Your third-trimester guide
The third trimester starts at 28 weeks pregnant.
At 28 weeks and 0 days, you enter the final trimester, which continues until birth. That leaves about 12 weeks until a due date at 40 weeks.
Here is how to understand 27 versus 28 weeks, where months fit into the timeline, and what to discuss at your next visit.
When does the third trimester start?
The third trimester starts at 28 weeks and 0 days pregnant. It follows the second trimester and continues until delivery. [1]
Pregnancy weeks describe gestational age. This is usually counted from the first day of your last menstrual period, with your clinician confirming or adjusting the dating when appropriate. It is not counted from your positive pregnancy test. [2]
Does the third trimester start at 27 or 28 weeks?
Using the American College of Obstetricians and Gynecologists (ACOG) trimester boundaries, 27 weeks is still the second trimester. The second trimester ends at 27 weeks and 6 days. The third begins the next day. [1]
- 27+0: 27 completed weeks, still the second trimester.
- 27+6: The last day of the second trimester.
- 28+0: The first day of the third trimester.
The number after the plus sign means additional days. If an app gives you a different trimester label, use the gestational age and due date documented by your OB-GYN.
How many weeks and months is the third trimester?
There are about 12 weeks between 28 weeks and a due date at 40 weeks. Your actual third trimester may be shorter or longer, depending on when you deliver.
Is 28 weeks seven months pregnant?
It is commonly described that way. The third trimester is often called months 7, 8, and 9, but these month labels are approximate. Calendar months have different lengths, so weeks and days give a clearer picture of how far along you are.
Does the third trimester mean your baby is full term?
No. The third trimester begins at 28 weeks, while full term is 39 weeks and 0 days through 40 weeks and 6 days. Birth before 37 weeks is preterm. [3] [4]
Pregnancy trimester timeline
- First trimester: Before 14 weeks.
- Second trimester: 14 weeks and 0 days through 27 weeks and 6 days.
- Third trimester: 28 weeks and 0 days until birth.
A due date is an estimate. Reaching 40 weeks does not automatically mean labor will begin that day. [1] [2]
What happens when the third trimester starts?
Your baby continues gaining weight while the organs mature in preparation for life after birth. [1]
For you, this is a useful point to review upcoming appointments, discuss delivery preferences, and plan support for recovery after birth. Bring questions about symptoms, work, sleep, feeding, or emotional wellbeing to your care team.
Common third-trimester symptoms
Fatigue, heartburn, constipation, and back discomfort can become more noticeable as pregnancy progresses. Tell your OB-GYN what you are experiencing, especially if it affects sleep or daily activities. [5]
- Fatigue: You may need more rest or changes to your usual routine.
- Heartburn or constipation: Ask which food changes or treatments are appropriate for you.
- Back discomfort: Your growing abdomen can place additional strain on muscles and joints.
- Swelling: Some ankle swelling can occur. Marked swelling of the hands or face needs prompt assessment.
A symptom should not be dismissed as routine if it is severe, persistent, or getting worse. [6]
Braxton Hicks or labor contractions?
Braxton Hicks tightenings generally do not build into progressively longer, stronger, more frequent contractions. If you think labor has started, or you are unsure, contact your maternity care team. Possible labor before 37 weeks needs urgent attention. [7]
What happens at third-trimester prenatal visits?
Visits may include blood pressure and weight checks, assessment of your baby's growth and position, and a discussion of symptoms and delivery plans. Ask your clinician what appointment schedule is appropriate for your pregnancy. [5]
| Timing | What to discuss |
|---|---|
| Around 28 weeks | Your next appointments, symptoms, and any outstanding screening results or follow-up. |
| 27 to 36 weeks | Tdap vaccination during each pregnancy, preferably early in this window. [8] |
| 36 to 37 weeks | Group B strep screening, generally at 36 weeks and 0 days through 37 weeks and 6 days, unless your history already indicates antibiotics during labor. [9] |
| Approaching your due date | Where to go for delivery, when to call, and your monitoring and delivery plan if pregnancy continues past the due date. |
An ultrasound is not automatically needed at every third-trimester appointment. Scans and additional monitoring depend on your pregnancy and clinical needs. [5]
Pay attention to your baby's usual movement
Get to know your baby's usual pattern. Ask your OB-GYN whether they recommend a particular movement-counting method. You should continue feeling movement through late pregnancy and labor. [10]
Contact your maternity care team immediately if movement decreases, stops, or changes from the usual pattern. Call even at night. Do not wait until the following day or use a home heartbeat device to reassure yourself. [10]
Third-trimester warning signs: when to seek care
Seek medical care immediately for:
- Reduced or absent baby movement.
- Vaginal bleeding or leaking fluid.
- A severe or persistent headache or changes in vision.
- Marked swelling of the hands or face.
- Fever of 100.4°F (38°C) or higher.
- Severe abdominal pain, chest pain, trouble breathing, or fainting.
- One-sided leg swelling, redness, or pain.
- Thoughts of harming yourself or your baby.
If you cannot reach your care team, go to an emergency department. Call 911 for a life-threatening emergency. Tell the treating team you are pregnant. [6]
Contact your maternity care team urgently if you think labor has started before 37 weeks. [7]
Your third-trimester checklist
- Confirm upcoming appointments and the after-hours contact number.
- Ask what to do about contractions, leaking fluid, or reduced movement.
- Discuss birth preferences, pain relief, and your support person.
- Plan transportation and check your hospital's packing guidance.
- Arrange help with meals, household tasks, and recovery after birth.
- Bring questions about feeding, postpartum care, and emotional wellbeing.
Frequently asked questions
When does the third trimester start?
It starts at 28 weeks and 0 days pregnant and continues until birth.
Is 27 weeks the third trimester?
Using ACOG's trimester boundaries, 27 weeks is still the second trimester. The third begins at 28 weeks and 0 days.
How many months pregnant are you at 28 weeks?
This is commonly described as about seven months. Month labels are approximate, so use weeks and days to track your pregnancy more precisely.
How long does the third trimester last?
There are about 12 weeks from its start at 28 weeks to a due date at 40 weeks. The actual length depends on when you deliver.
Does the third trimester mean my baby is full term?
No. The third trimester starts at 28 weeks. Full term is 39 weeks and 0 days through 40 weeks and 6 days.
Should my baby move less as the due date gets closer?
Movement should continue through late pregnancy and labor. Contact your maternity care team immediately if movement decreases, stops, or changes from the usual pattern. Do not wait until the next day.
Will I need an ultrasound at every visit?
Not necessarily. Your OB-GYN recommends scans and extra monitoring based on your pregnancy and clinical needs.
About your OB-GYN
Dr. Jessica White-Videa, DO, FACOG
Dr. White-Videa is a board-certified obstetrician and gynecologist and Fellow of the American College of Obstetricians and Gynecologists. She provides prenatal, obstetric, and postpartum care at Ideal Women's Healthcare in Coral Springs, Florida.
Meet Dr. White-VideaThird-trimester prenatal care in Coral Springs
Bring your questions about symptoms, upcoming appointments, and delivery preparation to Ideal Women's Healthcare.
2855 N. University Drive, Suite 300
Coral Springs, FL 33065
(954) 317-0772
For urgent symptoms, seek immediate medical assessment. Appointment request forms are not monitored for emergencies.
Medical sources
- ACOG: How Your Fetus Grows During Pregnancy
- ACOG: When Pregnancy Goes Past Your Due Date
- ACOG: Definition of Term Pregnancy
- ACOG: Extremely Preterm Birth
- MedlinePlus: Prenatal Care in Your Third Trimester
- CDC: Urgent Maternal Warning Signs and Symptoms
- NHS: Signs That Labour Has Begun
- CDC: Guidelines for Vaccinating Pregnant Women
- CDC: Screening for Group B Strep Bacteria
- NHS: Your Baby's Movements
This article provides general education. Your care team can advise you about your pregnancy, symptoms, and treatment.
