The 27-week mark signifies the final week of the second trimester and the gateway into the intensive growth period of the third trimester. This stage brings rapid changes for the developing fetus and noticeable shifts in the mother’s physical experience. Understanding the size, internal development, and accompanying maternal changes helps prepare for the final weeks of this remarkable journey.
The 27-Week Fetal Size Comparison
At 27 weeks, the fetus has reached an average size often compared to a head of cauliflower, an analogy that helps illustrate its increasing bulk and weight. The average length, head to heel, is between 14 and 14.5 inches. This reflects the body straightening out as space within the uterus becomes more limited.
Weight gain is accelerating; the fetus now weighs approximately 2 to 2.3 pounds (860 to 1,000 grams). This substantial weight gain is due to the continued accumulation of fat beneath the skin, which is transitioning from thin and wrinkled to smoother.
Key Developmental Milestones
The internal systems of the fetus are reaching significant levels of maturation during this period. The lungs are rapidly developing by beginning the production of surfactant, a substance composed of lipoproteins. Surfactant is deposited into the air sacs (alveoli) and works to lower surface tension, preventing the air sacs from collapsing when the baby takes its first breath after birth.
Sensory development is highly advanced; the eyes, which had been fused shut, are now capable of opening and closing to perceive light and dark. The auditory system is fully functional, and the fetus can increasingly distinguish the voices of its mother and partner. The brain is undergoing a period of rapid growth, beginning to form the characteristic folds and fissures seen in a mature brain.
This complex neurological activity is responsible for more defined sleep-wake cycles. The nervous system continues to mature, improving the coordination of movements that the mother feels as distinct kicks and jabs. These milestones indicate a growing physiological readiness for life outside the womb, though the remaining weeks are needed to fully solidify these systems.
Maternal Experiences and Symptoms
The significant growth of the fetus and the uterus causes several predictable physical symptoms for the mother at 27 weeks. Many women experience increased lower back pain and pelvic discomfort as the body’s center of gravity shifts forward. Hormones cause the ligaments and joints in the pelvis to loosen in preparation for delivery, contributing to aches and instability.
A common symptom is round ligament pain, which manifests as sharp, cramping feelings in the lower abdomen or groin area. This occurs when the ligaments supporting the expanding uterus are stretched by sudden movements. Braxton Hicks contractions, often described as a painless tightening of the abdomen, may become more frequent as the uterus practices for labor.
Increased blood volume and pressure from the growing uterus can lead to moderate swelling, known as edema, often seen in the feet and ankles. The physical discomfort and the need for frequent nighttime bathroom trips contribute to fatigue and disturbed sleep.
Important Medical Checkpoints
The 27-week mark is a time for important clinical monitoring and preventative care. Expectant mothers are advised to begin or continue monitoring fetal movement through kick counts. This practice involves tracking the time it takes to feel a certain number of movements, serving as a simple way to assess the fetus’s well-being.
For many, this period falls within the window for the oral glucose tolerance test, a screening for gestational diabetes, which is typically performed between 24 and 28 weeks. Healthcare providers often recommend the Tdap (tetanus, diphtheria, and pertussis) vaccine around this time, usually between 27 and 36 weeks, to pass on immunity to the newborn. Parents should be aware of the signs of pre-term labor, such as persistent abdominal cramping, pelvic pressure, or any unusual changes in vaginal discharge, and report them immediately.