One of the most exciting parts of pregnancy is feeling your baby grow and move inside of you. From the moment you conceive, your baby is constantly growing and changing, with key developmental steps occurring every day. Over the course of the next nine months, your baby will go through several phases of growth and you can track them according to what trimester of pregnancy you're in.
The First Trimester
Your baby begins the first trimester as a fertilized egg, which is a cluster of multiplying cells. According to the Mayo Clinic, the inner cluster of cells becomes the embryo while an outer cluster forms a protective membrane. The zygote travels down the fallopian tube until it reaches the uterus and burrows into the uterine wall. At this stage, the placenta and your baby's brain, heart and spinal cord will begin to form. The foundation for your baby's bones, muscles, kidneys and reproduction organs are also in place. The heart typically begins beating around week 5. By week 6, your baby's facial features will begin developing, along with tiny buds which will become limbs. Over the next few weeks, toes, ears, fingernails and genitalia will form. By week 12, your baby is approximately 2 1/2 inches long and weighs about 1/2 oz.
The Second Trimester
Your baby grows rapidly during the second trimester. According to the Mayo Clinic, by week 16 your baby is producing urine, making small movements, developing a bone structure and making facial expressions. The sex becomes apparent, fat begins to accumulate and your baby can now hear outside sounds. At week 20, you may begin to feel your baby's movements as he becomes aware of his surroundings. Hair, fingerprints and footprints begin to form and the fingernails are fully developed by week 26. By the end of the second trimester, your baby's length and weight have approximately tripled.
The Third Trimester
The third trimester is the home stretch for your baby's growth. According to Parents Magazine, your baby will begin to open his eyes, which are protected by his now-developed eyelashes. At the start of the third trimester, your baby weighs approximately 2 1/2 pounds and measures 14 to 16 inches in length. Your baby's brain continues to grow and he continues to accumulate fat. Fetal eye color typically develops around week 31 and your baby is practicing using his newly formed lungs. Your baby's movement may begin to slow as he grows larger. By week 37, your baby is considered full-term and all his organs are ready to function on their own. The baby typically achieves a head-down position and settles into your pelvis to await delivery. Parents Magazine advises that the average baby weighs 6 to 9 pounds and is 18 to 21 inches in length by week 40.
