A full term pregnancy lasts from 39 weeks 0 days through 40 weeks 6 days, according to ACOG; 37 and 38 weeks are early term, week 41 is late term, and 42 weeks or more is post term.
If you have been told you are “term” at 37 weeks and then heard someone else say full term is 39, both were once in common use. ACOG and SMFM split the old 37 to 42 week window into four categories in 2013, and the full term pregnancy window is now 39 weeks 0 days through 40 weeks 6 days.
This guide gives you the exact categories, why the 2013 change happened, what the ARRIVE trial found about induction at 39 weeks, how your due date works, what happens at 40, 41 and 42 weeks, and when to call your provider.
Key Takeaways
Full term is 39 weeks 0 days through 40 weeks 6 days (ACOG Committee Opinion 579, reaffirmed 2025).
37 and 38 weeks are early term, week 41 is late term, and 42 weeks or later is postterm. Before 37 weeks is preterm.
ACOG says a delivery before 39 weeks without a medical reason should be avoided.
Your due date is an estimate; NICHD says most labors start between weeks 37 and 42.
Call for urgent signs like bleeding, leaking fluid, or your baby moving less, at any week.
Table of Contents
What Is a Full Term Pregnancy? The Short Answer
Quick Answer
A full term pregnancy is one that reaches 39 weeks 0 days through 40 weeks 6 days. That is the definition used by the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) in ACOG Committee Opinion 579, which ACOG reaffirmed in 2025. Birth at 37 weeks 0 days through 38 weeks 6 days is early term, 41 weeks 0 days through 41 weeks 6 days is late term, and 42 weeks 0 days and beyond is postterm. Before 37 weeks is preterm.
Doctors write these weeks as fractions: “39 0/7” means 39 weeks and 0 days, and “40 6/7” means 40 weeks and 6 days. So full term starts on the first day of week 39 and ends on the last day of week 40. Put simply, full term covers roughly one week before your due date through roughly one week after it.
Pregnancy weeks are counted from the first day of your last menstrual period, not from conception, which is why a “40 week” pregnancy includes about two weeks before you were actually pregnant. If you want to translate weeks into months, our pregnancy weeks to months chart lines them up.
Early Term vs Full Term vs Late Term vs Postterm
Here are the four ACOG and SMFM categories for babies born at or after 37 weeks, plus the World Health Organization (WHO) preterm categories for babies born earlier.
Early term vs full term is the comparison most people are really asking about. An early term baby is not premature: the preterm cutoff is still before 37 weeks. But ACOG Committee Opinion 765 says the risk of adverse outcomes is greater for babies delivered in the early term period than for babies delivered at 39 weeks. That gap is the whole reason the labels exist.
Late term and post term pregnancy sit on the other side of full term. A late term pregnancy is in week 41. A post term pregnancy has reached 42 weeks. MedlinePlus, the National Library of Medicine’s consumer health site, calls a pregnancy that lasts more than 42 weeks “post-term (past due)” and notes it happens in a small number of pregnancies.
How Many Weeks Is Full Term? Why the Definition Changed in 2013
For decades, any birth from 37 to 42 weeks was simply called “term.” According to ACOG Committee Opinion 579, that window ran from 3 weeks before to 2 weeks after the estimated due date, with the expectation that outcomes for babies born anywhere in it were uniform and good.
Research kept showing otherwise. ACOG says neonatal outcomes, especially breathing problems (respiratory morbidity), vary depending on when in that 5 week range a baby is born. So a work group convened in late 2012 recommended replacing the single word “term” with four labels: early term, full term, late term and postterm. ACOG and SMFM published those definitions in 2013 and asked all clinicians, researchers and public health officials to use them the same way.
So, how many weeks is full term? 39 to 40 weeks (39 weeks 0 days through 40 weeks 6 days). Babies born at 37 and 38 weeks are early term, and babies born in week 41 are late term.
Is 37 Weeks Full Term? What About 38 Weeks?
No. Under the current definitions, 37 weeks is early term, and so is 38 weeks. Many parents still hear “you are term at 37 weeks,” which was true under the old wording. Today the more precise answer is that 37 weeks marks the end of preterm and the start of early term.
That does not mean a baby born at 37 or 38 weeks is in trouble. Many early term babies do well. It means that, as a group, babies born at 39 weeks or later tend to do better. The National Institute of Child Health and Human Development (NICHD) explains that before 39 weeks the fetus’s lungs, brain and liver are still developing, and that waiting until at least 39 weeks gives parent and baby the best chance for healthy outcomes.
If you go into labor on your own at 37 or 38 weeks, your care team will treat it as labor, not as an emergency. The guidance about waiting until 39 weeks is about scheduled deliveries, not about trying to stop labor that starts naturally. For week by week detail, see 37 weeks pregnant and 39 weeks pregnant.
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The final weeks of pregnancy are busy ones. Here is what the sources say happens, and what is at stake when birth comes earlier than it needs to.
Lungs, brain and liver are still maturing: NICHD says these organs are still developing before 39 weeks.
Short term risks are higher: ACOG Committee Opinion 765 states that the risk of adverse outcomes is greater for babies delivered in the early term period than for babies delivered at 39 weeks.
Longer term differences show up too: the same ACOG opinion notes that multiple studies have linked late preterm and early term delivery with adverse long term infant outcomes, and that a systematic review found lower scores on cognitive and educational measures among late preterm and early term children compared with full term peers. ACOG adds that more research is needed to separate the effect of timing from the medical reasons some babies are delivered early.
A mature lung test is not enough: ACOG says documenting fetal lung maturity alone does not show that other body systems are ready, so it does not recommend an amniocentesis lung test to time a delivery.
ACOG’s bottom line: a delivery before 39 weeks without a medical reason should be avoided. Committee Opinion 765, reaffirmed in 2025, is just as clear on the flip side: when there is a medical reason (for example, a condition that makes continuing the pregnancy riskier than delivering), avoiding nonmedical early delivery should not lead to delaying a medically needed one. Your provider weighs the risks of continuing the pregnancy against the risks of an early term birth for your specific situation.
The ARRIVE Trial: Elective Induction at 39 Weeks
If 39 weeks is the start of full term, is it better to wait for labor or to be induced at 39 weeks? The largest study to look at that question in first-time parents is the ARRIVE trial, published in the New England Journal of Medicine in 2018 (Grobman and colleagues, Eunice Kennedy Shriver NICHD Maternal-Fetal Medicine Units Network).
What ARRIVE looked at
What it found
Who
6,106 low-risk people having their first baby, with one baby in head-down position
Groups
Induction at 39 weeks 0 days to 39 weeks 4 days, or expectant management (waiting, with no elective delivery before 40 weeks 5 days)
Serious newborn problems (main outcome)
4.3% with induction vs 5.4% with waiting; relative risk 0.80, not statistically significant by the trial’s preset threshold
Cesarean birth
18.6% with induction vs 22.2% with waiting; a significant reduction
High blood pressure disorders of pregnancy
9.1% with induction vs 14.1% with waiting; a significant reduction
Source: Grobman WA et al. Labor Induction versus Expectant Management in Low-Risk Nulliparous Women. N Engl J Med. 2018;379(6):513-523.
What it means for you: in this group of low-risk first-time parents, inducing at 39 weeks did not significantly lower the main measure of serious newborn complications, but it did lower the rate of cesarean birth and of high blood pressure disorders. The authors noted the trial was not designed to detect differences in rare outcomes.
ARRIVE does not mean everyone should be induced at 39 weeks, and it does not mean you must be. It gives you and your provider evidence to discuss if you meet similar criteria. Ask what your hospital offers, how an induction would work for you, and what waiting would look like. Our guide to induced labor walks through the process.
How Your Due Date Is Calculated (and Why Few Babies Arrive on It)
Your due date marks the day you reach 40 weeks 0 days, right in the middle of the full term window. MedlinePlus explains that a due date is an estimate, not an exact date, based on the first day of your last period, the size of your uterus early in pregnancy, and an early pregnancy ultrasound.
Last menstrual period: weeks are counted from the first day of your last period. This assumes a fairly regular cycle, so it can be off if your cycles are long, short or irregular.
Early ultrasound: measuring the baby early in pregnancy helps confirm or adjust the date.
Uterine size: your provider’s early exam is one more clue.
Because the date is an estimate, many people who seem to go past 40 weeks are not truly post term. MedlinePlus says many women who go past their due date had a due date that was miscalculated. NICHD puts the normal range plainly: for most women, labor begins sometime between week 37 and week 42.
What Happens at 40, 41 and 42 Weeks
Reaching your due date without labor is common, and care follows a fairly predictable path from there. Here is what MedlinePlus describes, though your provider’s plan may differ.
Where you are
What usually happens
40 weeks (due date)
Still full term. MedlinePlus says before 41 weeks your provider usually does nothing extra unless problems come up.
41 weeks (late term)
Your provider checks on the baby, usually with a non-stress test and a biophysical profile (an ultrasound). Reassuring results may mean waiting for labor.
41 to 42 weeks
MedlinePlus says health risks to you and your baby become greater, and your provider will likely want to induce labor.
42 weeks and beyond (postterm)
The pregnancy is post-term (past due).
Source: MedlinePlus (National Library of Medicine), When you pass your due date.
Why the extra watching? MedlinePlus explains that past the due date the placenta may not work as well as before, the amount of amniotic fluid may decrease (which can let the umbilical cord get pinched or pressed), and a baby who grows very large can be harder to deliver vaginally. The non-stress test and biophysical profile check whether the baby is active and healthy and whether the fluid level is normal.
Induction methods MedlinePlus lists include medicine placed in the vagina to soften (ripen) the cervix, a catheter placed in the cervix, breaking the bag of water, and IV oxytocin. MedlinePlus also notes that for older patients, especially those over 40, induction may be recommended as early as 39 weeks. For the week by week view, see 40 weeks pregnant and 41 weeks pregnant.
Signs of Labor at Full Term
NICHD says the main sign of labor is regular contractions that get stronger, longer and more frequent over time. Other signs NICHD lists:
Lightening: the baby drops lower in the uterus. This may happen several weeks or only a few hours before labor, and not every baby drops.
Show: vaginal discharge that may be clear, pink or slightly bloody. It can appear several days before labor or right as it begins.
Pressure and cramps: pelvic pressure, a low dull backache, and menstrual-like cramps, with or without diarrhea.
Your cervix also softens, thins and opens as labor nears; our effacement guide explains what those numbers mean. NICHD also describes false labor, where contractions are weak or irregular or stop when you change position.
NICHD advises that regular contractions every 5 to 10 minutes for an hour are a reason to let your health care provider know. Many practices give their own timing rule, so follow the one your provider gave you. For the subtle early signals, see signs that labor is 24 to 48 hours away, and for the bigger picture of these final weeks, our third trimester guide.
Call your provider any time you are unsure. You will not be bothering anyone, and false alarms are part of the job.
Call 911 or go to the nearest emergency room if you have chest pain, trouble breathing, fainting, or thoughts of harming yourself or your baby. These are among the urgent maternal warning signs the Centers for Disease Control and Prevention (CDC) says need medical care immediately.
Seek care right away (call your provider or labor and delivery now) for any of the other CDC urgent maternal warning signs:
Your baby’s movements stop or slow down.
Vaginal bleeding, or fluid leaking from the vagina.
A headache that will not go away or gets worse, dizziness, or changes in your vision.
Fever of 100.4 F or higher.
Extreme swelling of your hands or face.
Severe belly pain that does not go away, or severe nausea and vomiting.
A fast-beating heart, overwhelming tiredness, or severe swelling, redness or pain in a leg or arm.
Call the office or follow your provider’s labor plan if:
You have regular contractions every 5 to 10 minutes for an hour (NICHD), or whatever timing rule your provider gave you.
You have regular or frequent contractions before 37 weeks (NICHD).
You think your water broke, even a slow trickle.
You reach 41 weeks and do not yet have a plan for monitoring (MedlinePlus).
This article is general education based on the sources below, not medical advice. Your own provider knows your history and is the right person to decide on timing.
Frequently Asked Questions
What is a full term pregnancy?
A full term pregnancy is one that reaches 39 weeks 0 days through 40 weeks 6 days. ACOG and the Society for Maternal-Fetal Medicine set this definition in 2013. Births at 37 and 38 weeks are early term, births in week 41 are late term, and births at 42 weeks or later are postterm.
Is 37 weeks considered full term?
No. Under ACOG’s definitions, 37 weeks 0 days through 38 weeks 6 days is early term, not full term. A baby born at 37 weeks is no longer preterm, but ACOG notes that early term babies have a higher risk of adverse outcomes than babies born at 39 weeks.
How many weeks is full term for a baby?
A baby is full term when born from 39 weeks 0 days through 40 weeks 6 days of pregnancy. Weeks are counted from the first day of the last menstrual period, so full term covers roughly the week before and the week after the estimated due date.
Is it safe to deliver at 38 weeks?
Many babies born at 38 weeks do well, and labor that starts on its own at 38 weeks is normal. ACOG says early term babies face more risk than babies born at 39 weeks, so a scheduled delivery before 39 weeks should happen only when there is a medical reason.
What happens if you go past 40 weeks?
At 40 weeks you are still full term. MedlinePlus says that at 41 weeks your provider will usually check the baby with a non-stress test and a biophysical profile, and that between 41 and 42 weeks your provider will likely recommend inducing labor because risks rise.
What is the difference between late term and post term pregnancy?
A late term pregnancy is 41 weeks 0 days through 41 weeks 6 days. A post term pregnancy has reached 42 weeks 0 days or beyond. Both terms come from ACOG Committee Opinion 579. Extra monitoring usually starts at 41 weeks, and induction is often recommended before 42 weeks.
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Grobman WA, Rice MM, Reddy UM, et al. Labor Induction versus Expectant Management in Low-Risk Nulliparous Women. N Engl J Med. 2018;379(6):513-523 (PubMed Central). https://pmc.ncbi.nlm.nih.gov/articles/PMC6186292/
