Here I have listed the Fetal Development of your Baby by week and sometimes combined weeks where the development overlaps. If you have any questions or concerns regarding this material, please do not hesitate to contact me at my office
Weeks One & Two
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
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 then called a morula. The morula becomes a blastocyst and will eventually end up in the uterus. Anywhere from day 6-12 days after conception. The blastocyst will embed into the uterine lining and begin the embryonic stage.
Week Three
The embryo is going through lots of basic growth at this time with the the beginning development of the brain, spinal cord, heart and gastrointestinal tract.
Weeks Four & Five
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 1/4 inch long by the end of these weeks.
Week Six
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 it's complex parts. A vaginal ultrasound could possibly detect an audible heartbeat at this time. The embryo is about a 1/2 inch in length.
Week Seven
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 Eight
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 Nine Through Twelve
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 may 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 Thirteen to Sixteen
Now we have arrived at the beginning of month four. The first trimester is complete and the baby has a heartbeat that we can detect using a handheld doppler applied to the lower abdomen. Fingernails and toenails are growing and some hair may have sprouted. Eyelids are fused shut, but eyelashes and eyebrows have begun to form. The kidneys have begun working and now produce urine. Your baby is moving, swallowing, and listening. Baby is about 3 ½ ounces, approximately 4 inches.
Weeks Seventeen to Twenty
Baby's teeth, eyelids, eyelashes and limbs are developing in detail and moving into position. Hands are becoming more functional; the baby may play with their fist or suck their thumb. Baby's neck is getting longer and the chin is not resting on the chest anymore. Very fine hair called lanugo and a waxy substance called vernix cover the baby's body. Lanugo and vernix protect the baby's skin while the baby floats in amniotic fluid. Baby weighs about 10 ounces and is more than 6 inches.
Weeks Twenty-one to Twenty- four
You may feel the baby move for the first time around 16-25 weeks. Baby may get very active for a day or two, then be quiet for a few days. The basic structure of the eye is forming and is positioned correctly on the head. The brain continues to develop rapidly. Baby weighs more than 1 pound and is about one foot long.
Weeks Twenty-five to Twenty-eight
Baby has reddish, wrinkled skin, is very thin and will now begin to put on needed fat until birth. Their eyes are beginning to open, and the eyelids and eyebrows are fully formed. Real hair begins to grow; fingernails have grown to the ends of the fingers. Babies sometimes suck on their thumbs and make grasping motions with their hands. Your baby can now hear you talk, read and sing. Baby is about 15 inches and about 2 pounds.
Weeks Twenty-nine to Thirty-two
With special care, babies born at this stage of development can survive. Your baby now kicks and stretches in response to sounds. The eyelids and nostrils have opened and the baby is able to sense light, smell and taste. Lungs form tiny air sacs called alveoli and baby starts making basic breathing movements. Different areas of the brain are continuing to develop. Baby is approximately 17 inches and may be 3 ½ pounds.
Weeks Thirty-three to Thirty-six
Babies born during this month are still premature but have an excellent chance of survival. The baby's bones and nails are getting harder. All vital organs except the lungs are mature. Wrinkles disappear as fat begins to deposit under the skin. The lanugo hair begins to shed but some may remain on the baby's back and shoulders. Many babies are now moving into birthing position. The baby's skull remains soft and flexible for birth. Baby is about 5 ½ pounds.
Weeks Thirty-seven to Forty
The baby has usually settled into a head-down position and waits for you to go into labor. Baby's lungs are now fully mature and ready to be functional. Regular fetal sleep patterns are developing that will continue after birth. Your baby adds fat tissue to protect their vital organs and to keep warm. They also start storing iron in their liver to get ready for life outside the womb. Waxy, white vernix on the baby's skin and lanugo hair are almost completely gone. The baby weighs an average of about 7 ½ pounds and is approximately 20 inches
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