What progesterone level is concerning in pregnancy?

During gestation progesterone should remain comfortably elevated (roughly above 5 ng/mL in most references). A value that falls below about 2 ng/mL is associated with pregnancy loss, and a sustained decline across serial tests — even while still 'normal' — is a red flag worth acting on before clinical signs appear.

Why serial testing instead of one value?

Because the trend is the signal. A single normal progesterone tells you the level is fine that day; a falling series tells you the corpus luteum is failing. Serial curves catch the decline early, when supplementation (progesterone or progestins) may still rescue the pregnancy.

Does every pregnant bitch need serial progesterone?

No — routine monitoring is overkill for a healthy bitch with no history. Serial testing is targeted: breeds or individuals with a history of pregnancy loss, older bitches, or any pregnancy where an early drop is suspected. Screening everyone dilutes the value of the test.

What can I do if progesterone is falling?

Supplementation with exogenous progesterone or a progestin can be considered to support the pregnancy, but it must be started early — before the pregnancy is already lost. This is precisely why serial monitoring, rather than waiting for signs, is the point.

Progesterone Curve in Pregnancy: Why Serial Testing Matters

TL;DR — Progesterone is the pregnancy-sustaining hormone in the bitch: after ovulation, the corpus luteum must keep it elevated for the full ~63-day gestation. That is why the number you cared about for timing (the breeding window) becomes a survival number once she is pregnant. The rule of thumb: progesterone should stay comfortably above ~5 ng/mL through gestation, and a fall below ~2 ng/mL is associated with pregnancy loss. The reason for serial testing is that the trend is the signal — a corpus luteum that is quietly failing shows a falling curve days before the pregnancy is lost, and that is the window when supplementation can still rescue the litter.

In Plain Terms

The same progesterone you used to time the breeding has a second, quieter job: keeping the pregnancy alive. Once the bitch is pregnant, the corpus luteum (the structure left behind after ovulation) becomes the pregnancy’s life-support system, pumping out progesterone to keep the uterus calm and the puppies attached. If that life support starts to fail, the first sign is not bleeding or illness — it is a number on a blood test, drifting downward.

The Two Jobs of Progesterone

Phase	Progesterone’s job	What you watch
Pre-ovulation / breeding	Times ovulation and the breeding window	The rise: 2–3 → 8–15 ng/mL
Pregnancy (~63 days)	Sustains the pregnancy	The plateau: should hold >~5 ng/mL

The transition between the two is the point most breeders miss: the marker they were using to time the breeding now becomes the marker they should be using to protect the pregnancy.

What the Curve Should Look Like

In a normal pregnancy, progesterone climbs through the breeding window, stays elevated through gestation, and only falls sharply in the ~24–48 hours before whelping. The useful reference points:

Sustained elevation — roughly above 5 ng/mL — is the expected picture for most of gestation.
Below ~2 ng/mL — associated with pregnancy loss; the pregnancy is in trouble.
A falling series — even while still “normal” — is the earliest, most actionable warning of luteal failure.

The key insight: you are not waiting for a single “too low” reading. You are watching the slope. A value that was 18 ng/mL two weeks ago and is 7 ng/mL today is more alarming than a stable 6 ng/mL, even though both are technically “normal.”

Hypoluteoidism: The Corpus Luteum That Fails

Hypoluteoidism (luteal insufficiency) is premature failure of the corpus luteum to maintain adequate progesterone, and it is a recognised cause of pregnancy loss and resorption. The problem is that it is silent — the bitch looks normal right up until she resorbs the litter, by which point it is too late.

This is exactly the case serial monitoring exists for. A bitch with a history of unexplained pregnancy loss, or a falling curve on a routine check, can be caught in the window where exogenous progesterone (or a progestin) may still hold the pregnancy. Miss that window — wait for clinical signs — and the litter is already lost.

Who Actually Needs Serial Testing

Serial progesterone in pregnancy is not for everyone. The honest targeting:

History of pregnancy loss or resorption — the highest-yield group.
Older bitches — luteal function can be less robust.
Breeds with known reproductive fragility — where a lost litter is a costly event.
Suspected early drop — a single low-ish value that warrants confirmation.

Screening every healthy, first-time, uneventful pregnancy dilutes the test’s value. This is a targeted tool, not a routine reflex — and the distinction is what separates a useful protocol from a wasteful one.

How the Test Runs

Once pregnancy is confirmed (relaxin ~day 28–30 or ultrasound), establish a baseline progesterone.
Repeat at intervals for at-risk pregnancies to watch the slope.
If the curve falls (especially toward ~2 ng/mL), intervene early with supplementation under veterinary guidance.
Confirm the pregnancy remains viable with follow-up ultrasound or relaxin.

Related products: Canine Progesterone Test · Canine Relaxin Test · FIA680 Analyzer

FAQ

Why does progesterone matter during pregnancy?

It is the pregnancy-sustaining hormone — the corpus luteum must hold it elevated for the full ~63-day gestation. A sustained fall is the earliest warning of loss.

What level is concerning?

Progesterone should hold above ~5 ng/mL; a fall below ~2 ng/mL is associated with pregnancy loss. A falling series — even “normal” — is the real red flag.

What is hypoluteoidism?

Premature corpus-luteum failure causing pregnancy loss. It is silent until resorption, which is why a curve falling toward 2 ng/mL — not waiting for signs — is the point.

Why serial testing?

Because the trend is the signal. A curve falling toward 2 ng/mL catches luteal failure days before the pregnancy is lost, when supplementation can still rescue it.

Does every pregnant bitch need it?

No — target bitches with a history of loss, older bitches, or a suspected early drop (toward 2 ng/mL). Screening everyone dilutes the test’s value.

What if progesterone is falling?

Supplement with progesterone/progestin early — before the ~2 ng/mL threshold is crossed — which is why you monitor the slope rather than wait for signs.

Key Takeaways

Progesterone has two jobs — timing at breeding, then life-support through ~63 days of gestation. The same marker you used to breed now protects the pregnancy.
Hold above ~5, worry below ~2 ng/mL — sustained elevation is normal; a fall toward ~2 ng/mL means the pregnancy is in trouble.
The slope beats the single value — a value falling from 18 → 7 ng/mL is more alarming than a stable 6 ng/mL, even though both read “normal.”
Hypoluteoidism is silent — the corpus luteum fails before signs appear; a curve falling toward 2 ng/mL is how you catch it while supplementation can still work.
Target, don’t blanket — serial testing is for at-risk pregnancies across the ~63-day gestation, not every healthy first-timer. Precision beats reflex.

References

Johnston SD, et al. Canine and Feline Theriogenology. Saunders.
England GCW. Progesterone and canine pregnancy maintenance.
Concannon PW. Endocrinology of canine pregnancy and parturition.

This content is for educational and product-selection purposes only. It is not a substitute for veterinary guidance — work with a theriogenologist for pregnancy monitoring. Product specifications are as published by Migibio (Guangzhou Magic Biotech Co., Ltd.) and may change.