Baby’s Health Center
Calculating the day your baby begins to develop and keeping track of your pregnancy dates can be a challenge. The development of pregnancy is counted from the first day of the woman’s last normal period, even though the development of the fetus does not begin until conception. Pregnancy is calculated from this day because each time a woman has a period, her body is preparing for pregnancy.
The following information is used as a general guide for healthy pregnancy development, although development may vary due to the mother’s health or a miscalculation of ovulation. Gestational age is the age of the pregnancy from the last normal menstrual period (LMP), and fetal age is the actual age of the growing baby. Most references to pregnancy are usually in gestational age rather than fetal age development, but we have included both so that it is clear what stage development is at. Measurements will be given in total length from head to toe, but each pregnancy can differ in weight and length measurements, and these are just a general guideline.
Pregnancy is also divided into trimesters which last about 12 – 14 weeks each. Similar to development, these can be calculated from different dates so not all trimester calculations will equal the same. The following information divides the three trimesters into a little over 3 completed months each. The first trimester is week 1 through the end of week 13. The second trimester usually ends around the 26th week and consists of the 4th, 5th and 6th completed months. The third trimester can end anywhere between the 38th – 42nd week and is the 7th, 8th and 9th completed months of pregnancy.
Week 1 & 2 – Gestational Age:
Your menstrual period has just ended, and your body is getting ready for ovulation. For most women, ovulation takes place about 11 – 21 days from the first day of the last period. During intercourse, several hundred million sperm are released in the vagina. Sperm will travel through the cervix and into the fallopian tube. If conception takes place, the sperm penetrates an egg and creates a single set of 46 chromosomes called a zygote, which is the basis for a new human being. The fertilized egg spends a couple days traveling through the fallopian tube toward the uterus, dividing into cells ; it is called a morula. The morula becomes a blastocyst and will eventually end up in the uterus. Anywhere from day 6-12 after conception, the blastocyst will imbed into the uterine lining and begin the embryonic stage.
Week 3 – Gestational Age (Fetal Age – Week 1):
The embryo is going through lots of basic growth at this time, with the beginning development of the brain, spinal cord, heart, and gastrointestinal tract.
Week 4 & 5 – Gestational Age (Fetal Age – Weeks 2 & 3):
Arm and leg buds are visible, but not clearly distinguishable. The heart is now beating at a steady rhythm. The placenta has begun to form and is producing some important hormones including hCG. There is movement of rudimentary blood through the main vessels. The early structures that will become the eyes and ears are forming. The embryo is ¼ inch long by the end of these weeks.
Week 6 – Gestational Age (Fetal Age – Week 4):
The formation of the lungs, jaw, nose, and palate begin now. The hand and feet buds have webbed structures that will become the fingers and toes. The brain is continuing to form into its complex parts. A vaginal ultrasound could possibly detect an audible heartbeat at this time. The embryo is about a ½ inch in length.
Week 7 – Gestational Age (Fetal Age – Week 5):
At 7 weeks gestation, every essential organ has begun to form in the embryo’s tiny body even though it still weighs less than an aspirin. The hair and nipple follicles are forming, and the eyelids and tongue have begun formation. The elbows and toes are more visible as the trunk begins to straighten out.
Week 8 – Gestational Age (Fetal Age – Week 6):
The ears are continuing to form externally and internally. Everything that is present in an adult human is now present in the small embryo. The bones are beginning to form, and the muscles can contract. The facial features continue to mature, and the eyelids are now more developed. The embryo is at the end of the embryonic period and begins the fetal period. The embryo is about 1 inch long and is the size of a bean.
Weeks 9 thru 13 – Gestational Age (Fetal Age – Weeks 7 thru 11):
The fetus has grown to about 3 inches in length and weighs about an ounce. The genitalia have clearly formed into male or female, but still could not be seen clearly on an ultrasound. The eyelids close and will not reopen until the 28th week of pregnancy. The fetus can make a fist, and the buds for baby teeth appear. The head is nearly half the size of the entire fetus.
Weeks 14 thru 16 – Gestational Age (Fetal age – Weeks 12 thru 14):
The fetus’s skin is transparent and a fine hair called lanugo begins to form on the head. The fetus begins sucking and swallows bits of amniotic fluid. Fingerprints which individualize each human being have now developed on the tiny fingers of the fetus. Meconium is made in the intestinal tract and will build up to be the baby’s first bowel movement. Flutters may be felt in the mom’s growing abdomen as the fetus begins to move around more. Sweat glands have developed, and the liver and pancreas produce fluid secretions. The fetus has reached 6 inches in length and weighs about 4 ounces.
Weeks 17 thru 20 – Gestational Age (Fetal Age – Weeks 15 thru 18):
The baby has reached a point where movements are being felt more often by the mom. The eyebrows and eyelashes grow in, and tiny nails have begun to grow on the fingers and toes. The skin of the fetus is going through many changes and begins to produce vernix at the twentieth week. Vernix is a white pasty substance that covers the fetus’s skin to protect it from amniotic fluid. A fetal heartbeat could be heard by a stethoscope now. The fetus has reached a length of 8 inches and weighs about 12 ounces.
Weeks 21 thru 23 – Gestational Age (Fetal Age – Weeks 19 thru 21):
Lanugo now covers the fetus’s entire body. The fetus is beginning to have the look of a newborn infant as the skin becomes less transparent while fat begins to develop. All the components of the eyes are developed. The liver and pancreas are working hard to develop completely. The fetus has reached about 10-11 inches in length and weighs about 1 – 1 ¼ pounds.
Weeks 24 thru 26 – Gestational Age (Fetal Age – Weeks 22 thru 24)- Beginning the third trimester:
If your baby was delivered now, it could survive with the assistance of medical technology. The fetus has developed sleeping and waking cycles and mom will begin to notice when each of these takes place. The fetus has a startle reflex, and the air sacs in the lungs have begun formation. The brain will be developing rapidly over the next few weeks. The nervous system has developed enough to control some functions. The fetus has reached about 14 inches in length and weighs about 2 ¼ pounds.
Weeks 27 thru 32 – Gestational Age (Fetal Age – Weeks 25 thru 30):
The fetus really fills out over these next few weeks, storing fat on the body, reaching about 15-17 inches long and weighing about 4-4 ½ lbs by the 32nd week. The lungs are not fully mature yet, but some rhythmic breathing movements are occurring. The bones are fully developed but are still soft and pliable. The fetus is storing its own calcium, iron and phosphorus. The eyelids open after being closed since the end of the first trimester.
Weeks 33 thru 36 – Gestational Age (Fetal Age – Weeks 31 thru 34):
This is about the time that the fetus will descend into the head down position preparing for birth. The fetus is beginning to gain weight more rapidly. The lanugo hair will disappear from the skin, and it is becoming less red and wrinkled. The fetus is now 16-19 inches and weighs anywhere from 5 ¾ lbs to 6 ¾ lbs.
Weeks 37 thru 40 – Gestational Age (Fetal Age – Weeks 35 thru 38):
At 38 weeks the fetus is considered full term and will be ready to make its appearance at any time. Mom may notice a decline in fetal movement as the fetus is now filling the uterus with little room to move. The fingernails have grown long and will need to be cut soon after birth. Small breast buds are present on both sexes. The mother is supplying the fetus with antibodies that will help protect against disease. All organs are developed, with the lungs maturing all the way until the day of delivery. The fetus is about 19 – 21 inches in length and weighs anywhere from 6 ¾ lbs to 10 lbs.
Perhaps your six month old has not rolled over yet, but the child development chart shows that some babies start rolling over at five months. Or possibly your neighbor’s eleven month old is walking, but your thirteen month old has not attempted to walk. Maybe you are worried that your baby’s development is not where it should be and wonder what this means for his or her future. Comparing your baby’s development to other infants or to norms on developmental charts should be avoided. Instead it is important to know that babies develop at different rates and should only be compared to their individual milestones from the previous week or month.
Infant Development Overview
The following milestones are listed under the FIRST month in which they may be achieved. However, remember that babies develop at different rates, so if your baby has not reached one or more of these milestones, it does not mean that something is wrong. He or she will probably develop these skills within the next few months. If you are still concerned, consider discussing this with your baby’s pediatrician. The delay could indicate a problem, but more than likely it will turn out to be normal for your baby. Premature babies generally reach milestones later than others of the same birth age, often achieving them closer to the adjusted age and sometimes later.
Infant development is divided into four categories:
Social: How your baby interacts to the human face and voice. Examples include learning to smile and coo. A social delay may indicate a problem with vision or hearing or with emotional or intellectual development.
Language: Receptive language development (how well baby actually understands) is a better gauge of progress than expressive language development (how well baby actually speaks). Slow language development can indicate a vision or hearing problem and should be evaluated.
Large motor development: Holding their head up, sitting, pulling up, rolling over, and walking are examples of large motor development. Very slow starters should be evaluated to be certain there are no physical or health risks for normal development.
Small motor development: Eye-hand coordination, reaching or grasping, and manipulating objects are examples of small motor development. Early accomplishments may predict a person will be good with their hands, but delays do not necessarily mean they are going to be all “thumbs” later.
The First Month:
- Can lift head momentarily
- Turns head from side to side when lying on back
- Hands stay clenched
- Strong grasp reflex present
- Looks and follows object moving in front of them in range of 45 degrees
- Sees black and white patterns
- Quiets when a voice is heard
- Cries to express displeasure
- Makes throaty sounds
- Looks intently at parents when they talk to him/her
The Second Month:
Lifts head almost 45 degrees when lying on stomach
Head bobs forward when held in sitting position
Grasp reflex decreases
Follows dangling objects with eyes
Visually searches for sounds
Makes noises other than crying
Cries become distinctive (wet, hungry, etc.)
Vocalizes to familiar voices
Social smile demonstrated in response to various stimuli
The Third Month:
Begins to bear partial weight on both legs when held in a standing position
Able to hold head up when sitting but still bobs forward
When lying on stomach can raise head and shoulders between 45 and 90 degrees
Bears weight on forearms
Grasp reflex absent
Holds objects but does not reach for them
Clutches own hands and pulls at blankets and clothes
Follows objects 180 degrees
Locates sound by turning head and looking in the same direction
Squeals, coos, babbles, and chuckles
“Talks” when spoken to
Recognizes faces, voices, and objects
Smiles when he/she sees familiar people, and engages in play with them
Shows awareness to strange situations
The Fourth Month:
Good head control
Sits with support
Bears some weight on legs when held upright
Raises head and chest off surface to a 90 degree angle
Rolls from back to side
Explores and plays with hands
Tries to reach for objects but overshoots
Grasps objects with both hands
Eye-hand coordination begins
Makes consonant sounds
Enjoys being rocked, bounced or swung
The Fifth Month:
Signs of teething begin
Holds head up when sitting
Rolls from stomach to back
When lying on back puts feet to mouth
Voluntarily grasps and holds objects
Plays with toes
Takes objects directly to mouth
Watches objects that are dropped
Says “ah-goo” or similar vowel-consonant combinations
Smiles at mirror image
Gets upset if you take a toy away
Can tell family and strangers apart
Begins to discover parts of his/her body
The Sixth Month:
Chewing and biting occur
When on stomach can lift chest and part of stomach off the surface bearing weight on hands
Lifts head when pulled to a sitting position
Rolls from back to stomach
Bears majority of weight when being held in a standing position
Grasps and controls small objects
Grabs feet and pulls to mouth
Adjusts body to see an object
Turns head from side to side and then looks up or down
Prefers more complex visual stimuli
Says one syllable sounds like “ma”, “mu”, “da”, and “di”
The Seventh Month:
Sits without support, may lean forward on both hands
Bears full weight on feet
Bounces when held in standing position
Bears weight on one hand when lying on stomach
Transfers objects from one hand to another
Bangs objects on surfaces
Able to fixate on small objects
Responds to name
Awareness of depth and space begin
Has taste preferences
“Talks” when others are talking
The Eight Month:
Sits well without support
Bears weight on legs and may stand holding on to furniture
Adjusts posture to reach an object
Picks up objects using index, fourth, and fifth finger against thumb
Able to release objects
Pulls string to obtain object
Reaches for toys that are out of reach
Listens selectively to familiar words
Begins combining syllables like “mama” and “dada” but does not attach a meaning
Understands the word no (but does not always obey it!)
Dislikes diaper change and being dressed
The Ninth Month:
- Begins crawling
- Pulls up to standing position from sitting
- Sits for a prolonged time (10minutes)
- May develop a preference for use of one hand
- Uses thumb and index finger to pick up objects
- Responds to simple verbal commands
- Comprehends “no no”
- Increased interest in pleasing parents
- Puts arms in front of face to avoid having it washed
The Tenth Month:
- Goes from stomach to sitting position
- Sits by falling down
- Recovers balance easily while sitting
- Lifts one foot to take a step while standing
- Comprehends “bye-bye”
- Says “dada” or “mama” with meaning
- Says one other word beside “mama” and “dada” (hi, bye, no, go)
- Waves bye
- Object permanence begins to develop
- Repeats actions that attract attention
- Plays interactive games such a “pat-a-cake”
- Enjoys being read to and follows pictures in books
- Walks holding on to furniture or other objects
- Places one object after another into a container
- Reaches back to pick up an object when sitting
- Explores objects more thoroughly
- Able to manipulate objects out of tight fitting spaces
- Rolls a ball when asked
- Becomes excited when a task is mastered
- Acts frustrated when restricted
- Shakes head for “no”
- Walks with one hand held
- May stand alone and attempt first steps alone
- Sits down from standing position without help
- Attempts to build two block tower but may fail
- Turns pages in a book
- Follows rapidly moving objects
- Says three or more words other than “mama” or “dada”
- Comprehends the meaning of several words
- Repeats the same words over & over again
- Imitates sounds, such as the sounds dogs and cats make
- Recognizes objects by name
- Understands simple verbal commands
- Shows affection
- Shows independence in familiar surrounding
- Clings to parents in strange situation
- Searches for object where it was last seen