Pregnancy Week by Week

Pregnancy lasts about 40 weeks, counted from the first day of your last menstrual period (LMP). Here is what happens at each stage, for both you and your baby.

First Trimester (Weeks 1-13)

Weeks 1-4

Your body: You may not know you are pregnant. Some women experience implantation bleeding.

Your baby: Fertilization occurs around week 2. The blastocyst implants in the uterine lining by week 4.

Weeks 5-8

Your body: Missed period, breast tenderness, nausea, fatigue, frequent urination.

Your baby: Neural tube forms, heart begins to beat, arm and leg buds appear. Embryo is about the size of a kidney bean by week 8.

Weeks 9-13

Your body: Nausea may peak, fatigue continues, breasts may be tender.

Your baby: All major organs have formed. Fingers and toes are visible. Embryo becomes a fetus at week 11 (ACOG).

Second Trimester (Weeks 14-27)

Weeks 14-16

Your body: Energy returns, nausea fades, you may start to show.

Your baby: Baby is about 3.5 inches long. Baby can make facial expressions.

Weeks 17-20

Your body: Quickening (first movement) typically 16-22 weeks. You may feel fluttering or bubbling.

Your baby: Baby is about 6.5 inches long. Baby can hear sounds. Anatomy scan at 18-22 weeks.

Weeks 21-24

Your body: Back pain, round ligament pain, heartburn, nasal congestion.

Your baby: Baby is about 12 inches long. Baby's lungs are developing. Baby has sleep-wake cycles.

Weeks 25-27

Your body: Leg cramps, Braxton Hicks contractions, shortness of breath.

Your baby: Baby is about 14 inches long. Baby's eyes can open. Baby can respond to light.

Third Trimester (Weeks 28-40)

Weeks 28-32

Your body: Shortness of breath, frequent urination, heartburn, swelling, Braxton Hicks contractions.

Your baby: Baby is about 15 inches long. Baby weighs about 2.5 pounds. Baby can open and close eyes.

Weeks 33-36

Your body: Lightening (baby dropping), increased pelvic pressure, difficulty sleeping.

Your baby: Baby is about 17-18.5 inches long. Baby weighs about 4-6 pounds. Baby's lungs are nearly mature.

Weeks 37-40

Your body: Full term at 37 weeks. You may experience signs of labor: regular contractions, water breaking, bloody show.

Your baby: Baby is full term. Baby's organs are fully mature. Baby is about 18.5-20 inches long and weighs about 6-7.5 pounds.

Key Milestones at a Glance

When to Call Your Clinician

Contact your healthcare provider if:

• You have bleeding, pain, or other concerns
• You have not felt movement by 24 weeks
• You are past your due date
• You have signs of labor before 37 weeks