Week 27 is the last week of the second trimester. Next week, the third trimester begins — and with it, the final stretch toward meeting your baby. This week marks a genuinely remarkable neurological milestone: your baby's brain is now extremely active, displaying distinct electrical patterns that correspond to sleep and wakefulness. Your baby is dreaming. Or at least, their sleeping brain looks just like the brain of someone who is.
Track your timeline and get ready for the home stretch with our Due Date Calculator.
Your Baby This Week
Size: Cabbage — about 36.6 cm (head to toe)
Weight: About 875 grams
Nearly a kilogram, closing in fast. Here's what's happening in your baby this week:
- The brain is highly active and showing sleep cycles. EEG-like studies of fetal brain activity have shown that by 27-28 weeks, brains display patterns consistent with REM (rapid eye movement) sleep — the stage associated with dreaming in adults and older children. Your baby has active and quiet periods that correspond to different sleep-wake states.
- The brain is producing billions of neurons. The cerebral cortex is developing at a staggering pace, laying down the neural architecture for thought, sensation, language, and emotion.
- The lungs continue maturing. Surfactant production is increasing, and the lung tissue is developing more air sacs. A baby born at 27 weeks has a high survival rate with intensive NICU care, though they will face challenges.
- Hiccups. Your baby likely hiccups regularly, and you may feel these as rhythmic, repetitive little pulses. They're caused by the diaphragm contracting as the baby practices breathing motions.
- Fat is accumulating. Subcutaneous fat is gradually filling in, giving the baby a rounder, less wrinkled appearance. This process accelerates in the third trimester.
- Eyelid movement is coordinated. The eyelids can open and close in response to light and other stimuli, and eye movements during sleep resemble those seen during REM sleep in newborns.
Your Body This Week
The end of the second trimester often brings a mix of energy and discomfort. Here's what many people experience:
- More pronounced Braxton Hicks. Practice contractions may become more frequent and noticeable as you approach the third trimester. They remain irregular and painless. If they become regular, intensify, or are accompanied by other symptoms, contact your provider.
- Lower back and hip pain. The relaxin hormone is doing its job loosening your ligaments, but that flexibility comes with instability. Strengthening the glutes and core, practicing good posture, and using a pregnancy support belt can all help.
- Fatigue returning. Many people experience a second wave of tiredness as they enter the third trimester. Your body is working hard, your sleep is probably fragmented, and your blood is being pulled in several directions. Rest is not optional — it's productive.
- Changes in baby's movement. As the baby grows and has less room to move, kicks and rolls may feel more concentrated, stronger, and occasionally uncomfortable. This is normal. The key is that movement continues consistently.
- Emotional preparation. The third trimester often prompts a psychological shift toward preparation and sometimes anxiety. Nesting instincts may kick in. Conversations about birth, parenting expectations, and postpartum support are all worth having now.
Tips for Week 27
1. Sign up for a childbirth class now. If you haven't yet, the window is closing. Most classes are designed to be completed by 36 weeks, and popular ones fill quickly. Whether in-person or online, a good class can significantly reduce anxiety about labor and delivery.
2. Begin preparing your home. The third trimester often comes with a strong urge to organize and prepare. Let it work for you: set up the bassinet or crib, wash baby clothes, research your newborn care basics. Practical preparation is one of the most anxiety-reducing things you can do.
3. Discuss Tdap vaccination with your provider. ACOG and the CDC recommend that pregnant people receive the Tdap vaccine between 27 and 36 weeks. This protects the newborn from whooping cough (pertussis) before they're old enough to be vaccinated themselves.
4. Stay on top of fetal movement. You're about to enter the third trimester, when fetal movement monitoring becomes more important. Get in the habit of noticing when your baby is most active, and take note if those patterns change.
5. Plan your glucose test follow-up. If you had an elevated one-hour glucose challenge test result, the three-hour follow-up test should happen before the end of this week or early next week. Don't delay this.
When to Call Your Doctor
- Regular contractions — more than 4-6 per hour before 37 weeks, with or without pain. At 27 weeks, every extra day matters enormously.
- Decreased fetal movement relative to your normal established pattern
- Fever over 38°C (100.4°F) — infections in late second trimester need prompt treatment
- Persistent, severe headache or visual changes — warrant same-day evaluation for preeclampsia
- Significant edema in the face or hands combined with any of the above symptoms
Related Tools & Articles
- Due Date Calculator — Calculate your estimated due date
- Pregnancy Week-by-Week Overview — full timeline
- Milestone Tracker — track your baby's development
- Hospital Bag Checklist — now is a good time to start packing