Week 27
Your baby is the size of a rutabaga
Week 27 is the last week of the second trimester per ACOG. By 28 weeks, you're officially in the third. Per Mayo Clinic, your baby's nervous system keeps maturing this week and fat is filling out under the skin, making it look smoother. Meanwhile, GERD symptoms climb sharply at the trimester switch. Here's what's actually new at 27 weeks, plus the body shift coming for most of you.
Key takeaways
- Week 27 is the last week of the second trimester per ACOG. The third trimester officially starts at 28 weeks.
- Your baby is gaining subcutaneous fat that smooths the skin, per Mayo Clinic. Nervous system maturation continues from here into the third trimester.
- GERD symptoms reach 55.93% in the third trimester, up from 33.40% in the second, per a 2025 BMC Pregnancy and Childbirth meta-analysis (n=9,497). The jump starts this week.
- Cortical gray matter shows a 4-fold increase during the third trimester, compared with a 2-fold increase in the late second trimester, per Andescavage et al. (Cerebral Cortex, 2017).
Your baby is gaining fat fast this week, and the brain ramp starts in seven days
Per Mayo Clinic, week 27 marks the end of the second trimester.
The headline shift is fat. Your baby is gaining subcutaneous fat under thin, translucent skin, which smooths it and starts to take on newborn proportions. That fat keeps accumulating into the third trimester, where it does the real work of regulating temperature after birth.
Eyes still closed.
As covered at week 26, the eyelids stay fused for about two more weeks per Mayo Clinic. Eyes typically open around week 28. This week, the work is mostly internal: the nervous system continues to mature, refining the patterns that support breathing rhythm, swallowing, and sleep-wake cycles.
The bigger picture: brain growth.
Per Andescavage et al. (Cerebral Cortex, 2017), cortical gray matter shows a 4-fold increase in volume during the third trimester, compared with a 2-fold increase in the late second trimester. The same paper describes growth across the second half of pregnancy as exponential rather than linear, particularly for cortical gray matter in the third trimester.
Here's the thing. The brain you'll meet is being built fast from here.
And your baby's hearing, online since week 18 per Mayo Clinic, has weeks of pattern recognition by now. The voices and sounds they meet in your house become the familiar ones at birth.
Crown-to-rump, your baby was around 9 inches and just under 2 pounds at week 26 per Mayo Clinic. They're inching past that now.
This is also the last week ACOG technically counts as the second trimester.
Why heartburn is about to jump from 33% to 56%, and the four things that help
If heartburn has been bearable so far, that's about to change for many of you.
A 2025 BMC Pregnancy and Childbirth meta-analysis (Khurmatullina et al., n=9,497) found GERD symptoms climb from 33.40% in the second trimester to 55.93% in the third. Heartburn alone affects 43.81% of pregnant women overall.
The jump sits right where you are.
The cause is mechanical plus hormonal. Progesterone relaxes the lower esophageal sphincter (the muscle that's supposed to keep stomach acid where it belongs), and a uterus pressing upward leaves less room for the stomach.
Acid backs up.
The bigger your bump gets, the more often it happens.
What helps:
- Smaller meals, more often. Big meals are the biggest trigger.
- Don't lie down for 2 to 3 hours after eating.
- Sleep with your upper body elevated. Reflux is gravity-dependent.
- Know your triggers. Common ones in late pregnancy: chocolate, citrus, mint, tomato sauce, coffee, and anything fried.
- Calcium-carbonate antacids (TUMS) are first-line in pregnancy. H2 blockers like famotidine (Pepcid) are commonly the next step. Talk to your provider before starting anything new.
Two other arrivals you'll notice this week or next:
- Braxton Hicks contractions. Per Cleveland Clinic, these practice contractions often become noticeable in the third trimester. They're irregular, not painful, and tend to ease with hydration or a position change.
- The travel cutoff. Per ACOG, mid-pregnancy (14 to 28 weeks) is the easiest window for travel. After 28 weeks, many providers and some international airlines tighten things. If you've been putting off a trip, the call is now.
Contact your provider right away if you have regular contractions that don't stop, fluid leakage, heavy bleeding, severe headache, vision changes, upper-belly pain, sudden swelling in the face or hands, or a sustained drop in your baby's movement once you've been feeling it regularly.
For dads
Here's your move:
Pack the hospital bag this weekend. Yes, you have 13 weeks. Do it anyway. The third trimester arrives in seven days and the energy curve goes the other way from here. Aim for a Saturday morning, two coffees, the list pulled up on a phone. You handle yours: chargers, two changes of clothes, snacks, ID, a hoodie because the rooms are cold. She'll handle hers. Anything she's triple-checked stays packed in a duffel by the door. While you're at it, if you haven't picked up a dad's pregnancy book or a data-led decisions guide yet, do that too. Walking into labor with the bag done and a few chapters read is one less decision in the most decision-heavy 48 hours of your life. The third trimester is the on-ramp. Use the next seven days to get the easy stuff out of the way.
Real talk:
Heartburn is about to be your shared problem. She can't sleep flat. She can't eat the dinner you both used to love after 7 PM. She wakes up at 2 AM tasting acid she swallowed by accident. Your job isn't to fix it. You can't. Your job is to stop suggesting she try eating earlier. She knows. What actually helps is a cold glass of water on her side of the bed each night, an extra pillow stacked where you'd normally sleep so she can prop up without asking, and not making a face when dinner shifts to 6 PM. Small accommodations she doesn't have to ask for. That's the work.
Common concerns
Is week 27 already the third trimester?+
No. Per ACOG, the third trimester begins at 28 weeks, so week 27 is the last week of the second (which runs through 27 weeks 6 days). You're seven days from the official switch, and a lot of the changes the third trimester brings start ramping this week.
When do I actually start counting kicks?+
Per ACOG, low-risk pregnancies typically start formal kick counting at 28 weeks, while high-risk pregnancies often start at 26. The common guideline is 10 movements in 2 hours during your baby's typically active stretch, but knowing the normal pattern matters more than any single count. A sustained drop in movement is always worth a same-day call.
Is the heartburn medication I'm taking safe in pregnancy?+
TUMS and other calcium-carbonate antacids are generally considered first-line during pregnancy, with H2 blockers like famotidine (Pepcid) commonly used when antacids aren't enough. Proton pump inhibitors like omeprazole are sometimes prescribed for more severe reflux, but the call is usually made with your provider. Loop them in before starting or continuing anything new in the third trimester.
Can my baby hear my partner's voice through the belly?+
Probably. Per Mayo Clinic, by the end of week 25 your baby may move in response to familiar sounds, especially familiar voices. Reading aloud now means your baby gets used to those voices before birth, which can help with newborn soothing.
Product picks for week 27
As an Amazon Associate, Cradlebug earns from qualifying purchases — at no extra cost to you. Learn more
TUMS Extra Strength Antacid Tablets, Assorted Fruit, 330 Count
330-count value pack. If GERD has settled in for the long stretch, the per-tablet price drops a lot vs. buying small bottles repeatedly.
Pepcid AC Original Strength Heartburn Relief, 10mg Famotidine, 30 ct
H2 blocker for when antacids aren't cutting it. Famotidine is commonly used in pregnancy, but check with your provider before starting.
Hiccapop Pregnancy Pillow Wedge for Belly Support
Wedge for side-sleeping support. Doubles as a torso prop for the upper-body elevation that helps overnight reflux.
Sources
- Mayo Clinic, Fetal Development: The 2nd Trimester (2025) — https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/fetal-development/art-20046151
- Khurmatullina AR et al., Global prevalence and risk of gastroesophageal reflux disease symptoms in pregnancy: a systematic review and meta-analysis. BMC Pregnancy and Childbirth (2025) — https://link.springer.com/article/10.1186/s12884-025-08569-x
- Andescavage NN et al., Complex Trajectories of Brain Development in the Healthy Human Fetus. Cerebral Cortex (2017) — https://academic.oup.com/cercor/article/27/11/5274/2354954
- ACOG, How Your Fetus Grows During Pregnancy — https://www.acog.org/womens-health/faqs/how-your-fetus-grows-during-pregnancy
- ACOG, Special Tests for Monitoring Fetal Well-Being — https://www.acog.org/womens-health/faqs/special-tests-for-monitoring-fetal-well-being
- Cleveland Clinic, Braxton Hicks Contractions — https://my.clevelandclinic.org/health/symptoms/22965-braxton-hicks
A quick note: This content is for informational purposes only and is not a substitute for professional medical advice. Always talk to your healthcare provider about any questions or concerns. Content based on guidance from the American College of Obstetricians and Gynecologists (ACOG), the American Academy of Pediatrics (AAP), Mayo Clinic, and peer-reviewed medical literature. Learn how we create our content.