What to Expect During Your First Trimester: A Week-by-Week Guide

The first trimester is a time of incredible transformation—both for your growing baby and for your body. While much of this development happens invisibly, understanding what's occurring can help you feel more connected to your pregnancy and know what to expect.

Weeks 1-4: The Beginning

What's Happening

Technically, pregnancy is dated from the first day of your last menstrual period, even though conception occurs around week 2. By week 4:

• The fertilized egg has implanted in your uterine lining
• The placenta begins forming
• Your baby is smaller than a poppy seed

What You Might Feel

Most women don't know they're pregnant yet during these early weeks. You might notice:

• Light spotting (implantation bleeding)
• Breast tenderness
• Mild cramping
• Fatigue

What to Do

• Start taking prenatal vitamins if you haven't already
• Avoid alcohol, smoking, and recreational drugs
• Schedule your first prenatal appointment

Weeks 5-8: Major Development

What's Happening

This is a critical period of development. Your baby:

• Week 5: Heart begins beating; neural tube forming
• Week 6: Facial features start developing; arm and leg buds appear
• Week 7: Brain developing rapidly; fingers and toes forming
• Week 8: All major organs are developing; baby moves (though you can't feel it)

By week 8, your baby is about the size of a raspberry.

What You Might Feel

The famous first trimester symptoms often kick in:

• Morning sickness (which can happen any time of day)
• Extreme fatigue
• Breast changes (tenderness, darkening areolas)
• Frequent urination
• Food aversions or cravings
• Heightened sense of smell
• Mood swings

What to Do

• Keep crackers by your bed for morning nausea
• Rest when you can—your body is working hard
• Eat small, frequent meals
• Stay hydrated
• Track symptoms to discuss with your provider

Weeks 9-12: Baby Takes Shape

What's Happening

Your baby is officially called a fetus now and is starting to look more human:

• Week 9: Bones begin forming; reproductive organs developing
• Week 10: Vital organs are functional; baby can kick and stretch
• Week 11: Fingers and toes are separated; baby can swallow
• Week 12: Reflexes developing; digestive system practicing

By week 12, your baby is about the size of a lime.

What You Might Feel

• Symptoms may peak around weeks 8-10 then start to ease
• You might notice a small belly bump (especially if it's not your first pregnancy)
• Fatigue often continues
• Emotional ups and downs are normal
• Constipation may become an issue

What to Do

• Attend your first ultrasound (usually around weeks 8-12)
• Complete any first trimester genetic screening if desired
• Start thinking about when and how to announce your pregnancy
• Begin researching prenatal classes

Common First Trimester Concerns

Morning Sickness

Nausea affects up to 80% of pregnant women. To cope:

• Eat small amounts frequently
• Try ginger (tea, candies, or supplements)
• Avoid strong smells
• Consider vitamin B6 (ask your provider)

When to call your provider: If you can't keep any food or water down for 24 hours, or you're losing weight.

Spotting

Light spotting is common and often harmless, but always mention it to your provider. Call immediately if you experience:

• Heavy bleeding (soaking a pad)
• Severe cramping
• Fever or chills

Extreme Fatigue

First trimester exhaustion is real. Your body is:

• Building a placenta
• Increasing blood volume
• Supporting rapid fetal development

Honor your body's need for rest when possible.

First Trimester Prenatal Care

Your First Appointment

Typically scheduled between weeks 8-12, this visit includes:

• Medical history review
• Physical exam
• Dating ultrasound
• Blood work (blood type, immunity levels, STI screening)
• Urine test
• Discussion of prenatal vitamins and medications

Genetic Screening Options

You'll be offered optional genetic screening tests:

• NIPT (Non-Invasive Prenatal Testing): Blood test that screens for chromosomal conditions; can be done as early as 10 weeks
• First Trimester Screen: Combines blood test and ultrasound (nuchal translucency) at 11-14 weeks

These tests are optional and personal—discuss them with your provider.

Lifestyle During the First Trimester

Exercise

Generally safe to continue your pre-pregnancy exercise routine with modifications:

• Avoid contact sports and high-fall-risk activities
• Stay hydrated and don't overheat
• Listen to your body
• Walking, swimming, and prenatal yoga are excellent options

Diet

Focus on:

• Folic acid: Leafy greens, fortified grains, prenatal vitamins
• Protein: Lean meats, beans, eggs, nuts
• Calcium: Dairy, fortified plant milks
• Iron: Red meat, spinach, beans

Avoid:

• Raw or undercooked meat, fish, and eggs
• Unpasteurized dairy and juices
• High-mercury fish (shark, swordfish, king mackerel)
• Excess caffeine (limit to 200mg/day)

Work and Daily Life

• Manage fatigue by prioritizing sleep
• Take breaks during the day when possible
• Consider when you'll tell your employer
• Know your workplace rights regarding pregnancy

Emotional Health

The first trimester can be emotionally complex:

• Joy mixed with anxiety is completely normal
• Hormones affect mood regulation
• The "secret" nature of early pregnancy can feel isolating

Take care of your mental health by:

• Talking to your partner or a trusted friend
• Connecting with other pregnant women (online or in-person)
• Practicing stress-reduction techniques
• Speaking with your provider if anxiety or depression feels overwhelming

Looking Ahead

As you approach the end of the first trimester:

• Miscarriage risk drops significantly after week 12
• Many women feel comfortable sharing the news
• Second trimester often brings more energy
• You'll start showing more visibly

The Bottom Line

The first trimester is a time of unseen miracles. While you may be dealing with nausea and fatigue, know that your body is doing incredible work. Each week brings new developments as your baby transforms from a cluster of cells to a fully formed (tiny) human.

Be patient with yourself, rest when you need to, and remember: this phase is temporary. The second trimester often brings welcome relief.

Track your baby's development week by week with our Development Tracker.