How Long Are Rats Pregnant? The Rat Pregnancy Timeline

by Joshua Paulson

How Long Are Rats Pregnant? The Rat Pregnancy Timeline


If you own a pet rat, you need to understand the pregnancy timeline. This is important for researchers, breeders, and owners because different species have different gestation periods. With a clear picture of the species, owners can prepare for pregnancy and plan for the coming litter. Breeders can tell when a rat is in heat and pair them accordingly. Researchers have an idea of what to expect and can therefore make better conclusions.

Most importantly, you need to provide the mother with a nutritious diet, extra nesting material, and exercise during pregnancy and after birth. Read on to learn about the rat pregnancy timeline, including the length, signs of pregnancy, birth, and caring for the young.

Basics of Rat Reproduction

Understanding the basics of a rat’s reproduction makes it easy to tell the female and male apart. It’s also easier to study fertilization and observe any gestational changes in female rats.

The estrous cycle plays a big role in reproduction and occurs in four stages. These are proestrus, estrus, metestrus, and diestrus. The cycle is rapid and takes four to five days to conclude. Proestrus is the period when the body of the rat starts preparing for ovulation and copulation. Though not receptive towards males, the vulva gapes, showing vaginal tissues that are reddish-pink and moist. This lasts for about 14 hours.

In the estrus phase, female rats become receptive to males and present themselves by pushing their hind legs into the air. They sway their heads, vibrate, and become still if touched. At this time, eggs are released for fertilization.

The eggs implant in the uterus and the pregnancy commences. The vulva still appears as it did in proestrus but the tissues are less moist and lighter pink. Some stripes may be visible. The phase takes 24-48 hours.

Metestrus and Diestrus

The metestrus phase occurs if the female doesn’t mate and gets pregnant. The rat’s body cools down from the cycle, and hormone levels decrease. Genitals go back to the normal color and size, and the vulva looks dry and pale.

The body resets in diestrus and starts getting ready for a new cycle. Metestrus takes six-eight hours while diestrus takes 48 to 72 hours, and then the cycle starts all over again. If pregnant, the diestrus phase lasts for the entire gestation period.

Baby rats on a basket

How Long Is a Rat’s Pregnancy?

The normal gestation period of a rat is 21 to 23 days. Postpartum pregnancies can last 28 days. Reproduction and rat breeding can be affected by inadequate nesting material, tumors, cysts in the ovaries, cold environments, abnormal light cycles, malnutrition, and age.

Females can abandon, eat, or abort their babies due to excessive noise, deformed or sick pups, inadequate nesting materials, overcrowding when in-group housing, lack of water, and inadequate rat food. When a rat is healthy, reproductive problems are less common.

Factors That Can Influence Rat Pregnancy Length

Embryo implantation happens after five to six days in rats. Various elements can influence the duration of rat pregnancy. One being a phenomenon referred to as embryonic diapause where embryo development is suspended at the blastocyst stage temporarily in the uterus. This can go on for 13 days. It mostly happens when the conditions are less than favorable and is done to safeguard the survival of the species.

Other factors include:

  • Species – Different species may have longer or shorter gestation periods.
  • Age of the rat – As the rats get older, the gestation period and labor may be prolonged.
  • Overall health and nutrition – Inadequate nutrition and poor health can reduce the length of pregnancy. Rats can abort a pregnancy if they feel the conditions are less than ideal.
  • Environmental stressors and living conditions – These include inadequate nesting materials, unfavorable climatic conditions, abnormal light cycles, and overcrowding.
  • Number of previous pregnancies – When there are many previous pregnancies, the gestation period may be longer, especially if the female is carrying many offspring.

The Rat Pregnancy Stages: A Detailed Look

Pregnancy is first detectable in rats in around two weeks. There are obvious pregnancy signs as it progresses. It is important to provide the female with enough nesting materials at this time.

two baby rats

Days 1-7: Early Gestation

The egg cells are released by the ovaries and into the oviducts. The oviducts are attached to the ovaries. If mating occurs, fertilization takes place in the oviduct’s upper third. Implantation happens farther along the system on the uterine horns. Several uterine horns allow a number of fetuses to develop at the same time.

The vulva is the external opening, which isn’t part of the urethral orifice. After fertilization, the blastula is formed. After the division of the zygote, the blastulas then travel to the oviducts where they are implanted. Differentiation into embryonic tissue starts. Nourishment comes from the mother through the umbilical cord. The placenta supplies oxygen and takes away waste.

A female rat’s body goes through different changes during pregnancy. This is how to tell if a rat is pregnant:

  • A mucous plug in the vagina
  • Missing an estrus cycle could mean the rat is pregnant
  • Increased appetite
  • Behavior changes
  • Response to males
  • Weight gain
  • Visible and more pronounced ripples
  • Nest building activity

Days 8-14: Mid Gestation

At this stage, the embryo already has a neutral white plate, the spinal cord, and brain arise. The leg and arm buds are visible by day 11. By day 13, the facial processes become prominent.

Days 15-21/23: Late Gestation to Birth

In this stage, the embryo grows fully with skeletal and organ systems forming as well. The nervous system pathways are fully developed, and the embryo is about 20 mm to 40 mm. The female starts preparing for birth by engaging in nest-building activities. The rat needs to be in a stress-free and quiet environment at this critical stage.

Signs of Labor and What to Expect

Birth happens naturally in rats, and the female rarely needs any assistance. But how do rats have babies? The sequence may take one to two hours. Spotting may occur when a female is about to give birth. Excessive bleeding isn’t normal. The female may squeak, hunch over, and stretch as the sides constrict. She may also try to clean herself at this time too. The amniotic sac appears, and the babies will make their way through the birth canal. They can be born rump first or head first. The female may assist with birth using her teeth or paws as needed.

Post-Pregnancy Care for the Mother and Her Litter

Baby rat on a human hand

Once the pups have been born, post-pregnancy rat care is important for both the female and the pups. It’s important to clean the rat cage and check on the newborns after birth. Any stillborn should be removed. However, be careful when trying to handle the mother and the litter, as she can become aggressive.

Proper nutrition ensures that the mother has sufficient milk for her young. Start handling the pups within 24 hours to see if any were injured at birth or if they have birth defects. It’s important to count the number of pups and take out any that are stillborn. Check that all the pups are being fed.

To ensure that’s the case, they should have a visible milk band, which is a whitish strip under the skin of the baby. This helps you determine whether the rats should be removed or not.

What Happens After Birth to Help Babies Survive?

The rat licks the babies to clear off the membrane that encases them to make sure they can breathe. After cleaning them, she ingests the protein-rich afterbirth. The sound and movement of the pup ensure that the mother doesn’t ingest it. Note that a mother may ingest a stillborn pup after delivery.

The mother rat should initiate nursing and keep the pups warm. Humans should provide enough nesting materials and feed the female to ensure she has enough milk to go around.

Caring for Difficult Births or Sickly Newborns

If some of the newborns are sickly, you may choose to separate them from the litter, especially if they’re not being fed. Ensure they’re placed in a warm area. The rats should be fed every three to four hours in the day and once at night. Feeding them too often may cause digestion issues. If you have issues feeding them, you should get a professional to help.

Advice for Unplanned Baby Rats

Sometimes pet owners may get an unexpected litter. To avoid such litters, ensure that you adopt your rats from experienced pet breeders. The females and males should never be housed together unless they’re spayed or neutered. This should be done to siblings as well.

The issue with unplanned baby rats is their unknown temperament. An unplanned litter can be taken back to the breeder or you may pass them on to anyone willing to take them in. However, it should be made clear that the litter was unplanned.

Ready to Support Your Pregnant Rat? Take the Next Step

Understanding the rat pregnancy timeline is important as it helps you prepare adequately for the litter. With the right information, you’ll know what to expect at different stages, which eliminates anxiety associated with peculiar rat behavior you might witness.

One of the best ways to help pregnant rats along the way is to create the ideal habitat for them. You need to stock up on the best rat supplies for your pet. One way to achieve this is to get a well-designed and spacious cage. Make sure your rat has enough room to move and explore. Quality Cage has some of the best options that allow your furry friends to live in comfort.


How long is a pet rat pregnant?

A pet rat may be pregnant for 21-23 days. A larger litter increases the chances of survival.

How many babies can a rat have at one time?

Female rates produce five to 12 pups at a time, but this depends on the species.

What months do rats have babies?

In cold areas, rats give birth in April, May, September, and October. In warmer climates, rats don’t have a specific reproduction timeline and can produce all through the year.

How often do rats give birth?

If not controlled, the female rat can be impregnated only 48 hours after birth. However, it’s better to wait for a few weeks after the pups are weaned for her to regain strength.


Have Questions About Taking Care of Pregnant and New Born Rats?

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Author: Joshua Paulson and Quality Cage Team
Josh is the owner and CEO at Quality Cage Crafters since 2015. During his time at Quality Cage Crafters, he has been able to learn from tens of thousands of pet owners and pet educators. He blends his ambition for manufacturing and passion for animal care to create solutions for pet owners, breeders, animal rescues, and zoos. He has brought together a team of great animal lovers to create high-quality pet care content for the Quality Cage Crafters audience.

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