The second trimester of pregnancy lasts about 15 weeks, running from week 13 through the end of week 27. That’s roughly the fourth, fifth, and sixth months of pregnancy. The American College of Obstetricians and Gynecologists defines it slightly more precisely as 14 weeks and 0 days through 27 weeks and 6 days, though most providers and hospitals use weeks 13 to 27 as the working range.
Why the Start Date Varies Slightly
You’ll notice some sources say the second trimester starts at week 13 and others say week 14. This isn’t a real disagreement. ACOG uses the more precise “14 weeks and 0 days” cutoff, while most clinical resources round to week 13 for simplicity. The difference is a matter of days, not a medical distinction. If you’re trying to figure out where you are, just know that once you’ve completed your 13th week, you’re solidly in the second trimester.
What Happens During These 15 Weeks
The second trimester is often called the most comfortable stretch of pregnancy, and there’s a reason for that. First-trimester nausea typically fades, energy returns, and the pregnancy becomes visible without yet being physically burdensome. Meanwhile, the fetus is growing rapidly. Bones begin to harden around week 13, and by week 27 the baby is roughly 14 inches long and weighs about 2 pounds.
One of the milestones many people look forward to is feeling the baby move for the first time, called quickening. If you’ve been pregnant before, you may notice it as early as 16 weeks. First-time pregnancies typically don’t produce noticeable movement until around 20 weeks. Early movements often feel like flutters or bubbles rather than kicks.
Key Screenings and Tests
Two major medical checkpoints fall in the second trimester. The first is the anatomy scan, an ultrasound typically done around 20 weeks. During this appointment, a sonographer takes detailed images and measurements of the baby’s heart, brain, spine, kidneys, lungs, limbs, and facial features. They also check the umbilical cord’s blood flow, the placenta’s position, amniotic fluid levels, and the length of your cervix. This is the scan where many people learn the baby’s sex, if they want to know.
The second major test is the glucose screening for gestational diabetes, which happens between 24 and 28 weeks. You’ll drink a sugary solution and have your blood drawn an hour later. A result at or below 140 mg/dL is typically considered normal. If the number comes back higher, a longer follow-up test is used to confirm or rule out gestational diabetes.
Physical Changes to Expect
Your belly becomes noticeably larger during these weeks, and that growth brings some new sensations. Round ligament pain is one of the most common. Two ligaments support your uterus like suspension cables, and as the uterus expands, these ligaments stretch and thicken. Quick movements, sneezing, coughing, or even laughing can cause a sudden, sharp pull on one or both sides of your lower abdomen. It’s harmless but can be startling.
If round ligament pain bothers you, a few strategies help: wear a supportive belly band, flex your hips before you sneeze or cough, move slowly when changing positions, and try a daily stretch on your hands and knees with your head lowered toward the floor and your hips raised. A warm (not hot) bath can also ease the tension. Acetaminophen is generally considered safe for more intense discomfort.
Weight gain picks up during the second trimester compared to the first. Total recommended gain for the entire pregnancy depends on your pre-pregnancy BMI. For someone who started at a normal weight (BMI 18.5 to 24.9), the target is 25 to 35 pounds total. For someone who started in the overweight range, it’s 15 to 25 pounds. Much of that gain accelerates in the second and third trimesters as the baby, placenta, and amniotic fluid volume increase.
Sleep Position Changes
By mid-second trimester, sleeping on your back can start causing problems. The growing uterus presses on the large vein that returns blood from your lower body to your heart, which can reduce blood flow to both you and the baby. Side sleeping is the recommended alternative, with the left side considered ideal because it maximizes blood flow to the placenta and improves kidney function.
If you’re not naturally a side sleeper, pillows make the transition easier. Placing one between your knees and another under your belly creates a slight tilt that takes pressure off your back and hips. A pillow behind your back can keep you from rolling over during the night. Many people find this setup comfortable enough to use through the rest of pregnancy.
How the Trimester Breaks Down by Month
Pregnancy math can be confusing because months and weeks don’t line up neatly. Here’s a rough translation for the second trimester:
- Month 4: Weeks 13 through 16
- Month 5: Weeks 17 through 20
- Month 6: Weeks 21 through 24
- Month 7 (early): Weeks 25 through 27
The tail end of the second trimester overlaps with what people casually call “seven months pregnant.” Once you cross into week 28, you’re in the third trimester, with roughly 12 weeks to go until your due date.