The second trimester of pregnancy spans months four, five, and six. In precise clinical terms, it runs from week 14 through week 27, covering roughly the middle third of a 40-week pregnancy. For most people, this stretch feels noticeably different from the first trimester, with morning sickness fading and energy returning.
How Weeks Map to Months
Pregnancy math can be confusing because calendar months and gestational weeks don’t line up neatly. A pregnancy month isn’t exactly four weeks, and doctors track progress by weeks rather than months. Here’s how the second trimester breaks down:
- Month 4: Weeks 14 through 17
- Month 5: Weeks 18 through 21
- Month 6: Weeks 22 through 27
The American College of Obstetricians and Gynecologists defines the second trimester as 14 weeks and 0 days through 27 weeks and 6 days. After that, you’re in the third trimester. If someone asks how far along you are, giving the week number is more precise than the month, which is why your provider will almost always reference weeks.
Why the Second Trimester Feels Different
Many people call months four through six the “honeymoon trimester,” and there’s a real physiological basis for that. The hormone surges that cause first-trimester nausea and fatigue begin to level off. You may feel less tired and notice a genuine boost in energy. That doesn’t mean the second trimester is symptom-free, but the symptoms shift.
Hormonal changes increase the number of pigment-producing cells in your skin, which can cause brown, tan, or gray patches on your face (sometimes called melasma) and a dark vertical line down the center of your belly known as linea nigra. Stretch marks may appear on your belly, breasts, buttocks, or thighs as your body expands. Some people also notice tiny spider veins on the face and legs.
Round ligament pain is another common second-trimester experience. As your uterus grows, the ligaments supporting it stretch, causing sharp or dull aches on one or both sides of your lower abdomen, especially when you change positions quickly.
How Your Baby Grows During These Months
The second trimester is a period of rapid growth and development. Your baby enters it roughly the size of a lemon and leaves it close to the length of a cucumber. By week 20, the midpoint, the baby is about 6⅓ inches long from crown to rump and weighs around 11 ounces. Organs are maturing, facial features are becoming more defined, and the skeleton is hardening from soft cartilage into bone.
Somewhere between weeks 16 and 22, most people feel their baby move for the first time. This is called quickening, and first-time parents tend to notice it later in that range. Early movements feel like flutters or bubbles rather than kicks. By the end of the second trimester, those movements become unmistakable and more regular.
Key Tests and Screenings
The biggest appointment of the second trimester is the anatomy scan, an ultrasound typically done around week 20. This isn’t just about finding out the sex of the baby. The sonographer takes detailed measurements of the heart, brain, spine, kidneys, lungs, stomach, intestines, and limbs. They check individual fingers and toes, examine facial structures like the lips and nose, record the heart rate, and assess the placenta’s position, the umbilical cord’s blood flow, and the amount of amniotic fluid. It’s the most comprehensive structural check your baby gets before birth.
Between weeks 24 and 28, you’ll be offered a glucose screening test for gestational diabetes. This involves drinking a sugary solution and having your blood drawn an hour later to see how your body processes the sugar. If results come back elevated, a longer follow-up test confirms whether gestational diabetes is present. This screening is routine for all pregnancies regardless of risk factors.
Weight Gain and Physical Activity
If you were at a healthy weight before pregnancy, the general guideline is to gain between half a pound and one pound per week during the second and third trimesters. That pace supports your baby’s growth without adding unnecessary strain. Your provider will adjust that target based on your starting weight and individual circumstances.
Exercise remains safe and beneficial for most people throughout the second trimester. Walking, swimming, prenatal yoga, and moderate-intensity workouts all support cardiovascular health and can reduce common discomforts like back pain and swelling. The main change to be aware of is your sleep and resting position. Lying flat on your back for extended periods puts pressure on a major vein that returns blood from your lower body to your heart, which can cause dizziness and reduce blood flow to the baby. Sleeping on your side, particularly your left side, improves circulation. A pillow between your knees or behind your back can make this position more comfortable as your belly grows.