How Long Are Guinea Pigs Pregnant? Gestation, Due Dates, and Birth Risks

Guinea pigs are pregnant for about 68 days on average, and the Merck Veterinary Manual gives a normal range of 59 to 72 days. That is roughly nine to ten weeks, which is remarkably long for a rodent, and it is why guinea pig pups arrive fully furred, with their eyes open, and nibbling solid food within hours. If you know the mating date, the free Creatures guinea pig gestation calculator turns it into an estimated due date and a planning window in a few seconds, no account needed.

The length of the pregnancy is the easy part. The harder questions are whether this sow should be pregnant at all, and what can go wrong near the end. This species carries two well-documented risks that catch owners out: difficult births in sows that have their first litter too old, and a fast-moving metabolic illness called pregnancy toxaemia. Both are covered below with their sources, because if you are planning a litter, the single most useful thing you can do is talk to a veterinarian who treats guinea pigs before the boar goes in, not after.

This guide covers the gestation numbers and why a due date is always a window, how to tell a sow is pregnant, the first-litter age question, care through the last weeks, what a normal birth looks like and the danger signs that mean you call a vet now. It ends with how to track the whole thing on Creatures, from the calculator to the breeding records that project the due date for you.

How long is a guinea pig pregnancy?

The standard figure is 68 days. The Merck Veterinary Manual’s owner guide gives a pregnancy range of 59 to 72 days, and the laboratory animal medicine reference Biology and Diseases of Guinea Pigs (Shomer, Holcombe and Harkness, 2015) gives the same average of 68 days within that same 59 to 72 day range. So if a boar and sow mated on a known day, pups are most likely around ten weeks later, and anything from about eight and a half weeks onward is within the normal range.

That is a long pregnancy for an animal that weighs around two pounds. Rats, mice and hamsters are pregnant for a few weeks and give birth to hairless, blind young. Cavies invest their time before birth instead: the Shomer chapter describes pups born “precocious,” with hair, teeth, and open eyes and ears, fully mobile and starting to eat and drink within hours. Even a rabbit, a much bigger animal, has a far shorter pregnancy; our sister guide on how long rabbits are pregnant covers that side of the comparison. A cat, several times heavier, is pregnant for a similar time, about nine weeks; see how long cats are pregnant.

Why a guinea pig due date is always a window

Three things make a single calendar date misleading.

• Litter size moves the date. The Shomer chapter notes that gestation length is generally inversely proportional to litter size, so a sow carrying a large litter tends to deliver earlier than one carrying a single pup.
• You often do not know the mating day. Guinea pigs cycle roughly every 16 days (a range of about 13 to 21 in the same reference), and if a boar lives with a sow, mating could have happened on any day he had access to her. Matings rarely leave evidence you can rely on; the chapter points out that not finding a copulatory plug tells you nothing.
• Sows can conceive again within hours of giving birth. A fertile postpartum heat occurs roughly 2 to 10 hours after birth. A sow living with a boar can be pregnant again before her pups are a day old, and back-to-back pregnancies are hard on her body.

The practical answer is to plan for the whole 59 to 72 day window from the first possible mating date, and to count from the last possible date as well if the boar was with her for a while.

How to calculate a guinea pig’s due date

The arithmetic is simple: add 68 days to the mating date for the estimate, 59 days for the start of the window, and 72 days for the end.

A worked example: a sow mated on October 1 has an estimated due date of December 8, with a planning window from November 29 to December 12. That is exactly what the guinea pig gestation calculator returns for that date, laid out on a small calendar so the window is easy to see.

If the boar lived with the sow for a stretch, run the calculator twice: once with the first day they were together and once with the day you separated them. Your real window runs from the earliest start to the latest end. If you have a veterinarian’s estimate from an ultrasound or an exam, trust that over any mating-date arithmetic.

How to tell if a guinea pig is pregnant

Early pregnancy is easy to miss. A cavy is a round animal to begin with, and a sow in her first few weeks looks and behaves much as she always has. The signs owners usually notice first are steady weight gain and a belly that widens into a pear shape over the second half of the pregnancy. Late in pregnancy the abdomen becomes obviously distended.

The more reliable routes run through a veterinarian:

• Palpation. In the Shomer chapter, firm, oval swellings about 5 mm across can be felt in the uterus from around day 15. Gentle abdominal palpation is a skill, and pressing on a pregnant sow’s belly carelessly can hurt her, so leave this to your vet rather than trying it at home.
• Ultrasound. The same reference reports fluid-filled swellings visible on ultrasound at day 16, with diagnosis approaching 100 percent by day 19 in the study it cites.
• Weight trend. Weighing her on a kitchen scale once a week and writing it down gives you and your vet a clear picture of a steady gain, and of any sudden loss, which is a warning sign (see pregnancy toxaemia below).

In the final week before birth the two halves of her pelvis separate. The Shomer chapter describes the gap widening to about 3 cm by the day of delivery and being readily palpable during that last week. Your vet can show you how to check it gently, and it is one of the most useful clues that birth is close.

The first-litter age risk: why older sows should not have a first litter

This is the part of guinea pig breeding that most often ends badly, and the evidence deserves a careful reading.

The two halves of a guinea pig’s pelvis are joined at the front by a band of fibrocartilage called the pubic symphysis. Before birth, a hormone called relaxin loosens it so the pelvis can open wide enough for pups to pass. The Merck owner guide on common health problems of guinea pigs says difficult labor is a serious problem in guinea pigs because the pelvic cartilage normally stiffens with age, making it harder for the pelvis to spread during birth. It adds that C-sections are risky, with a poor survival rate for the mother.

The traditional explanation, repeated in laboratory animal texts, is that the symphysis fuses in sows that have never given birth. The Shomer chapter says failure of the pelvic joint to separate “occurs most often in sows bred for the first time over 7 months of age,” and advises breeding for the first time before 7 months. The same chapter also says the joint calcifies and fuses between 6 and 9 months of age, and some references use 6 months as the cutoff. You will see that age rule everywhere, and the reason behind it is real: a sow whose pelvis cannot open is in a life-threatening situation.

The mechanism is less settled than the rule. A 2024 CT imaging study in Veterinary Medicine and Science (Vieu and colleagues) followed 23 female guinea pigs from 3 to 12 months of age and found no bony fusion of the symphysis in either breeding or non-breeding sows during their first year, contrary to earlier descriptions. The study was small, and it did not show that older first-time mothers give birth safely; it questions why the risk exists, not whether it does.

What that means in practice:

• If your sow is older than about 6 months and has never had a litter, do not breed her. Every source above agrees that difficult birth is a serious risk, and the surgical fallback carries a poor survival rate for the mother.
• Very young is not the answer either. Females can ovulate at 4 to 5 weeks old, and laboratory colonies breed them at 2 to 3 months, but a pet sow still growing is a different decision. The right age and weight for your sow is a conversation with a veterinarian who treats guinea pigs, before any mating.
• If an older sow is already pregnant by accident, book a vet appointment as soon as you suspect it, so there is a plan and a clinic ready before the due window opens.

Pregnancy toxaemia: the late-pregnancy emergency

Pregnancy toxaemia (also called pregnancy ketosis) is the other major risk, and it strikes in the last weeks of pregnancy or just after birth. The Shomer chapter describes two forms with similar signs: a circulatory form, where blood supply to the uterus and placenta fails, and a metabolic or fasting form, where a sow that stops eating starts breaking down her body fat faster than she can cope with. The circulatory form occurs in the last two weeks and immediately after birth, and is seen more often in obese, stressed sows carrying a large litter, though a normal sow can be affected too. The fasting form occurs in the last trimester, after about day 45, most often in the final one to two weeks.

The signs are easy to mistake for a sow simply being heavy and tired:

• Not eating, or eating much less than usual
• Dullness, weakness, or reluctance to move
• Looking dehydrated or losing weight in late pregnancy

Some sows die with no warning signs at all. The Shomer chapter reports that a sow may die after a fast of only one to three days, and that treatment is rarely successful. If a pregnant or newly delivered sow stops eating or becomes dull or weak, call a veterinarian now. Do not wait to see whether she improves overnight.

Prevention is the part you control. The same reference points to avoiding obesity, avoiding fasting during pregnancy, and keeping stress low. In plain terms: keep her at a healthy weight before breeding, never let her run out of hay or water, make any diet changes gradually, and keep her home calm and familiar.

Caring for a pregnant guinea pig

Most of what a pregnant sow needs is good everyday guinea pig care, done consistently.

Food and vitamin C. Guinea pigs cannot make their own vitamin C, and the Merck owner guide on nutritional problems of guinea pigs says pregnant females need about three times the usual daily amount. The usual approach is fresh guinea pig pellets fortified with vitamin C, unlimited grass hay, and vitamin C rich vegetables such as bell peppers. Ask your vet how best to meet her needs rather than adding supplements on your own. Our guide to what guinea pigs eat covers the everyday diet in detail.

Housing. Keep her on a single level with a solid floor and deep, clean bedding; the Shomer chapter warns that wire-mesh flooring injures feet and legs and reduces breeding performance. Ramps and upper platforms become awkward as she gets heavier. She can stay with her usual female companions, since guinea pigs are social and a familiar group lowers stress. The guinea pig cage size and setup guide has the space numbers.

Move the boar out before the due window. Because of the fertile heat within hours of birth, a boar left in the enclosure will very likely make her pregnant again straight away. Separate him well before the earliest due date, ideally where they can still see and hear each other if they are bonded.

Handle her gently and less. Support her whole body with two hands when you must pick her up, and keep handling to health checks and weigh-ins.

Labor and birth: what is normal

Guinea pig births are usually quick, which is why owners often miss them entirely. In the Shomer chapter, pups arrive every 3 to 7 minutes and the whole delivery is complete in about 30 minutes.

The pups are up and moving almost at once. They begin eating solids and drinking within hours but still depend on their mother’s milk; the same reference notes that pups that are undersized, or that do not get milk in their first 3 to 4 days, have much higher mortality, and that pups under about 50 g at birth generally do not survive. The Merck owner guide lists weaning at about 3 weeks. Young males should be separated from their mother and sisters around weaning, because females can start ovulating at 4 to 5 weeks. Ask your vet to confirm the sex of each pup if you are unsure.

Danger signs: call a veterinarian now

Guinea pigs hide signs of illness until they are very sick, as the Merck owner guide on routine care warns, and difficult births move fast. The Shomer chapter lists straining, depression, and vaginal discharge as signs of a difficult birth, along with a pelvis that is still narrow as the pregnancy approaches its end. Call a veterinarian immediately if you see any of these:

• Continuous straining for about 20 minutes without a pup, bloody or green discharge with no pup delivered, or contractions lasting over 2 hours with no progress. Vieu and colleagues (2024) list exactly these as signs of a difficult birth. Most births are over in about half an hour, so if she seems to be struggling, do not wait: call a veterinarian now
• Foul-smelling discharge from the vulva at any stage
• A sow that is dull, weak, not eating, or breathing hard in late pregnancy or after birth
• A pup visibly stuck in the birth canal
• The due window passing with a sow who still looks heavily pregnant and whose pelvis has not widened

Find a clinic that sees guinea pigs before the due window opens, and keep its number where everyone in the house can find it. Many general practices do not treat exotic pets, and a birth emergency is not the moment to start phoning around.

How to track a guinea pig pregnancy on Creatures

A pregnancy this long is easy to lose track of, especially if you have more than one sow. Creatures gives you a free way to calculate the dates and a free account to keep them, along with the reminders that matter.

1. Estimate the dates, no account needed. Enter the mating date in the guinea pig gestation calculator. It returns the estimated delivery date, the planning window on a small calendar, and buttons to copy the results, print them, or add them to your calendar. Calculators for other species live on the gestation calculators page, and using the gestation calculator explains the options. The result is an estimate, not a diagnosis.

2. Save the breeding to the sow’s profile. From the calculator you can create a free account and add the mother, and your calculation is kept so you can check which dates belong in her record. Once she has a profile, add a Breeding and Reproduction record, turn on breeding-cycle tracking, name the sire (a Creatures profile or just a name you type), and enter the service date. If the boar was with her for several days, enter a start and an end date and Creatures widens the likely window to match that uncertainty. If your vet gives you an expected date, you can override the projection instead of fudging the mating date. The steps are in recording a breeding.

3. Follow the pregnancy on her Breeding tab. The sow’s Breeding tab shows the active cycle, the likely window and milestones, and lets you add dated progress notes and photos. After a vet check, Adjust projection updates the expected date, the window and the linked reminders together. See tracking pregnancy and progress.

4. See every sow at once on the Breeding dashboard. If you keep several sows, the Breeding dashboard groups active cycles into Expecting, Due soon, and Overdue, with projected care reminders alongside. It is a planning view: the labels tell you timing, not whether a pregnancy is healthy. See the breeding dashboard.

5. Set reminders for the jobs that cannot slip. A reminder to move the boar out before day 59, a vet check in the last weeks, and a weekly weigh-in are the three worth setting. Log each weight as a measurement record so a drop stands out. The help articles on reminders and upcoming care and care, growth, and identity records show how.

6. Record the birth and the litter. When the pups arrive, record the outcome from the active cycle with the number born alive and stillborn. Creatures closes the cycle and creates a private group for the litter, and you can create individual profiles for each pup when you are ready, already linked to their mother. The walkthrough is in recording births and creating a litter.

Cavy breeders who already keep records in Cavy15 can bring them in with the WinRbro import rather than retyping them.

Should you breed your guinea pig?

For most pet owners the honest answer is no, or at least not without a plan. Merck’s owner guidance recommends preventing pregnancy by housing males and females separately or by spaying and neutering, and it describes difficult birth as a serious problem with a risky surgical fallback. A single litter can mean three or more pups who each need a home, and boars need separating from their mother and sisters within weeks. If you do want to breed, start with a veterinary check of the sow while she is still young, plan the homes before the pups exist, and keep the dates written down.

If you are looking for guinea pigs rather than breeding them, our guides on where to buy guinea pigs and how much guinea pigs cost are the better starting point, and the guinea pig species page has breed profiles from the American to the Peruvian.

Frequently asked questions

How many weeks is a guinea pig pregnant?

About 9 to 10 weeks. The average is 68 days, which is just under 10 weeks, and the normal range of 59 to 72 days runs from about 8.5 to just over 10 weeks.

How many babies do guinea pigs have?

Merck gives a litter size of 1 to 7 pups, usually about 3. Larger litters tend to be born a little earlier and, according to the Shomer chapter, are associated with more stillbirths.

Can a guinea pig get pregnant right after giving birth?

Yes. Sows have a fertile heat roughly 2 to 10 hours after giving birth. If a boar is in the enclosure at delivery, she is very likely to become pregnant again immediately, which is why he should be moved out before the due window opens.

How can I tell if my guinea pig is about to give birth?

The most useful sign is her pelvis widening in the last week; your vet can show you how to feel for it. She will also be at her heaviest and may be less active. Births are usually fast, so many owners find the pups already born.

What age is too old for a guinea pig’s first litter?

Sources commonly put the cutoff at around 6 to 7 months for a sow that has never given birth, because of the high risk of a difficult birth. A 2024 imaging study questioned the traditional explanation that the pelvis fuses, but not the risk itself. If your sow is older than about 6 months and has never had a litter, talk to a veterinarian who treats guinea pigs and do not breed her.

Do guinea pigs need a nest box to give birth?

Not the kind of nest box a rabbit doe uses; guinea pig pups are born furred and mobile. A pregnant sow does best with a familiar enclosure, deep clean bedding, a hideout large enough for her to turn around in, and constant access to hay and water.

Do this next on Creatures

Expecting pups, planning a first litter, or keeping records for a cavy herd, these are the next steps on Creatures.