If your mom is pregnant, you might be curious about what exactly is going on and how the baby is forming before it is ready to be born. This article will take you through a typical pregnancy month by month so that you understanding just what’s happening with your baby brother or sister — before you ever meet them!

Month 1

Your baby brother or sister starts out as a tiny fertilized egg!  About 7-10 days after the egg has been fertilized, it will attach itself to the wall of the womb (also called the uterus). This is called implantation and it is an important part of the pregnancy!  The cells reproduce quickly and the egg becomes what is called a zygote. The amniotic sac — where the baby will live while it is growing — and the umbilical cord — which will give the baby the nutrients that it needs — is already beginning to form.

By the end of month one, the baby will be about 2 millimeters long.

Month 2

During the second month, the zygote grows to become a fetus.  Very important parts of the fetus’s body begin to form at this time: the heart, the neural tube (which eventually becomes the spine), the arms and legs and all the major organs begin to form.  Sensory organs like the eyes, ears, and mouth begin to form as well.  Fingers and toes will often appear — but are webbed!  Pretty cool, huh?

By the end of the second month, the baby will only be about ½ to ¾ of an inch long.

Month 3

In the third month the baby’s arms and legs begin to move.  The major organs are developed by the end of this month and a fetal heartbeat can be detected with Doppler.  As the limbs, head and trunk develop, the fetus begins to take the recognizable shape of a baby.  The end of the third month marks the end of the first trimester of pregnancy.

By the end of the third month, the baby will be around 3-4 inches long.

Month 4

The fourth month will find an increase in the baby’s activity level and mom will usually be able to to feel him or her moving around!  Developmentally, the baby’s teeth and hair as well as its digestive system is beginning to form as well.  By the fourth month, it will be possible to tell if the baby is a boy or a girl.

By the end of the month four, the baby will be 5-6 inches long.

Month 5

During the fifth month of pregnancy, a fine downy hair called lanugo will cover a baby’s body. The baby’s eyelashes and eyebrows will develop as well at this point.  The baby will be doing simple movements like swallowing and sucking, important skills to learn for after its birth. One of the most exciting things about month 5 is that the baby’s ears are now fully developed and it can hear you — and your parents — even while inside the womb!

By the end of month 5, the baby will be 7-8 inches long.

Month 6

One of the most important things that happens during the 6 months is that the baby’s immune system — which will protect it from illness and disease — is beginning to develop.  He or she is creating its own antibodies, which will help kill off bacteria, viruses and other germs that can cause infections later on in life.  Another important thing that happens this month is that the lungs begin to develop so that the baby will be able to breathe after it is born.  The end of the sixth month marks the end of the second trimester of pregnancy.

By the end of month 6, the baby will be 9-10 inches long.

Month 7

The baby will begin to be very active in the seventh month.  His or her eyes will be open and he or she is capable of crying.  The baby’s bones and body fat is now developed.

By the end of month 7, the baby will be around 9-10 inches long.

Month 8

By the 8th month, everything that the baby is going to be born with is now formed so there is not a lot of new development at this point. The baby will sleep most of the time and continue to grow.  While the baby is still active, the space inside the womb is cramped so he or she cannot move around as much.

By the end of the 8th month, the baby will be around 13 inches long.

Month 9

In the last month of the pregnancy, the baby is still active but rests most of the time and continues to grow in the leaps and bounds!  At this point, the baby’s head will be facing downwards in preparation for birth.  The end of the ninth month and the birth of the baby marks the end of the third trimester of the pregnancy.

By the time the baby is born, he or she will be around 19-21 inches long and weigh, on average, 7-8 pounds!

So now you have a better idea of the 9 month journey from a fertilized egg to a full-grown baby ready to be born as your baby brother or sister!