Week 28 is the marker most providers use to draw the official line where the final stretch begins. It runs from week 28 through delivery, typically spanning weeks 28 to 40, and it can extend to week 42 for late-term births. This shift moves the focus from getting through pregnancy to preparing for a baby who could realistically arrive and do well.
The sections below walk you through what changes in your body, how your baby develops week by week, what happens at each prenatal visit, and when to call your provider right away.
The Trimester System and Why Week 28 Marks a Turning Point
Pregnancy is divided into three roughly 13-week blocks, each tied to distinct developmental and physical milestones. The first trimester covers conception through week 13, the second runs weeks 14 through 27, and the third begins at week 28. Some medical texts use week 27 as the cutoff, which is why you may see the boundary shifted by a week in different sources. Both framings overlap, but week 28 is the more widely accepted starting line in U.S. prenatal care.
Reaching week 28 signals a meaningful shift in fetal viability, with survival odds rising sharply from this point onward. While a fetus is generally considered viable after week 24, outcomes improve substantially by week 28, and the lungs and brain are mature enough that many babies born at this stage can survive with intensive neonatal support. That improvement is also why your visit cadence changes here, and why providers begin treating each remaining week as preparation for a baby who could arrive early and still do well.
The third trimester itself runs from week 28 until delivery, generally spanning weeks 28 through 40. Full-term birth is defined as 37 to 42 weeks of gestation, so the final stretch is longer than many people expect. That window gives you time to prepare, but it also means the work of late pregnancy, including discomfort, appointments, and planning, is real and worth taking seriously.
Fetal Development From Week 28 Until Birth
What Happens Before Week 37
During the final stretch, your baby gains roughly half of total birth weight through rapid fat and muscle accumulation. A fetus at 28 weeks weighs around 2 to 2.5 pounds, and by 36 weeks that number often doubles. Brain tissue expands rapidly, lungs mature through surfactant production, and the eyes begin responding to light filtering through the uterine wall. These changes show up as stronger kicks, more defined sleep and wake cycles, and occasional visible movement across your belly.
What Changes Around Full Term
Bones harden during this stage, though the skull remains soft to allow passage through the birth canal. The soft spots, called fontanelles, close during the first year of life, which is why a newborn’s head shape can look slightly uneven right after birth. By week 37, most babies are considered full-term, with continued growth and refinement through week 40 and beyond. Late-pregnancy ultrasounds may show position, amniotic fluid levels, and estimated weight, all useful details for planning delivery.
Common Symptoms and Physical Changes During the Final Stretch
Back pain, pelvic pressure, swelling in the feet and ankles, and frequent urination become routine as your uterus expands. The growing uterus puts direct pressure on the bladder, the lower back, and the pelvic floor, which is why even simple movements can feel heavier by week 32. Swelling in the feet and ankles is common, especially after long periods of standing, and it usually eases with elevation and rest.
Braxton Hicks contractions appear as your body rehearses for labor, and they differ from true labor patterns by their irregularity and intensity. Braxton Hicks feel like a tightening across the belly that fades within a minute or two and does not follow a predictable rhythm. Sleep disruption, heartburn, and shortness of breath intensify as your baby presses upward into the diaphragm, which is why propping up with pillows and eating smaller meals often helps. Pregnancy fatigue also returns in this stage, even if you felt energetic during the second trimester.
Most symptoms are manageable, but sudden severe headaches, rapid swelling in the face or hands, visual changes, or reduced fetal movement warrant an immediate call to your provider. These can be signs of preeclampsia or other complications that need same-day evaluation.
Prenatal Care Shifts to Every Two Weeks
The New Appointment Cadence
Visits shift from once a month to about every two weeks at week 28, then ramp up to weekly after week 36. This ramp-up reflects the rising chance of complications like gestational hypertension, preeclampsia, and preterm labor as pregnancy advances. Skipping appointments during this window means missing the chance to catch those conditions early.
Standard Checks at Each Visit
Standard checks include blood pressure, urine screening, fundal height measurement, and fetal heart rate monitoring. Fundal height, the distance from your pubic bone to the top of the uterus, helps track growth and amniotic fluid levels between ultrasounds. Later visits may add group B strep screening around weeks 35 to 37, cervical checks in the final weeks, and discussions about birth preferences. Each appointment is also a checkpoint for questions about symptoms, movement counts, and labor preparation, so bringing a written list pays off.
| Gestational Week | Visit Frequency | Typical Screenings |
|---|---|---|
| Weeks 28–35 | Every 2 weeks | Blood pressure, urine, fundal height, fetal heart rate |
| Weeks 36–40 | Weekly | Same as above plus Group B strep, cervical checks, position assessment |
| Week 40+ | 1–2 times per week | Non-stress tests, biophysical profile, fluid checks |
Preparing for Labor, Delivery, and the Postpartum Window
Building a birth plan, choosing a delivery setting, and identifying a support person are practical early steps. A birth plan does not need to be long; clear preferences about pain management, who is in the room, and immediate newborn care are enough to start. Choosing between a hospital, birthing center, or home birth, if your pregnancy is low-risk and your provider supports it, shapes the rest of the preparation. Identifying one or two support people, such as a partner, friend, or doula, makes a measurable difference during active labor.
Packing a hospital bag, arranging pet and household coverage, and outlining newborn essentials reduce last-minute stress. Aim to have the bag ready by week 36, since babies can arrive early. Essentials include toiletries, phone chargers, going-home clothes for both you and your baby, a car seat installed and inspected, and any documents your hospital requests. Childbirth education classes, lactation consultations, and hospital tours build confidence before the due date arrives, and many hospitals offer low-cost options.
Postpartum planning, including postpartum depression awareness, follow-up appointments, and sleep support, should begin alongside birth logistics. Postpartum depression affects roughly 1 in 7 new parents, and the strongest protective factor is having a plan and a support network already in place. Line up meals, identify someone who can stay for the first week, and know the signs of postpartum mood disorders before they arrive.
Even the best-laid plans can be upended if labor begins earlier than expected.
Recognizing Preterm Labor and Knowing When to Call the Provider
Red Flags Before Week 37
Contractions that come on regularly before week 37, along with steady lower back pain, pelvic pressure, or fluid leaking, signal a need to call the provider. Contractions that follow a pattern, grow stronger over time, and do not ease with hydration or position changes are different from Braxton Hicks. Fluid leaking rather than a gush can mean the amniotic sac has ruptured, which always requires evaluation regardless of gestational age.
Urgent Warning Signs at Any Point
Vaginal bleeding, sudden severe swelling in the face or hands, and a sharp drop in fetal movement require urgent evaluation. These symptoms can point to placental abruption, preeclampsia, or fetal distress, all of which benefit from minutes, not hours. Preterm labor caught early can sometimes be slowed with medical intervention, making timely contact essential.
How to Prepare Before Something Happens
Keeping a written log of symptoms, contraction timing, and baby movement helps providers triage quickly. Kick counts, tracking 10 movements within two hours during a calm period, are a simple daily habit starting around week 28. Bring the log to every appointment, and call right away if the pattern changes suddenly.
What Actually Matters and What to Skip at This Stage
Skipping the shift to more frequent appointments reduces your chance of catching complications like preeclampsia early. Preeclampsia can develop between visits without obvious symptoms, which is why blood pressure and urine checks every two weeks matter. Comparing your week-by-week progress against other pregnancies often creates unnecessary anxiety, since fundal height, weight gain, and symptom patterns vary widely between healthy pregnancies.
Postpartum planning is routinely delayed until after birth, leaving families underprepared for the first weeks at home. Setting up meals, sleep shifts, and visitor boundaries in advance removes dozens of small decisions during an exhausting window. Trusting symptom patterns over silent worry, and reaching out to your provider when something feels off, is the single best habit for the third trimester. Waiting to see if it passes can turn a manageable issue into an emergency.
FAQ
Is week 28 the start of the third trimester?
Most U.S. clinics and pregnancy resources point to week 28 as the most widely accepted starting line.S. prenatal care. Some medical texts use week 27 instead, which is why you may see a one-week difference between sources. Both framings cover the same final stretch of pregnancy.
How many weeks are in the third trimester?
From week 28 through delivery, the final phase typically spans 12 to 13 weeks. Full-term birth is defined as 37 to 42 weeks, so the length depends on when labor begins.
What are the signs of the third trimester?
Common signs include back pain, pelvic pressure, swelling in the feet and ankles, frequent urination, Braxton Hicks contractions, heartburn, shortness of breath, and a return of pregnancy fatigue. These reflect the uterus pressing on surrounding organs and the body’s preparation for labor.
When should I see my doctor in the third trimester?
Visits typically occur every two weeks from week 28 through week 35, then weekly from week 36 until delivery. After week 40, appointments often increase to one or two times per week with additional monitoring.
What helps with third trimester back pain?
Supportive shoes, a pregnancy pillow for sleep, warm baths, and gentle stretching often help. Physical therapy specifically trained in prenatal care can address pelvic and lower back pain when home measures are not enough.
When does the third trimester end?
The third trimester ends at delivery, which most often happens between weeks 37 and 42. Anything before 37 weeks is considered preterm, and anything after 42 is post-term and typically monitored closely.
