Your Baby's Development
By week 6, your baby’s brain and nervous system are developing at a rapid pace. Optic vesicles, which later form the eyes, begin to develop this week on the sides of the head, as do the passageways that will make up the inner ear.
Your baby's heart will begin to beat around this time, and it may even be detected on ultrasound examination. And the beginnings of the digestive and respiratory systems are forming, too. Small buds that will grow into your baby's arms and legs also appear this week.
Because their legs are curled up against the torso for much of the pregnancy, making a full-length measurement difficult, babies often are measured from the crown to rump rather than from head to toe. This week, your baby only measures 0.08 to 0.2 inches (2 to 5 millimeters) from crown to rump!
Common pregnancy complaints may hit in full force this week. You may feel extreme fatigue as your body adjusts to the demands of pregnancy. And tender, aching breasts and nausea and vomiting (morning sickness) may leave you feeling less than great. Despite its name, morning sickness can occur at any hour or all day, so don't be surprised if your queasy stomach doesn't pass by noon. Nausea isn't the only thing that has you running to the toilet, though — hormonal changes and other factors, such as your kidneys working extra hard to flush wastes out of your body, cause you to urinate more frequently, too.