The second trimester of pregnancy spans weeks 13 through 27, giving you about 15 weeks in this middle stretch. The exact starting point varies slightly depending on the source: the Cleveland Clinic places it at week 13, while the American College of Obstetricians and Gynecologists defines it as beginning at 14 weeks and 0 days and running through 27 weeks and 6 days. Either way, you’ll spend roughly the entire fourth, fifth, and sixth months of pregnancy in the second trimester.
Why the Start Date Varies by One Week
You’ll notice that some pregnancy apps and websites say week 13, while your OB’s office might say week 14. This comes down to whether a source rounds to the nearest full week or uses the precise clinical cutoff. ACOG, the professional organization that sets most U.S. obstetric standards, draws the line at exactly 14 weeks and 0 days. Many hospitals and popular health resources round down to week 13 for simplicity. The difference is minor, and your care won’t change based on which definition you follow.
What Your Body Feels Like
The second trimester is often called the most comfortable stretch of pregnancy. First-trimester nausea typically fades, and the baby isn’t yet large enough to make breathing or sleeping difficult. That doesn’t mean symptoms disappear entirely.
Your belly and breasts grow noticeably as your uterus expands. Lower back pain is common because shifting hormones loosen the ligaments in your pelvis, and your center of gravity changes as your bump grows. You may also notice skin changes: darker patches on your face (called melasma), a dark vertical line running down your belly, and stretch marks appearing on your stomach, breasts, thighs, or buttocks. Stuffy noses and nosebleeds happen because your body is producing significantly more blood, which swells the tissue inside your nasal passages.
Braxton Hicks contractions can start during this trimester. They feel like a mild tightening across your belly that comes and goes, often in the evening or after physical activity. They’re not a sign of labor. Leg cramps, especially at night, are also common, along with occasional dizziness from changes in blood flow.
The highlight for many people is quickening, the moment you first feel the baby move. This typically happens somewhere between weeks 16 and 22, though it can be subtle at first, more like flutters or bubbles than kicks.
How Your Baby Develops From Week 13 to 27
The second trimester is a period of rapid growth and increasingly detailed development. At the start, your baby’s skeleton begins to harden, particularly the skull and the long bones in the arms and legs. By week 15, a scalp hair pattern is forming. By week 16, the eyes can move slowly and the ears are nearly in their final position.
Around week 18, the ears start standing out from the head, and your baby may begin to hear sounds for the first time. The digestive system starts working, and by week 19, the baby is releasing urine that makes up most of the amniotic fluid. A protective, greasy coating called vernix starts covering the skin around this time.
By week 21, a fine layer of downy hair covers the entire body, and the sucking reflex develops enough that your baby may suck a thumb. At week 22, eyebrows and hair become visible, and the reproductive organs are forming. Week 23 brings the beginning of rapid eye movements during sleep, and ridges form on the palms and soles that will become unique fingerprints and footprints. The lungs start producing a substance that will eventually allow them to inflate with air after birth.
By week 25, your baby may respond to familiar sounds, including your voice. Eyebrows and eyelashes are fully formed by week 26, though the eyes typically stay closed for another couple of weeks. At week 27, the last week of the trimester, the nervous system is continuing to mature.
Key Screenings During the Second Trimester
Two major tests are scheduled during this stretch. The anatomy scan, sometimes called the 20-week ultrasound, takes place between 18 and 22 weeks. This is the detailed ultrasound where a technician checks the baby’s organs, limbs, brain, heart, and spine. It’s also often the appointment where you can learn the sex if you want to.
The glucose screening test for gestational diabetes is recommended between 24 and 28 weeks. You’ll drink a sugary liquid and have your blood drawn about an hour later to see how your body processes the sugar. If your results come back high, you’ll take a longer follow-up test to confirm or rule out gestational diabetes.
Warning Signs That Need Immediate Attention
Most second-trimester symptoms are uncomfortable but harmless. A few, however, signal something serious. Vaginal bleeding that goes beyond light spotting, fluid leaking from the vagina, or foul-smelling discharge all warrant immediate medical care. Extreme swelling of your hands or face, the kind where you can’t bend your fingers or your eyes look puffy, is different from the mild swelling that’s normal in pregnancy and can be a sign of a dangerous blood pressure condition.
Sudden pain, redness, or swelling in one leg, especially in the calf, can indicate a blood clot and needs prompt evaluation. These symptoms are uncommon, but recognizing them quickly makes a real difference in outcomes.