The second trimester spans weeks 14 through 27 of pregnancy and is often called the most comfortable stretch. Morning sickness typically fades, energy returns, and the baby undergoes dramatic growth, developing from a lemon-sized fetus into a roughly 2-pound infant with working senses. Here’s what’s happening week by week, what changes you’ll feel in your own body, and which screenings to expect.
How Your Baby Develops
At the start of the second trimester, bones in the skull and limbs begin hardening, and red blood cells start forming in the spleen. By week 16, the eyes can move slowly and the ears are nearly in their final position. Two weeks later, the ears stand out from the head and your baby may begin hearing sounds for the first time. The digestive system also kicks into gear around week 18.
Between weeks 19 and 22, a greasy coating called vernix forms over the skin to protect it from the amniotic fluid. The baby begins releasing urine that makes up most of that fluid. The sucking reflex develops around week 21, which is why ultrasounds sometimes catch a baby sucking its thumb. Reproductive organs are also taking shape: in males the testes begin descending, while in females the uterus, ovaries, and vagina are in place by week 22.
The final weeks of the trimester are all about the brain and lungs. Rapid eye movements begin around week 23, the same week the lungs start producing surfactant, a substance that will eventually allow the air sacs to inflate after birth. By week 25, your baby may move in response to familiar sounds like your voice. At week 27, the last week of the second trimester, the nervous system is still maturing, but the baby weighs about 2¼ pounds (1 kg) and measures roughly 13¾ inches (35 cm) long.
When You’ll Feel the Baby Move
The first flutters of fetal movement, called quickening, feel like bubbles, gentle taps, or a rolling sensation low in the abdomen. If you’ve been pregnant before, you may notice it as early as 16 weeks. First-time mothers more commonly feel it around 20 weeks. The difference isn’t because the baby moves later; it’s because experienced mothers recognize the sensation sooner. By the middle of the trimester the movements become unmistakable, and by week 20 the baby cycles between sleeping and waking and can be startled awake by noise or your own movement.
Physical Changes You’ll Notice
Your uterus grows rapidly during these weeks, and that growth pulls on the round ligaments that support it on each side. The result is a sharp or achy pain in the lower belly or groin, especially when you stand up quickly, cough, or roll over in bed. This round ligament pain typically starts around week 14 and can come and go throughout the trimester. It’s one of the most common complaints and is harmless, though it can be startling the first time it happens.
Rising hormone levels also trigger visible skin changes. The placenta produces a hormone that stimulates pigment-producing cells throughout your body. Around week 20, many people notice a dark vertical line running down the center of the abdomen, called the linea nigra. Existing freckles or moles may darken, and some people develop brownish patches on the face. These changes fade after delivery in most cases.
Other common shifts include nasal congestion from increased blood volume, mild swelling in the hands and feet, leg cramps (particularly at night), and lower back pain as your center of gravity shifts forward. Many people also notice their gums bleed more easily during brushing, another effect of higher blood flow.
Nutrition and Weight Gain
Your calorie needs increase modestly in the second trimester. The American College of Obstetricians and Gynecologists recommends about 340 extra calories per day, roughly the equivalent of a cup of yogurt with granola and fruit. The focus isn’t just on quantity. Iron needs climb because your blood volume is expanding, and calcium supports the baby’s rapidly hardening bones. Protein demand also rises to fuel the growth happening in nearly every organ system.
How much weight you should gain overall depends on your pre-pregnancy BMI. For someone who started at a normal weight, the general target is about a pound per week during the second and third trimesters. Gaining significantly more or less than expected is worth discussing at a prenatal visit, since it can signal nutritional gaps or fluid retention.
Key Screenings and Tests
The Anatomy Scan
The biggest appointment of the trimester is the 20-week ultrasound, also called the anatomy scan. A technician takes detailed measurements and images of the baby’s heart, brain, spine, kidneys, bladder, limbs, hands, feet, face, chest, lungs, stomach, and intestines. They also record the heart rate, check blood flow through the umbilical cord, note where the placenta is positioned, measure amniotic fluid volume, and examine your cervix. This is the scan where many parents learn the baby’s sex, though its primary purpose is to confirm that organs are developing normally.
Glucose Screening
Between weeks 24 and 28, you’ll be screened for gestational diabetes. The standard test involves drinking a sweet liquid containing 50 grams of sugar, then having your blood drawn one hour later. A blood sugar reading below 140 mg/dL is considered normal. A result between 140 and 189 mg/dL means you’ll need a longer, three-hour follow-up test to confirm or rule out gestational diabetes. A reading of 190 mg/dL or higher on the initial screen indicates gestational diabetes on its own. Some labs use a slightly lower cutoff of 130 mg/dL, so the threshold your provider uses may vary.
Rh Factor
If your blood type is Rh-negative and the baby’s father is Rh-positive, your immune system could potentially produce antibodies against the baby’s blood cells. To prevent this, an injection of Rh immunoglobulin is given during the second trimester or early third trimester. This is a routine precaution, not a sign that anything is wrong.
Warning Signs to Watch For
Most second-trimester symptoms are uncomfortable but normal. A few, however, deserve prompt attention. Preeclampsia, a condition involving high blood pressure and organ stress, can develop after week 20. Its hallmarks include severe headaches that don’t respond to rest or hydration, vision changes like blurriness or light sensitivity, pain in the upper right abdomen beneath the ribs, sudden swelling in the face and hands, shortness of breath, and nausea or vomiting that appears out of the blue in the second half of pregnancy. Sudden, significant weight gain over just a few days can also be a sign of fluid retention related to preeclampsia.
Other reasons to contact your provider include vaginal bleeding, fluid leaking from the vagina, persistent contractions before 27 weeks, or a noticeable decrease in fetal movement after you’ve been feeling regular kicks. None of these necessarily means something serious is happening, but all warrant a check.