Third trimester · 1 week to go
| Fact | Week 39 |
|---|---|
| Days of pregnancy | 267–273 since LMP |
| Gestational age span | 38w0d to 38w6d |
| Trimester | Third trimester (weeks 28–40) |
| Pregnancy month | Month 3 (weeks 9–13) |
| Average length | 20.0 in (crown to heel) |
| Average weight | 7.25 lb |
| Size comparison | a mini watermelon |
| Weeks remaining | 1 (40-week due date) |
Week 39 is full term, the ideal window. The chest becomes more prominent as the baby drops and prepares. Fat continues accumulating for warmth after birth.
The brain and lungs finish their final maturation. The placenta continues passing antibodies that immunize the baby for the first months. The baby has a firm grasp and turning, wiggling practice for the journey out.
Gestationally, week 39 means you are 38 weeks and 0 to 6 days pregnant, day 267 to day 273 counted from the first day of your last period. This is week 12 of the third trimester (weeks 28–40). Appointments are weekly from week 36 until delivery. You are in the due week; from 41 weeks your provider will usually talk induction. From here the baby gains roughly half a pound a week on average, which is why the third trimester feels measurably heavier by the day. Every number on this page is an average across pregnancies; your own scan dates and your baby's measurements are what actually describe your week 39.
Track contractions with a timer app. Trust the pattern: longer, stronger, closer together means go.
Weeks of pregnancy don't map cleanly to calendar months, but the common division puts week 39 falls in month 3 of pregnancy (weeks 9–13). Week 39 is part of the third trimester, which runs from week 28 to birth. Gestationally, week 39 means you are 38 weeks and 0 to 6 days pregnant.
At week 39 the baby averages 20.0 in long and weighs about 7.25 lb, roughly the size of a mini watermelon. Sizes come from fetal growth charts (crown-to-heel length from week 20), and normal variation week to week is wide; your ultrasound measurements always outrank a chart.