Week-By-Week Guide

The Ups And Downs And Changes For You And Your Growing Baby

Here you can find a breakdown of what to expect in the coming weeks, so that you will know what questions to ask your doctor, and what kind of plans to make to keep yourself and your baby safe.

You may see a lot of medical terms you are not familiar with along the way. It's okay; this guide will explain what you need to know, so that you can feel more empowered about the growth of your child. For now, here is a quick summary of the upcoming weeks.

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The first two weeks:

Because of the fact that you are not considered to be pregnant yet, you may have a period. It is actually the first day of your period that begins the first week of pregnancy. Nearing the end of the second week is when an ovary releases an egg. This is the time that chance of conception is the highest.

Week three:

This is the time in which conception actually takes place and your baby begins to develop. At this point, the baby is referred to an embryo. There are outer groups of cells, referred to as membranes, that provide nutrients to the embryo, as well as protect it. This is the start of the gestation period, or the time a baby is carried in a mother's womb.


Week four:

During week four, three important layers are developing with your baby:

  • The Ectoderm, which will become the nervous system, as well as your baby's hair, nails, skin, sweat and mammary glands, and teeth enamel.
  • The Mesoderm, which will become the circulatory system, heart, skeletal system, blood system, connective system, muscles and urogenital system.
  • The Endoderm, which will contain the lungs, and where the liver, pancreas, gastrointestinal tract and thyroid be.

In addition to the forming of the layers, arm and leg buds are beginning to form. The placenta is also beginning to form at this time.


Week five:

By week five, your baby's eye and ear structures are forming, and the skeleton is starting to form. Nerve cells, blood cells and kidney cells develop. The baby is now referred to as an embryo. This is an extremely important period of time in your baby's development. Because of this fact, the baby is most at risk for damage caused by the mother's use of certain medications, illegal drugs and alcohol. Make sure to ask your doctor about any over-the-counter medications you might take (say, for allergies or headaches), so that he or she can tell you whether or not they are still safe.


Weeks six and seven:

During week six, your baby's brain continues to grow, and the jaw, nose and palate have begun to form. The tiny hands and feet buds now have the beginnings of what will become fingers and toes. Your baby's heart now beats at a regular rhythm.



Week eight:

By now, every major organ has begun to form in your baby. In addition, the eyelids, tongue, and hair follicles are forming. The baby's arms and legs continue to grow longer, the hands and feet are webbed, and the lungs are beginning to form.


Because of these developments, it's time to start thinking about your first prenatal visit. Most women schedule it for somewhere between the 8th and 10th week of their pregnancy.

Week nine:

Your baby's hair follicles and nipples are forming. The toes can now be seen. The arms are growing, and the elbows are formed. Every major organ is now growing.


Week 10:

At the end of the 10th week, your baby will no longer be referred to as an embryo. He, or she, is now a fetus. By now, the facial features are more recognizable. Your baby's eyelids can now close, the ears are beginning to look like ears and the intestines are now able to rotate.


Week 11 through week 14:

The second trimester starts around week 13. By now, your baby's face is completely formed. The eyelids will close during this time and remain closed until around the 28th week. Your baby's nails are present on the tiny fingers and toes. The arms and legs are now long and thin. During this time, your baby's head accounts for half of his or her total size. Tooth buds will appear, and your baby is now capable of making a fist. It is during this time that the genitals appear. Your baby's liver is functioning and able to make red blood cells.1





Week 15 through week 18:

Your baby is now able to make sucking motions. The bones continue to grow and harden. Fine hair is growing on your baby's head. The skin is very thin and transparent. The liver and pancreas are working, and your baby is now able to move and stretch.





Week 19 through week 21:

During this time, you will be able to feel your baby's first movements, known as quickening. Your baby is very active. The baby can now hear, and at the end of this time, he, or she, will be able to swallow.




Week 22:

Your baby's body is now covered with fine hair, called lanugo. Eyelashes and eyebrows appear, and nails are growing on the fingers. What will become your baby's first bowel movement (meconium) is being formed in the intestinal tract. You can now feel your baby moving.


Week 23 through week 25:

Welcome to the third trimester, which starts at week 24. During this time, your baby begins to store fat, the bone marrow begins to make blood cells and your baby's lungs continue to develop.




Week 26:

Your baby's fingerprints and footprints are now forming. The eyebrows and eyelashes are completely formed, and the eyes are fully developed. The lungs continue to form. By now, tiny air sacs are present in the lungs, but it is too early for your baby to breathe outside of your womb. Your baby may react to a loud noise, which is possible by the development of the Moro reflex (often called the "startle" reflex).


Week 27 through week 30:

Your baby's eyelids can now open and close, and the nervous system is now able to control some body functions. Your baby's brain is growing at a fast rate, and respiratory system is producing surfactant, which will help the air sacs in the lungs fill with air.





Week 31 through week 34:

Your baby's bones are now fully formed, but they are still soft. Breathing now occurs, but your baby's lungs are not yet ready to breathe on the outside. The baby is growing at a fast rate and gaining fat. Your baby's body is now capable of storing calcium, iron and phosphorus.





Week 35 through 37:

Your baby continues to gain weight, usually weighing around 5 pounds. The heart and blood vessels are completely formed, the muscles and bones are developed, and the skin is less wrinkled due to the fat that has formed under the skin. Your baby now has developed a pattern for sleeping.




Week 38 through week 40:

At 38 weeks, most of your baby's organs are fully developed, with the exception of the brain and the lungs. If your baby is born at 38 weeks, these organs will continue to grow.

At 39 weeks, all of your baby's organs are prepared for life outside of the womb. The ability of your baby to suck and swallow has been developed, and he or she has enough fat stored to stay warm in a room that is normal temperature. A baby at 39 weeks' gestation is considered to be full term.

Although you are most likely uncomfortable and ready to deliver, a baby born before 39 weeks is more likely to have difficulties, especially with breathing. For this reason, the American College of Obstetricians and Gynecologists (ACOG) considers 39 weeks' gestation to be full term; therefore, unless there is a medical reason, you will not be scheduled for an elective induction of labor (meaning the doctor won't induce, or start, the labor process for you as opposed to waiting for the baby to make the decision, so to speak) until you are in your 39th week of pregnancy at the earliest. If you go into labor at 38 weeks, chances are that your baby will do just fine — but remember, 39 weeks and later are best.2




  1. Fetal development. (2016). Medline Plus. Retrieved from https://www.pacifcschoolserver.org
  2. Nonmedically indicated early-term deliveries. (2013). The American College of Obstetricians and Gynecologists, 561. Retrieved from https://www.acog.org