The second trimester runs from week 14 through week 27 of pregnancy. More precisely, the American College of Obstetricians and Gynecologists defines it as 14 weeks and 0 days through 27 weeks and 6 days. If you’ve just finished week 13, you’re crossing the threshold into what many people call the most comfortable stretch of pregnancy.
Why Sources Sometimes Disagree
You may see some pregnancy apps or websites say the second trimester starts at week 12 or week 13 instead of week 14. This is because pregnancy is divided into three roughly equal blocks of about 13 weeks each, and different organizations round the boundaries slightly differently. The standard clinical definition from ACOG places the start firmly at week 14. If your provider mentions a different week, they’re likely using a simplified rounding, not a different medical standard.
What Changes for You at the Start
The shift into the second trimester often brings noticeable relief. Morning sickness typically eases, and the deep fatigue and breast tenderness from the first trimester usually let up. These improvements happen because levels of the hormone hCG (the one responsible for that positive pregnancy test) drop, while your body adjusts to its new levels of estrogen and progesterone.
That said, new discomforts replace old ones. Round ligament pain is one of the most common. Two rope-like bands of tissue, each about 10 to 12 centimeters long, connect your uterus to your lower abdominal wall through the groin. As your uterus grows, these ligaments stretch and widen, which can cause sharp, stabbing sensations or cramp-like aches in your lower pelvis or groin. The pain usually lasts only seconds or minutes, and it’s often triggered by sudden movements like standing up quickly, coughing, or rolling over in bed.
How Your Baby Develops Week by Week
The second trimester is described as a period of rapid growth and development, and the changes are dramatic. Here’s a rough timeline of key milestones:
- Week 14: Red blood cells begin forming in the spleen.
- Week 16: The eyes can move slowly, and the ears are nearly in their final position.
- Week 18: The digestive system starts working, and your baby may begin to hear sounds.
- Week 19: Your baby starts releasing urine, which now makes up most of the amniotic fluid.
- Week 20: You may feel your baby move for the first time, sometimes called quickening. This is the halfway point of pregnancy.
- Week 21: The sucking reflex develops, so thumb-sucking becomes possible.
- Week 22: Reproductive organs are forming. In males, the testes begin descending into the scrotum. In females, the uterus, ovaries, and vagina are in place.
- Week 23: The lungs start producing surfactant, a substance that will eventually allow the air sacs to inflate and stay open after birth. Rapid eye movements begin.
- Week 25: Your baby may respond to familiar sounds, including your voice.
- Week 26: The eyes are fully developed but likely won’t open for another two weeks.
- Week 27: The nervous system continues to mature as the trimester wraps up.
Key Appointments and Tests
The second trimester includes a few important prenatal screenings. The mid-pregnancy anatomy ultrasound, often called the “20-week scan,” typically happens between weeks 18 and 22. This is the detailed ultrasound where a technician checks your baby’s organs, limbs, and growth, and it’s also when many parents find out the sex.
Between weeks 24 and 28, you’ll have blood work to check your iron levels and screen for gestational diabetes. The glucose screening involves drinking a sugary solution and having your blood drawn afterward. If the initial result is elevated, a longer follow-up test confirms or rules out the diagnosis.
Nutrition and Weight Gain
Your calorie needs increase modestly in the second trimester. The CDC recommends adding about 340 extra calories per day, roughly equivalent to a cup of yogurt with some fruit and nuts. Total weight gain across the entire pregnancy depends on your pre-pregnancy BMI:
- Underweight (BMI under 18.5): 28 to 40 pounds total
- Normal weight (BMI 18.5 to 24.9): 25 to 35 pounds total
- Overweight (BMI 25.0 to 29.9): 15 to 25 pounds total
- Obese (BMI 30.0 to 39.9): 11 to 20 pounds total
Most of this weight gain happens during the second and third trimesters, so you can expect the scale to start moving more noticeably now than it did in the first trimester.
Warning Signs to Take Seriously
While the second trimester is generally the most comfortable phase, some symptoms require immediate medical attention. Contact your provider or go to the emergency room if you experience any of the following: a severe headache that won’t go away or comes with blurred vision, a fever of 100.4°F or higher, sudden swelling of your hands or face, vaginal bleeding beyond light spotting, leaking fluid, sharp belly pain that worsens over time, or a noticeable decrease in your baby’s movements once you’ve started feeling them regularly. Swelling, redness, or pain in one leg (especially the calf) can signal a blood clot and also needs urgent evaluation.
Shortness of breath that comes on suddenly, chest tightness, or a racing heartbeat are other red flags. These symptoms are rare, but recognizing them early makes a significant difference in outcomes.