The second trimester of pregnancy lasts about 15 weeks, running from week 13 through the end of week 27. The American College of Obstetricians and Gynecologists defines it precisely as 14 weeks 0 days through 27 weeks 6 days, though most providers and resources round this to weeks 13 through 27. Either way, it covers roughly the middle third of a full-term pregnancy and is often considered the most comfortable stretch of the entire 40 weeks.
Why the Week Count Varies Slightly
You’ll see some sources say the second trimester starts at week 13 and others say week 14. The difference comes down to how individual providers draw the line between trimesters. ACOG uses “14 weeks and 0 days” as the official start, while the Cleveland Clinic and many pregnancy apps count from week 13. In practice, the gap is only a few days. The endpoint is more consistent: nearly all major medical organizations agree it ends at the close of week 27, with the third trimester beginning at week 28.
What Happens to Your Baby During These Weeks
The second trimester is a period of rapid growth and development. Your baby enters it roughly the size of a peach and leaves it weighing around 2 pounds. Along the way, nearly every organ system ramps up in complexity.
Around week 14, the spleen begins producing red blood cells. By week 15, the scalp hair pattern is forming. At week 18, the digestive system starts working and the ears stand out from the head, meaning your baby may begin to hear sounds for the first time. By week 21, a fine layer of downy hair called lanugo covers the entire body, and the sucking reflex develops, so thumb-sucking can start in the womb.
Weeks 22 and 23 bring major reproductive and respiratory milestones. In male babies, the testes begin descending. In female babies, the uterus, ovaries, and vagina are in place. The lungs start producing a substance that will eventually allow them to inflate with air after birth. By week 26, eyebrows and eyelashes have formed, and by week 27 the nervous system is continuing to mature as the trimester wraps up.
When You’ll Feel Movement
One of the most anticipated milestones of the second trimester is feeling your baby move for the first time, sometimes called quickening. This typically happens between weeks 16 and 20. If you’ve been pregnant before, you may notice it closer to week 16 because you recognize the sensation. First-time mothers more commonly feel it around week 20. Early movements often feel like flutters, gas bubbles, or a light tapping. By the end of the trimester, kicks and rolls become unmistakable.
Changes in Your Body
Many of the rough first-trimester symptoms, like nausea and extreme fatigue, tend to ease up early in the second trimester. In their place, a different set of changes takes over as your uterus expands.
Round ligament pain is common. It shows up as a sharp or dull ache on one or both sides of your lower abdomen, caused by the ligaments supporting your uterus stretching to accommodate growth. Stretch marks may start appearing on your belly, breasts, or thighs. Some women develop brownish patches on their face, sometimes called the “mask of pregnancy,” caused by increased pigment production. The skin around your nipples may darken as well. Later in the trimester, your feet and ankles may begin to swell, especially by the end of the day.
Key Appointments and Screenings
Two important medical milestones fall squarely in the second trimester. The anatomy scan, a detailed ultrasound that checks your baby’s organs, bones, and growth, is typically scheduled between weeks 18 and 22. This is often the appointment where parents learn the baby’s sex if they choose to find out. The sonographer examines the heart, brain, spine, kidneys, and other structures to check that everything is developing normally.
Between weeks 24 and 28, most pregnant women undergo a glucose screening test for gestational diabetes. This involves drinking a sugary solution and having your blood drawn about an hour later. If your blood sugar comes back above a certain threshold, a longer follow-up test confirms or rules out the diagnosis. Women with higher risk factors may be screened earlier.
Weight Gain During the Second Trimester
Weight gain typically picks up during these weeks after a relatively modest increase in the first trimester. The CDC recommends a total pregnancy gain of 25 to 35 pounds for someone who starts at a normal BMI (18.5 to 24.9). A large share of that total accumulates in the second and third trimesters, roughly a pound per week for most women. The targets shift if your starting weight is higher or lower: the range drops to 15 to 25 pounds for those beginning in the overweight category and rises to 28 to 40 pounds for those who are underweight at conception.