What Are the 3 Stages of Prenatal Development?

Whether you just noticed that second faint line on your pregnancy test (congrats!) or you’ve had a few weeks to process the excitement and shock of finding out you’re pregnant, you’ve probably done some research about that bun you’re slowly cooking in the oven.

From how big (or small) your blossoming little one currently is to those first-trimester symptoms you’re anxiously (but excitedly) waiting to experience, you might feel like a world-class expert on pregnancy. At least, you did until your trying to figure out what to do when you find out your pregnant and read something about “stages of prenatal development.”

Prenatal what now?

Not to worry—the phases of prenatal development throughout the prenatal period are much more simple than you might think. In total, there are three main stages you’ll move through over the course of your pregnancy: the germinal stage, the embryonic stage, and the fetal stage.

Sit back, enjoy a fruity mocktail, at put the list of popular baby names aside as we dive into each and learn more about how your tiny tot is progressing in their first fetal development weeks in utero and beyond.

The 3 Stages of Prenatal Development: A Guide

After they’ve taken up residence in your belly, child development begins as your baby has already begun their journey as a single-cell zygote. In only nine months, it’ll undergo cell division, and they’ll manage to form every limb, organ, and cell of their bodies, from developing one-of-a-kind fingerprints to growing 79 fully functioning organs, all in the meantime, you can focus on taking care of your physical and mental health.

For a more precise breakdown, let’s discuss the three exciting stages of prenatal development and all of your Little Einstein’s amazing accomplishments each step of the way.

#1 The Germinal Stage (Weeks 0 to 2)

The first stage of prenatal child development is the germinal stage. It’s only 2 weeks long and the quickest of all the phases—but there’s no shortage of exciting activities happening, as babys development undergoes a remarkable number of changes.

Chiefly, four processes occur during the germinal stage:

#1 Fertilization – After sexual intercourse, approximately 100 million sperm travel through the cervix and into the fallopian tubes vying for the chance to fertilize an egg for conception.

Fertilization occurs when one sperm deposits its genetic material inside of the ovum (colloquially known as your egg). Then they fuse together, creating a zygote, a fertilized egg. By this point, the genetic makeup of your little zygote has already been determined, including their sex and physical traits.

#2 Cleavage – A day after fertilization, the zygote’s single cell multiplies every 12 to 24 hours. After four days of multiplying, it becomes a solid ball called a morula. While it’s the same small size as the zygote, it contains significantly more cells.

#3 Blastulation – Around days 5 to 7, the morula becomes a blastocyst. This a tiny ball filled with fluid that contains an assortment of different types of cells, including:

1. Embryoblast cells, which eventually become the embryo
2. Trophoblast cells, which will later turn into the placenta
3. Blastocoele cells, which are fluid-filled cells within the blastocyst that eventually disappear

#4 Implantation – Some time between days 7 to 10, the blastocyst travels down the fallopian tubes and into the uterus. There, it implants itself into the lining of your uterus where it makes a warm and cozy abode and prepares for a transformation of epic proportions.

#2 The Embryonic Stage (Weeks 3 to 8)

After the blastocyst burrows into your uterine lining, it becomes an embryo. The embryonic stage refers to that phase of early life when your little one graduates with honors from being a ball of cells into an embryo that (by week eight) more closely resembles a human.

During this stage, they begin to form some of their appendages and start developing their internal organs. So when you see them on an ultrasound around week eight, you can say, “there’s my little peanut!” instead of “I don’t see it. Oh, wait. That teeny dot?”

Here’s what they’re up to during the embryonic development stage:

• Week four – During this time, the developing embryo has two layers of cells known as the epiblast and the hypoblast. The epiblast will form the amnion, which eventually becomes the amniotic sac encasing and cushioning your baby. The hypoblast will form the yolk sac, where the developing embryo will receive nourishment until you have fully formed the placenta.
• Week five – This week, your little one is forming a neural tube, which will eventually become their spinal cord and brain. They also begin developing their inner ears, arm buds, and pharyngeal arches, which will later become their face and neck. The cardiovascular system is also being established. They don’t have a fully formed heart just yet, but they do have two fused heart tubes that are already pumping blood.
• Week six – At six weeks, they’re finally beginning to take the shape of a real baby! While they may not have the fingers and toes you’ll later count out in the delivery room, they do have little paddles on the ends of their arms. Plus, they’re growing the next best thing to legs—leg buds! The start of their digestive and respiratory systems are developing, too. (Psst—while doctors can’t identify your baby’s sex on an ultrasound at six weeks, you can nevertheless learn their gender with over 99% accuracy¹ with a little help from a SneakPeek At-Home Gender Blood Test).
• Week seven – This is a big week for organ development. The lungs begin to grow, as well as the beginning formations of their external sex organs.
• Week eight – At last—the final week of the embryonic development stage. By this point, you will certainly be able to hear the pitter-patter of your little one’s heartbeat during an ultrasound. What’s more, all of their tiny organs have started to form. They’re also a little over a half-inch long and weigh approximately three-quarters of an ounce. It may not feel like much, but compared to where they were at the beginning of the embryonic stage, they’re huge.

#3 The Fetal Stage (Weeks 9 to 40)

At nine weeks, your little sweet pea is about the size of…a green olive! For the rest of your pregnancy, throughout the second trimester and third, they’ll be in the fetal stage enjoying their stay in Hotel Uterus, developing into a fully functioning little human.

With so much growth occurring during those final seven months, we’ll break this period down so you can grasp a clearer picture of what they’re up to while you’re waiting for delivery day:

• Weeks 9 to 12 – During these weeks, the fetus will finish growing all of their body parts, including their fingers, toes, and external genitalia (though it’s still difficult to determine their biological sex on an ultrasound). As neural pathways develop, your baby will sometimes have uncontrolled movements in their extremities. Since they’re only two inches long and weigh approximately two ounces at 12 weeks, you won’t be able to feel those tiny but mighty kicks just yet.
• Weeks 13 to 16 – By the time your baby has reached 16 weeks old, they’re about 4 to 5 inches long and are gaining about an ounce of weight a week. They’re growing soft hair all over their bodies called lanugo to keep themselves safe from potentially damaging substances in the amniotic fluid. Facial features, like eyelids, ears, and tooth buds, continue to form and move closer to their anatomically correct locations.
• Weeks 16 to 26 – At this point in your pregnancy, your little bun is really cooking. They gain the sense of touch, and you may even notice them sucking their thumb or stroking their face on an ultrasound.

Their bones also begin to harden at this phase, and blood marrow starts developing and making red blood cells, carrying oxygen through the body). They also boast stronger muscles, and around weeks 16 to 24, you’ll start to feel them as they practice their martial arts skills in your tummy (haven’t felt them drop-kick you yet? Just you wait!).

• Weeks 27 to 37 – During these last two months, your little one starts to pack on the pounds. The fetus gains a significant amount of subcutaneous fat to plump them up and have finally gained all five senses. By 32 weeks, their lungs are fully developed and they’ll practice breathing by moving their diaphragm while you anticipate their birth.

Rounding up on 38 weeks, your little bun is a bonafide loaf—and only one week away from full term! It’s the final countdown to birth, and just as you’re preparing the nursery and practicing your pre-labor deep breathing, they’re preparing to make a grand entrance by repositioning themselves for labor.

In just a few days’ or weeks’ time, you’ll cut the umbilical cord and bring your sweet bundle home from the hospital and your friends and family will coo over their tiny hands and feet. They’re 9 months in the making, with a lifetime of growing still to be done.

Take Your Prenatal Development Knowledge to the Next Level with SneakPeek

From budding blastocyst to beautiful baby, your little bundle is a busy bee during the nine months you’re preparing for their arrival. Now comes the hard part: waiting until you get to witness all of their hard work!

Cut down on your wait time with the SneakPeek At-Home Early Gender Blood Test. With SneakPeek, you can learn your baby’s gender at just six weeks into pregnancy with over 99% clinical accuracy¹ so you can start searching for unique baby boy names or baby girl names. Starting at just $79, you can easily collect your sample from the comfort of your home and receive your results as soon as the same day! It’s no wonder we’re the #1 OBGYN-recommended at-home gender test.

Join over 1 million moms who’ve allowed us to be a part of their pregnancy journeys by checking out SneakPeek Test today.

This post has been reviewed for accuracy by the following medical professional:

Dr. Heather Soper, Certified Nurse Midwife

Dr. Heather Soper brings over 15 years of experience in women's health and obstetrics to her role as the owner of The Genesis Resort for Birth. Complementing her clinical practice, she serves as an Assistant Professor of Nursing at James Madison University, where she educates nursing students with a focus on compassionate, patient-centered care. Her advanced training and dedication to midwifery are evident in her contribution to both academia and the wellness of expectant mothers.

Sources:

1. Healthline. What Are the Largest Organs in Your Body? https://www.healthline.com/health/largest-organs-in-the-body
2. Libre Texts. 23.2 Germinal Stage. https://bio.libretexts.org/Bookshelves/Human_Biology/Book%3A_Human_Biology_(Wakim_and_Grewal)/23%3A_Human_Growth_and_Development/23.2%3A_Germinal_Stage
3. Oakland University. Mechanisms of Sperm Motility: Dr. Charles Lindemann. https://files.oakland.edu/users/lindeman/web/spermfacts.htm
4. Iowa State University. Prenatal Development. https://iastate.pressbooks.pub/parentingfamilydiversity/chapter/prenatal-development/
5. NIH. Embryology, Yolk Sac. https://www.ncbi.nlm.nih.gov/books/NBK555965/
6. Libre Texts. 23.3. Embryonic Stage. https://bio.libretexts.org/Bookshelves/Human_Biology/Book%3A_Human_Biology_(Wakim_and_Grewal)/23%3A_Human_Growth_and_Development/23.3%3A_Embryonic_Stage
7. Libre Texts. 23.4 Fetal Stage. https://bio.libretexts.org/Bookshelves/Human_Biology/Book%3A_Human_Biology_(Wakim_and_Grewal)/23%3A_Human_Growth_and_Development/23.4%3A_Fetal_Stage
8. NIH. Embryology, Lanugo. https://www.ncbi.nlm.nih.gov/books/NBK526092/
9. BabyCenter. Growth chart: Fetal length and weight, week by week. https://www.babycenter.com/pregnancy/your-body/growth-chart-fetal-length-and-weight-week-by-week_1290794
10. What to Expect. 16 Weeks Pregnant. https://www.whattoexpect.com/pregnancy/week-by-week/week-16.aspx
11. NIH. Know Your Terms. https://www.nichd.nih.gov/ncmhep/initiatives/know-your-terms/moms
12. Pregnancy. Birth. Baby. Baby Movements During Pregnancy. https://www.pregnancybirthbaby.org.au/baby-movements-during-pregnancy