It's the last trimester of your pregnancy, and your baby is making her final growth spurt. During weeks 36 to 41 her prenatal development is nearing completion. As you reach the final few weeks, your pregnancy is categorized by "term." The 37th and 38th weeks define an "early-term pregnancy"; "full-term" refers to pregnancies in their 39th and 40th weeks; and those in the 41st and 42nd weeks are considered "late-term."
At week 36 your baby's overall length most likely ranges between 16 and 19 inches and his weight is roughly 6 pounds, according to the U.S. Office on Women's Health. His lungs are structurally developed now, but if he is born during this week he may need help breathing. Production of surfactant, the substance that will keep his air sacs open, isn't always complete at this time.
Week 37 marks the beginning of the early-term stage. From this point on your baby is sufficiently developed to leave your womb safely. She's starting to turn downward, getting into the final birth position. She has started to shed the fine hair called lanugo that has covered her body, according to Women's Healthcare Topics. Replacing it is fine, fuzz-like "vellus hairs."
Your still-growing baby is between 17 and 20 inches in length and may weigh as much as 7.5 pounds by week 38, according to the American Pregnancy Association. The U.S. Office of Women's health notes that by this time your baby's organs are fully formed and can function on their own.
The waxy coating — known as the vernix — that has coated your baby's skin is gone by week 39, according to the website KidsHealth. By this point your baby should have completely turned into the head-facing-down position and is ready for labor to begin.
Week 40 marks the time when your baby is completely ready to make his grand arrival. That said, only 5 percent of women actually give birth on their due dates, according to the website KidsHealth. Your baby has grown to reach his birth size, and may be 20 inches long or longer.
A delivery a week or longer after the 40th week is considered late. Even though you aren't overdue — or post-term — until 42 weeks and 0 days, your baby's size may make it uncomfortable to keep up with your normal daily routine. Given the already close quarters, your baby won't have much room to grow any more.