Is Your Rat Pregnant Or Just Fat? How To Tell

If you keep female rats and they spend time around male rats then it’s possible that sooner or later they will fall pregnant. But how do you tell if you’re expecting a litter or whether your rat is just getting obese from eating too much?

If your rat pregnant or just fat? How to tell – a fat rat will show signs of being fat (such as fat over their spines and tails) whereas a pregnant rat will show signs of pregnancy which include weight gain but also behavioral changes, hair loss, nest building, a failure to go into heat and potentially the shedding of a mucus plug.

Don’t worry – it’s really easy to identify these things and we’ll show you exactly what to look for and then how to take care of your rat if she does turn out to be pregnant!

How To Tell If Your Rat Is Pregnant

The good news is that a fat rat is usually obviously fat, in fact, we wrote an entire article on how to handle fat rats, recently. However, the nuts and bolts of it are – fat rats will be noticeably fat, they will have a fatty layer over the spine and at the base of the tail.

Pregnant rats, on the other hand, are a little more complicated – so, let’s take a look at the major signs of a rat pregnancy which include:

  • A mucus plug
  • An end of going into heat
  • Changes in behavior
  • Changes in weight
  • Hair loss
  • Building nests
  • And a pear-shaped body

What Not To Do

One thing that you definitely shouldn’t be doing, if you think your rat might be pregnant, is massaging or poking at their abdomen to feel for babies.

There are two reasons that this is a bad idea:

  • If the rat is newly pregnant the fetuses are going to be way too small for you to feel with your fingers, so you won’t learn anything
  • There is a good chance that your probing fingers might squash the fetuses in the womb and lead to their death, stillbirth or worse birth deformities

You can gently feel for babies once a rat has been pregnant for over 2 weeks but only with the greatest of care and ideally, you shouldn’t do this unless you know exactly what you are looking for and how to go about it.

The Mucus Plug

A mucus plug won’t tell you if your rat is pregnant, but it will tell you that your rat has had intercourse and that her body thinks she could get pregnant.

This “plug” forms in her vagina due to the presence of certain secretions from the male organ due to intercourse. Its evolutionary purpose is, of course, to prevent other male rats from then having intercourse and getting the rat pregnant.

So, if your rat has a mucus plug it is more likely that she is pregnant. These plugs often fall out after being in place for a while and can be found on the floor of the cage. If you find one, you might want to start keeping a careful eye on your potential rat momma.

She Won’t Go Into Heat

Rats follow an “estrus” cycle. That means when a female rat is at her most fertile, she’s also at her most frisky. That is she goes into heat which drives her to seek out a male rat and mate with him.

If a rat is pregnant, this behavior is clearly biologically unnecessary (rats can’t carry multiple litters at the same time), so, when a female rat becomes pregnant, she will stop going into heat.

This can be a very useful sign that your rat might be pregnant (though there are other possible reasons for an interrupted estrus cycle) but it’s worth remembering that not all female rats have obvious and observable estrus cycles.

She May Become Aggressive

The purpose of life is children. This is true in nearly every species of creature on the planet and that means when a rat is pregnant, she is programmed to defend her children against any possible threat.

This can include her cage mates and it might include you too. Docile rats often get angry during pregnancy. There’s not much you can do about this.

Oddly, occasionally an anxious rat or even an aggressive one goes the opposite way and chills out completely during pregnancy. Why this should be, scientists aren’t quite sure.

Pregnant rats also have a tendency to hoard food and hide it away from other rats. This is a fairly natural urge designed to have a stockpile to greet her young with. Some rats will even steal food directly from other rats in this stage of pregnancy.

She’ll Lose Interest In Male Scents

If you handle male rats before your handle female rats – then the females often get very excited by the smell of your hands. It’s the promise of a mate that drives this excitement.

Once a rat is pregnant, again she has no need of a mate, so her reaction to the smell of male rats will tail off (excuse the pun). She simply won’t react to the scent of male rats at all.

She Will Gain Weight

Possibly the most obvious sign of a pregnant rat is going to be weight gain. You can’t carry a bunch of rats around inside of you without putting on a few ounces.

Using A Scale To Track Weight Gain

The best way to measure a rat’s weight is to use a digital kitchen scale which has either a flat top or a removable plastic bowl on the top.

The scale should easily measure in either ounces or grams with a decent degree of accuracy. (We’d say +/- 1 gram). The maximum weight load of the scale should be under 10 lbs.

It’s very easy to buy these scales anywhere. You can find them on Amazon or in your local supermarket and they’re very cheap.

Patterns of Weight Gain In Pregnant Rats

Believe it or not, it only takes a day after your rat becoming pregnant for her to show some weight gain! Throughout the course of the pregnancy it’s likely that your rat will gain approximately 1/10th of an ounce every single day.

This daily increase is a good sign. It means that her babies are happy, healthy and growing normally. Of course, the exact amount of weight gain is directly linked to the number of babies that your rat mom is about to have.

When you weigh a suspected pregnant female, you should see a substantive weight gain in the first 2-3 days of pregnancy and then a steady gain every day after. Then in the last 3-4 days of pregnancy she may gain a lot of weight very quickly.

So, how much weight will they gain over the course of a pregnancy? Well, each baby will weight about 5-6 grams. That means a heavily pregnant rat will gain about 90 grams during pregnancy!

However, it is possible that she may only be carrying a very small litter (1-2 rats) and thus, you won’t see any marked change in weight.

Weight Fluctuations In Pregnant Rats

Not only is weight gain a good way to track pregnancy in a rat – it can also help identify if there are problems in the pregnancy.

Now, some days may see more gain than others, you might have a day or two with no gain, or a big burst of weight gain on a single day. None of these things are necessarily anything to worry about.

However, if a week passes without weight gain, this should raise serious concerns. If your rat is definitely pregnant, she ought to be gaining weight.

If she’s not – the babies may have died and her body has failed to reabsorb them as it should, or that she has other medical issues, or that she’s tried to give birth and the babies are now stuck in the birth canal. If her delivery time is up and this is the case – get her to a vet immediately.

If she’s losing weight over the course of her pregnancy – then it’s likely that her body is reabsorbing the fetuses and that they’ve died. You can expect losses of up to ½ an ounce in a single day for this process. This is quite normal, and it means your rat will almost certainly be healthy after it’s over, though, obviously, there will be no babies.

If your rat only partially absorbs the fetuses this can lead to an infection – so keep an eye on her for signs of fever, unpleasant discharge, bleeding, loss of appetite or other worrying symptoms and if they arrive, take her to the vet.

Losing Hair In Pregnant Rats

One peculiar side effect of pregnancy in rats is that mom tends to lose most of the hair around her nipples in the last few days before the babies arrive. This is a completely natural process; her body is trying to make it as easy as possible for the little ones to be able to suckle when they arrive in the world.

She Will Build A Nest: Babies Are Nearly Here!

Just as with humans as a rat progresses through pregnancy, she undergoes some fairly dramatic hormonal transitions and one of the last changes triggers the urge to build a nest.

When you see a rat nesting, you know that the babies are expected any time now.

In the wild, rats fetch their own nesting material but you will have to help your rat out by providing nesting material – make sure to avoid strings or cloth with holes in as the babies can get seriously hurt by getting trapped in them.

The Pear Shaped Body Of A Pregnant Rat

Finally, as your rat reaches the final stages of pregnancy her body will tend to gain a sort of pear shape as her lower abdomen distends and starts to become quite firm. This change can be very dramatic, indeed, though if the rat has a very small litter – it might not happen at all.

How To Care For A Pregnant Rat

OK, now, if you have a pregnant rat on your hands – you’re going to want to take care of her properly. So, here’s how you do that:

The Right Food For A Pregnant Rat

As you’d expect, being pregnant ups a rat’s need for nutrients and, in particular, you should look to increase the protein in her diet. We’d add a little dog food as a treat or some milk with soya bits to boost her protein levels safely.

You should also ensure she’s getting vitamins and minerals (fresh veg is good for this). You shouldn’t add any dietary supplements to her food, though, unless you’ve been instructed to by a vet.

The Right Fluids For A Pregnant Rat

You shouldn’t need to provide anything more than regular clean, fresh water to a pregnant rat which is otherwise healthy. Hopefully, you’re already providing enough water for your rats to drink freely but if you’re not – now is definitely the time to start and we’d recommend that you provide more than one source of water, just in case.

If you think your pregnant rat might be dehydrated – take her to the vet. This can be a serious issue in pregnancy.

The Key Numbers For Pregnancy In Rats

There are some simple rules that can help you monitor a rat’s pregnancy and birth:

  1. The whole process takes about 3 weeks from impregnation to birth
  2. It is much more common for pups to be born at night than during the day
  3. A typical litter will contain up to 12 pups
  4. The whole birth can take up to 4 hours

Isolate The Mother-to-be

Remove the pregnant rat from being around other rats until she gives birth. This will reduce the chance of her fighting with other rats and hurting the babies or the other rats (or being harmed herself for that matter).

You should not house other pregnant rats with her, either.

The Right Home For A Pregnant Rat

You should provide a cage of a similar size to the rat’s regular cage with the usual wire surroundings for your mom-to-be. Don’t use a fish tank because this will cut down on ventilation and can lead to poisoning or worse for the mother and the babies.

However, try to avoid wire floors in a pregnancy cage because the babies can get caught in the wires and injure themselves. A plastic floor is best.

Removing Hazards From A Pregnant Rat’s Life

While we love to give our rats toys and fun during their ordinary lives – some of them are potentially dangerous to a pregnant rat or her babies. So, take any exercise wheels, high climbing structures, and anything you think might present a hazard out of the cage until the pups are grown.

Keeping Things Clean For Your Pregnant Rat

It’s even more important than normal that you keep things sanitary for a rat during pregnancy and after the birth. Bacteria and rat poop and urine can easily build up and cause serious health issues if you don’t.

Bedding should be changed daily, the cage should be cleaned every two days (this is because pregnant rats tend to smell a lot stronger than ordinary rats) and the cage should always be in a position with clear air flow providing solid ventilation.

Stay Away From Her Nest!

It’s important to keep things clean but please don’t interfere with her nest in any way at all. Clean around it and leave a bit of a border between the nest and the clean part of the cage. This is the safe environment that she will build to be a mother in. Leave it be.

Don’t Handle Her Very Often

Given the mood changes of the average pregnant rat and the fact that you might harm the babies – it’s best only to handle her when absolutely necessary. Otherwise, stick to gentle petting (or if she doesn’t like that – just be around for companionship).

Make Sure She’s Got Peace And Quiet

Pregnancy is an exhausting process for rats as much as it is for humans. Don’t allow any other stress to creep into your mom-to-be’s life. Keep her cage in a place with little noise and away from other animals and children.


If your rat is pregnant or just fat? How to tell: while weight gain is a sign of pregnancy in rats, you will also find behavioral changes, hair loss, a failure to go into heat, the shedding of a mucus plug and nest building to be telltale symptoms of pregnancy.

As you can see, it’s not too hard to spot a pregnant rat and distinguish it from a fat one. It’s also very easy to take care of a pregnant rat until she has her pups. We hope that if your rat is pregnant that she will have a safe pregnancy and a healthy litter.

Darren Black

I'm Darren Black, the owner, and author of I am from Scotland, United Kingdom and passionate about sharing useful information and tips about properly caring for an animal's wellbeing.

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