Modern obstetric science has dramatically advanced our understanding of fetal development, particularly in the brain. Historically, babies born at 37 weeks were considered “full-term,” but current research says something else. This blog aims to clarify common myths surrounding brain development in newborns, especially the crucial difference between early term (37–38 weeks) and full term (39–40 weeks). Whether you are a parent preparing for childbirth or a professional supporting maternal care, these insights are essential.
MYTH : “A baby born at 37 weeks is full-term and fully developed.”
FACT:While 37 weeks was once labeled “full-term,” research by the American College of Obstetricians and Gynecologists (ACOG) redefined gestational age categories:
- Early Term: 37–38 weeks
- Full Term: 39–40 weeks
According to studies published in JAMA Pediatrics and The Journal of Pediatrics, at 37 weeks, a baby’s brain is only 65–70% of its full-term size. The final weeks contribute significantly to:
- Myelination (insulation of neurons)
- Cortical folding (formation of cognitive and sensory brain regions)
- Rapid brain weight increase
- Development of memory and attention functions
References:
- Spong CY. (2013). Defining “term” pregnancy: recommendations from the Defining Term Pregnancy Workgroup. JAMA.
- Kinney HC. (2006). The near-term (late preterm) human brain and risk for periventricular leukomalacia. Semin Perinatol.
MYTH : “There’s no harm in scheduling delivery at 37 weeks for convenience.”
FACT: Elective inductions or cesarean sections without medical necessity before 39 weeks increase the risk of:
- Respiratory distress
- Feeding difficulties
- Neonatal jaundice
- Learning and developmental delays
The last two weeks in utero are essential for brain maturity. Delaying delivery until at least 39 weeks improves long-term cognitive and behavioral outcomes.
Reference:
- Tita ATN et al. (2009). Timing of elective repeat cesarean delivery at term and neonatal outcomes. NEJM.
MYTH : “If the lungs are mature at 37 weeks, the baby is ready.”
FACT: Lung maturity is just one milestone. The brain, liver, and immune system continue to develop through 39–40 weeks.
Babies born early may face:
- Poor temperature regulation
- Immature suck–swallow reflexes
- Higher NICU admission rates
Reference:
- Raju TNK et al. (2006). Moderate late preterm infants and risks of neurodevelopmental disorders. Pediatrics.
MYTH : “Once a baby is outside the womb, development is the same.”
FACT: The intrauterine environment provides:
- Neurotrophic factors (for neuron growth)
- Hormonal regulation
- Protection from overstimulation
Missing this period may lead to:
- Sensory processing disorders
- Feeding issue
- Delayed motor milestones
Reference:
- Volpe JJ. (2009). Brain injury in premature infants: a complex amalgam of destructive and developmental disturbances. Lancet Neurol.
MYTH : “A baby’s brain develops mostly after birth.”
FACT: While postnatal brain development is significant, the architecture is largely laid down in the final prenatal weeks:
- At 35 weeks: Brain = ~2/3 of full-term size
- By 39–40 weeks: Brain volume increases by over 30%
- Critical areas like the cortex, cerebellum, and hippocampus mature rapidly
Reference:
- Hüppi PS et al. (1998). Quantitative magnetic resonance imaging of brain development in premature and mature newborns. Ann Neurol.
MYTH : “Developmental delays only occur with very premature birth (<34 weeks).”
FACT: Even early term babies (37–38 weeks) may show subtle but significant delays in:
- Executive functions
- Emotional regulation
- Speech and language development
Children born at 37–38 weeks have increased likelihood of needing special education later in life.
Reference:
- Noble KG et al. (2012). Neonatal brain structure and socio-economic disparities. Dev Psychobiol.
MYTH : “Elective C-sections at 37–38 weeks are safe if the baby looks healthy on ultrasound.”
FACT: Ultrasound cannot accurately assess:
- Cortical development
- Synaptic pruning
- Functional brain readiness
Delaying delivery until 39 weeks reduces risk of:
- NICU admissions
- Apnea
- Hypoglycemia
Reference: Clark SL et al. (2009). Neonatal morbidity associated with elective delivery before 39 weeks. Am J Obstet Gynecol.
MYTH : “There’s no difference between babies born at 37 vs 39 weeks.”
FACT: MRI studies show marked differences:
- Gray and white matter volumes increase significantly between 37 and 39 weeks
- Neurobehavioral assessments at birth are more favorable at 39 weeks
Babies born at 39 weeks typically show:
- Better sleep–wake cycles
- Stronger reflexes
- More stable brainstem responses
Reference:
- Thompson DK et al. (2007). MR-determined hippocampal asymmetry in full-term and preterm neonates. Hippocampus.
Summary Table: 37 Weeks vs 39 Weeks
| Aspect | 37 Weeks (Early Term) | 39–40 Weeks (Full Term) |
| Brain Weight | ~65% of full-term brain | 100% brain mass |
| Myelination | Incomplete | Accelerated |
| Sensory System | Under-responsive or sensitive | Well-regulated |
| Feeding & Suck | Poor coordination possible | Mature feeding |
| NICU Risk | Higher | Lower |
| Learning Outcomes | Mild delays possible | Optimal cognitive outcomes |
| Motor Skills | Risk of hypotonia | Better tone & control |
Golden Message: Delaying birth until at least 39 weeks, when medically possible, provides the baby with the best foundation for:
- Brain development
- Emotional regulation
- Motor control
- Learning potential
Whether we’re a parent, therapist, or healthcare provider, support full-term pregnancy and educate others about the hidden power of the last two weeks(38&39).
About Shama Foundation
We at Shama Foundation are committed to empowering families and professionals with evidence-based resources that support early childhood development, maternal health, and neurodevelopmental care.
