4 Month Old Baby: Developmental Milestones

In the fourth month, your baby will show a marked improvement in terms of physical, cognitive and communicative development. Let us take a brief look at what you can expect from your four-month-old.

Physical development

Growth Details Boys [33] Girls [34]
How much should a 4-month-old weigh 12.34 to 18.95 pounds 11.24 to 17.85 pounds
What should the height of a 4-month-old be 23.62 to 26.69 inches 22.8 to 26.06 inches
How much should his head size be (97 percentile babies) [11] 15.5 to 17.28 inches 15.03 to 16.92 inches

What should your baby be doing at 4 months

Motor development

Being able to use both his hands in a flexible way, your baby’s grasping and grabbing skills are improving, making him able to shake or play with a toy [1]. Having a better head control, he can hold it in an upright position along with his chest when lying on his tummy [1].

Most infants begin rolling over from their stomach to back [3], also displaying kicking and pushing motions of their feet [1] as well as arching their backs [18]. Babies also develop the habit of putting everything into their mouth, which is probably their way of exploring the world around them [14].

Cognitive development

With an advanced brain development, he can convey to you whether he is pleased or displeased as well as respond to your affection [3]. The baby also starts establishing eye contact with his parents and acquires the skill of memorizing. He will smile to acknowledge something amusing whereas some may even laugh out loud. Most of them may demand their parent’s attention all the time desiring to be cuddled or held [2].

They even start anticipating things, for instance in case your baby is formula fed, the sight of the bottle will make him think that it is time to eat [2].

Communicative development

Though crying may still be a way of communication, your baby will go on to express himself by making a lot of vowel sounds such as ‘aahh’, ‘ooh’, followed by squeals, laughter, coos and giggles [1]. He even shows variation in his crying to convey different emotions such as hunger, tiredness or pain [3].


By the fourth month, the Moro reflex seems to go away completely. Moreover, the rooting or sucking reflexes also begin to diminish or lessen by this time [38].

Sensory development

How clearly can babies see

Their sharp vision enables them to distinguish similar-shaded colors such as red and orange [5], as well as subtle color contrasts like a blue spoon on a blue plate [1]. With an improved hand-eye coordination, they look at toys and attempt getting them [3]. Their tracking and following ability has improved [3], though preference for close-ups remain [1,2].

How well can a four-month-old hear

A four-month-old can recognize his mother’s voice well, responding by smiling on hearing her speak. He will even react in an excited way on hearing new sounds [6].

What sleep schedule do babies follow

Most babies will sleep for seven to nine hours at a stretch at night.  In fact, he will be sleeping fourteen to sixteen hours in a day with the two naps being taken into count [1,2].

Sleep regression in babies

Sleep regression is a common trait mostly observed in four-month-olds, characterized by inconsistent sleeping patterns [7]. Its symptoms include changes in feeding pattern, fussiness, prolonged crying, remaining awake for a longer time, missing naps or sleeping for short periods [9]. One of the main causes may be that he does not directly enter into a deep non-REM sleep, thus getting distracted easily [8].

How much should a 4-month-old eat

Formula-feds will have four to five feeds a day at increased intervals [12] whereas breastfed babies take six to eight feeds daily. As your little one’s brain is maturing, he may get easily distracted and restless while feeding [27].

Should you start solids at four months

Although some babies show teething symptoms like drooling or excessive saliva secretion at this age, with a few of them actually cutting their first tooth [17], solid food is not recommended yet as they get all the required nutrients from the breast milk or formula food [12]. Their tongue-thrust reflex goes away by this month, but they are still not ready for solid foods [16].

However, if your baby is not contented with the breast or formula milk he gets, talk to the doctor about the same. He may recommend solid food such as rice cereals, as long as the infant has a good control of head and neck, being able to sit with support [1].

Babies on solids may get constipated as their body is beginning to adjust to the new food [20]. Moreover, it is normal for kids to pass stool once in three days as long as it is soft and they are gaining weight [19].

 When to call a doctor

  • The baby gets dehydrated on passing watery stools, also showing symptoms such as fussiness, lethargy, dry mouth and no tears while crying [21, 22].
  • Fever exceeds 101 °F, accompanied by symptoms such as decreased sleeping, reduced food intake, flushed cheeks, seizures or convulsions and breathing difficulty [23,35].
  • Baby is passing very hard stools, accompanied by blood or has reduced appetite and has even lost weight [36].
  • If your baby’s cold stays for more than five days and comes along with other symptoms like discharge of brown, green or yellow mucus with his cough, fever above 102.2°F, respiratory troubles or rubbing ears too often [37].
  • The baby has gas pains as well as lessened bowel movements, vomiting, bloody stools, fussy behavior, and fever [28].
  • Throws up yellow or green fluid and has breathing difficulties [32]. Though bouts of spitting is common in this month, occurring because of gastroesophageal reflux [31,32].
  • Clicking jaws too often while opening or closing his mouth, which might be a symptom of TMJ (temporomandibular joint) disorders [25]. However, moderate jaw clicking may be normal while teething [24].


5-in-1 vaccine (DTaP/IPV/Hib): The third dose of this shot is given to fight against five different diseases namely tetanus, polio, whooping cough (pertussis), diphtheria and Hib (Haemophilus influenza type b) [29].

Pneumococcal: At this month the second dose of this vaccine is given to help the body combat pneumococcal diseases leading to pneumonia, ear infections and meningitis [30].

Rota: A second dose of rota vaccine is given at the fourth month to fight against rotavirus that may lead to fever, vomiting, severe diarrhea, and dehydration [30].


  1. http://www.webmd.com/parenting/baby/baby-development-4-month-old
  2. http://www.nlm.nih.gov/medlineplus/ency/article/002007.htm
  3. http://www.cdc.gov/ncbddd/actearly/milestones/milestones-4mo.html
  4. http://www.parents.com/toddlers-preschoolers/safety/toddlerproofing/when-your-baby-puts-everything-in-his-mouth/
  5. http://www.babycentre.co.uk/a719/your-four-month-olds-development
  6. http://www.babycentre.co.uk/a6509/developmental-milestones-hearing
  7. http://www.babycenter.com/0_baby-sleep-basics-3-to-6-months_7656.bc
  8. http://www.weebeedreaming.com/my-blog/4-month-sleep-regression
  9. http://www.babysleepsite.com/how-we-sleep/4-month-old-sleep-regression/
  10. http://kidshealth.org/parent/pregnancy_newborn/growth/grow47m.html
  11. http://www.cdc.gov/growthcharts/html_charts/hcageinf.htm
  12. http://www.babycentre.co.uk/a719/your-four-month-olds-development
  13. http://kidshealth.org/parent/pregnancy_newborn/formulafeed/formulafeed_often.html#
  14. https://www.childrensmercy.org/content/uploadedFiles/Care_Cards/CMH-02-210p.pdf
  15. http://www.babycenter.com/0_introducing-solids_113.bc
  16. http://www.babycenter.com.au/x546061/can-i-give-my-baby-solid-food-at-four-months
  17. http://www.babycenter.com/0_developmental-milestones-teething_6574.bc
  18. http://kidshealth.org/parent/growth/movement/move47m.html
  19. http://www.parents.com/baby/diapers/dirty/poop/
  20. http://www.babycentre.co.uk/a79/constipation
  21. http://www.webmd.com/parenting/baby/baby-diarrhea-causes-treatment
  22. http://www.seattlechildrens.org/medical-conditions/symptom-index/diarrhea/
  23. http://www.webmd.com/parenting/baby/fever-in-babies
  24. http://www.medicinenet.com/teething/page2.htm
  25. http://kidshealth.org/parent/general/eyes/tmj.html#
  26. http://www.thebump.com/a/gas-pain-baby
  27. http://www.babycenter.com/0_your-4-month-olds-development-week-1_1477216.bc
  28. http://www.webmd.com/parenting/baby/features/infant-gas
  29. http://www.nhs.uk/conditions/vaccinations/pages/vaccination-schedule-age-checklist.aspx
  30. http://www.babycenter.com/shots
  31. http://www.healthline.com/health/gerd/recognize-gerd-infants
  32. http://www.mayoclinic.org/healthy-lifestyle/infant-and-toddler-health/in-depth/healthy-baby/art-20044329?pg=1
  33. http://www.babycenter.in/a1052194/baby-boys-growth-chart-0-to-12-months
  34. http://www.babycenter.in/a1052197/baby-girls-growth-chart-0-to-12-months
  35. http://www.babycenter.com/0_fever-in-babies_84.bc?showAll=true
  36. http://www.babycenter.com/0_constipation-in-babies_79.bc#articlesection4 
  37. http://www.babycentre.co.uk/a78/common-cold
  38. http://www.whattoexpect.com/baby-behavior/newborn-reflexes.aspx[/ref]