PregnancyPregnancy Week by Week — Your Complete Guide from Conception to Birth
Forty weeks. Three trimesters. One complete guide to every stage of pregnancy — what's happening with your baby, what's happening in your body, and what to expect at each milestone along the way.
Pregnancy is measured in weeks, not months, and there’s a good reason for it. Your baby changes more in a single week of early pregnancy than most adults change in a decade. A pregnancy week by week guide gives you a running picture of those changes: what's forming, what's growing, and what to expect from your own body at every stage.
This guide walks through all 40 weeks by trimester, with key milestones, body changes, symptoms, and decision points for each phase. Whether you're newly pregnant and staring at two pink lines or deep into the third trimester and counting the days, this is the reference you'll come back to.
If you don't know exactly how far along you are, start with a due date calculator — that number anchors everything else.
First Trimester: Weeks 1–13
The first trimester is a paradox. More happens during these 13 weeks than in the rest of pregnancy combined. But most women don’t look or feel pregnant for a lot of it. Your body is quietly building an entire human from scratch. And it takes a ton of energy, even if there’s nothing visible to show for it yet.
Week 4 — Implantation and the Positive Test
Most women discover they're pregnant around week 4, when the embryo implants into the uterine wall and starts producing hCG — the hormone that turns a pregnancy test positive. At this point, the embryo is a ball of cells smaller than a poppy seed. Some women notice light spotting (implantation bleeding) or mild cramping. Others feel nothing at all.
Week 6 — The First Heartbeat
By week 6, a heartbeat is detectable on transvaginal ultrasound. It’s fast, around 110 beats per minute. In my experience, hearing that can be one of the most surreal moments in early pregnancy. The embryo is forming a neural tube (the precursor to the brain and spinal cord), and tiny limb buds are beginning to appear. Morning sickness often kicks in hard around this week. The word "morning" is misleading — nausea can hit at any time of day and affects roughly 80% of pregnant women.
Week 8 — Major Organ Formation
All major organ systems are forming by week 8: brain, heart, lungs, kidneys, liver, and intestines. The embryo is about half an inch long, roughly the size of a raspberry. Fingers and toes are starting to differentiate. But they’re still webbed. Honestly, this is a really important period for your baby’s development. That’s one reason the first trimester has the highest risk of miscarriage. Your first prenatal appointment usually happens around weeks 8–10. It usually includes bloodwork, a urine test, and a medical history review. That first visit often includes a dating ultrasound.
Week 10 — From Embryo to Fetus
At week 10, the embryo is officially reclassified as a fetus. All the essential organs are in place now, and they’ll keep maturing over the coming months. The baby’s head is disproportionately large at this point. The head is about half its total body length because the brain is developing very fast. Bones begin to harden, and tiny tooth buds form beneath the gums.
Week 12 — End of the Danger Zone
The risk of miscarriage drops significantly after a heartbeat is confirmed at the 12-week mark. That’s why a lot of couples wait until around now to share the news. A nuchal translucency scan (NT scan) is often offered between weeks 11 and 14. The NT scan screens for chromosomal conditions like Down syndrome. The baby is about 2 inches long and can open and close its fists.
Common first-trimester symptoms: nausea, fatigue so deep it feels like you've been drugged, breast tenderness, food aversions, heightened sense of smell, frequent urination, mood swings, and bloating. Some women experience none of these. That's also normal.
Second Trimester: Weeks 14–27
If the first trimester is survival mode, the second is the payoff. Nausea usually fades by week 14 or 15. Energy returns. The baby bump becomes visible. And pregnancy starts feeling less like an abstract concept and more like something real you can see (and eventually feel).
Week 14 — The Relief Week
For most women, week 14 marks a turning point. Morning sickness usually eases up. The exhaustion lifts. You might actually feel good, maybe even better than you’ve felt in months. The baby is about 3.5 inches long. The baby is starting to make facial expressions. These expressions are reflexive, not intentional. By now, the placenta has fully taken over hormone production. That’s one reason nausea often eases.
Week 16 — Early Flutters
Women who've been pregnant before sometimes feel the baby move as early as week 16. First-time mothers usually don't recognize it until weeks 20–22. These early movements are called quickening. Quickening can feel like bubbles, flutters, or gentle tapping. They're easy to mistake for gas. The baby’s skeletal system is hardening from cartilage to bone. Fine hair called lanugo covers the baby’s skin. Lanugo helps regulate body temperature.
Week 18 — The Anatomy Scan Approaches
The anatomy scan is usually scheduled between weeks 18 and 22. It’s the most detailed ultrasound of pregnancy. The sonographer looks at the baby’s brain, heart, spine, kidneys, stomach, bladder, and limbs. They check the placenta’s position. They also measure amniotic fluid levels. This is often when parents find out the baby’s sex, if they want to know. The baby is roughly 5.5 inches long. The baby weighs about 7 ounces.
Week 20 — The Halfway Point
You're halfway there. The baby can hear sounds now. That includes your heartbeat, your voice, and loud noises from the outside world. Some parents start talking or reading to the baby around this week. The baby’s skin is covered in a waxy coating called vernix caseosa. Vernix caseosa protects the baby’s skin from amniotic fluid. The baby’s movement usually gets more consistent around now. In my experience, it starts to feel pretty unmistakable.
Week 24 — The Viability Milestone
Week 24 is medically significant. Week 24 is generally recognized as the threshold of viability. It’s the earliest point when a baby has a realistic chance of surviving outside the womb with intensive neonatal care. Survival rates at 24 weeks range from roughly 40% to 70%. The exact odds depend on the hospital. The exact odds also depend on individual factors. The lungs are developing air sacs (alveoli) but are not yet mature enough for independent breathing. From this point forward, every additional week in the womb dramatically improves outcomes.
Common second-trimester symptoms: round ligament pain (sharp aches on the sides of the abdomen), nasal congestion, nosebleeds, increased appetite, skin changes like linea nigra and melasma, visible baby bump, leg cramps at night, and — finally — the undeniable sensation of your baby kicking.
Third Trimester: Weeks 28–40
The home stretch. The baby gains weight rapidly, roughly half a pound per week. Your body adjusts to accommodate a 6-to-9-pound passenger. The baby is running out of room. The third trimester is equal parts anticipation, discomfort, and preparation. In my experience, it can feel like you’re counting down and nesting at the same time.
Week 28 — Third Trimester Begins
You've entered the final act. The baby’s eyes can open and close. The baby can respond to light filtering through the abdominal wall. Brain development accelerates around this time. The brain’s surface starts folding into the wrinkled pattern you’d recognize in a newborn. Many providers recommend starting daily kick counting around this week — tracking 10 movements within a 2-hour window helps monitor fetal wellbeing between appointments.
Week 30 — Rapid Brain Growth
The baby's brain is growing so fast that the head circumference increases measurably each week. The bone marrow has taken over making red blood cells from the liver. The baby weighs about 3 pounds. The baby practices breathing movements by moving amniotic fluid in and out. The lungs still won't be used for actual breathing until birth.
Week 32 — Lungs Maturing
The lungs are producing surfactant, a substance that prevents the air sacs from collapsing after each breath. Without enough surfactant, premature babies can develop respiratory distress syndrome. By 32 weeks, survival rates for babies born early exceed 95%. Most babies born at 32 weeks still need weeks in the NICU. The baby has usually settled into a regular sleep-wake cycle by now. You’ll probably notice a pattern in when kicks are strongest, like after you eat or when you finally sit down.
Week 36 — Head Down, Appointments Weekly
Most babies turn head-down by week 36 in preparation for delivery. If your baby is still breech, your provider may discuss options including external cephalic version (ECV) — a manual technique to turn the baby. Prenatal visits become weekly now. The Group B Strep (GBS) test is usually done between weeks 36 and 37. The baby is about 6 pounds. The baby is roughly 18.5 inches long.
Week 37 — Early Term
At 37 weeks, the baby is considered early term. The lungs are nearly mature. The brain and liver are still developing, which is one reason the medical definition of "full term" was moved to 39 weeks. If there's no medical reason for early delivery, most providers encourage waiting. The nesting instinct often hits hard around this week — a sudden urge to clean, organize, and prepare the house.
Weeks 38–39 — Full Term
The baby is adding about half an ounce of fat per day, building the layer that will regulate body temperature after birth. The brain is developing at a remarkable pace — it will increase by about a third in size between weeks 35 and 39. At 39 weeks, the pregnancy is considered full term. The baby is ready. You might lose the mucus plug. You might notice more Braxton Hicks contractions. You might feel “lightening” when the baby drops lower into the pelvis.
Week 40 — Due Date
Only about 5% of babies arrive on their exact due date. Your due date is a statistical midpoint, not a deadline. If you reach 40 weeks and labor hasn’t started, your provider will assess the situation. If the baby is healthy and the amniotic fluid levels are adequate, waiting is usually safe for a few more days. But you’ll likely be monitored more often.
Common third-trimester symptoms: back pain, heartburn, Braxton Hicks contractions, shortness of breath, swollen feet and ankles, difficulty sleeping, pelvic pressure, frequent urination (again), and the nesting instinct. Knowing the difference between Braxton Hicks and real contractions becomes increasingly important. Use a contraction timer to track any patterns.
Beyond 40 Weeks: Overdue, Induction, and Post-Term Pregnancy
Roughly half of all pregnancies go past the due date. Going overdue is common and, in most cases, it isn’t immediately dangerous. But the risks do go up over time.
At 41 weeks, your provider will likely recommend more frequent monitoring. Non-stress tests (NSTs) check the baby’s heart rate. Ultrasounds assess amniotic fluid volume. The placenta, which has been sustaining the baby for nine months, gradually becomes less efficient after 40 weeks. This is called placental aging or insufficiency.
Most guidelines recommend induction between 41 and 42 weeks. After 42 weeks (post-term), the risk of stillbirth increases meaningfully. After 42 weeks (post-term), the risk of meconium aspiration increases meaningfully. After 42 weeks (post-term), the risk of macrosomia (an unusually large baby) increases meaningfully. Induction doesn't mean something has gone wrong — it means the balance of risk has shifted toward delivery.
If you're approaching 41 weeks, talk to your provider about the specific monitoring plan and what would trigger an induction recommendation. Know the stages of labor in advance so you feel prepared regardless of when things begin.
What Changes in Your Body Each Trimester
Pregnancy doesn't only happen to the baby. Your body undergoes some of the most dramatic physiological changes it will ever experience — and understanding those changes trimester by trimester makes the process less alarming.
First Trimester: The Invisible Overhaul
Your blood volume begins increasing — it will eventually rise by 40–50% above pre-pregnancy levels. Progesterone surges, slowing digestion (hello, bloating and constipation) and relaxing smooth muscle throughout your body. Your heart rate increases. Your kidneys filter blood more efficiently, so you pee more often. Breast tissue starts changing almost immediately. It’s getting ready for eventual milk production. Your uterus, which is normally the size of a pear, starts expanding. None of this is visible to anyone else.
Second Trimester: The Visible Shift
The baby bump appears, usually around weeks 14–16 for second-time mothers and weeks 18–20 for first pregnancies. Your center of gravity shifts forward as the uterus grows, which can affect balance and posture. The linea nigra is a dark line running from the navel downward. It appears in many women. Skin may darken in patches (melasma). Stretch marks may start forming on the abdomen, breasts, or thighs when your skin stretches fast. Your ligaments soften because of the hormone relaxin. Relaxin helps prep your pelvis for delivery. Relaxin can also make your joints feel less stable.
Third Trimester: The Endurance Phase
Your uterus is now pushing against your diaphragm, lungs, and stomach — producing shortness of breath and heartburn. The added weight can strain your lower back and pelvic floor. Most people gain 25–35 pounds total by the end of pregnancy. Fluid retention causes swelling in the feet, ankles, and hands. Braxton Hicks contractions become more noticeable. In the final weeks, the baby "drops" into the pelvis (called lightening), which relieves pressure on the lungs but increases pressure on the bladder and pelvis. Your cervix starts to soften and thin out as your body gets ready for labor.
When to Call Your Doctor During Pregnancy
Most pregnancy symptoms are uncomfortable but harmless. Some are not. Knowing the difference can save your life or your baby's. Call your healthcare provider or go to the hospital if you experience any of the following at any point during pregnancy:
- Vaginal bleeding — light spotting in early pregnancy can be normal, but any significant bleeding at any stage needs immediate evaluation.
- Severe abdominal pain — especially if one-sided (which could indicate ectopic pregnancy in the first trimester) or accompanied by bleeding.
- Fluid leaking from the vagina — this could indicate ruptured membranes (water breaking). Before 37 weeks, this is a medical emergency.
- Reduced or absent fetal movement — if your baby's kick pattern changes significantly or you can't reach 10 movements in 2 hours during the third trimester, contact your provider immediately.
- Severe headache or vision changes — persistent headache, blurred vision, or seeing spots can be signs of preeclampsia, a serious blood pressure condition.
- Sudden swelling of the face or hands — mild ankle swelling is normal; rapid swelling of the face, fingers, or around the eyes may indicate preeclampsia.
- Regular contractions before 37 weeks — this could be preterm labor. Use a contraction timer to track the pattern and call your provider.
- Fever above 100.4°F (38°C) — infection during pregnancy can affect the baby and requires prompt evaluation.
- Painful urination or blood in urine — urinary tract infections are common in pregnancy and can lead to kidney infection if untreated.
When in doubt, call. Your provider would always rather hear from you than have you wait at home wondering. No question is too small when you're pregnant.
How Pregnancy App Tracks Your Weeks
Pregnancy App is a free pregnancy tracker on iOS and Android that follows your pregnancy week by week from the moment you enter your due date. It's designed to be a single, calm companion for all 40 weeks — not a firehose of notifications and social noise.
Here's what it includes:
- Weekly pregnancy updates — baby's size, development, and what symptoms to expect at your exact stage.
- Due date calculator — enter your last menstrual period and cycle length for an adjusted due date estimate.
- Baby kick counter — log fetal movements with a single tap from week 28 onward. The app timestamps and stores your kick counts for daily review.
- Contraction timer — track duration, frequency, and intervals during labor. The app flags when your pattern matches the 5-1-1 rule for heading to the hospital.
- Hypnobirthing meditations — audio sessions for each trimester that use evidence-based relaxation techniques. Hypnobirthing helps many women manage labor anxiety and pain.
- Breathing exercises — specific techniques you can practice daily and then use during actual contractions.
Everything works offline — contraction timer, meditations, kick counter — so hospital Wi-Fi is never a factor. Data stays on your device. No account, no login, no email required. Over 200,000 mothers have used Pregnancy App across iOS and Android.
TL;DR
- Pregnancy lasts about 40 weeks, divided into three trimesters. Each trimester has its own developmental milestones and symptoms.
- The first trimester (weeks 1–13) covers implantation, heartbeat detection, organ formation, and the highest miscarriage risk window.
- The second trimester (weeks 14–27) brings the anatomy scan, first kicks, the viability milestone at week 24, and usually less nausea.
- The third trimester (weeks 28–40) is rapid weight gain, kick counting, labor preparation, and delivery.
- Only 5% of babies arrive on their due date. Going overdue is normal but requires monitoring. Most providers recommend induction by 41–42 weeks.
- Call your provider for bleeding, fluid leakage, reduced fetal movement, severe headache or vision changes, or regular contractions before 37 weeks.
- Pregnancy App tracks your pregnancy week by week for free — with a kick counter, contraction timer, due date calculator, and hypnobirthing meditations. No account needed.
Limitations & Safety
This guide provides general educational information about pregnancy development based on widely accepted medical timelines. This isn’t medical advice. Every pregnancy is different. These week-by-week descriptions are population averages. Your baby may develop faster or slower than the average. Both are typically normal.
No website, app, or guide can detect complications, diagnose conditions, or replace the clinical assessments your doctor, midwife, or OB-GYN performs during prenatal visits. The symptom info here is general. It can tell you headaches are common in pregnancy. But it can’t tell you if your headache is from dehydration or a sign of preeclampsia. That distinction requires clinical evaluation.
Go to all your scheduled prenatal appointments. Stick with your provider’s recommendations for screenings, blood tests, glucose testing, and fetal monitoring. If you have severe pain, bleeding, fluid leakage, reduced fetal movement, or vision changes, contact your healthcare provider immediately. If something feels off or worries you, don’t wait for your next scheduled visit.
Pregnancy App is not affiliated with any hospital, clinic, or medical organization. The content on this page and in the app is for informational purposes only.
Frequently Asked Questions
How many weeks is a full-term pregnancy?
A full-term pregnancy is 39 to 40 weeks, measured from the first day of your last menstrual period (LMP). Babies born at 37–38 weeks are considered early term, 39–40 weeks is full term, 41 weeks is late term, and 42 weeks or beyond is post-term. Most providers will talk about induction if you haven’t delivered by 41 weeks.
What are the three trimesters of pregnancy?
The first trimester covers weeks 1 through 13. The baby's major organs form during this time. The risk of miscarriage is highest in the first trimester. The second trimester spans weeks 14 through 27. For a lot of people, it’s the most comfortable stretch. You’ll usually start feeling the baby move in this trimester. Most people also have the anatomy scan in the second trimester. The third trimester runs from week 28 to delivery (around week 40), marked by rapid fetal weight gain and labor preparation.
When can you feel the baby move during pregnancy?
Most women feel the first fetal movements (called quickening) between weeks 16 and 25. First-time mothers typically notice movement around weeks 20–22, while women who have been pregnant before may feel it as early as week 16. Early movements can feel like flutters or bubbles. As the baby grows, those movements usually turn into stronger kicks and rolls.
What happens at the 20-week anatomy scan?
The 20-week anatomy scan is a detailed ultrasound. It’s usually done between weeks 18 and 22. The sonographer looks at the baby’s brain, heart, spine, kidneys, and limbs. They also check other organs for proper development. They measure the amniotic fluid. They examine the placenta's location. And they can often tell the baby’s sex. If something looks concerning, your provider may suggest follow-up imaging or testing.
When is a baby considered viable outside the womb?
Survival rates and outcomes vary a lot by hospital, available neonatal care, and individual circumstances. At 24 weeks, survival rates with intensive care are roughly 40–70%. By 28 weeks, survival exceeds 90%. Babies born before 24 weeks face extremely high risks of serious complications.
What are signs that labor is starting?
One common early labor sign is pelvic pressure when the baby drops lower. If your contractions settle into a steady pattern, like every 5 minutes, lasting 1 minute, for at least 1 hour, call your provider or head to the hospital.
What happens if you go past your due date?
About 50% of pregnancies go past the estimated due date. If you reach 41 weeks, your provider will likely increase fetal monitoring — typically with non-stress tests and amniotic fluid checks. Most providers recommend induction between 41 and 42 weeks because the risk of complications (including stillbirth, meconium aspiration, and placental insufficiency) rises after 42 weeks. The exact timing depends on your health, the baby's condition, and your provider's judgment.
Can an app track my pregnancy week by week?
Yes. Pregnancy tracker apps usually send weekly updates about baby development, expected symptoms, and upcoming milestones. Pregnancy App is a free tracker on iOS and Android that includes week-by-week updates, a contraction timer, kick counter, due date calculator, and hypnobirthing meditations — all stored locally on your device with no account required.