The Fourth Trimester by the Numbers

By Kerry Weiss
Reviewed by Terri Major-Kincade, M.D.
December 13, 2022

For the text version of this infographic, read on:

The Fourth Trimester by the Numbers

Just had a baby? Welcome to the fourth trimester. This is a term for the first 12 weeks of a newborn’s life.

It’s called a trimester because it lasts about 3 months, just like each of the 3 trimesters of pregnancy.

During this time, your baby is adjusting and you’re healing.

According to the World Health Organization, the first 28 days of your baby’s life are considered the newborn stage.

From feedings to dirty diapers to hours slept, there are plenty of things you’ll be counting during the fourth trimester.


Most babies born between 37 and 40 weeks weigh between 5 pounds, 8 ounces and 8 pounds, 13 ounces at birth.

Some babies weigh slightly more or less. If there’s a significant difference, the pediatrician may want to do additional testing or monitor your baby more closely.

Most infants lose up to 10% of their birth weight in those first few days—and should regain it within 2 weeks, as newborns typically gain around 1 ounce each day.

Your baby will likely double their birth weight by the time they’re 4 months old.


Feed your newborn on demand to promote proper nutrition and healthy weight gain. This means whenever they want to eat!

This may be 8+ times each day!

Chest/Breastfed Babies

  • Typically feed every 2–3 hours.
  • Aim for 10–15 minutes on each breast per feeding.

Formula-Fed Babies

  • Typically feed every 3–4 hours.
  • Aim for 2–3 ounces per feeding.

Burp your baby between breasts or after every 2–3 ounces to prevent gas-related fussiness.

By 2 months old, babies typically eat 4–5 ounces in one feeding and may go longer in between.

By 4 months old, babies can eat up to 6 ounces in one feeding and may go even longer in between.

Of course, all babies are different, and these are just averages. Keep track of how much and how often your baby is feeding, and share it with their pediatrician.


Once your baby is a few days old, expect to change 6–8 wet diapers each day. Breastfed babies should also poop several times a day. Formula-fed babies should poop at least once a day, typically.

Your baby’s first few poops will be sticky, thick, and dark. This is known as meconium and is completely normal.

After that, there’s a range in what’s considered “normal” baby poop. It can range from loose to peanut butter consistency. The color can vary, too.

  • Chest/breastfed babies’ poop tends to be yellow and have a mustardy look.
  • Formula-fed babies can have tan poop, sometimes with a yellowish tinge or a bit of green in it.
  • White, red, or black poop? Call the doctor to check for potential problems.


Newborns need 16+ hours of sleep each day, typically in short, 2–4 hour spurts.

By the 3-month mark, your baby may start sleeping in 6–8 hour stretches at night!

Sleep training may help. This teaches your baby to self-soothe and fall back asleep on their own if they wake. You should be able to start around the 4-month mark.

The safest place for a baby to sleep is on a flat, firm mattress in their own bassinet or crib. Their sleep space should be in the same room as you for a minimum of 6 (and ideally 12) months.

For safety, keep the crib free of:

  • Blankets
  • Pillows
  • Bumpers
  • Stuffed animals

Your baby just needs a fitted sheet and a light receiving blanket for swaddling if they like it.

Try to avoid naps in carriers, car seats, strollers, and swings whenever possible.

Place your baby on their back to sleep throughout their first year of life to significantly lower their risk of sudden infant death syndrome (SIDS).


The main way your newborn communicates their needs is through crying.

Babies don’t typically produce tears until 2 weeks to 2 months of age. (But sometimes tears happen because of an infection like pink eye. If your baby has tears that aren’t from crying, talk to the pediatrician.)

If your baby is crying, they may want to be fed, need a diaper change, be cranky, or want to be held.

The 5 S’s

Try soothing a fussy baby with the 5 S’s, which work together to provide womblike comfort:

  • Swaddle your baby.
  • Use side- or stomach-down positioning when holding the baby. *Holding them with their left side down promotes digestion!
  • Shush your baby with sounds from a white noise machine.
  • Swing or rock your baby slowly and steadily.
  • Let your baby suck on a pacifier or feed them.

The 5 S’s can also be used to help your baby sleep.

1 in 4

Babies have colic, which is when a baby:

  • Cries continuously for at least 3 hours a day
  • More than 3 days per week
  • For more than 3 weeks

Colic tends to peak around 6 weeks of age and typically disappears on its own by the time the baby is 3–4 months old.

Remember: The newborn stage and fourth trimester go by quickly. If you find yourself in a challenging phase, remind yourself of the popular parenting mantra “This too shall pass.”

Call your baby’s pediatrician if you have any concerns. And don’t be afraid to ask for help.


American Academy of Pediatrics. (2020) Tips for Keeping Infants Safe During Sleep from the American Academy of Pediatrics.

Cleveland Clinic. (2021) When and How to Sleep Train Your Baby.

Goldfarb, I. T. (2021) The fourth trimester: What you should know. Harvard Health Publishing. American Academy of Pediatrics.

Hoecker, J. L. (2022) I'm breastfeeding my newborn and my baby's bowel movements are yellow and mushy. Is this normal for baby poop? Infant and Toddler Health. Mayo Clinic.

Isenberg, S. J. et al. (1998) Development of Tearing in Preterm and Term Neonates. JAMA Ophthalmology.

Jain, S. (Last updated May 2022) How Often and How Much Should Your Baby Eat? American Academy of Pediatrics.

Johns Hopkins Medicine. Colic. Accessed November 1, 2022.

National Institute of Child Health and Human Development. Research on Back Sleeping and SIDS. Accessed November 1, 2022.

Nemours KidsHealth.

Safe Sleep Academy. How to Soothe a Fussy Baby (5S’s). Accessed November 1, 2022.

World Health Organization. Newborn health. Accessed November 1, 2022.