6 weeks pregnant baby size: - Pregnancy weeks are counted

- Pregnancy weeks are counted from your last menstrual period. - Weeks 3-19, measurements are taken from head to rump. - Weeks 20-40, measurements are taken from head to toe. Your baby is about the size of a poppy seed during week 3. Your baby is about the size of a sesame seed during week 4. Your baby is as big as a sweet pea at 6 weeks pregnant. Learn about your baby's development, common symptoms and body changes, and how to cope with frequent urination, heartburn and nausea. Baby development at 6 weeks pregnant Your baby has been doing some serious growing over the past few weeks and one of the main events this week is that they'll develop their face and double in size by next week. That's right, your little one's facial features are starting to form! At 6 weeks, your baby is the size of a lentil and you may begin to have morning sickness. Learn more about what to expect at 6 weeks pregnant.