Why is 37 weeks full term?

Pregnancy typically lasts about 40 weeks or 9 months from the first day of a woman’s last menstrual period. While a normal pregnancy can range from 38 to 42 weeks, a full-term pregnancy is considered to be 39 to 40 weeks. However, in recent years there has been a shift to defining a full-term pregnancy as 37 weeks or later.

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What is full term pregnancy?

A full-term pregnancy is one that lasts between 39 to 40 weeks. Previously, 37 to 42 weeks was considered full term. However, in 2013 the American College of Obstetricians and Gynecologists redefined a full-term pregnancy to only include deliveries from 39 to 40 weeks.

Here is how pregnancy is broken down by weeks:

Early term: 37 to 38 weeks
Full term: 39 to 40 weeks

Late term: 41 to 42 weeks
Postterm: 43 weeks and beyond

Babies born between 37 and 38 weeks are considered “early term.” While still very close to full term, some organizations are cautious about labeling 37 to 38 weeks as full term.

Why did the definition change?

The definition was changed because research shows important development occurs for the baby in the last few weeks of pregnancy.

Lungs and brain continue developing late into pregnancy. Waiting until 39 weeks allows the baby’s lungs and brain more time to fully mature.

Additional reasons for the change include:

Babies born at 37 weeks are at higher risk for complications than those born at 39 weeks.
C-sections and inductions should not be scheduled before 39 weeks unless medically necessary.
Defining full term as only 39 to 40 weeks reinforces that pregnancies should not be ended early for non-medical reasons.

Risks of delivering at 37 weeks

While most babies born at 37 weeks do well, they are still at higher risk for complications than those born later. Possible complications include:

Breathing problems: Lungs may not be fully matured, increasing risk for respiratory distress syndrome.
Feeding difficulties: Early term babies are more likely to have problems coordinating sucking and swallowing.

Low birth weight: Babies gain significant weight in late pregnancy. Early term babies are more likely to be born underweight.
Underdeveloped brain: The brain continues developing connectivity in the last weeks of pregnancy. Early deliveries interrupt this process.
Jaundice: Jaundice requiring phototherapy is more common in early term infants.

Infection: Underdeveloped immune system can make fighting infections harder.

In addition, early term babies are more likely to be admitted to the NICU or require respiratory support after birth.

When is 37 weeks safe to deliver?

For some pregnancies, delivery at 37 weeks is recommended. These include:

Pregnancies with medical complications like preeclampsia or placental problems.
Pregnancies significantly past due dates.
Multifetal pregnancies like twins or triplets.

In these cases, the risks of continuing the pregnancy may be greater than the risks of an early delivery.

However, for most low-risk pregnancies there is no medical reason to deliver before 39 weeks. Elective inductions and c-sections should be avoided.

What is done for 37 week babies after birth?

Babies born at 37 weeks often do very well. However, extra precautions may be taken such as:

Monitoring breathing, heart rate, temperature, blood sugar.
Delaying first bath for several hours to allow adapting to temperature changes.
Keeping baby skin-to-skin for warmth and bonding.

Feeding more frequently to encourage practice with sucking and swallowing.
Using bilirubin lights preventatively for jaundice.
Allowing longer hospital stay 2-4 days to monitor for problems.

Outcomes for 37 week babies

The majority of babies born at 37 weeks have no long term health problems. However, some studies have found subtle differences compared to those born at 39-40 weeks:

Increased risk for weaker neurodevelopmental scores at 2 years old.
Slightly lower IQ scores at age 5.

Higher rates of behavioral disorders and ADHD later in childhood.
Increased chance of having vision and hearing problems.

These effects appear relatively small but show the importance of those last few weeks of brain development.

When is elective delivery okay?

The American College of Obstetricians and Gynecologists recommends no elective deliveries before 39 weeks unless necessary for the health of mom or baby.

Elective deliveries include:

Scheduled cesarean sections for non-medical reasons.

Induced labor for convenience or scheduling purposes.
Other intentional early deliveries without a specific medical indication.

These should be avoided. However, sometimes elective delivery at 37-38 weeks may be considered on an individual basis when risks and benefits are carefully weighed.

What should I do if I’m 37 weeks pregnant?

If you are 37 weeks pregnant here are some things you can do:

Talk to your doctor about risks and benefits of delivering now versus waiting.
Understand any medical reasons prompting an early delivery.

Ask about delaying elective delivery until at least 39 weeks if possible.
Make a birth plan for extra monitoring or care your baby may need.
Prepare breastfeeding support and jaundice management options.

Rest and avoid physically taxing activities that could trigger labor.
Monitor baby’s movements and call your doctor with any concerns.

Staying pregnant at least until 38 weeks allows your baby the best preparation for birth. Make delivering as close to your due date as possible a priority in your birth plans.

Conclusion

While 37 weeks was previously considered full term, current recommendations define full term as 39 to 40 weeks. Important development occurs in the last weeks of pregnancy.

Delivering earlier without medical reason increases risks for babies. Elective deliveries should be avoided before 39 weeks if possible.

However, for some high risk pregnancies or health situations, delivery at 37 weeks may be recommended. In these cases, extra monitoring and care after birth help overcome challenges of early term birth.

The bottom line is that carrying to at least 39 weeks should be the goal for most pregnancies. Reaching full maturity in the womb benefits babies both in the short and long term. Defining full term as 39 to 40 weeks reinforces avoiding early optional deliveries.