The second trimester officially ends at the completion of **week 27**, or 27 weeks and 6 days, marking the transition to the final stage of pregnancy.
Reaching the end of the second trimester is a massive milestone. You have likely moved past the early nausea of the first few months and enjoyed the “golden period” of energy. Now, as you approach week 28, your body prepares for the final stretch. Understanding exactly when this phase concludes helps you schedule important prenatal tests, track fetal movements, and prepare for the physical changes ahead.
This guide breaks down the precise timing, what is happening with your baby right now, and the specific shifts you will feel as you cross the threshold into the third trimester.
When Does The End Of The 2nd Trimester Occur?
Confusion often arises around pregnancy math because months do not perfectly align with weeks. However, medical standards provide a clear answer. The second trimester spans from week 14 through the end of week 27.
To be precise, the last day of this trimester is 27 weeks and 6 days. Once you wake up on the morning of week 28, you have officially entered the third trimester. This timing is standard among major health organizations, including the American College of Obstetricians and Gynecologists (ACOG).
Why The Calculation Varies
You might see slight variations depending on the source. Some simplified charts divide the 40 weeks into three equal parts of roughly 13.3 weeks. In those models, the split might look different. However, your doctor will almost certainly use the 28-week mark as the start of your third trimester. This aligns with crucial developmental milestones for your baby and specific protocols for your prenatal care.
Weekly Breakdown Of The Second Trimester
The second trimester covers months four, five, and six. It is often the most enjoyable phase, but it is also a time of rapid growth. Below is a detailed look at what occurs during this specific window.
| Month | Week Range | Key Fetal Milestones |
|---|---|---|
| Month 4 | Weeks 14–17 | Sex becomes visible on ultrasound; fingerprints form; baby begins sucking thumb. |
| Month 5 | Weeks 18–22 | Hearing develops; movement (quickening) is felt; lanugo (fine hair) covers body. |
| Month 6 | Weeks 23–27 | Lungs produce surfactant; eyes open and blink; rapid brain growth occurs. |
| End Stage | Week 27 Day 6 | Sleep cycles regulate; baby weighs nearly 2 pounds; survival rate outside womb increases. |
| Transition | Week 28 (Start of 3rd) | Eyelashes fully formed; central nervous system can control breathing movements. |
| Size Context | By Week 27 | Baby is roughly the size of a head of cauliflower or a large lettuce. |
| Sensory | Weeks 26-27 | Baby responds to loud noises and bright lights outside the womb. |
Fetal Development At Week 27
As you approach the finish line of this trimester, your baby is doing much more than just gaining weight. The final weeks of the second trimester involve complex maturation of organ systems.
Lungs And Breathing Practice
One of the most critical developments at the end of the 2nd trimester is in the lungs. Your baby begins producing a substance called surfactant. This substance helps the air sacs in the lungs stay open, which is vital for breathing air. While the lungs are not fully mature yet, this step is a massive leap toward viability.
You may also notice rhythmic jerking movements in your belly. These are fetal hiccups. Your baby is inhaling and exhaling amniotic fluid to practice the mechanics of breathing. It is a strange sensation, but a healthy sign of development.
Brain And Sensory Growth
The brain surface, which was previously smooth, starts to develop grooves and indentations. This increases the amount of brain tissue significantly. Around week 27, your baby can open their eyes and blink. They can see light filtering through your skin and may turn away from a bright source.
Hearing is also acute. Your baby can distinguish your voice from others. Talking or singing to your bump now helps bond with them before birth. They may even jump in response to a sudden loud noise, a reflex known as the startle response.
Physical Symptoms As The Trimester Ends
The “honeymoon phase” of pregnancy usually fades as you hit week 27. Your uterus has grown significantly, shifting your center of gravity and putting pressure on your organs. Here is what you can expect physically during this transition.
Return Of Fatigue
While you might have had a burst of energy in weeks 16 through 20, the extra weight you are carrying now takes a toll. Your body is working harder to pump blood and support the baby. You might find yourself needing a nap during the day or feeling winded after climbing stairs. This is your body’s way of telling you to slow down.
Aches And Pains
Back pain becomes more prominent as your belly pulls forward. You might also experience leg cramps, especially at night. These can be sharp and wake you from a deep sleep. Stretching your calves before bed and staying hydrated can help.
Many women find relief by adjusting their routine, such as wearing supportive shoes or checking if hot baths are safe during pregnancy to soothe sore muscles safely.
Braxton Hicks Contractions
You may start feeling your abdomen tighten and harden specifically around week 26 or 27. These “practice contractions” are called Braxton Hicks. Unlike real labor, they are usually irregular and painless, though they can be uncomfortable. They occur as your uterine muscles tone up for the big job ahead. Dehydration often triggers them, so keep your water bottle handy.
Critical Tests Around Week 27
The end of the second trimester is a busy time for prenatal appointments. Your doctor will schedule specific screenings to ensure you and the baby are healthy before the final trimester begins.
Glucose Screening
Between weeks 24 and 28, you will take a glucose challenge test. This screens for gestational diabetes, a form of high blood sugar affecting pregnant women. You will drink a sweet liquid and have your blood drawn an hour later. If your levels are high, further testing will be needed. Managing blood sugar is vital for preventing complications like excessive fetal growth.
Rh Factor Screening
If your initial blood work showed you are Rh-negative, your doctor will check for antibodies. If your baby is Rh-positive, your body might produce antibodies that attack the baby’s blood cells. To prevent this, you will likely receive a RhoGAM shot around week 28. This simple injection protects your current pregnancy and future ones.
Warning Signs To Watch For
While discomfort is normal, certain symptoms at the end of the 2nd trimester warrant immediate medical attention. Preterm labor is a risk during this window. Knowing the signs can make a huge difference.
- Consistent Contractions: If you feel more than four contractions in an hour, especially if they are rhythmic or painful, call your provider.
- Vaginal Bleeding: Any spotting or bleeding should be reported immediately.
- Fluid Leakage: A sudden gush or a steady trickle of watery fluid could mean your water has broken early.
- Decreased Movement: You should have a sense of your baby’s daily patterns by now. If movement slows down significantly or stops, seek help right away.
- Pelvic Pressure: A sensation that the baby is pushing down heavily could indicate cervical changes.
According to the American College of Obstetricians and Gynecologists, acting fast on these symptoms gives doctors the best chance to delay delivery or prepare the baby for an early arrival.
Preparing For The Third Trimester
Crossing into week 28 shifts your focus from “growing” to “preparing.” The final trimester is physically demanding, so use the end of the second trimester to get organized.
Nursery And Gear
Now is the time to assemble the crib and wash baby clothes. As your belly gets bigger, bending over to screw in bolts or paint walls will become much harder. Aim to have the heavy lifting done by week 30. If you are having a baby shower, week 27 or 28 is a great time to hold it, so you have time to sort through gifts and buy what is missing.
Classes And Tour
Sign up for childbirth education, breastfeeding, and infant care classes. These fill up quickly. Also, schedule a tour of your hospital or birth center. Knowing exactly where to park and where to go when labor starts reduces anxiety later.
Final Travel
Many couples take a “babymoon” during the second trimester. If you plan to fly, try to do it before week 28 or shortly after. Most airlines allow travel up to 36 weeks, but sitting in a cramped seat gets increasingly uncomfortable. Always check with your doctor before booking a trip this late in the game.
Comparison: Second vs. Third Trimester
The shift from trimester two to three brings distinct changes. Knowing what lies ahead helps you adjust your mindset and expectations.
| Feature | End of 2nd Trimester (Weeks 24-27) | Start of 3rd Trimester (Weeks 28+) |
|---|---|---|
| Doctor Visits | Typically once every 4 weeks. | Increases to every 2 weeks, then weekly. |
| Energy Levels | Moderate to high; manageable fatigue. | Low; physical exhaustion is common. |
| Baby Position | Floating freely; lots of flipping/rolling. | Settles head-down; movements feel like jabs. |
| Sleep | Disrupted by leg cramps or vivid dreams. | Difficult due to size, heartburn, and bladder. |
| Breathing | Generally normal, slight shortness of breath. | Baby pushes on diaphragm; shallow breathing. |
| Focus | Growth and anatomy scans. | Labor prep, positioning, and delivery. |
| Calorie Needs | Increase by ~340 calories/day. | Increase by ~450 calories/day. |
The Emotional Shift
Hormones play a huge role during this transition. You might feel a return of the mood swings you experienced early on. Anxiety about birth and parenthood often spikes around week 27. This is normal.
You may also experience “nesting” urges—a sudden burst of energy to clean and organize. While productive, be careful not to overdo it. Listen to your body and rest when you need to.
Diet And Nutrition For The Final Weeks
Your baby triples in weight during the upcoming third trimester. This rapid growth demands specific nutrients. At the end of the second trimester, focus on iron and calcium.
Your blood volume has expanded massively, diluting your iron stores. This can lead to anemia, causing fatigue. Lean red meat, spinach, and fortified cereals are excellent choices. Calcium is crucial because your baby is hardening their bones. If you do not get enough from your diet, the baby will take it from your bones, which can impact your long-term health.
Hydration Importance
Water is essential for maintaining amniotic fluid levels and preventing preterm labor symptoms. Aim for at least 8 to 10 cups a day. If plain water tastes boring, infuse it with lemon or cucumber.
Final Thoughts On Your Timeline
Reaching the end of the second trimester at 27 weeks and 6 days is an achievement. You have nurtured your baby through critical developmental stages and are now ready for the final leg of the journey.
Use these last few weeks of relative comfort to finish your preparations. Pack your hospital bag, finalize your birth plan, and enjoy some quiet time. The third trimester brings its own set of challenges, but it also brings you one step closer to meeting your child. Trust your body, attend your prenatal checkups, and keep track of those precious kicks.
For more detailed week-by-week guidance, trusted resources like Mayo Clinic’s fetal development guide offer extensive insights into what is happening inside the womb right now.