Pregnancy, while an exciting time in your life, can also leave you on the edge of your seat as you wonder how your baby is growing and developing inside you. Just as you mark each of his developmental milestones once he is born, knowing how his transformation occurs in the womb allows you to do the same. The easiest way to track his growth and changes is by each trimester of your pregnancy.
First Trimester Milestones
Weeks one through 12 constitute the first trimester, and this is when conception, fertilization and basic development begins. During this time, your baby's major organs, such as his heart and brain, begin to form along with his spinal cord.
By the sixth week of pregnancy, or four weeks after conception, his heart will begin pumping blood and some of his facial features are apparent. A mere week later, his nostrils can be seen and the lenses of his eyes take shape. He will begin moving once you have reached your eighth week, however it is generally so slight it cannot be felt.
By the end of this trimester, his arms are growing and bones develop, allowing him to bend his elbows. His head is larger than his body, his external genitals begin developing and his fingernails start to grow. At this point, he is approximately 2 1/2 inches long.
Second Trimester Milestones
Weeks 13 through 27 mark the second trimester and is an exciting time for parents who wish to know the sex of their baby; it is during this trimester that the genitals are developed and the gender can be seen.
Your baby's facial muscles are also further developed, allowing her to squint or frown, according to the Mayo Clinic. By week 18, she can hear sounds inside the womb, such as your heartbeat. The following week, she may be able to hear conversations taking place outside the womb and begin recognizing your voice.
The second trimester is when the baby begins sleeping and waking on a regular schedule, and hair begins growing on her head. Toward the end of this stage, her hands are fully developed, as are her fingernails, although her lungs and immune system are still in the developmental process.
Third Trimester Milestones
Your baby begins preparing for his arrival by practicing the opening and closing of his eyes. While still soft, all of his bones are now formed, and gender development is still continuing.
He begins to practice breathing while in your womb, around your 32nd week, and when he kicks, it may feel quite a bit more powerful. He can now see light through the womb and may blink when it is too bright.
By 36 weeks, his weight gain will increase drastically; during week 34 he may weigh approximately 4 lbs., however beginning around week 36, he will begin to gain a 1/2 lb. each week. Once you reach week 37, your baby is considered full-term and may arrive any time. This is when he may descend, head down, into your pelvis. Provided your baby chooses to wait until week 40 to make his appearance, his toenails will continue to grow, meeting the edge of his toes. You may deliver a week or two late; the length of time your doctor permits before inducing your labor is at his discretion.
