The second trimester of pregnancy spans week 13 through the end of week 27, covering roughly 15 weeks in the middle stretch of pregnancy. For most women, this is the period when early symptoms like nausea and fatigue ease up, energy returns, and the pregnancy becomes physically visible. It’s also when some of the most significant fetal development and important medical screenings take place.
When It Starts and Ends
The second trimester begins around the start of your fourth month of pregnancy (week 13) and lasts through the end of your seventh month (week 27). It falls between the often-difficult first trimester and the physically demanding third trimester, which is why many women describe it as the most comfortable phase of pregnancy. First-trimester symptoms like morning sickness and extreme tiredness tend to fade, while third-trimester discomforts like back pain and difficulty sleeping haven’t yet set in.
How the Baby Grows
Fetal growth during the second trimester is dramatic. At the start (around week 14), the fetus is about 5 inches long and weighs roughly 4 ounces. By the midpoint at week 20, the baby has reached 9 to 10 inches and about 1 pound. By the end of the second trimester at week 27, the fetus measures 14 to 15 inches and weighs between 2 and 3 pounds.
Beyond just getting bigger, the baby develops critical capabilities during these weeks. Bones that were soft cartilage begin to harden starting around week 13. Facial features become more defined, and the baby starts practicing movements like sucking, swallowing, and gripping. Organs continue to mature, with the lungs and digestive system taking shape even though they won’t be fully functional until later.
Feeling the Baby Move
One of the most anticipated milestones of the second trimester is “quickening,” the moment you first feel the baby move. This typically happens between weeks 16 and 20, though the timing depends on whether you’ve been pregnant before. Women who have had a previous pregnancy often notice movement as early as 16 weeks because they recognize the sensation. First-time mothers commonly don’t feel it until closer to 20 weeks. Early movements feel like flutters, bubbles, or a light tapping, and they gradually become stronger and more distinct as the weeks progress.
Changes in Your Body
Your uterus grows rapidly during the second trimester, rising out of the pelvis and becoming visible as a baby bump. This growth triggers some of the most common physical changes of this period.
Round ligament pain is one of the hallmarks. Two thick ligaments run from the front of your uterus down into the groin, and as the uterus expands, these ligaments stretch and widen to support it. That stretching creates an aching or sharp pain, usually on one or both sides of the lower belly. It tends to flare with sudden movements like standing up quickly, laughing, or rolling over in bed. The pain is most common between weeks 14 and 27 because the uterus is growing at its fastest rate during this window.
Other normal changes include skin darkening (particularly a line down the center of the abdomen), breast growth, mild swelling in the feet and ankles, nasal congestion from increased blood flow, and occasional leg cramps. Some women also notice stretch marks appearing as the skin accommodates a growing belly.
Sleep Position Matters
After about 20 weeks, sleeping on your back can become a problem. The growing uterus presses against the large blood vessels running along your spine, reducing blood flow back to your heart. This can cause dizziness, lightheadedness, or a drop in blood pressure. Sleeping on your left side is the standard recommendation from this point forward, as it takes pressure off those vessels and improves circulation to both you and the baby. A pillow between your knees or behind your back can make side sleeping more comfortable.
Key Medical Screenings
The second trimester includes two major screenings that most pregnant women will go through.
The 20-Week Anatomy Scan
Around week 20, you’ll have a detailed ultrasound commonly called the anatomy scan. This is a thorough head-to-toe evaluation of the baby. The sonographer takes pictures and measurements of the heart, brain, spine, kidneys, bladder, lungs, stomach, intestines, arms, legs, hands, feet, fingers, toes, and facial features including the lips, chin, nose, and eyes. They also record the heart rate, check blood flow through the umbilical cord, note the position of the placenta, measure amniotic fluid levels, and evaluate your cervix and uterus. This is often the appointment where you can learn the baby’s sex if you want to know. The scan typically takes 30 to 45 minutes and is one of the most detailed looks at fetal health you’ll get during the entire pregnancy.
Gestational Diabetes Screening
Between weeks 24 and 28, you’ll be screened for gestational diabetes. The standard approach involves drinking a sugary liquid and having your blood drawn about an hour later to see how your body processes the sugar. If your blood glucose comes back at 140 or higher, you’ll need a longer follow-up test that involves fasting overnight and having blood drawn multiple times over several hours. High readings at two or more of those blood draws confirm gestational diabetes. Women who have risk factors like a family history of diabetes or a high pre-pregnancy weight may be tested earlier in pregnancy as well.
Other Medical Considerations
If your blood type is Rh-negative (meaning your blood lacks a specific protein that most people carry), you’ll receive an injection called RhoGAM between weeks 26 and 28. This prevents your immune system from producing antibodies against the baby’s blood cells in cases where the baby is Rh-positive. It’s a routine precaution, given as a single shot, and it protects both the current pregnancy and future ones.
Prenatal visits during the second trimester are generally spaced about four weeks apart. At each visit, your provider will check your blood pressure, measure your growing uterus, and listen to the baby’s heartbeat. Urine tests for protein and sugar are also common at each appointment. For many women, the second trimester is a stretch of relative calm between the anxiety of early pregnancy and the anticipation of delivery, making it a good time to prepare practically for the baby’s arrival.