Your Baby's Development
By week 6, your baby's brain and nervous system are developing quickly. Optic vesicles, which later form the eyes, begin to develop 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 might 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 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 (from the top of the head to bottom the buttocks) 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 might hit with full force this week. You may feel very tired 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 happen 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 might have you running to the bathroom — hormonal changes and other things, such as your kidneys working extra hard to flush wastes out of your body, can make you need to pee more often too.