The second trimester of pregnancy runs from 14 weeks and 0 days to 27 weeks and 6 days, as defined by the American College of Obstetricians and Gynecologists (ACOG). That puts it squarely in the middle third of a full 40-week pregnancy, starting once you finish week 13 and ending as you complete week 27. This is the period often called the “honeymoon phase” because early pregnancy nausea tends to fade and the baby isn’t yet large enough to cause significant discomfort.
Why Trimester Dates Can Seem Confusing
You’ll find slight variations depending on where you look. Some sources say the second trimester starts at week 13, others at week 14. The difference comes down to whether a source counts the completion of week 13 as the start (which is the same as 14 weeks and 0 days) or rounds down. ACOG’s clinical definition is the most precise: your second trimester begins at exactly 14 weeks 0 days and ends at 27 weeks 6 days. All pregnancy weeks are counted from the first day of your last menstrual period, not from conception, which is why the timeline can feel about two weeks “off” from when you actually became pregnant.
What Happens to Your Baby
The first trimester is when all the major organs form. The second trimester is when everything grows rapidly and starts to function. By around 18 weeks, your baby’s ears begin to stand out on the head and may start picking up sound. Around 20 weeks, you might feel your baby move for the first time, a milestone called quickening. By 21 weeks, a fine layer of downy hair called lanugo covers the entire body, helping regulate temperature.
Your baby goes from roughly the size of a lemon at 14 weeks to about 14 inches long and over 2 pounds by the end of week 27. The lungs, brain, and digestive system are all maturing throughout this period, though they won’t be fully ready for life outside the womb until later in the third trimester.
How Your Body Changes
Most people notice a significant energy boost compared to the exhaustion of the first trimester. Nausea typically eases, and many describe this stretch as the most comfortable part of pregnancy.
Physically, the changes become visible. Your bump usually becomes noticeable between 16 and 20 weeks if this is your first pregnancy. If you’ve been pregnant before, you may show earlier, sometimes in the first trimester. Your breasts continue to grow, and your uterus expands enough that you’ll likely need to transition into maternity clothing during this period.
Several other changes are common:
- Round ligament pain. Sharp or aching pain on the sides of your lower belly as the ligaments supporting your uterus stretch.
- Skin changes. A dark line down the center of your belly (linea nigra), darkening of the skin around your nipples, and brownish or grayish patches on your face caused by increased pigment production. Stretch marks may appear on your belly, breasts, thighs, and buttocks. Small spider veins can show up on your face and legs.
- Back pain. Hormonal shifts loosen your joints while your growing uterus shifts your center of gravity forward, putting extra strain on your lower back.
- Braxton Hicks contractions. Mild, irregular tightening sensations in your belly. These are not true labor contractions and typically come and go without a pattern.
Key Tests and Appointments
The second trimester includes some of the most significant prenatal screenings. Genetic blood tests can screen for conditions like Down syndrome and spina bifida, and these are typically offered in the earlier part of the trimester.
The biggest appointment for most people is the 20-week anatomy scan. This detailed ultrasound checks your baby from head to toe: heart, brain, spine, kidneys, bladder, lungs, stomach, intestines, limbs, and even individual fingers and toes. The technician also records the heart rate, checks blood flow through the umbilical cord, measures amniotic fluid levels, and evaluates the position of the placenta and your cervix. This is also when you can find out your baby’s sex if you want to know.
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, then having your blood drawn to see how your body processes the sugar.
Warning Signs That Need Immediate Attention
While the second trimester is generally the most comfortable stretch of pregnancy, certain symptoms warrant urgent medical care at any point. Vaginal bleeding that’s heavier than light spotting, fluid leaking from the vagina, or foul-smelling discharge all need immediate evaluation. The same applies to severe belly pain that comes on suddenly or worsens over time, and to a noticeable decrease or stop in your baby’s movements once you’ve begun feeling them regularly.
Other red flags include a persistent or worsening headache, vision changes, extreme swelling of your hands or face (not the mild puffiness that’s normal in pregnancy, but swelling severe enough to make it hard to bend your fingers or open your eyes fully), sudden shortness of breath, chest pain, and a fever of 100.4°F or higher. Severe swelling, redness, or pain in one leg or arm can signal a blood clot and also needs prompt attention.