The second trimester runs from week 13 through the end of week 27 and is often considered the most comfortable stretch of pregnancy. First-trimester nausea and fatigue typically fade, energy returns, and the baby undergoes dramatic growth, developing from a lime-sized fetus into one that can hear your voice and respond to light. Here’s what’s happening to both your body and your baby during these 15 weeks.
How Your Baby Grows
At the start of the second trimester, your baby’s major organs are already formed. The work now shifts to growing larger and refining those systems. By week 20, the midpoint of pregnancy, the baby measures roughly 6⅓ inches from crown to rump and weighs about 11 ounces. By the end of week 27, that weight will have more than tripled.
Several key milestones happen during this window. Bones begin to harden, replacing the soft cartilage that made up the early skeleton. Fingerprints form. The skin, initially translucent, starts building layers of fat underneath. The baby begins swallowing amniotic fluid and producing urine, which helps the kidneys mature. Taste buds develop, and the baby can detect flavors from the foods you eat that pass into the amniotic fluid.
Hearing comes online around weeks 18 to 22, so by the middle of the second trimester your baby can pick up sounds: your heartbeat, your digestive system, and eventually external voices and music. The eyes, which have been fused shut, begin to open toward the end of this trimester, and the baby starts responding to bright light shone against your belly. The lungs are also growing, but they won’t produce enough of the substance that keeps air sacs open (called surfactant) to support breathing outside the womb until later in the third trimester.
Feeling Your Baby Move
One of the most anticipated moments of the second trimester is quickening, the first time you feel your baby move. This typically happens between 16 and 20 weeks, though the timing varies. If you’ve been pregnant before, you may notice flutters as early as 16 weeks because you recognize the sensation. First-time mothers often don’t feel distinct movement until closer to 20 weeks. Early movements feel like bubbles, light taps, or a fluttering sensation that’s easy to mistake for gas. Over the following weeks, those subtle flutters turn into unmistakable kicks and rolls.
Changes in Your Body
Your uterus expands significantly during the second trimester, rising above the pelvic bone and becoming visible as a growing belly. This is when most people start “showing.” That expansion comes with a cascade of physical changes, some welcome and some less so.
Many women notice their skin changing. A dark line called the linea nigra may appear running down the center of the belly. Patches of darker skin can develop on the face, sometimes called the “mask of pregnancy.” Stretch marks may begin forming on the abdomen, breasts, or thighs as skin stretches to keep up with growth. Breast tenderness from the first trimester often eases, but your breasts will continue to grow, and some women begin producing small amounts of early milk (colostrum) by the end of this trimester.
Nasal congestion and occasional nosebleeds are common because the increased blood volume in your body causes the small blood vessels in your nose to swell. You may also notice your gums bleeding more easily when brushing your teeth, for the same reason.
Round Ligament Pain
As your uterus grows, two thick bands of tissue called the round ligaments stretch to support it. That stretching can cause sharp, stabbing pain or a dull ache in the lower abdomen or groin area, usually triggered by sudden movements like standing up quickly, coughing, or rolling over in bed. Round ligament pain is one of the most common complaints of the second trimester, typically appearing between weeks 14 and 27. It usually lasts only a few seconds to a few minutes and occurs on one or both sides of the pelvis. Moving more slowly during position changes and supporting your belly when you sneeze or cough can reduce the intensity.
How Hormones Affect Your Joints and Posture
A hormone called relaxin loosens the ligaments and muscles around your pelvis, back, and abdomen throughout pregnancy, peaking during the second trimester. This loosening helps your body accommodate a growing uterus and prepares the pelvis for delivery, but it also has side effects. Your lower back and hips may feel unstable or achy. Posture often shifts as your center of gravity moves forward, which can lead to back pain. Relaxin can also weaken the pelvic floor, sometimes affecting bladder control, so you may notice occasional leaking when you laugh, sneeze, or exercise. A supportive belly band can help with posture and take pressure off your lower back.
The Anatomy Scan
The biggest prenatal appointment of the second trimester is the anatomy scan, an ultrasound typically done around week 20. This is a detailed head-to-toe evaluation of your baby’s development. The sonographer measures the head circumference, the width of the skull, the length of the thigh bone, and the circumference of the abdomen. These measurements help confirm your due date and track growth.
Beyond size, the scan checks the structure of the brain, looking at fluid-filled spaces in the brain that should measure under 10 millimeters and the cerebellum at the back of the skull. The face is examined for normal eye spacing, the presence of a nasal bone, and proper formation of the lips. The heart is assessed for correct positioning on the left side of the chest, a normal rate of 120 to 160 beats per minute, and the presence of all four chambers and three major vessels. The sonographer also checks the stomach, kidneys, spine, and limbs. If you want to know your baby’s sex, this is usually the appointment where it’s visible.
The anatomy scan also evaluates the placenta’s position and the amount of amniotic fluid. Most findings are reassuring, but if something looks unusual, your provider may recommend a follow-up scan or additional testing.
Gestational Diabetes Screening
Between weeks 24 and 28, you’ll be screened for gestational diabetes. The most common approach is a glucose challenge test: you drink a sugary solution, then have your blood drawn one hour later. If your blood sugar comes back elevated, you’ll take a longer follow-up test that involves fasting overnight and having your blood drawn at one, two, and three hours after drinking a higher concentration glucose solution. Gestational diabetes is diagnosed if two or more of those readings exceed specific thresholds (for example, a fasting level at or above 95 mg/dL, or a one-hour reading at or above 180 mg/dL).
Being diagnosed with gestational diabetes doesn’t mean you did anything wrong. It develops because pregnancy hormones can interfere with how your body uses insulin. Most women manage it with dietary changes and blood sugar monitoring, and it typically resolves after delivery.
Warning Signs to Watch For
While the second trimester is generally the smoothest phase of pregnancy, certain symptoms need prompt attention because they can signal preterm labor or other complications. Contact your provider if you experience regular or frequent tightening in your belly (contractions), a persistent dull ache in your lower back, pressure in your pelvis or lower abdomen, vaginal spotting or bleeding, or a gush or steady trickle of fluid from the vagina. Mild, occasional cramping is normal as your uterus grows, but contractions that come at regular intervals before 37 weeks are not.
Severe headaches, sudden swelling in the face or hands, or visual disturbances like seeing spots can point to a blood pressure condition called preeclampsia, which requires immediate evaluation. Decreased fetal movement after you’ve established a pattern of regular kicks (usually by the later weeks of this trimester) is also worth reporting.