A pregnancy comprises of 3 Trimesters counting from the first day of last menstrual period totaling 40 weeks. We have detailed the 3-trimester development stages for the fetus in below link:
The Fertilized egg grows into a microscopic ball of cells & implants on the wall of your uterus. This implantation triggers a series of physical and hormonal changes in your body. As the fertilized egg grows, a water-tight sac forms around it, gradually filling with fluid. This is called an amniotic sac, and it helps cushion the growing embryo in the womb. The tiny “heart” will beat approximately 65 times a minute by the end of the fourth week. By the end of the 1st month, your baby is about 1/4 inch long which will be smaller than a grain of rice!
In this month your baby’s facial features will continue to develop. Each ear begins with a little layer of skin at the side of the head. Tiny arms and legs are forming along with Fingers, toes, and eyes.
The neural tube (brain, spinal cord and other neural tissue of the central nervous system) is well-formed and developing. The digestive tract and sensory organs will also begin to develop. Bone starts to replace cartilage in this month.
The head is large in proportion to rest of the body of the baby. Your baby is about 1 inch long and weighs about 1/30 of an ounce by the end of the second month. At around 6 weeks, your baby’s heartbeat can usually be detected.
The 3rd Month of pregnancy marks the development of your baby’s arms, hands, fingers, feet, and toes. Now your baby can also open and close its fists and mouth. The Fingernails and toenails are beginning to develop and the external ears are formed by this month. The teeth are forming at this stage. Your baby’s reproductive organs will also develop.
By the end of the third month, your baby is fully formed. Your baby is about 4 inches long and weighs about 1 ounce. However baby’s most critical development has taken place, your chance of miscarriage drops considerably after three months.
You can listen to your baby’s heartbeat through a doppler. The fingers and toes are well-defined. The formation of Eyelids, eyebrows, eyelashes, nails, and hair is also completed. You may be surprised to know that your baby can even suck his or her thumb, yawn, stretch, and make faces.
The nervous system is starting to function in the fourth month. The reproductive organs are now fully developed. Your baby is about 6 inches long and weighs about 4 ounces by the end of the fourth month.
You may begin to feel your baby’s movement as he/she is developing muscles and exercising them. Hair begins to grow on the baby’s head. Soft fine hairs cover your baby’s shoulders, back, and temples. This hair protects your baby and shed at the end of the baby’s first week after birth.By the end of the fifth month, your baby is around 10 inches long and weighs about 1/2 to 1 pound.
Your baby’s skin is reddish in color and wrinkled. The veins are visible through the baby’s translucent skin. The eyelids begin to part and the eyes can be open too.
Baby responds to the surround sounds by moving or by increasing the pulse. You may notice the jerking motions if baby hiccups in the womb.
If born premature, your baby may survive after the 23rd week with intensive care and positive parenting. Your baby is about 12 inches long and weighs about 2 pounds by the end of the sixth month.
The baby will continue to mature and develop reserves of body fat. Your baby’s hearing ability is fully developed. He or she can change its position frequently and responds to the stimuli, including music, pain, and light. The amniotic fluid begins to diminish by the seventh month. At the end of this month, your baby is about 14 inches long and weighs from 2 to 4 pounds.
Your baby will continue to mature and develop reserves of body fat during this month too. You will notice the frequent kicks from your baby. At this time your Baby’s brain is developing rapidly and your baby can also see and hear. Most internal systems are well developed, but the lungs may still be immature by this month. Your baby is around 18 inches long and weighs as much as 5 pounds.
Your baby continues to develop and mature: the lungs are nearly fully developed and grown.
Your baby’s reflexes are coordinated in order to blink, close the eyes, turn the head, grasp firmly, and respond to sounds, light, and touch. Baby is definitely ready to enter the world by now! Your baby’s position also changes to prepare itself for labor and delivery. The baby drops down in your pelvis to get into the position. Most probably, the baby’s head is down toward the birth canal.
Your baby is around 18 to 20 inches long and weighs about 7 pounds by the delivery time.