The second trimester lasts about 15 weeks, running from week 13 through the end of week 27. The American College of Obstetricians and Gynecologists officially defines it as 14 weeks 0 days through 27 weeks 6 days, while many hospitals and pregnancy resources count it from week 13. Either way, you’re looking at roughly the middle third of a 40-week pregnancy.
Why the Start Date Varies Slightly
You’ll notice some sources say the second trimester begins at week 13 and others say week 14. This isn’t a real disagreement. ACOG uses the precise cutoff of 14 weeks and 0 days, while Cleveland Clinic and other patient-facing resources round to “around week 13.” The difference is a matter of days, not medical significance. Your provider will track your pregnancy by exact gestational age regardless of which trimester label applies.
The endpoint is more consistent across sources: the second trimester ends at week 27, and your third trimester begins at week 28.
What Changes in Your Body
The second trimester is often called the most comfortable stretch of pregnancy, and there’s a real physiological reason for that. The fatigue and nausea that dominate the first trimester tend to ease up, and many people notice a genuine energy boost. Your belly and breasts grow noticeably as the uterus expands to accommodate a rapidly growing baby.
Weight gain picks up during these weeks. If you started pregnancy at a healthy weight, the general guideline is about 1 pound per week through the second and third trimesters. If you started at a higher weight, the target is closer to half a pound per week. Calorie needs increase modestly: most people need around 2,200 calories per day during the second trimester, which works out to roughly 300 extra calories compared to pre-pregnancy intake.
Round ligament pain, a sharp or aching sensation on either side of your lower belly, is common as the ligaments supporting your uterus stretch. Back pain, mild swelling, and skin changes (like a darkening line down the center of your abdomen) also show up for many people during these weeks.
How Your Baby Develops
The second trimester is a period of rapid growth and development. At week 13, the baby’s skeleton begins hardening from soft cartilage into bone. Over the following weeks, the changes come fast: facial features become more defined, fingerprints form, and the baby starts practicing breathing movements using amniotic fluid.
By the midpoint of this trimester, the baby can hear sounds from outside the womb. By the end, at week 27, the baby’s eyes can open and close, the nervous system is maturing quickly, and the lungs are developing the structures they’ll eventually need to breathe air. The baby goes from a few inches long at the start of the second trimester to roughly 14 inches and about 2 pounds by its end.
Feeling Your Baby Move
One of the biggest milestones of the second trimester is feeling fetal movement for the first time, sometimes called quickening. If you’ve been pregnant before, you may notice flutters as early as 16 weeks. First-time parents typically don’t feel movement until around 20 weeks. Early movements feel like bubbles, light tapping, or a fluttering sensation that’s easy to dismiss as gas. By the later weeks of the second trimester, kicks and rolls become unmistakable.
Key Tests and Appointments
The anatomy scan, one of the most detailed ultrasounds of pregnancy, happens between weeks 18 and 22. This ultrasound checks the baby’s organs, limbs, spine, and brain development, and it’s the appointment where many people learn the baby’s sex. Your provider will also measure the placenta’s position and check amniotic fluid levels.
Gestational diabetes screening typically happens toward the end of the second trimester, around weeks 24 to 28. This involves drinking a sugary solution and having your blood drawn to check how your body processes glucose. Throughout the trimester, your provider will monitor your weight and blood pressure at regular prenatal visits, which usually happen about once a month during this stretch.
A Quick Week-by-Week Overview
- Weeks 13–16: Bones harden, energy returns, and some experienced parents feel early movement.
- Weeks 17–20: The baby’s hearing develops, first-time parents begin feeling kicks, and the anatomy scan is scheduled.
- Weeks 21–24: Rapid weight gain for the baby, more noticeable movement patterns, and glucose screening approaches.
- Weeks 25–27: The baby’s lungs and nervous system mature, eyes open, and the trimester wraps up as you approach the final stretch of pregnancy.