The second trimester of pregnancy runs from week 13 through week 27, covering months four, five, and six. It sits between the often-exhausting first trimester and the physically demanding third trimester, and many people consider it the most comfortable stretch of pregnancy.
How the Weeks Break Down
Pregnancy is divided into three trimesters, each roughly 13 to 14 weeks long. The first trimester covers weeks 1 through 12, the second trimester spans weeks 13 through 27, and the third trimester begins at week 28 and lasts until delivery. These weeks are counted from the first day of your last menstrual period, not from conception, which is why the numbering can feel slightly confusing. Conception typically happens around week 2, so “week 13 of pregnancy” is actually about 11 weeks after fertilization.
You’ll sometimes see slight variations in where one trimester ends and the next begins. Some providers place the start of the second trimester at week 14, and some define the third trimester as beginning at week 28 or even week 29. The differences are small and mostly matter for scheduling purposes. The 13-to-27 range is the most widely used framework.
What Happens to Your Baby
The second trimester is when your baby shifts from forming basic structures to refining them. By week 18, the ears begin to stand out from the head and your baby may start to hear sounds. Around week 19, a greasy, cheese-like coating called vernix starts forming over the skin. It protects the baby’s delicate skin from chapping and hardening in the amniotic fluid. By week 21, fine downy hair called lanugo covers the entire body, helping the vernix stay in place. The sucking reflex also develops around this time, and your baby may begin sucking a thumb.
Growth accelerates significantly. At the start of the second trimester, your baby is roughly the size of a lemon. By week 27, the baby is closer to the size of a head of cauliflower, weighing around 2 pounds and measuring about 14 inches long. Organs continue maturing throughout this stretch, with the lungs, brain, and digestive system all taking shape.
When You’ll Feel Movement
One of the hallmarks of the second trimester is feeling your baby move for the first time, an experience called quickening. Most people feel it somewhere between weeks 16 and 24. If this is your first pregnancy, you may not notice movement until after week 20. The early sensations are subtle, often described as flutters, bubbles, or a light tapping. They become more distinct and frequent as the weeks progress.
How Your Body Changes
For many people, the second trimester brings a noticeable boost in energy. The nausea and fatigue that dominated the first trimester tend to ease, and you may feel more like yourself again. Your belly starts to visibly grow as the uterus expands above the pelvis, and you’ll likely begin wearing maternity clothes somewhere in this range.
Round ligament pain is common during these weeks. It shows up as a sharp or aching sensation on one or both sides of your lower belly, usually triggered by sudden movements like standing up quickly or rolling over in bed. It’s caused by the ligaments supporting your uterus stretching to accommodate growth. Some people also notice skin changes, including darkening of the line running down the belly and increased pigmentation on the face.
Key Tests and Screenings
Two major screenings happen during the second trimester. The first is the anatomy scan, a detailed ultrasound typically performed around week 20. During this scan, a technician takes pictures and measurements of the baby’s heart, brain, head, spine, kidneys, bladder, arms, legs, hands, feet, lips, face, chest, lungs, stomach, and intestines. They also record the fetal heart rate, check blood flow through the umbilical cord, evaluate the position of the placenta, measure amniotic fluid levels, and examine your cervix. This is often the appointment where you can learn the baby’s sex if you want to know.
The second major screening is the glucose challenge test, which checks for gestational diabetes. It’s performed between weeks 24 and 28 for most pregnancies. You’ll drink a sugary solution and have your blood drawn about an hour later to see how your body processes the sugar. If the results are elevated, a longer follow-up test confirms whether gestational diabetes is present. Your provider may schedule this test earlier if you have risk factors for diabetes or if routine urine tests have shown high glucose levels.
Weight Gain and Nutrition
Steady weight gain becomes more important starting around week 14. If you began pregnancy at a healthy weight, the general guideline is to gain about 1 pound per week through the second and third trimesters. If you started out overweight or obese, the recommendation drops to about half a pound per week during the same period. These are averages, and individual weeks will vary.
Calorie needs increase modestly. Most people need about 300 extra calories per day during the second trimester, bringing the total to roughly 2,200 calories daily for someone who started at a normal weight. That’s not a dramatic increase. It’s the equivalent of a small extra snack, not an additional meal. The quality of those calories matters more than the quantity: iron, calcium, folate, and protein all support the rapid growth happening during these weeks.
Warning Signs to Watch For
While the second trimester is generally the calmest stretch, certain symptoms need immediate attention regardless of what week you’re in. Vaginal bleeding that goes beyond light spotting, fluid leaking from the vagina, severe or sudden belly pain, and a noticeable decrease in fetal movement (once you’ve been feeling it regularly) all warrant a call to your provider right away.
Other red flags include a persistent headache that worsens over time or comes with blurred vision, a fever of 100.4°F or higher, extreme swelling of the hands or face, trouble breathing, chest pain or a racing heartbeat, and severe nausea or vomiting that prevents you from keeping fluids down for more than 8 hours. Swelling, redness, or warmth in one leg, particularly the calf, can signal a blood clot and also requires prompt evaluation.