The Second Trimester: Week-By-Week What Happens in Pregnancy
The second trimester of pregnancy is often called the “golden trimester” for good reason. It’s a time of rapid development for your baby and, for many pregnant individuals, a period of reduced discomfort. From feeling your baby’s first movements to discovering their sex, this trimester is full of milestones. Whether you’re wondering, "Does the second trimester start at 13 or 14 weeks?" or need to know what to expect during this stage, our ANB Baby guide has all the information you need!
When Does the Second Trimester Start? Week 13 or 14?
The second trimester starts at week 13 and lasts until week 27, according to the Cleveland Clinic. This period marks the middle of your pregnancy, bridging the critical early developmental stages with the rapid growth and preparation for birth that occurs later.
Second Trimester Weeks in Months
To simplify:
- Month 4: Weeks 13-16
- Month 5: Weeks 17-20
- Month 6: Weeks 21-27
Understanding this breakdown can help you track your pregnancy more effectively.
What Happens in Each Week of the Second Trimester?
The second trimester is a time of incredible growth and development for your baby. Here's a week-by-week look at what to expect, according to the Mayo Clinic:
Week 13: Urine Forms
Your baby begins to make and release urine into the amniotic fluid. Their bones start to harden, and the skin, though still thin, will thicken in the coming weeks (Mayo Clinic).
Week 14: Baby’s Sex Becomes Apparent
The neck becomes more defined, and the baby’s spleen starts forming red blood cells. An ultrasound might reveal the baby’s sex.
Week 15: Scalp Hair Pattern Develops
Rapid growth continues, and your baby’s scalp hair pattern forms. Bones become visible on ultrasound.
Week 16: Baby’s Eyes Move
Your baby’s eyes begin to move slowly, and their ears near their final position. Limb movements can be seen on an ultrasound, but they’re still too faint for you to feel.
Week 17: Toenails and Movement
Toenails start developing, and your baby begins rolling and flipping in the amniotic sac. At this stage, the heart is pumping about 100 pints of blood each day.
Week 18: Baby Begins to Hear
Your baby’s ears stand out, and they might start to hear sounds. Their digestive system begins working, and their eyes face forward.
Week 19: Protective Coating Forms
The vernix caseosa, a greasy layer, starts forming to protect your baby’s delicate skin. If you’re having a girl, the uterus and vaginal canal are developing.
Week 20: The Halfway Mark
You may feel the first baby movements (quickening). Your baby’s sleep-wake cycle becomes more regular, and they might respond to noises or movement.
Week 21: Thumb-Sucking Begins
Lanugo, a fine layer of hair, covers your baby’s body to help retain vernix caseosa. The sucking reflex develops, enabling thumb-sucking.
Week 22: Hair Becomes Visible
Hair and eyebrows become visible, and brown fat forms, helping your baby regulate body temperature after birth. For boys, the testes begin descending.
Week 23: Fingerprints and Hiccups
Fingerprints and footprints form. Your baby might begin hiccuping, causing jerking movements.
Week 24: Wrinkled Skin
Your baby’s skin becomes wrinkled and pinkish-red. By this time, they may weigh more than 1 1/3 pounds.
Week 25: Responding to Your Voice
Your baby may respond to familiar sounds, such as your voice. Most of their sleep is spent in REM.
Week 26: Lung Development
The lungs start producing surfactant, crucial for breathing after birth. By now, your baby might weigh nearly 2 pounds.
Week 27: The End of the Second Trimester
Your baby’s nervous system continues maturing, and they’re gaining fat to smooth their skin. This marks the transition to the third trimester.
Second Trimester Weeks Symptoms: How You May Be Feeling
While many people feel better during this trimester, some discomforts persist. According to the Cleveland Clinic, common symptoms include:
- Increased appetite
- Swelling in hands and feet
- Round ligament pain
- Skin changes, such as a linea nigra
How Do I Know My Baby Is OK at 17 Weeks?
At week 17, you may not feel regular movements yet, but ultrasounds can confirm your baby’s activity and growth. If you’re concerned, always consult your healthcare provider.
Signs Your Pregnancy Is Going Well in the Second Trimester
Signs of a healthy pregnancy include:
- Feeling baby movements by 18-20 weeks
- Normal growth and weight gain
- No unusual symptoms, such as severe cramping or bleeding
Regular prenatal visits ensure that your pregnancy is progressing as it should.
Preparing for the Third Trimester: Looking Ahead
As you near the third trimester, focus on preparing for your baby’s arrival. Attend childbirth classes, choose a pediatrician, and take a hospital tour to familiarize yourself with labor and delivery procedures.
Shop for Your Second Trimester Needs at ANB Baby
Congratulations on reaching this exciting stage! To make your journey smoother, visit ANB Baby for all your pregnancy and baby essentials. From nursing bras to bassinets and baby monitors, we have everything you need for a happy and healthy pregnancy and beyond. The second trimester is a remarkable period of growth and connection with your baby. By staying informed and preparing well, you can embrace this time with confidence and joy!