Pregnancy Week by Week: Complete Guide from Conception to Birth

Wondering what’s happening to your baby each week of pregnancy?

From a tiny cell to a fully developed baby, every week brings incredible changes. Here’s your complete week-by-week pregnancy guide to help you understand every stage.

Pregnancy unfolds over 40 weeks of remarkable transformation—for your baby and for you. Each week brings new developments, milestones, and changes that happen almost invisibly inside your body. Understanding what’s happening week by week helps you feel connected to your pregnancy, recognize what’s normal, and know when to reach out to your healthcare provider.

This comprehensive guide walks you through all 40 weeks, explaining exactly what’s happening with your baby’s development, what changes you can expect in your body, and what to prioritize at each stage. Whether you’re just discovering you’re pregnant, in the thick of your second trimester, or preparing for delivery, this week-by-week breakdown gives you the knowledge to navigate pregnancy with confidence.

THE FIRST TRIMESTER: Weeks 1-12

The first trimester is a period of remarkable transformation. Your baby develops from a single cell into a recognizable human form with all major organs forming. Meanwhile, your body undergoes dramatic hormonal and physical changes that often leave you exhausted and queasy.

Weeks 1-2: Conception Phase

What’s happening with your baby:

Weeks 1-2 are actually counted from the first day of your last menstrual period (LMP), even though conception hasn’t technically happened yet. This is why pregnancy is calculated from LMP rather than conception date. Around day 14 of your cycle, ovulation occurs—your ovary releases an egg into the fallopian tube, ready for fertilization.

What’s happening with you:

You likely have no idea you’re pregnant yet. Your body is preparing for either conception or menstruation. You might feel normal, or you might notice typical pre-menstrual symptoms like breast tenderness or mood changes.

What to do:

If you’re trying to conceive, this is when conception most likely occurs. If you’re not actively trying but might become pregnant, start taking prenatal vitamins containing folic acid (400 micrograms daily).

Week 3: Fertilization

What’s happening with your baby:

Fertilization occurs when a sperm successfully penetrates the egg. Within hours, the genetic material from both egg and sperm merge, creating a new genetic blueprint. This single cell, called a zygote, immediately begins dividing. By the end of week 3, the zygote has divided into approximately 50 cells.

The cluster of cells begins moving through the fallopian tube toward your uterus, a journey that takes about 4 days.

What’s happening with you:

Still nothing obvious. Your body doesn’t “know” you’re pregnant yet. No pregnancy hormone (hCG) is detectable in blood or urine tests.

What to do:

Continue healthy habits: adequate sleep, balanced nutrition, exercise, and stress management. Avoid alcohol, smoking, and recreational drugs.

Week 4: Implantation

What’s happening with your baby:

The cluster of cells, now called a blastocyst, reaches your uterus and attaches to the uterine lining in a process called implantation. This crucial event establishes the connection between your baby and your body. Specialized cells begin forming what will become the placenta and umbilical cord.

Your baby is about the size of a poppy seed.

What’s happening with you:

Implantation triggers your body to produce human chorionic gonadotropin (hCG), the pregnancy hormone. This hormone tells your ovaries to stop releasing eggs and maintains the uterine lining. You still likely don’t feel pregnant, though some women notice light spotting during implantation.

What to do:

If you’ve been trying to conceive, a home pregnancy test becomes detectable around this time (though some are more sensitive than others). Early symptoms may include breast tenderness and mild fatigue.

Weeks 5-6: Embryonic Development Begins

What’s happening with your baby:

Your baby is now called an embryo. Though barely the size of a sesame seed (about 2mm long), rapid development is underway. The neural tube forms—this will become the brain and spinal cord. The heart begins forming and will start beating around week 6. The foundations for all major organs are being established.

What’s happening with you:

Many women experience their first pregnancy symptoms now: nausea (morning sickness), fatigue, breast tenderness, and food aversions. Hormonal surges cause these symptoms. Your uterus is beginning to expand, and you might need to urinate more frequently due to hormonal changes affecting your bladder.

Emotions: Excitement, anxiety, or a mix of both are completely normal.

What to do:

Schedule your first prenatal appointment if you haven’t already. Start (or continue) prenatal vitamins. Begin tracking your symptoms. If morning sickness is severe, discuss with your healthcare provider—they can recommend safe remedies.

Weeks 7-8: Embryo Becomes Fetus

What’s happening with your baby:

Around week 8, your baby officially graduates from “embryo” to “fetus.” The heart is beating (though not yet audible without an ultrasound). Tiny buds that will become arms and legs are sprouting. Facial features are beginning to form—eye indentations, nostrils, and mouth are becoming visible. The neural tube is closing, sealing the beginning of the brain and spinal cord.

Your baby is now approximately ½ inch (1.2 cm) long—about the size of a raspberry.

What’s happening with you:

Morning sickness often peaks around this time for many women. Extreme fatigue is common—you might be sleeping 10+ hours nightly and still feel exhausted. Breast changes continue, becoming tender and possibly darkening. Your emotions might feel heightened.

What to do:

Attend your first prenatal visit if scheduled. You’ll likely get:

• Confirmation of pregnancy via ultrasound
• Due date calculation
• Discussion of prenatal screening options (optional first-trimester screening)
• Basic health history and vital signs

If you’re struggling with morning sickness during these early weeks, you’re not alone. Many pregnant women experience nausea that can make daily life difficult. The good news is that natural remedies like ginger have been shown to significantly reduce symptoms.

👉 Discover the best ginger supplements for pregnancy nausea to find safe and effective relief.

Weeks 9-10: Fingers and Toes Form

What’s happening with your baby:

Tiny fingers and toes are forming, though still webbed. Your baby’s head makes up about half of total body length. Eyelids are forming but remain closed. Teeth buds are beginning to develop in the gums. The placenta is now functioning, supplying nutrients and oxygen through the umbilical cord.

Your baby is now about the size of a grape (about 1 inch long).

What’s happening with you:

Morning sickness might continue or begin improving. Fatigue often remains intense. Your breasts might continue changing, becoming larger and more tender. Food cravings or aversions might intensify. Mood swings are common due to hormone fluctuations.

What to do:

Continue prenatal vitamins and healthy habits. Start thinking about prenatal care: discuss screening options, nutritional needs, and any concerns with your healthcare provider.

Weeks 11-12: Nearly Human

What’s happening with your baby:

Your baby now has distinct human characteristics: hands and feet with individual fingers and toes (though still webbed), ears in proper position, a nose with nostrils, and reflexes beginning. The thyroid gland is developing. Nails are starting to form. Your baby is producing urine.

Most importantly: you can now hear your baby’s heartbeat at your prenatal appointment (around 110-160 beats per minute).

Your baby is about the size of a lime (approximately 2 inches long, weighing about ½ ounce).

What’s happening with you:

You’re likely starting to show a small bump, though it might still be mistaken for weight gain. Morning sickness often begins improving this week. Fatigue might persist. You’ve probably gained 3-5 pounds by this point.

Milestones: If you’re having genetic screening (like nuchal translucency ultrasound), this typically happens around week 12.

What to do:

Congratulations—you’re wrapping up your first trimester! Many women share pregnancy news publicly around this point. Schedule anatomy ultrasound for week 20 (second trimester). Begin thinking about fitness and nutrition for optimal pregnancy health.

THE SECOND TRIMESTER: Weeks 13-26

The second trimester is often called the “honeymoon phase” of pregnancy. Morning sickness usually fades, energy returns, and you begin feeling baby movements. This is often the easiest, most enjoyable trimester.

Weeks 13-14: Welcome to Second Trimester

What’s happening with your baby:

Congratulations—you’ve completed your first trimester! Your baby is now officially a fetus with all major organs formed (though still maturing). The baby is producing insulin and the liver is producing bile. Vocal cords are forming. Fingerprints are becoming distinct.

For girls: ovaries now contain approximately 2 million eggs—more than she’ll have at birth. Reproductive organs are developing.

Your baby is now the size of a lemon (approximately 3-4 inches, weighing about 1 ounce).

What’s happening with you:

This is often when morning sickness finally improves. Your energy returns noticeably. Your belly is growing, and you probably look distinctly pregnant now. Ligaments connecting your uterus are stretching, sometimes causing round ligament pain (sharp pain on sides of lower belly).

Emotions: Relief at entering a new trimester, growing excitement about meeting your baby, and sometimes anxious anticipation about upcoming tests.

What to do:

Embrace this energy surge! This is the ideal time for:

• Planning a babymoon (second trimester is best for travel)
• Starting pregnancy fitness classes (swimming, prenatal yoga)
• Planning maternity wardrobe updates
• Discussing delivery options with your healthcare provider

Weeks 15-16: Baby’s Sex Becomes Visible

What’s happening with your baby:

If you’re having a boy, his reproductive organs are now fully formed. If you’re having a girl, her reproductive organs are developing (though fully visible sex differentiation may not be clear on ultrasound yet). The baby’s bones are hardening, though still mostly cartilage. Muscles are strengthening. The baby is becoming more active, though you still might not feel movements yet.

Your baby is about the size of an avocado (approximately 4-5 inches, weighing about 2-3 ounces).

What’s happening with you:

You’re likely feeling more energy and appetite. Your weight gain might be more noticeable now (typical gain is ½-1 pound per week at this point). Libido often increases during second trimester—sexual activity is perfectly safe if your healthcare provider hasn’t restricted it.

Some women experience pregnancy “glow”—improved skin and hair.

What to do:

Schedule your anatomy ultrasound (if not already scheduled) for around week 20. Start prenatal classes if available. Discuss any concerns with your healthcare provider.

Weeks 17-20: Anatomy Scan and Quickening

What’s happening with your baby:

The baby’s nervous system is developing rapidly. The baby can now hear sounds—your voice, your heartbeat, external sounds (though muffled). Meconium (baby’s first stool) is beginning to form in the intestines. Sweat glands are developing.

Around week 20, the anatomy ultrasound gives you a detailed look at your baby’s structures: brain, heart, lungs, kidneys, limbs, and spine are all visible and measurable.

Your baby is about the size of a banana (approximately 6-7 inches, weighing about 5 ounces).

What’s happening with you:

Most women feel their baby move for the first time during these weeks—a sensation often described as flutters, gentle kicks, or even “like gas bubbles.” First-time mothers often feel movement slightly later than experienced mothers.

You’re halfway through your pregnancy! Your uterus has grown from the size of a pear to the size of a melon and is now at your belly button.

Major milestone: Your anatomy ultrasound (typically at week 20) provides detailed information about your baby’s development and checks for any structural concerns.

What to do:

After anatomy ultrasound, celebrate seeing your baby’s detailed features! If the technician asks, you can typically find out baby’s sex at this appointment. Continue healthy habits, prenatal vitamins, and regular exercise.

As your belly grows, finding a comfortable sleeping position becomes more challenging. Many women start experiencing back and hip discomfort during this stage, especially at night.

👉 Check the best pregnancy pillows for side sleepers to improve your sleep quality and reduce pressure on your body.

Weeks 21-26: Kicks Intensify and Third Trimester Nears

What’s happening with your baby:

Baby movements become noticeably stronger and more frequent. The baby’s taste buds are developing—they can taste amniotic fluid. Eyebrows and eyelashes are becoming visible. The baby’s skin is developing layers and would be capable of surviving outside the womb (with medical support) at this point, though continued development is crucial.

By week 26, the baby can respond to sounds and vibrations. Sleep-wake cycles are beginning to establish.

Your baby is about the size of a carrot (approximately 9 inches, weighing about 1.5-2 pounds).

What’s happening with you:

You’re visibly pregnant now, and strangers might offer congratulations or unsolicited advice. Backaches might develop as your center of gravity shifts and hormones relax your ligaments. Sleep might become difficult—finding a comfortable position is challenging. Heartburn, constipation, and hemorrhoids are common.

You might experience Braxton-Hicks contractions—practice contractions where your uterus tightens for 30 seconds to 2 minutes. These are normal and not labor.

What to do:

Start prenatal classes (childbirth education, infant care). Discuss birth plans with your healthcare provider. Consider hiring a doula if desired. Begin preparing your home for baby’s arrival.

THE THIRD TRIMESTER: Weeks 27-40

The final trimester is about preparation, growth, and anticipation. Your baby is putting on weight rapidly, and you’re feeling the physical reality of pregnancy more acutely. This trimester often includes more frequent prenatal visits and preparation for labor and delivery.

Weeks 27-30: Weight Gain Accelerates

What’s happening with your baby:

Baby is now in a position (usually head-down) for delivery. The lungs are developing surfactant, a substance that will allow them to expand after birth. The baby’s nervous system is developing rapidly. The baby is practicing breathing movements (though breathing amniotic fluid, not air).

Your baby gains significant weight rapidly now—approximately ½ pound per week.

Your baby is about the size of a large cauliflower (approximately 10 inches, weighing about 2.5-3 pounds).

What’s happening with you:

Weight gain accelerates during this trimester—you’re gaining about 1 pound per week. Total pregnancy weight gain by this point is typically 20-25 pounds.

Fatigue returns as your body carries more weight and prepares for labor. Swelling might develop in your feet and ankles, especially by end of day. Sleep becomes very difficult as your belly is large and finding comfortable positions is nearly impossible.

Frequent urination intensifies as the baby drops lower and presses on your bladder. Some women experience stress incontinence (small leaks when laughing, coughing, or sneezing).

What to do:

Attend prenatal appointments every 2 weeks now (moving to every week around week 36). Discuss signs of labor and preterm labor. Finalize birth plans and hospital/birthing center arrangements.

Swelling in your feet and legs becomes more common as you enter the third trimester. This is completely normal, but it can feel uncomfortable by the end of the day.

👉 Explore the best maternity compression socks to reduce swelling and improve circulation during pregnancy.

Weeks 31-34: Baby Drops (Lightening)

What’s happening with your baby:

The baby’s skin is becoming less wrinkled as fat deposits increase. Toenails are fully formed. The baby is now responding well to sounds and light. Brain development continues rapidly—about two-thirds of brain weight is still to be added.

Your baby is about the size of a pineapple (approximately 11-12 inches, weighing about 4-5 pounds).

What’s happening with you:

Around week 32-34, you might experience “lightening”—the baby drops into the pelvis in preparation for delivery. This relieves pressure on your ribs and lungs (breathing becomes easier!) but increases pressure on your bladder and pelvis. You might waddle when walking.

Pelvic pressure and increased vaginal discharge are normal. Braxton-Hicks contractions might increase. Sleep remains challenging.

What to do:

Begin weekly prenatal visits (if not already). Discuss Group B Strep (GBS) testing (typically around week 35). Prepare your home for baby’s arrival. Pack hospital bag. Arrange postpartum help.

As you prepare for your baby’s arrival, setting up your nursery becomes an exciting part of the journey. One essential item many parents invest in is a reliable baby monitor for peace of mind.

👉 See the best WiFi baby monitors to stay connected with your baby anytime, anywhere.

Weeks 35-37: Full Term Approaches

What’s happening with your baby:

By week 37, your baby is considered “full term.” All organs are sufficiently mature for life outside the womb. The baby is still gaining about ½ pound per week. The vernix (protective coating) is decreasing. Lanugo (fine body hair) is mostly gone.

Your baby is about the size of a small honeydew melon (approximately 13-14 inches, weighing about 5.5-6.5 pounds).

What’s happening with you:

You’re likely tired of being pregnant and ready to meet your baby! Pelvic pressure might intensify. Vaginal discharge increases. The cervix might begin softening and thinning (effacing) in preparation for labor, though this can happen weeks before labor actually starts.

Some women experience nesting instinct—an overwhelming urge to prepare the home for baby.

What to do:

Hospital bag should be packed and ready. Car seat should be installed and ready. Final prenatal preparations completed. Know the signs of labor: regular contractions, water breaking, bloody show.

Weeks 38-40: Ready for Baby

What’s happening with your baby:

Your baby is fully developed and ready for delivery anytime after week 39. The baby weighs approximately 6-9 pounds and measures 18-20 inches (though both measurements vary widely). The baby is cramped in the womb, with limited movement space, though you should still feel regular movements.

What’s happening with you:

You’re likely experiencing increased pelvic pressure, frequent urination, and significant fatigue. You might lose your mucus plug (a bloody or clear mucous discharge), which means your cervix is preparing for labor. You might feel more energy (nesting) or remain exhausted.

The waiting: This period can feel long if you go past your due date. Remember: due dates are estimates. Most pregnancies deliver between 38-42 weeks.

What to do:

Attend weekly prenatal visits. Discuss any signs of labor. Rest as much as possible. If you go past your due date (week 40), discuss induction options with your healthcare provider. For healthy pregnancies, waiting until at least week 39 for labor to begin naturally is recommended.

Labor signs to watch for:

• Regular, increasingly intense contractions (not Braxton-Hicks)
• Water breaking (gush or trickle of fluid)
• Bloody show (pink or blood-tinged mucus)
• Lower back pain combined with contractions

Important Pregnancy Milestones Summary

Frequently Asked Questions About Pregnancy Week by Week

When can I find out the baby’s sex?

During the anatomy ultrasound at week 20, if the baby’s position allows and you want to know. Some parents discover sex earlier via blood tests (around week 10) that analyze fetal DNA in maternal blood.

Is my baby’s development normal if different from this guide?

Yes. Every pregnancy is unique. Babies develop at slightly different rates. At your prenatal appointments, your healthcare provider measures your baby’s development and confirms everything is progressing normally. Don’t panic if your baby is slightly ahead or behind the “typical” timeline.

When should I stop exercising?

Continue exercise throughout pregnancy unless your healthcare provider restricts it. Low-impact activities like walking, swimming, prenatal yoga, and stationary cycling are safe for most pregnancies. Discuss specific activities with your healthcare provider.

Can I travel during pregnancy?

Most women can travel safely until week 36. The second trimester (weeks 14-20) is considered safest for travel. Air travel is typically safe until week 36. Discuss travel plans with your healthcare provider.

How often should I have prenatal appointments?

Standard schedule:

• Every 4 weeks through week 28
• Every 2 weeks from week 28-36
• Every week from week 36-delivery

Your healthcare provider might recommend more frequent visits if there are concerns.

What if I go past my due date?

Due dates are estimates. Most pregnancies deliver between week 38-42. If you go past week 42, your healthcare provider will discuss induction or other options due to increased risks.

Is morning sickness dangerous?

Mild morning sickness is normal and doesn’t harm your baby. Severe morning sickness (hyperemesis gravidarum) requires medical attention as it can lead to dehydration and nutritional deficiencies. If you can’t keep food or fluids down, contact your healthcare provider.

When should I be concerned about a symptom?

Contact your healthcare provider immediately if you experience:

• Severe abdominal or pelvic pain
• Heavy vaginal bleeding
• Severe nausea and vomiting (unable to keep anything down)
• Fever above 101°F
• Severe headaches
• Blurred vision
• Swelling in face or hands
• Decreased fetal movement

Planning ahead for feeding your baby is an important step as you approach your due date. Whether you plan to return to work or simply want flexibility, choosing the right breast pump can make a big difference.

👉 Find the best breast pump for working moms to make your postpartum journey easier.

Final Thoughts

Pregnancy is a 40-week journey of transformation—both for your baby and for you. Each week brings new developments and preparations for birth. Some weeks feel easy, others feel overwhelming. All of this is normal.

Stay connected with your healthcare provider, trust your body, and don’t hesitate to ask questions. Your pregnancy is unique—trust your instincts and seek help when something doesn’t feel right.

The 40 weeks pass quickly. Enjoy the moments, document the memories, and prepare yourself mentally and physically for the incredible experience of birth and parenthood.

You’ve got this.

Disclaimer: This article is for informational purposes and should not replace guidance from your healthcare provider. Every pregnancy is unique. Discuss any concerns about your specific pregnancy with your OB-GYN or midwife. Information based on March of Dimes, Mayo Clinic, Nemours KidsHealth, and The Bump guidelines current as of April 2026.