The second trimester of pregnancy spans weeks 13 through 27, covering months four, five, and six. It’s often called the most comfortable phase of pregnancy because the nausea and fatigue of the first trimester typically fade, while the physical demands of the third trimester haven’t yet set in. But a lot is happening during these 15 weeks: the fetus grows from roughly the size of a lemon to over a foot long, major prenatal screenings take place, and your body undergoes visible changes that go well beyond a growing belly.
Why You Start Feeling Better
The shift in how you feel around week 13 has a hormonal explanation. Levels of human chorionic gonadotropin, the hormone largely responsible for first-trimester nausea, drop significantly. Meanwhile, your body adjusts to the rising levels of estrogen and progesterone that have been climbing since conception. The result for most people is a noticeable boost in energy and appetite. Morning sickness either disappears or becomes much less frequent.
That said, estrogen and progesterone are still doing plenty. The increased blood flow and hormone levels affect mucous membranes throughout your body. Your nose may become congested or prone to nosebleeds. Your gums can become spongier and bleed more easily when you brush. These are normal, if annoying, side effects that tend to resolve after delivery.
How Your Body Changes
The most obvious change is your belly. The uterus expands significantly during these weeks, rising above the pelvic bone and becoming visible to others. That growth stretches the round ligaments, two cord-like structures on either side of the uterus that help support it. As they get longer and wider, sudden movements like standing up quickly, coughing, or rolling over in bed can cause a sharp, brief pain in the lower abdomen or groin. This is called round ligament pain, and while it can be startling, it’s one of the most common second-trimester complaints and is harmless.
Other changes you may notice include darkening skin along the midline of your abdomen (the linea nigra), patches of darker pigmentation on the face, and stretch marks as your skin accommodates rapid growth. Breast tenderness from the first trimester usually eases, though your breasts continue to grow. By mid-second trimester, some people begin producing colostrum, an early form of breast milk.
Fetal Growth Week by Week
Fetal development accelerates dramatically during these weeks. By month four, the fetus has eyelids, eyebrows, eyelashes, nails, and hair. Facial features become distinct enough to see on an ultrasound. The skeletal system hardens from soft cartilage into bone, and the nervous system matures rapidly.
By week 20, the midpoint of pregnancy, the fetus measures about 6⅓ inches from crown to rump and weighs roughly 11 ounces (320 grams). That’s about the size of a banana. Movements become strong enough to feel, a milestone often called “quickening.” First-time parents typically notice it between weeks 18 and 22, while those who’ve been pregnant before may recognize it a few weeks earlier.
In the final weeks of the second trimester, the fetus can hear sounds from outside the uterus, including your voice. The lungs are developing but aren’t yet mature enough to function independently. Fat begins to accumulate under the skin, and the fetus starts cycling between periods of sleep and wakefulness.
The Anatomy Scan
The biggest prenatal appointment of the second trimester is the anatomy scan, a detailed ultrasound typically performed between weeks 18 and 22. This isn’t a quick check. The sonographer systematically evaluates the fetus from head to toe: the shape and integrity of the skull, the brain’s structures, the face and upper lip, the spine (both lengthwise and in cross-section), and the heart’s chambers and outflow tracts. They also examine the lungs, diaphragm, stomach, liver, kidneys, bladder, abdominal wall, and all four limbs, including hands and feet.
Several measurements are taken during this scan, including the head circumference, abdominal circumference, and femur length. Together, these help confirm gestational age and assess whether the fetus is growing on track. This is also when many parents learn the sex, if they want to know. If the sonographer can’t get a clear view of a particular structure, you may be asked to come back for a follow-up scan. That alone isn’t a reason to worry; fetal position sometimes makes certain angles difficult.
Glucose Screening
Between weeks 24 and 28, most pregnant people undergo a glucose screening test to check for gestational diabetes, a condition where blood sugar levels become elevated during pregnancy. The standard screening involves drinking a sugary solution and having your blood drawn one hour later. A result at or below 140 mg/dL is considered normal.
If your result comes back above that threshold, it doesn’t mean you have gestational diabetes. It means you’ll take a longer, more detailed test. In the one-step version, you fast overnight and then have your blood drawn at fasting, one hour, and two hours after drinking a glucose solution. Abnormal values are a fasting level of 92 mg/dL or above, a one-hour level of 180 mg/dL or above, or a two-hour level of 153 mg/dL or above. Most people who get flagged on the initial screening pass the follow-up test.
Fetal Viability at the End of the Second Trimester
One of the most significant thresholds in pregnancy falls near the end of the second trimester. The periviable period, weeks 20 through 25, is when survival outside the uterus becomes theoretically possible but remains extremely uncertain. Deliveries before 23 weeks carry a survival rate of only 5 to 6 percent, and significant complications affect nearly all survivors. At 23 weeks, survival rates range from 23 to 27 percent. By 24 weeks, that rises to 42 to 59 percent, and at 25 weeks, 67 to 76 percent.
These numbers depend heavily on factors beyond gestational age alone. The fetus’s weight, sex, genetics, the circumstances of delivery, and whether a neonatal intensive care team is immediately available all influence outcomes. According to the American College of Obstetricians and Gynecologists, there is no single test that can definitively determine whether a fetus could survive outside the uterus. Viability is a clinical judgment, not a fixed line.
Warning Signs to Know
While the second trimester is generally the calmest stretch of pregnancy, certain symptoms require prompt attention. Preeclampsia, a condition involving high blood pressure and protein in the urine, can develop after 20 weeks of gestation. Early signs include persistent headaches, visual changes like blurriness or seeing spots, sudden swelling in the face or hands, and upper abdominal pain. Preeclampsia affects both the pregnant person and the fetus and can progress quickly if not managed.
Other warning signs during the second trimester include vaginal bleeding, a gush or steady leak of fluid (which could indicate ruptured membranes), regular contractions before 37 weeks, and a noticeable decrease in fetal movement after you’ve started feeling it consistently. Pain or pressure in the pelvis that feels different from round ligament pain, particularly if it’s constant or accompanied by changes in vaginal discharge, can signal cervical changes that need evaluation.