Medical Information
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pregnancyThe Complete Week-by-Week Pregnancy Guide: From Conception to Delivery
Comprehensive guide covering all 40 weeks of pregnancy with medical facts, symptoms, what to expect, and expert tips for each trimester.
PregnancySprout Editorial Team Published June 8, 2026 10 min read
The Complete Week-by-Week Pregnancy Guide: From Conception to Delivery
Pregnancy is a remarkable 40-week journey of profound physical and emotional changes. This comprehensive guide walks you through each stage, explaining what's happening in your body, how your baby is developing, and what you can expect at each week of pregnancy.
Understanding the Pregnancy Timeline
Before we dive into the week-by-week breakdown, it's important to understand how pregnancy is dated. Healthcare providers count pregnancy from the first day of your last menstrual period (LMP), even though conception typically occurs about 2 weeks later during ovulation. This means:
- Week 1-2: Pre-conception and ovulation
- Week 3-4: Conception and early implantation
- Week 5+: Detectable pregnancy hormones
This system means you're already "4 weeks pregnant" on the day your period is missed—a concept that confuses many first-time parents.
FIRST TRIMESTER (Weeks 1-13)
Weeks 1-4: The Beginning
What's Happening in Your Body:- Week 1 begins with menstruation
- Around day 14, you ovulate (release an egg)
- If sperm fertilizes the egg, it begins dividing as it travels to your uterus
- By week 4, the blastocyst (early embryo) implants in your uterine lining
- Implantation triggers hormonal changes that stop menstruation
- Your baby is microscopically small (smaller than a grain of rice)
- The neural tube (future brain and spinal cord) begins forming
- The heart begins to develop primitive beating cells
- Period-like cramps (implantation)
- Light spotting or "implantation bleeding"
- Tender breasts
- Fatigue
- Mild nausea (may not start until week 5-6)
- Take prenatal vitamins with folic acid (400 micrograms daily)
- Avoid alcohol, smoking, and harmful drugs
- Schedule your first prenatal appointment when you miss your period
- Continue healthy habits (exercise, good nutrition)
Weeks 5-8: Major Organ Development
What's Happening in Your Body:- Rapidly rising hCG (pregnancy hormone) causes morning sickness symptoms
- Your blood volume increases by 10%
- You may feel extreme fatigue
- Frequent urination begins
- Embryo grows from pinhead to ½ inch long
- Head comprises half the body length
- Eyes, ears, and mouth begin forming
- Limb buds appear
- Heart pumps blood
- Brain development accelerates
- Morning sickness (despite the name, can occur any time)
- Food cravings and aversions
- Constipation
- Frequent urination
- Mood swings
- Shortness of breath
- Ultrasound (usually week 8-10) confirms pregnancy location and checks for multiple babies
- Heartbeat visible on ultrasound (fetal pole with heartbeat at week 5-6)
- Blood work screens for infections and blood type
Weeks 9-13: Refining Features
What's Happening in Your Body:- Morning sickness peaks around week 9-12
- You might begin showing (varies widely based on body type)
- Mood stabilizes somewhat as hormone levels equilibrate
- Skin changes: melasma (brown patches) or acne may develop
- Fingers and toes are separating
- External genitalia forming (sex may be determined via cell testing)
- Teeth buds forming in gums
- Baby can make facial expressions
- Reflexes beginning (like the startle reflex)
- Many parents announce pregnancy after week 12-13 (miscarriage risk drops significantly)
- First trimester screening may include genetic testing
- NT (nuchal translucency) ultrasound measures fluid at back of baby's neck
SECOND TRIMESTER (Weeks 14-27)
The "honeymoon period" of pregnancy—energy often returns and discomfort is minimal.
Weeks 14-18: Energy Returns
What's Happening in Your Body:- Morning sickness usually subsides
- Energy levels improve dramatically
- Appetite increases
- Skin often glows from increased blood flow
- Baby weighs about 6 ounces
- Fine hair (lanugo) covers baby's body
- Baby may start moving (quickening) around week 16-18
- Sex organs fully developed; sex is clearly visible on ultrasound
- First movements feel like flutters, bubbles, or gentle kicks
- Usually felt first by second-time mothers
- Start monitoring patterns (babies have sleep-wake cycles)
Weeks 19-23: Growth Accelerates
What's Happening in Your Body:- Your uterus is now at belly button level
- You need 300 extra calories daily
- Braxton-Hicks contractions may begin (practice contractions)
- Linea nigra (dark line on belly) often appears
- Back pain begins as you adjust posture
- Baby doubles in weight (around 1 pound by week 20)
- Vernix caseosa (white coating) protects skin
- Baby's movements become stronger and more defined
- Sleep-wake patterns establish
- Baby can hear (responds to loud noises)
- Detailed anatomy scan checks all organs
- Placenta location confirmed
- Umbilical cord blood vessel count verified
- Growth and development measured
Weeks 24-27: Viability and Fat Deposition
What's Happening in Your Body:- Heartburn and indigestion increase
- Swelling in feet and ankles begins
- Sleep becomes uncomfortable
- Shortness of breath may worsen
- Baby now weighs about 1.5-2 pounds
- Brain size increases rapidly
- Baby practices breathing (amniotic fluid in lungs)
- Fingernails and toenails form
- Viability: After week 24, babies can survive with medical intervention
- Gestational diabetes screening (glucose tolerance test)
- Rh antibody screening if you're Rh-negative
THIRD TRIMESTER (Weeks 28-40)
Weeks 28-32: Weight Gain Accelerates
What's Happening in Your Body:- Rapid weight gain continues
- Hemorrhoids and varicose veins may appear
- Your ribcage expands
- Carpal tunnel symptoms may develop
- Sleep disruption from baby's movements
- Baby weighs 2.5-3.75 pounds
- Most babies move into head-down position
- Eyes open and close (practice for outside world)
- Baby may hiccup (you feel rhythmic jerks)
- Fingernails reach fingertips
- Non-stress tests begin if you have complications
- Monitor for signs of preeclampsia (swelling, headaches, vision changes)
Weeks 33-36: Final Position Adjustment
What's Happening in Your Body:- Pelvis softens and spreads (symphysis pubis relaxation)
- Perineal care begins (prevent tearing)
- Cervix begins softening and thinning (effacement)
- Practice breathing techniques for labor
- Baby weighs 4-5.5 pounds
- Most babies are head-down
- Baby "drops" lower into pelvis (lightening) around week 35-37
- Fat deposits under skin smooth out appearance
- Brain development continues rapidly
- Group B Strep (GBS) screening (week 35-37)
- Position confirmation via ultrasound or examination
- Blood pressure monitoring (preeclampsia risk)
Weeks 37-40: Final Countdown to Delivery
What's Happening in Your Body:- Braxton-Hicks contractions increase in frequency
- True labor signs: regular contractions, cervical changes
- Cervix dilates progressively (checked at appointments)
- Nesting instinct strong (organizing, cleaning, preparing)
- Baby weighs 5.5-8 pounds (varies widely)
- Lungs fully mature (ready for breathing outside womb)
- Baby is confined in uterus (less movement)
- Immune system receives mother's antibodies
- Cervical exams weekly or more frequently
- Induction discussion if approaching due date
- Review labor signs and when to go to hospital
- Final ultrasound may measure baby size
Key Medical Tests Throughout Pregnancy
First Trimester Tests
- Pregnancy test (blood or urine): Confirms pregnancy
- Ultrasound: Confirms location, viability, dates
- Blood work: Blood type, Rh factor, infections, anemia
- Quad screen or combined screening: Genetic risk assessment
- Nuchal translucency ultrasound: Fetal development assessment
Second Trimester Tests
- Anatomy ultrasound (week 18-22): Detailed organ scan
- Quad screen: Screens for Down syndrome, neural tube defects
- Glucose tolerance test (week 24-28): Screens for gestational diabetes
- Anemia screening: Checks for iron deficiency
Third Trimester Tests
- Non-stress tests: Monitor baby's heart rate and movements
- Contraction stress tests: If complications present
- Group B Strep test (week 35-37): Checks for infection risk
- Biophysical profile: Evaluates baby's well-being if concerns
- Amniotic fluid assessment: Checks adequate fluid levels
Common Pregnancy Discomforts by Trimester
First Trimester
- Morning sickness and food aversions
- Fatigue and sleep disturbances
- Tender breasts
- Constipation
- Frequent urination
- Mood swings
Second Trimester
- Round ligament pain
- Heartburn and indigestion
- Leg cramps
- Congestion and nosebleeds
- Back pain beginning
- Linea nigra and skin changes
Third Trimester
- Increased back and joint pain
- Insomnia
- Braxton-Hicks contractions
- Hemorrhoids and varicose veins
- Swelling in feet and ankles
- Shortness of breath
- Increased urination
Nutrition Throughout Pregnancy
Your baby depends entirely on your nutrition. Key nutrients and daily needs:
Protein: 70 grams daily (builds baby's tissues)- Chicken, fish, eggs, dairy, beans, nuts
- Milk, yogurt, cheese, leafy greens, fortified foods
- Red meat, poultry, fish, dried beans, fortified cereals
- Leafy greens, asparagus, Brussels sprouts, fortified grains
- Fatty fish, egg yolks, mushrooms, fortified milk
- Salmon, mackerel, sardines, walnuts, flaxseed
Activities and Exercise Throughout Pregnancy
Most women can continue normal activities through pregnancy:
- Walking: Low-impact, excellent throughout pregnancy
- Swimming: Weightless feeling, great for joint pain
- Yoga: Modified poses safe through pregnancy
- Strength training: Continue with lighter weights
- Cycling: Stationary bikes safer as belly grows
- Contact sports
- Activities with fall risk
- Lying flat on back (after first trimester)
- Scuba diving
- Hot yoga/sauna
Preparing for Labor and Delivery
As you approach due date:
Birth plan considerations:- Hospital vs. birthing center vs. home birth
- Pain management preferences
- Who will be present
- Interventions you want to avoid or prefer
- Labor and delivery classes
- Breastfeeding information
- Newborn care classes
- Partner preparation
- Install car seat (required to leave hospital)
- Pack hospital bag
- Tour hospital/birthing facility
- Arrange time off work
- Set up newborn area at home
Signs Labor is Beginning
True labor signs:- Regular contractions (every 5 minutes or closer)
- Contractions don't stop with movement or rest
- Lower back pain that radiates to belly
- Cervical changes (confirmed by provider)
- Bloody show (pink/brown mucus)
- Water breaking (clear, odorless fluid)
- Water breaks
- Heavy vaginal bleeding
- Severe abdominal pain
- Dizziness or fainting
- Vision changes
- Sudden swelling
The Essential Takeaway
Pregnancy is a 40-week transformation, each phase bringing predictable changes and preparing both you and baby for birth. Understanding what to expect helps you embrace the changes and address concerns early. Trust your body, communicate with your healthcare team, and remember—every pregnancy is unique. What matters most is that you and your baby reach delivery day healthy and ready to meet.
Related Articles
- Pregnancy Symptoms Week by Week
- Prenatal Vitamins Guide
- Complete Pregnancy Diet
- Hospital Bag Checklist
- Birth Plan Template
This guide is for informational purposes. Always consult with your healthcare provider for personalized medical advice.
Frequently Asked Questions
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PregnancySprout Editorial Team
Our editorial team researches every article against primary medical sources — NHS, WHO, NICE, and RCOG guidelines. We are health writers and parents, not doctors; content is reviewed for accuracy but does not constitute medical advice.
✓ Fact-checked against NHS, WHO, and NICE guidelines
Published 8 June 2026Editorial standards
