Week-by-Week Fetal Development During Pregnancy

Pregnancy can be frustrating for so many reasons. All of the waiting and bloating can really take a toll on you. If only you could take a peek at your growing baby, instead of having to watch yourself grow. By learning about the changes your baby is undergoing, you can let pleasant dreams about your little one distract you from your growing ankles, belly and other body parts.


Your baby will grow from a microscopic cell to your fully matured infant in a matter of just nine months. In the first two trimesters of your pregnancy, you may wonder about the size of your infant. For the first eight weeks of your pregnancy, your baby will be considered a zygote and then an embryo. During that time, it grows from microscopic to approximately 3 centimeters. By the time your baby has fully grown, at 39 to 42 weeks, the baby will be 15 to 25 inches long.


Over the course of your 40 weeks of pregnancy, your baby will grow from a mound of quickly dividing cells into a miniature person, with head, torso, legs, arms and digits. Around the fourth to eighth week of development, your baby will have a disproportionally large head and will be curled inward toward its belly. It will have its digits, although they may be held together with a webbing. Around week 29, your baby starts putting on some fat, getting ready for the world.

Mind and Body

Although not as cute, your baby’s inner development is just as important as his outer development. Around week three, his digestive system already starts coming together. By the following week, his brain is already in different hemispheres and sections. Organs form around week seven. By week 21, lungs develop all their sections. By week 25, the lungs are operational. This is the same week that the nervous system develops the ability to control some of the organs.

Your Participation

Because your baby’s healthy development mostly relies on your own health, continue to eat a healthy diet. Diets full of vitamins and minerals will ensure that your fetus has all the nutrients its body needs to grow.

A Look Inside

Ask your doctor about the ultrasounds that are included in your insurance policy. Take advantage of these opportunities to take a peek inside. You can see how the baby is growing and your doctor can check on his development. See if your doctor or your local library has charts or pamphlets on the development of fetuses. Although each child is different and you can’t guess exactly when your child grows each bit, you can get a general idea of his growth each week.



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