The final weeks of pregnancy are a time of rapid development and preparation for birth. As your due date approaches, your baby is fine-tuning essential bodily functions, gaining weight, and positioning for delivery. These last few weeks are crucial for brain development, lung maturity, and overall growth. Understanding what’s happening inside your womb can help you prepare for labor and delivery while appreciating the incredible changes your baby is undergoing.
Weeks 32–36: Rapid Growth and Fat Storage
Weight Gain and Fat Development
During weeks 32 to 36, your baby undergoes a significant growth spurt, gaining about half a pound per week. By the end of this period, most babies weigh between 4 and 6 pounds and measure around 17 to 19 inches long. This rapid weight gain is primarily due to fat accumulation, which plays a vital role in regulating body temperature after birth. Previously, your baby’s skin appeared thin and wrinkled, but as fat layers develop, the skin becomes smoother and more resilient.
Bone and Skeletal Development
Your baby’s skeleton continues to harden during this time, although the skull remains soft and flexible. This flexibility allows the baby’s head to mold and pass more easily through the birth canal. The bones in the rest of the body, such as the arms and legs, are also strengthening, thanks to the continuous absorption of calcium from the mother. This is why getting enough calcium during pregnancy is crucial for both you and your baby.
Organ Maturation and Functionality
By 30 weeks pregnant, most of your baby’s organs are fully developed, with the exception of the lungs, which continue maturing. The digestive system is also functioning efficiently, as the baby regularly swallows amniotic fluid, which gets processed by the intestines and kidneys. This swallowing reflex helps prepare the baby for feeding after birth.
At this stage, the kidneys are producing urine, and your baby is actively passing it into the amniotic fluid. The liver is continuing to develop, storing iron and producing enzymes needed for metabolism. The pancreas is also working hard to regulate insulin, which will be crucial for managing blood sugar levels after birth.
Brain Development and Sensory Growth
The brain is growing rapidly during this period, developing more complex neural connections. By week 36, your baby’s brain is about two-thirds the size of an adult brain, with millions of neurons forming every day. This growth supports learning, memory, and sensory processing.
Your baby’s senses are also sharpening. They can now recognize your voice and may even respond to familiar sounds with movement. Their vision is improving, and they can distinguish between light and darkness. If you shine a flashlight on your belly, your baby might react by turning their head or blinking. Taste buds are also well-developed, and since flavors from the mother’s diet pass into the amniotic fluid, your baby is already experiencing different tastes.
Weeks 37–39: Final Development and Lung Maturity
At 37 weeks, your baby is considered full-term. However, the final weeks before birth are still crucial for lung and brain development. The lungs begin producing more surfactant, a substance that helps keep the air sacs open for breathing after birth. Babies born before 39 weeks sometimes experience respiratory distress because their lungs might not yet be fully mature.
Brain growth is also significant during these weeks. Neural connections continue to form rapidly, enhancing cognitive abilities and sensory functions. Research suggests that babies born closer to 39 or 40 weeks have better brain development than those born earlier.
Your baby is also refining reflexes needed for survival, such as sucking and grasping. This means they are preparing for their first feeding moments outside the womb.
Week 40 and Beyond: Readiness for Birth
By week 40, your baby weighs an average of 6 to 9 pounds and measures around 19-21 inches long. Most babies are in the head-down position, ready for delivery. If your baby has not yet engaged in the pelvis, they may drop lower, preparing for labor.
The placenta continues to provide essential nutrients, but after 40 weeks, it starts aging, which is why doctors monitor overdue pregnancies closely. Some babies take their time and arrive after 41 or even 42 weeks, but medical professionals may recommend induction if the pregnancy extends too long.
The Bottom Line
The final stretch of pregnancy is a time of remarkable growth and development for your baby. Every extra day in the womb allows for improved brain function, lung maturity, and fat accumulation, ensuring your baby is ready to thrive outside the womb. While the anticipation of labor can be overwhelming, knowing that each additional week supports your baby’s health makes the wait worthwhile. As you approach delivery, trust that your body and baby are working together for a smooth transition into the world.
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