The second trimester of pregnancy lasts 15 weeks, running from week 13 through the end of week 27. It covers months four, five, and six and is often called the “honeymoon phase” of pregnancy because many of the rough early symptoms ease up while the belly hasn’t yet grown large enough to cause significant discomfort.
When It Starts and Ends
The second trimester begins at the start of week 13 and wraps up at the end of week 27. This places it squarely in the middle third of a full-term pregnancy (which typically runs about 40 weeks). After week 27, you enter the third trimester, which continues until delivery.
If you’re trying to map weeks to months, the math isn’t perfectly clean because calendar months aren’t exactly four weeks long. Roughly, week 13 falls near the start of month four, and week 27 falls near the end of month six.
Why It Often Feels Better Than the First Trimester
For many people, the second trimester brings a noticeable energy boost. The nausea and fatigue that dominated the first 12 weeks typically fade. You may feel less tired overall and find that your appetite returns to something closer to normal. At the same time, the baby isn’t large enough yet to press on your bladder, ribs, or lungs the way it will later, so day-to-day comfort tends to be at its peak.
That said, the second trimester introduces its own set of changes. Hormonal shifts increase pigment-producing cells in the skin, which can cause brown, tan, or gray patches on the face (a condition called melasma) and a dark vertical line down the belly known as linea nigra. Stretch marks may appear along the belly, breasts, buttocks, or thighs as skin stretches to accommodate a growing uterus. Some people also notice tiny spider veins showing up on the face and legs.
What’s Happening With the Baby
The second trimester is when a fetus transforms from a small, mostly formed shape into something that looks and moves like a baby. At week 13, bones are beginning to harden. Over the following weeks, the baby develops the ability to move, swallow, hear sounds, and respond to light. Most people feel their baby’s first movements, often described as flutters or bubbles, somewhere between weeks 16 and 22.
By the end of week 27, the baby has grown dramatically. The organs are increasingly functional, the lungs are developing the structures they’ll need to breathe air, and the baby has regular cycles of sleeping and waking. This growth is part of why the second trimester is such a critical window for prenatal screening.
Weight Gain During These Weeks
If you were at a healthy weight before pregnancy, the general recommendation from the American College of Obstetricians and Gynecologists is to gain between half a pound and one pound per week during the second and third trimesters. That pace feels slow on a weekly basis but adds up to meaningful, healthy weight gain over 15 weeks. The target range shifts if your pre-pregnancy BMI was higher or lower, so your specific number may differ.
Key Tests and Screenings
The second trimester is when several important prenatal screenings take place. The anatomy ultrasound, usually scheduled between weeks 18 and 22, gives a detailed look at the baby’s organs, bones, and growth. It’s also when many parents learn the baby’s sex, if they choose to.
A glucose screening test is typically offered during the later part of this trimester or early in the third. It measures blood sugar levels to check for gestational diabetes, a condition that can develop during pregnancy even in people who have never had blood sugar problems before. A higher-than-normal result on the initial screen leads to a longer follow-up test to confirm or rule out a diagnosis.
Warning Signs to Watch For
While the second trimester is generally the most comfortable stretch of pregnancy, certain symptoms at any point require immediate attention. These include vaginal bleeding that goes beyond light spotting, a sudden gush or steady leak of fluid, and a noticeable decrease in fetal movement once you’ve started feeling it regularly.
Other urgent warning signs: a headache that won’t go away or feels like the worst you’ve ever had, especially with blurred vision or dizziness. Significant swelling of the hands or face that makes it hard to bend your fingers or fully open your eyes. Sharp or persistent abdominal pain. Chest tightness, a racing heartbeat, or trouble breathing. A fever of 100.4°F or higher. Severe swelling, redness, or pain concentrated in one leg, which could signal a blood clot.
The CDC also flags mental health changes as urgent: feeling hopeless, out of control, or having thoughts of harming yourself or your baby. These symptoms deserve the same immediate response as any physical warning sign.