Week by Week (Gestation Age)

Woman holding a calendar
Week 1-2

A lot is happening now, but you can’t see it with the naked eye. This is when your body is ovulating and your uterus is getting ready to possibly conceive by the thickening of the uterine wall and releasing an unfertilized egg.

Week 3

Egg and sperm meet for the first time and make a zygote. This zygote has 46 chromosomes, 23 from each that define the DNA of the human.  The fetus’s eye color, hair color, gender and more have already been determined.

Right now, the fetus is actually called an embryo and some major things are happening. The embryo’s brain, spinal cord, heart, and gastrointestinal tract are all being developed.

Week 4

Time to Take a Pregnancy Test

The zygote becomes a blastocyst on its way to becoming a fully developed human! It settles in to the uterus and gets ready to grow!

It’s now time to take a pregnancy test. Most women discover their pregnancies between 4-7 weeks. Pregnancy symptoms may start to develop such as a missed period or breast tenderness. Since ovulation times are different for every woman, it’s important that you take a free, medical-grade pregnancy test and receive a free ultrasound so we can determine exactly how far along you are.

Your embryo is experiencing some major growth here. The beginning stages of the nervous system, skin, nails, hair, mammary glands, sweat glands and enamel for teeth begin to develop. Also, the foundations of the heart, lungs, skeletal system, liver and much more are being created. Even arms and legs begin to develop this week.

Week 5

The tiny buds appear that will form the arms and legs. The brain, spinal cord and backbone along with the eyes and ears are starting to form.

Week 6

Introducing the Heartbeat and Toes

Hormones are increasing and we now have an embryo with a steady heartbeat and those toes are starting to form. You might start to experience heartburn, some slight cramping, and even light bleeding are super normal this week. Your breasts may still be pretty tender and you might even notice that they may look a little bit darker than normal.

Week 7

Essential Organs, Eye Lids, and Hair Follicles.

Your baby is now developing a tongue, hair follicles, and eyelids. Every essential organ that a human being needs to survive has already been forming at this point

And it keeps going! So what exactly happens in there for the whole nine months?

Of course, the baby grows physically, but that’s definitely not all! In fact, your womb is their first classroom. They’re exploring and learning and even beginning to interact with the world around them before birth!

There are two main ways we know what is happening in the womb. We have ultrasounds in 3D, which provide a clearer picture of your baby’s details and features, and 4D, which is like a live stream video from the womb! Also, researchers design experiments specifically to gain insight into the more complex aspects of human development.  Here is more of what we know!

Sensory Development: First Trimester – Weeks 1-12

Your tiny baby is already moving. These early movements are mostly random and spontaneous, so researchers refer to them as motor babbling3. Their brain uses this exercise to gather information about their body and environment. Near the end of the first trimester, babies begin to make some controlled isolated movements, and they seem especially interested in touching their faces.

Sensory Development: Second Trimester – Weeks 13-26

Early in the second trimester, babies develop the ability to swallow and begin ingesting amniotic fluid, the protective liquid that surrounds them in the womb. How it tastes is affected by the food you eat and can affect your baby’s future taste preferences2 .

By week 22, your baby’s ears are functional, and soon after, they begin to react to sounds with movement and changes in heart rate. Your baby can hear your voice, and even though they are not able to understand what you’re saying, these early sounds establish pathways in the brain for future hearing and language skills4. At this point, your baby is making more controlled and purposeful movements, such as scratching their temples, tickling their feet, and grasping their hands or umbilical cord. With these movements, babies are doing something called body mapping3, where they repeat specific motions to learn about their body.

You’re feeling those kicks at this point, and they can feel you too. Your baby responds to you rubbing your growing belly by increasing their arm, head, and mouth movements5. Not only is it exciting to connect with your baby through touch, but it can actually improve your mood too!

Sensory Development: Third Trimester – Weeks 27-40

The most frequent movements in the third trimester are facial. In fact, using 4D ultrasound, scientists have observed babies creating increasingly complex facial expressions, including furrowing their brows and wrinkling their noses6. Your baby’s eyes are still maturing and will continue to months after birth. Brain scans show that they can react to visual stimulation, such as flashes of light outside the womb. This exposure helps develop the retina7– the inner part of the eyeball that forms what we see.

Unlike the eyes, your unborn baby’s ears are functional, and they now not only process sounds, but also have a more social response to it. In an experiment, mothers were asked to repeat a certain nursery rhyme aloud twice a day for six weeks. After that, their babies were more likely to respond with a decreased heart rate – a sign of comfort – to that same nursery rhyme when it was read by someone else8.

After birth: Evidence of learning in the womb

At only a few days old, babies seem to discern between well-formed syllables, sounds that are used in language, and ill-formed syllables made of letters in a jumbled order9. Research shows that babies pick up some patterns from music and language they hear repeatedly10.

Your role as a woman and soon to be mom? Prioritize You & Your Health

Prioritize your self-care and making choices that help you relax and stay healthy is important for both you and your growing baby. Many studies have shown what does affect growing babies and their mothers during pregnancy is stress11. When stress is severe or long lasting, it may have a more negative effect on the baby. If you are experiencing extreme stress, seek help from your medical provider. If you are dealing with normal, everyday stressors, here are some natural ways to combat it12:

  • Understanding your triggers
  • Prioritizing rest
  • Eating healthy
  • Getting exercise
  • Relaxing
  • Counseling

1 “Fetal Development: What Happens during the 1st Trimester?” Mayo Clinic, Mayo Foundation for Medical Education and Research, 30 June 2020, www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-care/art-20045302.

2 Beauchamp, Gary K, and Julie A Mennella. “Flavor perception in human infants: development and functional significance.” Digestion vol. 83 Suppl 1,Suppl 1 (2011):

1-6. doi:10.1159/000323397. www.ncbi.nlm.nih.gov/pmc/articles/PMC3202923/

3 Fagard, Jaqueline et al. “Fetal Origin of Sensorimotor Behavior.” Frontiers in neurorobotics vol. 12 23. 23 May. 2018, doi:10.3389/fnbot.2018.00023. www.ncbi.nlm.nih.gov/pmc/articles/PMC5974044/

4 Webb, Alexandra R., et al. “Mother’s Voice and Heartbeat Sounds Elicit Auditory Plasticity in the Human Brain before Full Gestation.” PNAS, National Academy of Sciences, 10 Mar. 2015, www.pnas.org/content/112/10/3152.

5 Marx, Viola, and Emese Nagy. “Fetal Behavioural Responses to Maternal Voice and Touch.” PLOS ONE, Public Library of Science, 8 June 2015, journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0129118.

6 Reissland, Nadja, et al. “Can Healthy Fetuses Show Facial Expressions of ‘Pain’ or ‘Distress’?” PLOS ONE, Public Library of Science, journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0065530.

7 Bardi, Jason. “Light Exposure During Pregnancy Key to Normal Eye Development.” | UC San Francisco, 16 Jan. 2013, www.ucsf.edu/news/2013/01/98768/light-exposure-during-pregnancy-key-normal-eye-development.

8 “UF Research Shows Rhymes Can Inspire Reasoning during the Third Trimester in the Womb.” News, 22 July 2014, news.ufl.edu/archive/2014/07/uf-research-showsrhymes-can-inspire-reasoning-during-the-third-trimester-in-the-womb.html.

9 Gómez, David Maximiliano, et al. “Language Universals at Birth.” PNAS, National Academy of Sciences, 22 Apr. 2014, www.pnas.org/content/111/16/5837ijkey=64859199949f2cf5b9c04858e894c94c72783127&keytype2=tf_ipsecsha.

10 Partanen, Eino, et al. “Prenatal Music Exposure Induces Long-Term Neural Effects.” PLOS ONE, Public Library of Science, 30 Oct. 2013, journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0078946.

11 Coussons-Read, Mary E. “Effects of Prenatal Stress on Pregnancy and Human Development: Mechanisms and Pathways.” Obstetric Medicine, SAGE Publications, June 2013, www.ncbi.nlm.nih.gov/pmc/articles/PMC5052760/.

12 “Stress During Pregnancy.” American Pregnancy Association, americanpregnancy.org/healthy-pregnancy/pregnancy-health-wellness/stress-during-pregnancy/

13 https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-care/art-20045302

14  https://www.marchofdimes.org/pregnancy-week-week#6

The content on this page has been reviewed and approved by our Medical Director.