Third trimester milestones

ACOG describes the fetus responding with movement to familiar sounds during this range. The lungs are formed but not ready to function independently and begin producing surfactant, a substance needed for breathing after birth. Fat accumulates, and vernix develops as a protective barrier over the skin.

Formation and maturity are different. At an early gestational age, prognosis depends on the clinical circumstances, including findings that a public week guide cannot collect or interpret.

During weeks 29 through 32, the fetus can stretch, kick, grasp, open and close the eyes, and respond to changes in light. Bone marrow forms red blood cells, major structural development is largely complete, and weight gain continues. Lanugo begins disappearing, although timing varies.

During weeks 33 through 36, the brain develops rapidly, bones harden while the skull remains flexible, fat accumulates under the skin, and fingernails reach the fingertips. ACOG notes that most fetuses turn head-down during week 36 or 37. Position is checked clinically and can still change.

ACOG divides the period from 37 weeks into early term, full term, late term, and postterm. Early term is 37+0 through 38+6. Full term is 39+0 through 40+6. Late term is 41+0 through 41+6, and postterm begins at 42+0.

These labels correct the misleading idea that every week from 37 through 42 is equivalent. They still do not provide an individual delivery recommendation. Timing of monitoring, induction, or birth depends on the best obstetric estimate, maternal and fetal health, pregnancy history, preferences, and the plan made with the care team.

As space changes, movements may feel like stretches, rolls, kicks, or shifts rather than the same sensations noticed earlier. NHS guidance says movement should continue right up to and during labor. It does not endorse one universal daily count; the important reference is the baby's own usual pattern.

Call the midwife or maternity unit immediately if movement becomes less than usual, stops, or changes from the usual pattern. Do not wait until the next day, use a home Doppler for reassurance, or assume reduced movement is expected because the due date is close. Direct assessment is the safe response.

During weeks 37 through 40, the lungs, brain, and nervous system continue developing. The circulatory and musculoskeletal systems are complete in the broad developmental description, and the fetal head may move lower into the pelvis. None of these observations predicts the date labor will begin.

Use a milestone calendar to understand terminology and prepare questions, not to decide whether a symptom is normal or whether delivery should occur. Contact the maternity team for contractions, waters breaking, bleeding, changed movement, severe pain, or any concern according to the local plan. Pregnancy care continues after the estimated due date when birth has not yet occurred.