When is a baby considered full term?
A full-term pregnancy lasts about 40 weeks from the first day of the woman’s last menstrual period (LMP) to delivery. This is equal to about 9 months. A baby born during week 37 to week 42 is considered full term. Full term is also divided into early term (37-38 weeks), full term (39-40 weeks), and late term (41-42 weeks).
What does full term mean?
Full term means the baby has had adequate time to fully develop before being born. Important growth and development occurs throughout pregnancy, but the final weeks are critical for organs like the brain, lungs and liver. Full term babies have fully developed organs and are ready for life outside the womb.
What is considered late term?
Late term refers to babies born between 41 weeks 0 days and 41 weeks 6 days. Late term falls within the full term range, but some doctors may recommend induction after 41 weeks to prevent complications. After 42 weeks the pregnancy is considered post-term.
Why inductions may be recommended after 41 weeks
After 41 weeks, the placenta may not work as well to provide the baby with nutrients and oxygen. The amniotic fluid levels may start to decline as well. This can lead to problems like low fetal movement, meconium in the fluid, and poor fetal growth. Inducing labor prevents these issues.
What is post-term pregnancy?
A post-term pregnancy is one that lasts longer than 42 weeks (294 days) from the first day of a woman’s last menstrual period. The medical term for post-term pregnancy is post-dates. About 10% of pregnancies continue past 42 weeks.
Risks of post-term pregnancy
After 42 weeks, risks to the baby increase, including:
- Placental insufficiency: The placenta ages and can’t deliver enough oxygen and nutrients to the baby.
- Meconium aspiration: The baby could inhale a mixture of amniotic fluid and stool.
- Excessive fetal growth: Lead to shoulder dystocia during delivery.
- Stillbirth: The risk of stillbirth doubles after 42 weeks.
Risks to the mother also increase, like the need for cesarean delivery or experiencing hemorrhage during birth.
What is the longest a pregnancy can safely go?
Most doctors agree that pregnancies should not continue past 42 weeks or 294 days from the start of the woman’s last period. The risks to both mother and baby increase substantially after this point.
Some organizations also set limits earlier:
- ACOG: Recommends delivery by 42 weeks.
- WHO: Sets the post-term period at 41 weeks plus 0-6 days.
- NICE: Advises induction between 41-42 weeks to avoid complications.
So 42 weeks is generally the longest a pregnancy should safely continue before risks increase. However, every pregnancy is different, so this should be discussed with your doctor.
Can a baby come late but still be premature?
Yes, it’s possible for a baby to be born past the due date but still be premature. Here’s how:
– The due date is calculated based on the mother’s last menstrual period. But not all women have a precise LMP date or regular cycles.
– If the due date calculation is off by a week or two, the baby could be born up to 2 weeks “late” but still be premature.
– Late preterm is defined as 34-36 weeks gestation. So a baby thought to be 38 weeks along based on the due date could actually be born at 36 weeks and be late preterm.
– An ultrasound, especially early on, gives a more accurate due date than LMP alone. So a late but premature baby often means the due date was incorrect.
What causes a pregnancy to go past the due date?
A few key factors influence when labor begins:
- Genetics: Labor timing can run in families.
- Placenta: Older placentas may be less responsive to signals to start labor.
- Baby’s size: Larger babies may have longer pregnancies.
- First pregnancy: First labors are often longer.
But even with these factors, it is difficult to predict exactly when any woman will go into labor. Some women may simply carry longer pregnancies while maintaining a healthy placenta and fluid levels.
Does induction increase the risk of complications?
Inducing labor medically does increase the chance of needing interventions like vacuum or forceps delivery. But after 41-42 weeks, the risk of waiting often outweighs induction risks.
The benefits of induction after 41-42 weeks are:
- Lower risk of placental problems
- Lower risk of poor fetal growth
- Lower chance of perinatal death
So while induction has risks, it is often safer than waiting after 42 weeks. Your doctor can help weigh the pros and cons.
Records for longest pregnancy
Some remarkable records have been set for the longest known pregnancies:
- In 1945, a woman was reported to be pregnant for 375 days, or 54 weeks.
- Another woman was pregnant for 368 days with a healthy baby.
- The longest confirmed pregnancy was 375 days, almost a full year.
However, these extraordinary cases are extremely rare. Most doctors today induce labor by 42 weeks at the latest.
Are long pregnancies more common in certain ethnic groups?
Research has looked at whether going past the due date is more common in different ethnic groups. Some studies have found:
- Caucasian women are more likely to deliver after 40 weeks compared to African American women.
- Pregnancies lasting over 42 weeks are more common in Caucasian and Hispanic women compared to Asian women.
However, more research is needed to confirm if ethnicity reliably influences the length of pregnancy. Many factors like genetics and environment play a complex role.
How can you tell if you’ve gone past your due date?
Here are some signs your pregnancy may be past 40 weeks:
- You reach and pass your estimated due date
- No signs of labor starting such as contractions, cramping or other changes
- Your belly seems to be “dropping” as the baby’s head moves down
- Symptoms like heartburn, trouble breathing, and swelling get worse
- Your doctor cannot find evidence of increasing dilation or effacement
However, every pregnancy is different. Some women may be past 40 weeks with few symptoms. Talk to your doctor about monitoring if you pass your due date.
How will my doctor monitor a late pregnancy?
If you go past your due date, your doctor will increase monitoring to check on you and baby. This may include:
- Weekly stress tests to monitor the baby’s heart rate
- Ultrasounds to check amniotic fluid levels and growth
- Fetal kick counts to monitor movement
- Checking for meconium in the amniotic fluid
- Monitoring the placenta for signs of aging
If results become concerning, your doctor may recommend induction. Otherwise, monitoring provides reassurance that you and baby remain healthy.
What happens if a pregnancy goes too far past the due date?
If a pregnancy continues too long past the due date, risks to both mother and baby increase substantially. Your doctor will closely monitor you and baby for any signs of complications.
Potential complications include:
- Placental deterioration
- Oligohydramnios (low amniotic fluid)
- Poor fetal growth
- Meconium aspiration
- Stillbirth
To prevent complications, most providers will induce labor by 42 weeks at the latest. With close monitoring and proactive management, long pregnancies can still result in healthy moms and babies.
Conclusion
A full-term pregnancy typically ranges from 37-42 weeks. After 41 weeks, the pregnancy is considered late term and monitoring increases due to risks like placental aging. By 42 weeks the pregnancy is post-term and induction is often recommended. While babies have been born healthy after longer pregnancies, 42 weeks is the common limit before risks rise substantially. With a late pregnancy, work closely with your doctor for monitoring and make a plan for induction by 42 weeks if labor doesn’t start naturally. This helps ensure the best possible outcome.