Each month of pregnancy leads to increased fetal development and prepares your future child for life outside of the womb. Following the month-by-month development of a baby can give expectant parents a fascinating look at just how much changes during approximately 40 weeks of pregnancy.
Each phase of pregnancy is critical, as certain developmental milestones, such as the formation of sexual organs, fingernails and fingerprints, usually happen during specific points of each expectant mom’s term. Keep in mind that pregnancy weeks are typically counted from the first day of your last menstrual period, which means the first two weeks of the pregnancy timeline generally occur before conception, according to the Mayo Clinic.
The First Month
By the end of your first month of pregnancy, your future child has implanted in your uterine wall, according to the Mayo Clinic. Implantation occurs when the developing blastocyst burrows into the lining of the uterus.
At this early stage, the outer layer of cells will eventually contribute to the placenta, which provides nourishment throughout pregnancy. Although your baby is still incredibly tiny, some of the structures needed to support the pregnancy are already beginning to develop.
The Second Month
During this stage of the first trimester, your baby’s brain, spinal cord and other vital organs have begun to form, according to the Mayo Clinic. Growth and development rapidly accelerate, creating facial features in your future son or daughter.
By around week six, the neural tube, which will develop into the brain and spinal cord, is closing. The heart and other organs are also beginning to form. Over the following weeks, the eyes and ears become more noticeable, while small buds develop into arms and legs. Fingers also begin to form during the second month.
The Third Month
By week 12, your baby is about 2 1/2 inches long from crown to rump and weighs approximately 1/2 oz., according to the Mayo Clinic. By now, the facial features should have developed into a more baby-like appearance. Your child’s fingernails have also begun developing.
During this month, the fingers and toes become longer and lose the webbing seen earlier in development. The elbows can bend, the outer parts of the ears continue developing and buds for future teeth appear. By week 11, the developing baby is referred to medically as a fetus rather than an embryo.
The Fourth Month
The beginning of the second trimester might be an exciting time for you and your partner. Your baby’s sex organs have developed further, and by about week 14, the sex may become clearer on an ultrasound, although many parents learn their baby’s sex during an anatomy ultrasound later in the second trimester.
Your future son or daughter’s skeletal bones are also developing. At around week 13, bones begin to harden, especially in the skull and the long bones of the arms and legs. By week 16, your baby’s head is more upright, the eyes can move slowly and movements of the arms and legs are becoming coordinated—even if you cannot feel those movements just yet. You can learn more about second-trimester fetal development from the Mayo Clinic.
The Fifth Month
Around week 20, you might feel your baby moving, according to the Mayo Clinic. These first noticeable movements are sometimes called “quickening.” By now, your child might weigh about 11 oz. and measure approximately 6 1/3 inches from crown to rump.
Your baby is becoming increasingly active and developing regular patterns of sleeping and waking. Hearing is also developing, and your baby may begin reacting to sounds. A protective coating called vernix caseosa starts covering the skin, helping protect it from prolonged exposure to amniotic fluid.
The Sixth Month
By the sixth month of pregnancy, the ridges that will form your future child’s unique fingerprints and footprints are developing, according to the Mayo Clinic. Your baby’s hands, fingernails and other small features continue to become more developed.
The lungs are also reaching an important stage. Around week 23, they begin producing surfactant, a substance that will eventually help the air sacs in the lungs inflate after birth. Your baby’s eyebrows and hair may now be visible, and the sucking reflex is developing.
The Seventh Month
The third trimester of pregnancy is often considered the “home stretch,” but development is far from finished.
During the seventh month, your future son or daughter’s eyelids can partially open. The nervous system continues to mature, and the brain is increasingly capable of controlling important functions such as body temperature and triggering breathing movements. Your baby can also kick, stretch and make grasping movements.
The Eighth Month
By the eighth month, your baby has completed much of his or her major development, and rapid weight gain becomes an increasingly important part of preparing for birth.
Around week 32, the soft, downy hair known as lanugo that has covered much of the baby’s body begins to disappear. Toenails are visible, the bones continue to harden and the pupils can react to light. However, the bones of the skull remain softer and more flexible, which will help during delivery.
Your baby is also taking up more room inside the uterus, so movements may begin to feel different as space becomes limited. The Mayo Clinic provides a detailed look at third-trimester fetal development.
The Ninth Month
As labor nears the ninth month of pregnancy, your baby continues to gain body fat and weight while preparing for life outside the womb.
By about week 36, many babies have moved into a head-down position in preparation for delivery. At week 37, your baby can firmly grasp with his or her hands, and the head may begin moving farther down into the pelvis. By week 39, a pregnancy is considered full term.
At 40 weeks, the Mayo Clinic notes that a baby might measure around 14 inches from crown to rump and weigh approximately 7 1/2 lbs., although healthy newborns vary considerably in size.
From implantation during the first month to rapid weight gain during the final weeks, the month by month development of a baby is an extraordinary process. While these milestones provide a useful general timeline, every pregnancy and every baby develops a little differently. Your healthcare provider can help you understand your baby’s growth and development throughout your individual pregnancy.
