How Many Weeks is a Full Term Pregnancy?

A full term pregnancy lasts between 39 to 40 weeks. This is measured from the first day of the woman’s last menstrual period up until she gives birth. Anything less than 37 weeks is considered preterm, while 41 to 42 weeks is still considered full term. There are important milestones at the end of a full term pregnancy that determine when the baby is ready to deliver.

Key Takeaways on Full Term Pregnancy

A full term pregnancy is 39 to 40 weeks from the woman’s last menstrual period to birth.
37 to 38 weeks is early term, 41 to 42 weeks late term, but all are still considered full term pregnancies.
Important fetal developments happen in the final weeks of pregnancy to prepare the baby for life outside the womb.
Going into labor naturally signals the baby is mature and ready for delivery at full term.
Inducing delivery or scheduled c-sections are typically done no earlier than 39 weeks unless medically necessary.

How Pregnancy Weeks Are Calculated

Pregnancy length is measured starting from the first day of the woman’s last menstrual period prior to conceiving. This day counts as part of week one even though conception doesn’t actually occur until around two weeks later when ovulation and fertilization happen. From the start of the last period, a full 40 week pregnancy is average. This 40 weeks is divided up into trimesters:

First trimester: Week 1 through end of Week 13
Second trimester: Week 14 to end of Week 26
Third trimester: Week 27 through delivery

The third trimester spans the final 13 to 14 weeks of pregnancy leading up to birth. Even though it is measured at 40 weeks, some sources consider 37 to 42 weeks to be full term. The due date estimated by a doctor is based on the start of the woman’s previous menstrual cycle. But not every pregnancy lasts exactly 40 weeks.

Factors like the actual conception date, the mother’s health, genetics, and the baby’s size can all influence the length of a normal pregnancy. While most fall between 38 and 42 weeks, delivery can happen anytime in that window and be considered full term.

Pregnancy Milestones Leading to Full Term

Important developmental milestones happen in the fetus during the last weeks before full term that determine when the baby is ready for delivery:

Lung Development

Between weeks 36 and week 38, the lungs become fully mature.
Lung surfactant production increases, allowing the air sacs to inflate with ease after birth.
Respiratory movements prime the lungs to breathe air.

Brain Development

Around week 33, the brain begins developing important complex functions.
The folds and grooves of the cerebral cortex that control reasoning, problem solving, and emotional control form.
Cerebellum development controlling vital motor skills, coordination, and reflexes continues through week 40.

Body Fat Accumulation

Fat layers underneath the skin increase between weeks 33 and 40.
Brown fat around the shoulders, neck, and back store calories to generate heat and prevent drops in temperature after birth.

Immune System Buildup

Antibodies from the mother transfer to the baby through the placenta and breast milk from weeks 36-40.
The newborn relies on these antibodies until its own immune system matures around 6 months old.

Organs Finish Developing

The liver, kidneys, pancreas, lungs, brain, intestinal tract, muscles, bones and nervous system complete development.
Organs shift into position for birth and prepare to function independently of the mother.

Timing Delivery at Full Term Pregnancy

Left entirely to nature, labor will spontaneously start when the baby is fully developed and ready to deliver, most often between weeks 38 and 42. However, there are medical reasons why a doctor may induce labor or schedule a cesarean section (c-section) delivery before this happens.

The American College of Obstetricians and Gynecologists states it is reasonable to induce delivery at 39 weeks in healthy first time mothers with an uncomplicated pregnancy. Scheduled c-sections and elective inductions should not happen before 39 weeks unless medically necessary.

Here are factors that go into scheduling delivery for full term pregnancies:

Due Date Estimates: Doctors estimate the due date based on menstrual cycles, but this is not an exact science. They will schedule delivery or induction after 39 weeks based on their best estimate.
Baby’s Size: If routine ultrasounds suggest the baby is measuring larger than average, the doctor may schedule an earlier delivery to avoid complications.
Medical Risks: Conditions like gestational diabetes, preeclampsia, or placental problems can prompt delivery at 37-39 weeks.
Previous C-section: Women with a prior c-section often schedule a repeat one about 39 weeks to avoid going into labor and risking uterine rupture.
Mother’s Health: Medical issues in the mother like high blood pressure may warrant induction or c-section around 37-39 weeks.
Special Circumstances: In vitro fertilization pregnancies, twins or other multiples, or other unique situations sometimes call for scheduled delivery between 37-39 weeks.

Ideally, naturally going into labor signals the baby is fully developed and ready for delivery. But doctors must balance this with potential medical risks to the mother and baby when scheduling birth for full term pregnancies.

What Happens in Early and Late Full Term Births?

Pregnancies that result in birth from 37-42 weeks are considered full term, even though 37-38 weeks is still somewhat early. Here is how these early and late term births compare:

Early Term Birth 37-38 Weeks

Babies born at 37-38 weeks may have:

Immature lungs leading to possible respiratory distress
Jaundice from underdeveloped liver function
Poor feeding, low blood sugar, and dehydration
Delicate skin and blood vessels
Greater risk of infection
Difficulty regulating body temperature

They often require extra monitoring, IV fluids, nursing assistance, and blood tests after birth. Most outcomes are still favorable, but early term babies may have slightly higher risks for cerebral palsy, asthma, and other complications.

Late Term Birth 41-42+ Weeks

Pregnancies lasting beyond the estimated due date are considered late term or post-term. At 41-42 weeks, potential risks include:

The placenta deteriorating, providing less oxygen and nutrients
The amniotic fluid volume decreasing
Compression of the umbilical cord compromising blood flow
Larger birth weight and risk of shoulder dystocia during vaginal delivery
Higher chance of needing a c-section due to stalled labor

To avoid complications, doctors typically induce labor after 41 weeks if it doesn’t start naturally before then.

Outcomes for Full Term Babies

Barring any medical issues, babies born between 37 and 42 weeks at full term have excellent outcomes:

They can breathe, suck, swallow, and cry at birth with mature lungs
Digestive system and liver can process milk and food normally
Able to maintain proper temperature, blood sugar, and hydration
Strong immune function to fight infections
Developed nervous system and reflexes
Expected physical growth and abilities on track developmentally

Any birth from 37-42 weeks allows the organs to function on their own at birth without intensive medical interventions. These full term babies are monitored closely and may require some extra support as needed before being discharged home by 5-7 days old in most cases.

Preparing for Delivery at Full Term

If you’ve reached 37 weeks, you’re nearly at the end of your pregnancy journey. Here are some tips to prepare both physically and mentally for delivery at full term:

Pack your hospital bag with clothes, toiletries, electronics, and any other comfort items. Have your birth plan ready to share with your doctor.
Take childbirth, breastfeeding, and infant care classes if desired. Tour potential hospitals and prepare your home.
Understand the signs of labor like regular contractions, water breaking, and mucus discharge that signal it’s time.
Make arrangements for older children and pets during the hospital stay. Store up easy frozen meals and snacks.
Stay in close contact with your doctor to discuss any symptoms and get guidance on timing induction or c-section.
Rest and relax as much as possible! Make time for yourself before baby arrives.
Take care of any final tasks at work and settle any outstanding to-do list items to minimize stress beforehand.
Discuss pain relief preferences with your doctor and options like epidurals.
Connect with your partner and support system about their role during labor to make sure everyone is ready.
Don’t hesitate to call your doctor with any questions or concerns as you reach full term! Staying informed will help ease anxiety.

Reaching the 37 week mark means you could go into labor at any time. While exciting, this period of waiting can also create nervous anticipation. Staying proactive and focused on self-care will help you feel empowered leading up to delivery.

Frequently Asked Questions About Full Term Pregnancy

Can you go into labor before 37 weeks at full term?

No, delivering before 37 weeks is preterm labor. Full term is considered 37 weeks to 42 weeks. Anything before 37 weeks is premature and more dangerous for the baby.

What if you go past your due date at 40 weeks?

It is common for pregnancy to last longer than the estimated due date. Up to 42 weeks is still considered full term. After 41-42 weeks doctors may induce labor to avoid potential problems.

Are babies bigger if you go past your due date?

Babies continue gaining about an ounce per day in late pregnancy. Going one to two weeks past the due date can mean a slightly larger baby. There are greater risks of shoulder dystocia with bigger babies.

Can you request an induction at 39 weeks without medical need?

Some doctors allow elective inductions or scheduled c-sections starting at 39 weeks without other medical factors. However, there are risks to mother and baby with early intervention without need.

Is it better to induce or have a c-section if indicated before due date?

It depends on the reasons for early delivery and a woman’s health factors. Vaginal delivery is possible with induction but higher likelihood of ending in c-section. Scheduled c-sections provide more control.

Ensuring the Best Outcomes at Full Term

Reaching 39 to 40 weeks pregnant is an exciting milestone signaling the arrival of your baby is near! With careful planning, monitoring, and proactive communication with your doctor, you can optimize your health and your baby’s during the final stretch before delivery.

Staying informed on what to realistically expect during full term, how delivery timing decisions are made, and preparing yourself emotionally can help you feel empowered leading up to the big day. Don’t hesitate to ask your medical providers questions or voice any concerns you have during this critical transition period.

Whether your baby decides to arrive a little early, right on time, or slightly late, you can ensure the best outcomes by working closely with your support team and trusting the process. Focus on maintaining your own health, rest and nutrition levels so you feel your absolute best going into labor. At full term, you made it to the home stretch!