The third trimester begins the final stretch of pregnancy. At 30 weeks, visualizing the baby’s progress can be difficult, which is why comparisons to familiar objects, like fruits or vegetables, are often used to illustrate growth. This stage marks a period of rapid weight gain and refinement as the baby prepares for life outside the womb.
The 30-Week Size Comparison
At 30 weeks of gestation, your baby has reached a substantial size, often compared to a large head of cabbage or a coconut. The average measurement at this point shows the baby weighs approximately 3 pounds. In terms of length, the average fetus measures around 15.5 to 16 inches from head to heel. Your baby is now growing quickly, gaining about half a pound each week until birth. This means the space inside the womb is becoming more limited, leading to stronger, more noticeable movements.
Key Developmental Milestones
The brain undergoes a significant growth spurt during this time, rapidly maturing to support cognitive and physical functions. The surface of the brain begins to develop the characteristic complex folds and grooves. This structural change is a major step in preparing the central nervous system for coordinating life outside the uterus.
The accumulation of white fat is being deposited beneath the skin. This fat serves as a form of insulation, helping the baby regulate their own body temperature after birth. The addition of these fat layers also smooths out the wrinkled appearance of the skin, making the baby look plumper and more like a newborn.
The lungs continue their path toward maturity. The baby regularly performs practice breathing movements, inhaling and exhaling amniotic fluid. Specialized cells within the lungs are producing surfactant, a slippery substance that coats the air sacs and prevents them from collapsing upon the first breath. Red blood cells, essential for oxygen transport, are now being produced within the bone marrow.
Maternal Changes in the Third Trimester
Entering the third trimester brings several physical changes for the expectant parent. Fatigue often returns, sometimes due to the sheer effort of carrying the extra weight and the difficulty of finding a comfortable position for restorative sleep. This exhaustion is compounded by the need to wake more frequently to use the restroom, which interrupts continuous rest.
Shortness of breath is common at this stage because the expanding uterus pushes upward on the diaphragm, restricting the lungs’ ability to fully inflate. As the uterus extends further up underneath the rib cage, deep inhalation becomes more challenging. The pressure from the growing uterus can also contribute to heartburn, as stomach acids are more easily pushed back up into the esophagus.
Expectant parents may notice the tightening sensation of Braxton Hicks contractions, which are the body’s way of practicing for labor. These contractions are typically irregular and painless, unlike true labor. They are an expected part of the uterine muscles preparing for birth. Back pain and swelling in the ankles and feet are also frequent symptoms. These are caused by weight gain and the pressure of the uterus on the pelvic veins.