When Does the Second Trimester Start?
The length of a pregnancy and the three trimesters can be confusing.
To keep it simple, UPMC uses the trimester definitions from the American College of Obstetricians and Gynecologists (ACOG).
ACOG notes that the second trimester starts at 14 weeks, zero days (so, the beginning of the 15th week), and ends after 27 weeks, six days (the 28th week). It lasts 14 weeks, which is about 3.5 months.
The third trimester starts at the beginning of the 29th week (28 weeks, zero days).
What Happens With the Fetus in the Second Trimester?
All of the fetus's major organs form during the first trimester but they are underdeveloped. The goal of the second trimester is for these organs to develop further and mature.
Here are some of the key changes happening with the fetus in the second trimester:
- Your baby's kidneys start working — processing and releasing urine into the amniotic fluid.
- Tissue that will become bone develops around your baby's brain and in their arms and legs.
- Your baby's genitals fully develop, becoming visible by the 20-week ultrasound.
- Your baby might be able to suck their thumb.
- Fat stores begin to develop under your baby's skin.
- Your baby's ears form, and your baby may begin to hear.
During the second trimester, the fetus also grows rapidly in size. At the beginning, it is about the size of a peach. By 27 weeks, it is about the size of a cauliflower.
With all these major organ systems in place and developed, the second trimester is when fetuses reach "viability." Many preterm fetuses born at 24 weeks survive outside the womb with neonatal intensive care.
Second Trimester Symptoms
By the second trimester, your body has adapted to hormone changes. Morning sickness, fatigue, and mood swings are likely behind you.
Some women experience nausea throughout their pregnancies. Talk to your doctor if you still have morning sickness in the second trimester. They can ensure you're getting adequate nutrition and help with solutions.
Changes you might notice in the second trimester include the following:
- A baby bump — Thanks to all the rapid growth in the second trimester, your body changes become much more noticeable, and you start to "show."
- A "pregnancy glow" — Having rosier cheeks is due to your higher blood volume during pregnancy, which supplies nutrients to your fetus.
- Anxiety — In the second trimester, you may be awaiting fetal test results. It becomes "real" that you're about to embark on a major life change as the parent of a newborn. Talk to your doctor if your anxiety is severe, making it difficult to sleep and enjoy your life.
- Heartburn — This symptom may start earlier but ramp up in the second trimester. As the uterus grows, it puts pressure on the stomach, pushing stomach acid up the esophagus. Hormones cause the esophagus muscles to relax more, letting acid burble up.
- Increased appetite — You usually don't need to eat more in your first trimester when the fetus is still small. But you'll want to eat more in the second trimester to support your baby's growth. You need to eat 340 more calories a day in your second trimester.
- Feeling fetal movement — Most people start to feel fetal movement around 20 weeks, but you might feel it as early as 16 weeks. At first, the fetus's movements may feel like a little flutter, like gas, or like air bubbles bursting.
- Larger breasts — While your breasts may not be as tender as they were in the first trimester, they continue to grow and prepare for breastfeeding.
- Sore hips and back — The hormones and weight gain can throw you off balance and begin the aches and pains of later pregnancy. Relaxing ligaments in your body stretch to widen your pelvis for birth. This can also reduce the stability of your joints and lead to pain.
- Stretch marks — These stripes can show up on the skin of your belly, hips, or other areas as your skin stretches. You may notice this more so toward the end of your second trimester, or they may not show up until after you've delivered.
- Itchy skin — Your stretching and expanding skin can be itchy.
Prenatal Visits in the Second Trimester
Your prenatal visits will be similar to your first trimester. Expect routine weight and blood pressure checks and urine samples to check for signs of health problems. Your provider will also share general education about pregnancy and birth.
One difference is that your provider will start measuring your fundal height around week 24. Using a measuring tape, they will note the distance from your pubic bone to the top of your uterus. This measurement helps your provider track fetal growth over time.
Prenatal visits in the second trimester are usually every four weeks. Your doctor may see you more often if you have a health problem or high-risk pregnancy. Your pregnancy could be high-risk due to a test result, a problem with a previous pregnancy, or another reason, like your age.
Prenatal Tests in the Second Trimester
You'll see your baby in detail in your 20-week anatomy scan. Your doctor will also screen you for gestational diabetes around week 28. If you didn't get fetal screening tests in the first trimester, you can get them around week 14.
The 20-week anatomy scan
The 20-week anatomy scan is an ultrasound that can take around 45 minutes. The sonographer evaluates your baby's organs, size, and movement. They also examine the placenta and reproductive organs and measure the amniotic fluid level.
The sonographer can confirm your baby's sex during the scan unless the baby's position is hiding their genitals. If you want the baby's sex to be a surprise, let the sonographer know before the ultrasound starts.
The best part? You'll get a digital and printed photo of your baby in the womb to take home.
If the anatomy scan reveals any abnormal result with the fetus, your doctor will explain what it means for you. In many cases, an abnormal finding on the ultrasound turns out to be meaningless. Sometimes, abnormal findings can indicate a serious health problem.
If the anatomy scan shows a potential problem with the fetus, placenta, or amniotic fluid, you may need more monitoring. A problem may mean more ultrasounds as your pregnancy progresses. You may also opt for an amniocentesis test to confirm or rule out certain diagnoses.
Quad Screen
The quad screen is a blood test that measures certain proteins that may be higher in your blood if your baby has certain congenital disabilities. These include spina bifida, Down syndrome, trisomy 18, and others.
Doctors recommend this test between 15 and 22 weeks of pregnancy.
Amniocentesis
Because it poses a slight risk to the fetus, doctors only suggest this test when another test or your health history shows a higher risk of a fetal problem. This test is optional. Reasons to do this test could include an abnormal prenatal screen result or a congenital disability in a previous pregnancy.
Doctors can perform this test when you're between 15 and 20 weeks pregnant. They take a sample of amniotic fluid using a long needle inserted into the belly. Because the fetus sheds cells into the fluid, a laboratory can analyze the baby's DNA for genetic problems.
Oral Glucose Screening Test
Between weeks 24 and 28, your doctor will give you an oral glucose screening test.
For this test, you drink a standard sugary solution and then get a blood draw one hour later. If your blood sugar levels are high, you'll need a second test to confirm or rule out gestational diabetes.
If you have gestational diabetes, your provider will help you adjust your diet and give you medication if needed. They will also monitor your pregnancy more closely to keep your baby safe.
How to Have a Healthy Pregnancy in Your Second Trimester
The fetus remains vulnerable to toxins and infections throughout pregnancy. Continue to avoid alcohol and substances in the second trimester. Avoid ocean fish high in mercury and foods that could cause food-borne illnesses.
With your increased appetite, aim to fill up on nutrient-dense foods. These include fruits and vegetables, whole grains, lean meats and fish, beans and legumes, and lower-fat dairy products like yogurt.
Your provider will offer you any vaccines, including flu and COVID-19 vaccines, during respiratory virus season. Vaccines reduce the risk of getting an infection that could harm your baby. They can also help protect your baby after they're born.
You can read our full guidelines for a healthy pregnancy here.
Are there activities to avoid in the second trimester?
You can continue to exercise in your second trimester. But you may need to modify exercise to avoid back or hip pain. You may need to switch to walking, swimming, and other forms of low-impact exercise.
You may also need work accommodations. Prolonged sitting or standing may cause back pain, for instance. You may also need to avoid lifting heavy items or bending frequently if it causes pain.
Trust your body, and don't perform tasks that cause you pain. Read more about asking for workplace accommodations from the U.S. Equal Employment Opportunity Commission.
Your Second Trimester To-Do List
Here's what you should do in your second trimester:
- Sign up for childbirth classes. UPMC offers pregnancy, birthing, breastfeeding, and newborn care classes.
- Think about your birth preferences and consider writing your birth plan. Your prenatal provider can help with this.
- Purchase items you'll need for your baby, including a car seat, crib, blankets, and clothes. As your pregnancy progresses, you'll have much more to do, so it helps to start early.
- Talk to your employer or human resources representative. Many people inform their employers about their pregnancy at the end of the first trimester or the beginning of the second trimester. You'll need time to learn about parental leave options and plan your time off work.
Second Trimester Warning Signs
In the second trimester, you're at risk of blood clots, preterm birth, and preeclampsia (high blood pressure due to a problem with the placenta). These require emergency care.
If you have any of the following warning signs, seek care right away:
- Severe headache — A headache that doesn't go away or comes with other symptoms, like blurred vision, nausea, and swelling of the face and hands, could be preeclampsia.
- Difficulty breathing—It can get harder to breathe during pregnancy, but breathing issues, along with chest pain after eating or an insect bite, could be serious.
- Fast-beating heart or chest pain — Your expanding body and blood supply can strain your heart, causing heart palpitations. More serious complications can cause chest pain.
- Fever above 100.4 F — Infections are dangerous to you and your baby.
- Pain when urinating — This could mean you have a urinary tract infection.
- Severe stomach pain — Strong cramps could be contractions and preterm labor.
- Swelling, redness, and warmth in one leg — Together, these could be signs of a blood clot.
- Thoughts of harming yourself — Depression can strike at any point in pregnancy.
- Vaginal bleeding — Bleeding could signal an issue with the placenta.
Last reviewed by a UPMC medical professional on 2024-09-05.