What's happening with your baby at 27 weeks
At 27 weeks, your baby typically measures around 36 cm (about 14 inches) from head to heel and weighs close to 875 grams (about 1.9 lb) — roughly the size of a cauliflower, though every baby grows at their own pace. These figures are averages, not a target to hit.
Your baby's brain is growing rapidly this week, with new grooves and folds forming on its surface. Their eyes can open and close, and they may already be responding to light and sound from outside the womb.
The lungs are still maturing and won't be ready for independent breathing until later in the third trimester. Hiccups are common now — you might feel small, rhythmic jerks that last a few minutes at a time.
Common symptoms at 27 weeks
Backaches, leg cramps, and mild swelling in your feet and ankles are common as your growing uterus shifts your center of gravity and puts pressure on nearby nerves and blood vessels. Heartburn and shortness of breath often start or worsen as your uterus pushes up against your stomach and diaphragm.
Braxton Hicks contractions — brief, irregular tightening of the uterus — may begin appearing this week or in the coming weeks. They're usually painless and settle down with rest or water, unlike true labor contractions.
Itchy skin across your belly is common as it stretches, and restless legs or trouble sleeping can show up too. These are typical third-trimester experiences, though persistent or severe symptoms are always worth mentioning to your provider.
Is 27 weeks the start of the third trimester?
Many providers mark 27 weeks as the start of the third trimester, though others count from 28 weeks — the exact cutoff varies by source and doesn't change your care, since your due date and individual checkups matter more than the trimester label. Either way, you have roughly 13 weeks left until your due date.
The trimester boundaries are a convenient way to talk about pregnancy, not a medical checkpoint. What's tracked at your appointments — your baby's growth, your blood pressure, your symptoms — is based on your specific week, not which trimester you're in.
What to do at 27 weeks pregnant
This week is often when you'll take your one-hour glucose screening test for gestational diabetes if you haven't already, since it's typically done between 24 and 28 weeks, and it's also the start of the recommended window for the Tdap vaccine, which runs from 27 to 36 weeks. If you're Rh-negative, your provider may also talk with you about a Rhogam shot around this time.
The glucose screening checks how your body processes sugar. A higher-than-expected result doesn't mean you have gestational diabetes — it means you'll be offered a longer follow-up test to confirm.
The Tdap vaccine helps pass protective antibodies to your baby against whooping cough before they're old enough for their own vaccines. This is also a reasonable week to start a childbirth class and get familiar with your baby's regular movement patterns.
When to call your provider
Call your provider the same day for reduced fetal movement, vaginal bleeding, fluid leaking from the vagina, a severe or persistent headache, sudden vision changes, or swelling in your face and hands — these can signal problems that need prompt evaluation.
Regular contractions, pelvic pressure, or lower back cramping before 37 weeks should also be checked, since they can be early signs of preterm labor. If something feels different or wrong, it's always reasonable to call rather than wait it out.