Week 39 of Pregnancy
Learn about your baby's development and what to expect at 39 weeks pregnant.
Baby's Size This Week
Baby Development at Week 39
- ● Your full-term baby is approximately 50.7 cm long and weighs about 3288g.
- ● Lung development is complete, with the alveoli fully coated in surfactant — your baby is physiologically ready for independent breathing from the moment of birth.
- ● Your baby's skull bones remain soft and flexible, connected by open fontanelles that allow the head to mold as it passes through the birth canal.
- ● The brain is continuing its final rounds of maturation — brain and nervous system development that began in the womb will continue actively for years after birth.
- ● The vernix caseosa (the white waxy coating protecting the skin) has largely absorbed into the skin, which has now developed its own protective barrier function.
- ● All reflexes are fully established: rooting, sucking, swallowing, Moro (startle), palmar grasp, and plantar reflex — all will be assessed in your baby's first newborn exam.
Your Body at Week 39
- ● You may experience lightening — the baby has fully dropped into the pelvis, making breathing easier but increasing pelvic pressure and frequent urination dramatically.
- ● Signs of labor to watch for include regular contractions (5 minutes apart, 1 minute long, for 1 hour), water breaking, or a bloody show.
- ● Stay close to home, keep your hospital bag in the car, and make sure your support person is on standby.
- ● Cervical ripening (softening), effacement, and dilation are actively occurring — your provider assesses this at weekly visits.
- ● Extreme nesting may drive you to complete every task on your list — rest is equally important, as labor requires significant energy reserves.
- ● Emotional fluctuations are common: excitement, impatience, anxiety, and even grief over the end of pregnancy can all coexist this week.
Week 39 Checklist
- ☐ Review the signs of labor so you can act quickly: regular contractions following the 5-1-1 rule, water breaking, or bloody show are your cues to go.
- ☐ Contact your healthcare provider immediately if you notice decreased fetal movement — do not wait and monitor at home if something feels wrong.
- ☐ Finalize postpartum support plans: confirm your home help schedule, food plan, and pediatrician appointment within 3–5 days of discharge.
- ☐ Rest as much as possible — sleep when the baby sleeps will start now; your body is building reserves for labor.
- ☐ Know when to call your doctor: call immediately for heavy bleeding, no fetal movement for 2 hours, severe headache with vision changes, or water breaking.
- ☐ Double-check the car seat installation one final time, and rehearse the route to your birth facility including alternate routes.
Frequently Asked Questions
What should I expect at 39 weeks pregnant?
At 39 weeks pregnant, you have reached full term. Your baby is about the size of a Mini watermelon (50.7 cm) and is fully ready for birth. Labor can begin at any time. Common experiences include cervical changes, intense pelvic pressure, nesting, emotional fluctuations, and early signs of labor. Always consult your healthcare provider for personalized guidance.
How big is my baby at 39 weeks?
At week 39, your baby is approximately 50.7 cm in length and weighs around 3288g — roughly the size of a Mini watermelon. These measurements are averages based on WHO fetal growth charts; individual babies vary naturally in size.
Should I be induced at 39 weeks?
ACOG supports offering elective induction of labor at 39 weeks for low-risk pregnancies based on the ARRIVE trial (2018), which found that induction at 39 weeks was not associated with higher rates of C-section and may slightly reduce them. However, induction is a significant medical decision that depends on cervical readiness, individual health factors, and personal preference. Discuss the benefits and risks thoroughly with your provider before deciding.
What does it mean when my cervix is effaced and dilated at 39 weeks?
Effacement refers to the cervix thinning and shortening from its pre-labor length of about 3–4 cm; 100% effaced means the cervix has completely thinned. Dilation refers to the cervix opening from 0–10 cm — 10 cm is fully dilated and ready for pushing. At 39 weeks, you may be anywhere from 0–4+ cm dilated and partially to fully effaced. The rate of change varies widely; some women dilate slowly over weeks, others progress rapidly.
What natural methods might help induce labor at 39 weeks?
Some commonly discussed methods include walking (may encourage engagement), nipple stimulation (releases oxytocin), and sexual intercourse (semen contains prostaglandins that may help ripen the cervix). Evidence for these methods is limited, but they are generally safe in low-risk pregnancies at full term. Methods such as castor oil, herbal supplements, or membrane sweeping (done by a provider) carry more risks and should only be considered in consultation with your healthcare provider.
Track Your Exact Pregnancy Week
Use our free Pregnancy Week Tracker to find out exactly how far along you are based on your last menstrual period or due date.
Track My Pregnancy →Sources
- ACOG
- WHO Fetal Growth Charts
- Mayo Clinic
Medical disclaimer: This content is for informational purposes only and is not intended as medical advice. Always consult a qualified healthcare provider for guidance specific to your pregnancy.