At 39 weeks the baby is full term. The brain and lungs are still maturing, and the baby keeps building the fat needed to regulate body temperature after birth. The umbilical cord passes antibodies for early immunity.
You may struggle to tell Braxton Hicks from early labor contractions.
This week's tip: Learn the 5-1-1 rule (contractions 5 minutes apart, lasting 1 minute, for 1 hour) as a general guide for when to call.