When is Baby Full Term: The Importance of a 40 Week Pregnancy

The Last Few Weeks of a Full Term Pregnancy

A full-term pregnancy is important for a baby’s health. Crucial developmental processes need the full 40 weeks to complete. Various organs also need the full 40 weeks to develop.

Lung Development: The final weeks of pregnancy are essential for baby’s lungs to fully develop. During the last few weeks of pregnancy, the baby’s body has time to make surfactant. Surfactant helps the air sacs in the lungs inflate and keeps them from collapsing. This is critical for the baby’s ability to breathe independently after birth.

Brain Development: The baby’s brain undergoes significant growth and development throughout the pregnancy. The final weeks are crucial for fine-tuning and completing this process. This helps ensure optimal cognitive function and neurological development.

Immune System: As pregnancy nears its end, the immune system keeps getting stronger. Spending more time in the womb allows antibodies to pass from the mother to the baby through the placenta. This helps the baby fight off infections and sickness better once they’re born. Although the baby’s immune system gets better during the early years, it doesn’t fully mature until they reach adolescence.

Body Fat Accumulation: In the last weeks of pregnancy, the baby accumulates body fat. This serves as insulation and a source of energy. Preterm infants, those born before 37 weeks, face many challenges in maintaining a stable body temperature. This is especially true for babies born very early. The lack of body fat hinders their ability to conserve heat. Preterm babies also have limited brown fat, which generates heat in response to cold temperatures. Their delicate skin also contributes to increased heat loss. This further complicates temperature regulation. The underdeveloped temperature regulation mechanisms pose difficulties for preterm infants. These mechanisms include shivering and blood vessel constriction. They make it hard for preterm infants to respond to temperature changes. 

Digestive System Preparation: Around 30 weeks of pregnancy, baby’s intestines start absorbing nutrients. By 32 weeks, they’re fully functional. Even though the baby doesn’t eat or digest food in the womb, a substance called meconium starts building up in their intestines before birth. Meconium is a mix of amniotic fluid, mucus, skin cells, and other things the baby swallows in the womb. It usually stays in their intestines until after they’re born.

Refinement of Senses: In the final weeks of pregnancy, a developing fetus refines its sensory abilities. The nervous system undergoes maturation. The eyes continue to develop, allowing the baby to respond to changes in light. The auditory system refines its ability to hear and process sounds, including the mother’s voice. The senses of taste and smell further develop. Baby is even able to experience different flavors through the amniotic fluid. The sense of touch, one of the earliest to develop, becomes more responsive. Additionally, baby becomes more aware of its own movements. This will contribute to the development of motor control and coordination. While the senses start in the womb, their full development continues after birth.

Fetal Positioning: Towards the end of pregnancy, the baby often moves into a head-down position. This is the perfect position for a smoother and safer delivery.

Full-term pregnancies contribute to the health and well-being of baby, providing them with the best possible start in life. The last few weeks before a baby is born are like the finishing touches on a masterpiece. Babies born at 40 weeks or later are more physically mature. This means they’re less likely to have problems that babies born too early might have.

Preterm Birth

Preterm birth refers to the delivery of a baby born before 37 weeks of the pregnancy. This means the baby arrives earlier than expected. If baby hasn’t had enough time to fully develop in the womb, this can pose some challenges. Preterm births can require special medical attention and care to support the well-being of both the baby and the mother.

While most pregnancies last around 40 weeks, some factors can increase the risk of preterm labor including:

• Multiple pregnancies (twins, triplets, etc.): Women carrying more than one baby are at a higher risk of preterm birth.
• Infections and chronic conditions: If the mother has infections, it might raise the chances of preterm labor.
• Previous preterm birth: Women who have had a preterm birth in a previous pregnancy are at a higher risk of experiencing it again.
• Certain pregnancy complications: Preeclampsia or gestational diabetes can increase the risk of preterm birth as well.
• Cervical issues: Short cervical length or cervical insufficiency may contribute to preterm labor.  This is a condition that causes the cervix to thin out and open too early. In women with cervical insufficiency, dilation can happen without any contractions. This condition causes about 1% of preterm births. This is different from cervical dilation which is caused by contractions and signals labor.
• Maternal age: Teenagers and women over 35 may have a slightly higher risk.

When babies are born too early, they can have some problems with how their bodies develop. Their organs, like their lungs, might not be fully grown yet. That can lead to things like Respiratory Distress Syndrome (RDS), where they have trouble breathing and might need help from machines or extra oxygen.

Neurological problems, such as cerebral palsy, may arise from the underdevelopment of the brain. Preterm babies may also struggle with regulating their own body temperature and need extra monitoring.

Despite these challenges, advances in neonatal care has significantly improved in recent years. With the right help, many preterm babies go on to lead healthy lives. Regular follow-up care is important for monitoring and addressing any developmental concerns as baby grows.

How likely is labor before 37 Weeks?

Preterm labor is defined as labor before 37 weeks of pregnancy. Statistically, the majority of mothers have full-term pregnancies. According to the World Health Organization (WHO), the global rate of preterm birth is around 10%, but this can vary by region and population.

Early Term Birth

An early-term birth happens when a baby is born between 37 weeks and 38 weeks and 6 days of pregnancy. While they’re considered full term after 37 weeks, babies born during this period aren’t quite at the optimal 39 to 40 weeks mark.

The lowest risk of problems is seen in babies born between 39 and 40 weeks. Early-term births are usually safer than being born too early. However, babies in this time frame might still face some difficulties.

Early-term babies could have trouble with their lungs not being fully developed. They may also struggle to maintain the right temperature and get jaundice more often.

Babies might also find it hard to coordinate sucking, swallowing, and breathing while feeding. This can make feeding a challenge for them.

Many early-term infants thrive with proper care. Parents and healthcare providers should monitor their development. This helps find and address any challenges that may arise during this stage of early life. 

How likely is labor at 37 Weeks?

According to the National Center for Health Statistics², most babies are born full term, but 26% of births occur at 37 to 38 weeks.

Full Term 

A full-term pregnancy represents the expected duration of pregnancy. Babies born within this time frame are more likely to have fully developed organs and systems. Underdeveloped organs is the main driver of complications associated with preterm birth.

A normal full-term pregnancy is 40 weeks. However, every woman is different and timing can vary.

Even in full-term pregnancies, jaundice can cause yellowing of the skin and eyes. Some full-term infants may experience difficulties with feeding. Learning to coordinate sucking, swallowing, and breathing is not an easy task. Newborns may need help to stay warm. The majority of full-term babies are healthy. 

How likely is labor at 39 Weeks?

According to the National Center for Health Statistics², most babies are born full term. For recorded births, 57.5% occur between 39 and 41 weeks.

Late-Term Pregnancy

A late-term birth refers to the delivery of a baby between 41 weeks and 41 weeks and 6 days of gestation. It occurs after the full-term period. Late-term births are still within the normal range. However, there is an increased risk of certain complications. Healthcare providers may check moms who go beyond the 40-week mark. Most pregnancies, however, result in healthy babies during the late-term period. In certain circumstances, labor induction may be needed to speed up the labor process.

Late-term births are considered within the normal range. The likelihood of developmental issues is relatively low compared to preterm births. As pregnancies extend beyond the due date, there is a possibility of placental aging. This can impact the placenta’s ability to provide nutrients and oxygen to the baby. Late-term babies tend to also vary in size. Large babies can present challenges during delivery. Healthcare providers can keep track of the baby’s growth throughout the pregnancy. This can be a factor in the decision to induce labor.

The passing of meconium, the baby’s first stool, before birth happens more often in late-term pregnancies. If the baby breathes in meconium, it can lead to breathing problems. Though the risk is generally low, late-term pregnancies that go past the due date have a higher chance of stillbirth. A decrease in amniotic fluid may be linked to late-term pregnancies. Despite these factors, many late-term births happen without any issues. Healthcare providers keep a close eye on pregnancies during this time. If there are worries about the mom’s or baby’s health, they might suggest taking action. For instance, starting labor early can ensure a safe and healthy birth.

How likely is labor at 41+ Weeks?

According to the National Center for Health Statistics², about 6.5% of births occur at week 41 or later.

Besides Pregnancy Week, What Criteria Determine if a Baby is Full Term?

In addition to the number of weeks of pregnancy, several criteria determine if a baby is full-term:

1. Weight: A full-term baby typically weighs between 5.5 and 8.8 pounds (2.5 to 4 kilograms). Individual variations exist, but this is generally considered full size.
2. Length: A full-term baby usually measures between 18 and 22 inches (45 to 55 centimeters) in length.
3. Organ Development: A full-term baby’s organs should be fully developed and functioning properly. The lungs, brain, and liver are the last organs to fully develop.
4. Physical Appearance: Full-term babies typically have a certain appearance. They have well-defined features, a plump body, and fully-formed genitalia.
5. Muscle Tone: A full-term baby generally has good muscle tone, and is able to move their limbs freely.
6. Reflexes: Full-term babies usually exhibit reflexes such as sucking, swallowing, and gripping.
7. Skin: Their skin is typically smooth and may have a layer of vernix, a white, waxy substance that protects the skin in utero.

How the PreTRM Test Can Help

When a pregnancy is known to be at high risk of an early delivery, there are steps doctors and mothers can take to improve a baby’s chance of a healthy start.

Until recently, clinicians have had limited resources for predicting the risk of preterm birth. Up to half of all pregnant women who deliver prematurely have no known risk factors.^3,4  The PreTRM® Test for risk management predicts the risk of spontaneous preterm birth (before 37 weeks) in asymptomatic women (no signs or symptoms of preterm labor, with intact membranes) with a singleton pregnancy.³ The PreTRM Test is performed via a single blood draw between 18 and 20 6/7 weeks of gestation (126-146 days). It is not intended for use in women who have a multiple pregnancy, have a known or suspected fetal anomaly, or are on any form of progesterone therapy after the first trimester.

References:

1. “1 in 10 Babies Worldwide Are Born Early, with Major Impacts on Health and Survival.” World Health Organization, World Health Organization, www.who.int/news/item/06-10-2023-1-in-10-babies-worldwide-are-born-early–with-major-impacts-on-health-and-survival. Accessed 13 Nov. 2023. 
2. “National Vital Statistics Reports – Centers for Disease Control And …” CDC (Centers for Disease Control and Prevention), www.cdc.gov/nchs/data/nvsr/nvsr67/nvsr67_08-508.pdf. Accessed 13 Nov. 2023. 
3. Institute of Medicine Committee on Understanding Premature Birth and Assuring Healthy Outcomes. Preterm Birth: Causes, Consequences, and Prevention. Behrman RE, Butler AS, eds. Washington (DC): National Academies Press (US) 
4. Iams JD, et al. Prevention of Preterm Parturition N Engl J Med 2014;370:254-61. DOI: 10.1056/NEJMcp1103640