From Poppy Seed to Pumpkin: The Ultimate Fetal Growth and Development Chart

What a Fetal Growth and Development Chart Actually Shows (And Why It Matters)

A fetal growth and development chart maps your baby's size, weight, and key milestones from the first weeks after conception all the way to birth. Here is a quick overview of what to expect at each stage:

Stage	Weeks	Size Range	Key Milestone
First Trimester	1–12	Poppy seed → Plum	Major organs begin forming
Second Trimester	13–27	Avocado → Banana	Movement felt; viability reached
Third Trimester	28–40	Eggplant → Pumpkin	Rapid weight gain; lungs mature

At 40 weeks, the average baby is about 20 inches long and 8 pounds. But long before that, remarkable things are already happening — often before many women even know they are pregnant.

Within just 24 hours of fertilization, a single cell starts dividing rapidly. By week 5, a tiny heart tube is already pulsing. By week 9, your baby has a beating heart, forming fingers, and a distinctly human shape.

If you are facing an unexpected pregnancy right now and want to know exactly how far along you are, an early ultrasound is the most accurate way to find out. LivingWell Pregnancy Centers in Orange, CA offers free, confidential ultrasounds performed by licensed medical professionals — no insurance or appointment needed — at 2010 N. Tustin St., Suite C, Orange, CA 92865.

I'm Leo Kim, Executive Director of LivingWell Pregnancy Centers, where since 1985 we have supported over 170,000 women through unplanned pregnancies with free medical services including the ultrasounds used to track a fetal growth and development chart in real time. In this guide, I'll walk you through everything — week by week — so you know exactly what is happening inside the womb at every stage.

Understanding Gestational Age vs. Fertilization Age

When you first begin looking at a fetal growth and development chart, the way pregnancy weeks are counted can be incredibly confusing. You will quickly encounter two different terms: gestational age and fertilization (or conceptual) age.

• Gestational Age: This is the standard timeline used by obstetricians, midwives, and pregnancy tests. It is calculated starting on the first day of your last menstrual period (LMP). Because your body is preparing for ovulation during those first two weeks, you are not actually pregnant yet during weeks 1 and 2 of gestational age.

• Fertilization Age: This is the actual biological age of the developing baby, measured from the moment the sperm penetrates the egg (conception).

Because ovulation typically occurs about two weeks after your period starts, fertilization age is exactly two weeks behind gestational age. For example, when a doctor says you are 6 weeks pregnant (gestational age), your baby is biologically 4 weeks old (fertilization age). To explore how these early weeks unfold anatomically, you can read more about From Conception to Fully Formed: Your Baby's Development in the First Trimester.

Why the Two-Week Difference Matters

This two-week difference is vital for calculating an accurate due date and tracking milestones. Because most women do not know the exact day they ovulated, using the first day of the last menstrual period provides a consistent, universal baseline for medical providers.

During early pregnancy, ultrasound scans are highly accurate at establishing gestational age. In the first trimester, measuring the baby's length can pin down your due date to within 5 to 7 days. This baseline ensures that later growth assessments are measured against the correct week on the chart. To see how researchers establish these global baselines, you can view the International Fetal Size Standards in Early Pregnancy.

The Three Stages of Prenatal Development

The journey from a single cell to a fully formed infant is divided into three distinct biological stages: the germinal stage, the embryonic stage, and the fetal stage. Throughout these phases, the developing organism progresses through critical periods of organogenesis (organ formation) during which it is highly vulnerable to environmental factors, maternal health, and teratogens (substances that can cause birth defects). For a deeper look at how your own body responds during these initial phases, check out our guide on An Invisible Miraculous Transformation: Body Changes in the First Trimester of Your Pregnancy.

The Germinal and Embryonic Phases

The germinal stage is the shortest phase, lasting from fertilization (conception) to implantation in the uterine wall—roughly gestational weeks 3 and 4 (embryonic weeks 1 and 2). It begins as a single-celled zygote that rapidly divides into a cluster of cells called a blastocyst as it travels down the fallopian tube to nestle into the lining of the uterus.

Once implanted, the embryonic stage begins, running from gestational week 5 through the end of week 10. This is the most critical window of development. Major structures form rapidly:

• The Neural Tube: The foundation of the brain and spinal cord closes by week 6.

• The Heart Tube: A simple tube forms and begins pulsing at roughly 110 beats per minute by the end of week 5.

• Physiological Gut Herniation: By week 8, the baby's rapidly growing intestines actually herniate outside the abdomen into the base of the umbilical cord because the abdominal cavity is too small to hold them. They safely rotate and tuck back inside by week 12.

Because all major organs are mapping out during these weeks, the embryo is highly vulnerable to birth defects if exposed to harmful substances like alcohol, nicotine, or certain medications.

The Transition to the Fetal Stage

The transition from embryo to fetus occurs precisely at 10 weeks gestational age (8 weeks after fertilization). This milestone is marked by several major shifts:

• The embryonic tail completely disappears.

• The first real bone cells begin to replace flexible cartilage.

• The face, fingers, and toes become clearly defined, giving the baby a distinctly human appearance.

From this point forward, the baby is officially called a fetus (a Latin word meaning "young one" or "offspring"). The focus of development shifts from creating new organ systems to growing and maturing the ones already in place.

Your Week-by-Week Fetal Growth and Development Chart

To help visualize this journey, parents love comparing the baby's size to common fruits and vegetables. Below is a detailed breakdown of the fetal growth and development chart week-by-week, utilizing both clinical measurements and relatable size comparisons. To track your baby's size dynamically, you can use this interactive Fetal Size by Week Chart.

First Trimester Milestones on the Fetal Growth and Development Chart

The first trimester (weeks 1 to 12) is characterized by rapid structural layout. Because the baby is curled up, medical providers measure Crown-Rump Length (CRL)—the distance from the top of the head to the buttocks—rather than measuring down to the feet.

• Week 4: Size of a poppy seed (approx. 2 mm long). The blastocyst has successfully implanted.

• Week 8: Size of a black bean (approx. 1 inch long, 1 gram). The heart has transitioned into a four-chambered structure, and tiny limb buds form.

• Week 12: Size of a plum (approx. 3 inches long, 1 ounce / 28 grams). All major organs are formed but are still highly immature.

Crucially, the risk of miscarriage drops significantly after the end of the 12th week, bringing immense peace of mind to expectant parents. To learn more about navigating early pregnancy myths, read Pregnancy: Separating Fact from Fiction Part 1.

Second Trimester Milestones on the Fetal Growth and Development Chart

Often called the "golden trimester," weeks 13 to 27 bring noticeable physical changes as the baby stretches out. From week 13 onward, measurements transition from CRL to Crown-Heel Length (CHL).

• Week 16: Size of an avocado (approx. 5 inches long, 4 ounces / 113 grams). The baby can make faces, stretch, and yawn.

• Week 20: Size of a banana (approx. 10 inches long, 10.6 ounces / 300 grams).

  • Quickening: Around this time, mothers begin to feel the baby's first movements, which often feel like gentle bubbles or fluttering butterfly wings.

  • Vernix and Lanugo: The skin is covered in a thick, waxy coating called vernix caseosa to protect it from amniotic fluid, held in place by fine, downy hair called lanugo.

• Week 24: Size of a cantaloupe (approx. 12 inches long, 1.3 pounds / 600 grams). This is the general threshold of fetal viability, meaning the baby has a chance of survival outside the womb with intensive medical care.

For a detailed look at this active phase of growth, see Grow Baby Grow: Your Baby's Development in the Second Trimester.

Third Trimester Milestones and Preparing for Birth

From week 28 until birth (around week 40), the baby's primary jobs are putting on fat and maturing the lungs.

• Week 28: Size of an eggplant (approx. 15 inches long, 2.5 pounds / 1.1 kg). The eyes can open and close, and the baby can hear external sounds.

• Week 35: The brain is growing rapidly, though at 35 weeks it still only weighs about two-thirds of what it will weigh at full term.

• Week 40: Size of a pumpkin or watermelon (approx. 20 inches long, 8 pounds / 3.6 kg).

A pregnancy is clinically categorized based on the delivery week:

• Early Term: 37 weeks 0 days to 38 weeks 6 days

• Full Term: 39 weeks 0 days to 40 weeks 6 days

• Late Term: 41 weeks 0 days to 41 weeks 6 days

• Post-Term: 42 weeks 0 days and beyond

Understanding these categories is vital, as babies born full-term generally experience fewer breathing and feeding complications. Read more about preparing for delivery in Getting Ready for Baby's Birth: Your Baby's Development in the Third Trimester.

How Doctors Assess Fetal Growth via Ultrasound

Medical professionals do not rely on fruit charts to monitor health; they use advanced ultrasound biometry. By measuring specific skeletal and abdominal dimensions, ultrasound software uses mathematical equations—most commonly the Hadlock formula—to calculate the Estimated Fetal Weight (EFW). You can explore how these measurements translate to percentiles using a clinical Fetal Growth Calculator.

Ultrasounds are the gold standard for tracking development, verifying viability, and ensuring your baby is growing on a healthy curve. If you want to understand why these scans are so critical to prenatal health, read Are Ultrasounds That Important?.

Key Ultrasound Measurements Explained

During a standard anatomy scan (usually performed between weeks 18 and 20), the sonographer will take several key measurements:

1. Crown-Rump Length (CRL): Used exclusively in the first trimester to establish dating.

2. Biparietal Diameter (BPD): The side-to-side width of the fetal head.

3. Head Circumference (HC): The total distance around the head, which helps assess brain development.

4. Abdominal Circumference (AC): The distance around the baby's belly. This is the single most sensitive indicator of fetal nutrition and growth restriction.

5. Femur Length (FL): The length of the thigh bone, which tracks skeletal growth.

Because ultrasound weight estimates have an inherent margin of error of about ±7.5% to 15%, doctors look at growth velocity and trends over time rather than any single standalone measurement.

Understanding SGA, AGA, and LGA Classifications

Once the EFW is calculated, the baby's size is plotted on a percentile curve compared to national or international standards:

• Small for Gestational Age (SGA): An EFW below the 10th percentile. Severe SGA (below the 3rd percentile) may point to Fetal Growth Restriction (FGR), where the placenta is not delivering enough nutrients.

• Appropriate for Gestational Age (AGA): An EFW between the 10th and 90th percentiles, indicating typical, healthy growth.

• Large for Gestational Age (LGA): An EFW above the 90th percentile. While many LGA babies are delivered vaginally without issue, macrosomia (weight over 8.8 to 9.9 pounds at birth) can sometimes increase the risk of delivery complications.

To see how modern 3D ultrasound data has updated these growth curves, you can read the Normal Fetal Growth Profile Study.

Frequently Asked Questions about Fetal Growth

When can a baby's heartbeat first be detected?

A baby's heart begins as a simple tube pulsing around week 5. A visible flickering heartbeat can typically be detected via a transvaginal ultrasound as early as 6 weeks gestational age. The fetal heart rate starts around 110 beats per minute (bpm), peaks at an astonishing 170 to 180 bpm at week 9, and eventually stabilizes into a healthy range of 110 to 160 bpm for the rest of the pregnancy. If you are hoping to hear or see this milestone yourself, you can learn about getting a Free Ultrasound Baby Heartbeat.

When can you find out the sex of the baby?

While your baby's genetic sex is locked in at the exact millisecond of fertilization (determined by whether the sperm carried an X or Y chromosome), the external genitalia do not look different on an ultrasound until later. Sonographers can usually identify the baby's anatomical sex during a mid-pregnancy anatomy scan between weeks 16 and 20.

What are the survival rates for babies born prematurely?

With modern neonatal intensive care (NICU) developments, premature survival rates have improved dramatically:

• Week 24: Approximately 60% survival rate, though there is a 40% to 50% risk of long-term developmental complications.

• Week 26: Approximately 85% survival rate.

• Week 28: Survival increases to approximately 91% to 94%.

• Week 34: Over 99% survival rate, with many babies requiring minimal intensive intervention.

Conclusion

Watching a baby grow from a microscopic cell into a fully formed newborn is nothing short of a biological miracle. Whether you are actively planning a pregnancy or navigating the sudden shock of an unplanned one, understanding what is happening week-by-week can bring clarity, confidence, and peace of mind.

If you are facing an unplanned pregnancy and need accurate, compassionate support, you do not have to walk this path alone. At LivingWell, we provide free, medical-grade pregnancy tests, confidential options counseling, and professional ultrasounds performed by licensed medical professionals.

Our clinic has been serving local women since 1985. In 2025 alone, we walked alongside 1,420 local women in our community, giving them the medical facts and support they needed to make informed choices.

We invite you to visit us at our clinic located at 2010 N. Tustin St., Suite C, Orange, CA 92865. You can find directions to our office directly via Google Maps. To learn more about our completely free resources, schedule an appointment, or speak with a nurse, explore More info about our pregnancy services today. We are here for you.