How your Baby is growing based on Week by Week Pregnancy
Pregnancy is a whole transformative journey, your body undergoes a huge change and you have excitement, curiosity and alot of questions. From the day you discover there’s a life coming in to the day you finally meet your little one, your body undergoes remarkable transformation. But nothing is as fascinating as looking at the growth of your baby in your tummy every week.
Based on Week by Week Pregnancy - How your Baby is growing?
Understanding baby development week by week not only helps you feel more connected to your pregnancy but also gives you insight into your baby’s needs as they grow. Whether you’re newly pregnant or nearing your due date, this week-by-week pregnancy breakdown offers a glimpse into the amazing process of life taking Shape.
Weeks 1–4: The Beginning of Life
Pregnancy begins with the first day of your last menstrual period, even though actual conception typically occurs around two weeks later. During the first four weeks, fertilization and implantation take place. Once the sperm fertilizes the egg, it forms a zygote, which begins dividing rapidly and travels through the fallopian tube to the uterus. By the end of week 4, the fertilized egg—now called a blastocyst—implants itself into the uterine wall. This is the beginning of baby growth during week by week pregnancy.
At this stage, you might use a pregnancy due date calculator to estimate when your baby is expected to arrive. The calculator typically counts 40 weeks from the first day of your last period to estimate your due date.
Weeks 5–8: Vital Foundations
By week 5, your embryo is the size of a sesame seed. Major systems and structures begin to form, including the brain, spinal cord, and heart. Around week 6, the baby’s heart starts to beat and can sometimes be detected through an early ultrasound.
In week 7, limb buds appear—these will become your baby’s arms and legs. By week 8, all the major organs have started developing. Your baby now looks more like a human, though still tiny, around the size of a kidney bean.
Weeks 9–12: Baby’s Features Form
During this stage of fetal development, your baby’s facial features become more defined. Eyes, ears, nose, and mouth all begin to take shape. The heart, which has been beating since week 6, now has four chambers and beats at a regular pace.
By the end of week 12, your baby—now officially called a fetus—is about 2.5 inches long. Fingernails, toenails, and external genitalia begin to form, although it may still be too early to determine the gender via ultrasound. This trimester concludes with the baby having all essential organs formed and ready to grow.
Weeks 13–16: Rapid Growth Begins
Your second trimester begins around week 13. Between weeks 13 and 16, your baby undergoes a growth spurt. The body begins to grow faster than the head, allowing a more balanced appearance. Bones harden, and the skin remains translucent, revealing developing blood vessels.
By week 16, your baby is roughly the size of an avocado. Muscles and bones are getting stronger, and the baby begins to make subtle movements, although most moms won’t feel them just yet. Ultrasounds at this time can often determine the baby’s sex, offering a deeper connection during this week by week pregnancy phase.
Weeks 17–20: Movements and Milestones
Now that you’re halfway through your pregnancy, you may begin feeling the first signs of fetal movement—often described as fluttering or “quickening.” These are subtle at first but will become more distinct in the coming weeks.
During week 18, the baby can yawn, hiccup, and even make facial expressions. Around week 20, your healthcare provider may conduct a detailed anatomy scan to assess your baby’s development and check for any abnormalities. Your baby is now about the size of a banana and weighs around 10 ounces.
Weeks 21–24: Developing the Senses
Between weeks 21 and 24, your baby’s senses begin to develop rapidly. Taste buds are forming, and your baby may start to recognize your voice. The inner ear bones harden, improving the ability to hear. The lungs continue to develop but are not yet fully functional.
At week 24, the baby reaches a milestone known as “viability,” meaning that with medical intervention, survival outside the womb becomes possible. Your baby now weighs about 1.3 pounds and is roughly 12 inches long.
Weeks 25–28: Preparing for Life Outside
The third trimester starts around week 27. During this period, your baby’s brain develops rapidly. Nerve connections form at a fast pace, and the baby begins responding to touch and sound. Eyelashes, eyebrows, and hair may start growing.
Your baby also begins to store fat under the skin, helping regulate body temperature after birth. By week 28, your baby is about the size of an eggplant and may begin to settle into a head-down position in preparation for birth.
Weeks 29–32: Gaining Weight and Strength
During this stage, your baby’s muscles and lungs continue maturing. The bones are fully developed but still soft. The baby practices breathing by inhaling amniotic fluid and develops a regular sleep-wake cycle.
Around week 32, the baby weighs about 4 pounds and measures up to 17 inches. Movements may feel more intense as space in the womb becomes tighter. This phase is crucial for lung and brain development.
Weeks 33–36: Final Touches
As your due date approaches, your baby’s body prepares for life outside the womb. The skin becomes less wrinkled as fat continues to accumulate. The immune system strengthens, and the lungs prepare for the first breath.
At week 36, your baby is considered “early term” and may drop lower into your pelvis—a process called “lightening”—in preparation for birth. The baby weighs around 6 pounds and is close to 18 inches long.
Weeks 37–40: Full Term and Ready for Birth
From week 37 onwards, your baby is considered full term. Organs are fully developed, and your baby is ready for birth. The average baby at 40 weeks weighs around 7 to 8 pounds and measures about 20 inches.
Labor can begin at any time now. Using a pregnancy due date calculator helps track how close you are, but remember, only about 5% of babies are born exactly on their due date.
Tracking Baby Growth and Development
Keeping track of baby development week by week helps parents feel more involved and informed. Many parents rely on tools like pregnancy due date calculators and pregnancy tracking apps to stay updated. These tools provide a daily breakdown of what’s happening in your body and how your baby is growing.
Understanding pregnancy week and days also equips you to have meaningful conversations with your healthcare provider. You’ll know what to expect and what signs to look out for during each phase of week by week pregnancy.
Final Thoughts
Pregnancy is a miraculous journey, and witnessing your baby’s development unfold over the weeks is nothing short of amazing. From a tiny cluster of cells to a fully developed human being, baby growth during week by week pregnancy is a complex, beautiful process. Staying informed about your fetal development not only helps you prepare for birth but also strengthens your bond with the baby before they’re even born.
Whether you’re at the beginning of your pregnancy or nearing the finish line, each week brings new milestones. Keep track, stay informed, and enjoy every moment of this extraordinary experience.
