with progesterone concentrations that would indicate pregnancy in almost any other species. This is also why pseudopregnancy is so common and so convincing in dogs.
What to use for pregnancy diagnosis instead
A common and sensible protocol combines relaxin or ultrasound in the fourth week to confirm pregnancy, then radiography in the final week to establish the count before whelping.
Progesterone during pregnancy, and a word on supplementation
Although progesterone cannot tell you whether a bitch is pregnant, it does have a role once pregnancy is confirmed by another method. Drawing on Gorlinger and colleagues’ work on hypoluteoidism, concentrations above roughly 2.6 ng/mL are required throughout the entire pregnancy to maintain it, and midpregnancy peaks typically run 15 to 90 ng/mL before declining. Following Verstegen-Onclin and Verstegen’s review of canine pregnancy endocrinology, serum progesterone is commonly monitored every one to two weeks in females with a history of pregnancy failure or luteal insufficiency.
Because dogs depend entirely on luteal progesterone throughout gestation, with no placental production to take over, supplementing a bitch with a history of loss has obvious intuitive appeal. It is also a decision that belongs firmly with a veterinarian. True luteal insufficiency is uncommon, most pregnancy losses have other causes, and De Cramer is explicit that progestogen supplementation must be discontinued before the expected parturition date to avoid prolonged gestation and fetal death.
Frequently asked questions
How accurate is a due date calculated from progesterone?
Counting 65 days from the LH surge is the most accurate approach. Kutzler and colleagues found prediction from the first rise past about 2 ng/mL correct within ±1 day in 67% of cases, ±2 days in 90%, and ±3 days in 100%. Plan a window, not a date.
What progesterone level means whelping is close?
De Cramer and Nöthling found that below 2.8 ng/mL there is a 99% probability of whelping within 48 hours, and below 1.0 ng/mL that probability reaches 100%. Conversely, 5 ng/mL or above means under a 2% chance of spontaneous whelping in the next 12 hours.
Can progesterone be used to schedule a cesarean section?
It is used as an input, but the researchers behind the thresholds explicitly note that sufficiently large controlled studies are still needed to confirm it is safe to schedule surgery routinely on a progesterone threshold alone. This is a veterinary decision.
Why can’t a progesterone test confirm pregnancy in a dog?
Because the corpus luteum persists after every ovulation whether or not conception occurred. Pregnant and non-pregnant bitches produce nearly identical progesterone profiles for most of the luteal phase, so there is no signal to detect.
Sources
Kutzler MA, Mohammed HO, Lamb SV, Meyers-Wallen VN. Accuracy of canine parturition date prediction from the initial rise in preovulatory progesterone concentration. Theriogenology. 2003;60(6):1187–1196.
De Cramer KGM, Nöthling JO. The precision of predicting the time of onset of parturition in the bitch using the level of progesterone in plasma during the preparturient period. Theriogenology. 2018;107:211–218.
Gorlinger S, Galac S, Kooistra HS, Okkens AC. Hypoluteoidism in a bitch. Theriogenology. 2005;64(1):213–219.
Verstegen-Onclin K, Verstegen J. Endocrinology of pregnancy in the dog: a review. Theriogenology. 2008;70(3):291–299.
De Cramer K. Simplifying the Canine Reproductive Cycle Using the Concentration of Progesterone. IDEXX Laboratories, CLD-12211-00.
Keep reading
Threshold values in this article are drawn from published veterinary literature and are assay-dependent: absolute numbers are not interchangeable between analyzers. Always interpret results against the reference range for the instrument you are using. This article is educational and is not a substitute for veterinary advice. Whelping management, cesarean scheduling, pregnancy diagnosis, and any hormone supplementation must be directed by your veterinarian.