In just nine months, an unborn baby goes from a small cluster of cells called a zygote into a fully developed infant. Your doctor will monitor proper physical development in the womb to reduce the risk of complications for you and your baby. Always follow your doctor’s advice regarding your diet, exercise, medications and other lifestyle habits to encourage your baby’s healthy development.
Internal Development
During the fifth week of pregnancy, your baby’s brain, heart, spinal cord and gastrointestinal tract begin to form, according to the University of Maryland Medical Center. The heart will begin to beat regularly by the sixth or seventh week of pregnancy.
The lungs begin to form by week eight, and all of your baby’s essential organs begin to grow and develop by week nine. Your baby’s bones and muscle tissues develop, and the liver and pancreas start to produce fluids by the end of your first trimester or the beginning of your second trimester.
Bone marrow will start making blood cells during the second trimester, and your baby’s body will start to store fat. Your baby’s brain will also go through a rapid development stage.
During the third trimester, your baby’s organs and internal tissues become fully developed, and he starts to practice breathing in the womb.
External Development
Babies start developing limbs as early as the sixth or seventh week of pregnancy, explains the University of Maryland Medical Center. Eyes and ears also form during this time. Toes and fingers form before the end of the first trimester, and facial features begin to manifest. Your baby’s genitals start to form at the end of the first trimester.
The second semester sees your baby gaining weight quickly and developing visible hair around 23 weeks. At this time, your baby’s fingerprints and footprints also form.
Your baby will continue gaining weight to prepare for birth during the third trimester. Sexual development continues, with boys developing testicles and girls developing the clitoris by 31 weeks, according to the Mayo Clinic. By week 36, most babies gain about 1/2 lb. per week until birth.
Senses
Your baby’s senses develop throughout the second and third trimesters. Babies begin to hear low and loud noises by week 18, according to the Mayo Clinic. Hearing continues to develop over the next few weeks so that your baby may be able to distinguish your voice in conversations. Your baby will open her eyes toward the beginning of the first trimester and continue to open them further in the following weeks. By 33 weeks, your baby will be able to detect light.
Movement
Many mothers start feeling their babies move by the time they are halfway through their pregnancies, though some do not feel movement for several more weeks. Babies typically begin to move considerably and explore their surroundings by week 25, explains the Mayo Clinic. Your baby will continue to move throughout the rest of the second and third trimesters and may react to loud sounds or sudden movements.
Considerations
Maintaining a healthy diet and exercise habits can help your baby’s physical development considerably. The mercury in certain kinds of seafood can damage your baby’s nervous system as it develops, according to the Mayo Clinic. Opting for shrimp, tuna, salmon and other fish that contain little mercury can help give your baby the protein and iron he needs without the risk.
Raw or undercooked meat and eggs can make your baby sick. Caffeine can affect your baby’s heart rate and slow fetal growth, so avoid caffeine as much as possible. Alcohol can cause deformities, heart problems, mental retardation and even miscarriage or stillbirth, so it is best to avoid it entirely during your pregnancy, cautions the Mayo Clinic.
