Second Trimester, Week by Week
Pregnancy runs 40 weeks, split into three trimesters, and full term means making it to at least 37 weeks. A baby born earlier than that is considered premature, and premature babies can face real challenges with breathing, digestion, and growth. Pregnancy is counted from the first day of your last period rather than conception, which is why your baby is already considered about two weeks old by the time fertilization actually happens. Our Your Pregnancy, Month by Month guide covers this same stretch broken into monthly chunks if that’s easier to follow.
How Long Is the Second Trimester
Most providers count the second trimester from week 14 through week 27. That’s about 14 weeks, covering months 4 through 6. The cards below start at week 13, since some sources place the line a week earlier. Our page on the trimesters of pregnancy explains why. Read about month 4, month 5, and month 6, or check your exact week with the pregnancy weekly calculator.
Fetal Development
Your baby is now 3 to 4 inches long and weighs just
over an ounce. Bones are starting to harden, especially in the skull and the long bones of the arms and legs, and muscles are lengthening and getting more organized. Some people start feeling the first faint flutters of movement around now, though for a lot of first pregnancies that’s still a few weeks off. Curious what your doctor checks at this stage? Our second trimester testing guide covers it.
Taste buds are forming, and the skin, still thin as parchment, is growing a coat of ultra fine, downy hair called lanugo that mostly disappears before birth. Nutrition matters just as much now as it did earlier, our nutrition guide is worth another look if it’s been a while.
Your baby is around 4 ounces now and roughly 4 and three quarters inches long, and movements are getting more coordinated, small kicks, grasping motions, even the occasional somersault, even if you can’t feel most of it yet.
The circulatory system and urinary tract are both up and running. The lungs are practicing too, moving amniotic fluid in and out, which is how they train for that first real breath after birth.
Your baby is about 5 and a half inches long and weighs around 7 ounces. Ears are starting to stand out from the head, and hearing is coming online, so sounds from outside are starting to register. If your baby cooperates with positioning, an ultrasound around now can often reveal the sex. A protective coating called vernix is starting to form on the skin, and your baby has begun urinating into the amniotic fluid, which is completely normal.
You’ve hit the halfway point. This is often when
“quickening,” the first movements you can actually feel, gets noticed for the first time. Nerve cells for each of the senses, taste, smell, hearing, sight, and touch, are developing into their own specialized areas of the brain, making this a big week for sensory wiring even though your baby is still small and fragile.
Your baby is steadily adding a bit of fat to help with temperature regulation, and the sucking reflex is developing, useful practice for feeding after birth.
Your baby is about 7 and a half inches long and close to a pound. Eyebrows and fine hair are becoming visible, and fingernails now cover the fingertips. Conversations at a normal volume are loud enough to reach your baby in the uterus, so talking, reading, or singing out loud isn’t wasted on an audience that can’t hear you, they likely can.
Your baby is close to a pound and about 8 inches long, proportioned more like a newborn now, just a thinner version since body fat hasn’t filled in yet. Fingerprints and footprints have fully formed, and the lungs are starting to produce surfactant, a substance that helps tiny air sacs stay open. This is roughly the edge of viability, meaning a baby born from this point on has a real chance of survival with intensive neonatal care, though every week further along improves those odds significantly.
Fine hair and a waxy protective coating called vernix
cover your baby’s skin, some of which may still be present at birth and gets absorbed quickly afterward. Your baby is practicing breathing by moving amniotic fluid through developing lungs.
Your baby weighs over a pound and a quarter now, reasonably well proportioned even though body fat and skin are both still thin. The brain is growing fast, and your baby is starting to take up noticeably more room in your uterus, and may respond to familiar sounds like your voice.
Breathing movements continue even though there’s no air in the lungs yet to actually breathe. A fetal brain scan at this stage would show a clear response to touch.
Your baby weighs just over 2 pounds and is about 11 inches long. Eyes that have been fused shut since around week 10 start to open around now, marking the close of the second trimester.
How You May Feel
Nausea often fades, and many people notice more energy and a bigger appetite. Your belly grows, and that can bring some new aches. A sharp pain in your side when you stand up or roll over is common. It’s usually your stretching ligaments. Leg cramps, heartburn, a stuffy nose, bleeding gums, and skin changes are common too.
Your baby’s first movements can feel like flutters or bubbles. First-time moms often notice them around week 20 or a little later. People who’ve been pregnant before may feel them sooner. If you haven’t felt anything and you’re worried, ask your provider at your next visit.
Eating and Weight Gain
The CDC says you need about 340 extra calories a day in the second trimester. That’s about a small snack and a glass of milk, not a second dinner. Total weight gain depends on your weight before pregnancy. For one baby, the CDC suggests 25 to 35 pounds if you started at a healthy weight. It’s 28 to 40 pounds if you started underweight, 15 to 25 if overweight, and 11 to 20 if you have obesity.
Our pregnancy weight gain chart helps you track it.
Tests in the Second Trimester
According to March of Dimes, the quad blood screen is done between weeks 15 and 22. Amniocentesis, a diagnostic test, is usually done at weeks 15 to 20 for those who need it. The anatomy ultrasound happens between weeks 18 and 22. It checks your baby’s growth and organs. It’s also the visit where you can learn your baby’s sex if you’d like to.
Glucose screening comes at weeks 24 to 28. It checks for gestational diabetes, which is common and manageable. Read our guide to gestational diabetes before your test so you know what to expect. The ultrasound page explains what your scans show.
Vaccines to Plan For
The Tdap vaccine protects newborns from whooping cough. It’s recommended in the 27th through 36th week of every pregnancy, preferably early in that window, according to the CDC. That means the window opens at the very end of this trimester.
Advice on flu and COVID-19 shots during pregnancy has been changing. ACOG and the CDC don’t fully match this season. Ask your provider what they recommend for you.
Getting Ready
This is a good time to sign up for a childbirth class and tour your hospital or birth center. Start thinking about who’ll be with you, and read about midwives if you’re still choosing a provider. You can also begin a birth plan. If you work, now is a good time to learn your leave options.
Sleep can get harder as your belly grows. A pillow between your knees or under your belly may help. Many providers suggest lying on your side rather than your back as you get further along. Ask yours what they prefer.
When to Call Your Provider
Call right away, or get emergency care, if you have any sign on the CDC’s list of urgent maternal warning signs. These include a headache that won’t go away, vision changes, and swelling in your face or hands. They also include trouble breathing, chest pain, and a fever of 100.4 degrees or higher. So do severe belly pain, vaginal bleeding or leaking fluid, and your baby moving less than usual.
After about 20 weeks, a bad headache or vision changes with sudden swelling can point to preeclampsia, so don’t wait. Regular tightening before 37 weeks also deserves a call, because it could be preterm labor. Our page on Braxton Hicks contractions explains how to tell the difference.
Questions Parents Ask
When will I feel my baby move?
Often around week 20, though it can happen a little earlier or later. Early movements are subtle and easy to mistake for gas.
Can I find out my baby’s sex?
Often yes, at the anatomy ultrasound. It depends on your baby’s position, so it isn’t guaranteed. Some blood screenings can also reveal it.
Is the second trimester safe for exercise?
Many people can stay active. Walking and swimming are popular choices. Check with your provider first, especially if you have any complications.
Why does my belly sometimes feel hard?
You may be feeling practice contractions. They’re usually painless, irregular, and ease when you change position or drink water. Call if they become regular or painful.
The second trimester is when a lot of people finally start feeling like themselves again. More energy, less nausea, and the first real sense that there’s an actual baby in there. Our Third Trimester guide picks up from here. Our nutrition guide is worth revisiting again since your needs keep shifting as your baby grows.
Sources
- Prenatal Tests, March of Dimes
- Weight Gain During Pregnancy, CDC
- Tdap Vaccination for Pregnant Women, CDC
- Urgent Maternal Warning Signs, CDC
Worth knowing. This page is general guidance and can’t replace the advice of your own doctor or midwife. For more to read, browse our pregnancy section.