Week 40 of Pregnancy
Learn about your baby's development and what to expect at 40 weeks pregnant.
Baby's Size This Week
Baby Development at Week 40
- ● Your full-term baby is approximately 51.2 cm long and weighs about 3462g — your due date has arrived.
- ● Lung development is complete, with mature surfactant coating all the air sacs for independent breathing from the first breath.
- ● Your baby's skull bones remain soft and flexible with open fontanelles, allowing the head to mold during passage through the birth canal.
- ● The digestive system is ready for the transition from placental nutrition to oral feeding — the first feeds will be colostrum, ideally within the first hour of birth.
- ● Your baby is at peak neurological readiness for birth — the stress hormones released during labor (catecholamines) play an important role in facilitating lung clearance and alertness at birth.
- ● All reflexes are fully established and robust: the rooting reflex guides the baby to the breast, while the sucking and swallowing reflexes enable feeding immediately after birth.
Your Body at Week 40
- ● You may experience lightening — the baby has fully dropped into the pelvis, making breathing easier but dramatically increasing pelvic pressure.
- ● Signs of labor to watch for include regular contractions (5 minutes apart, 1 minute duration, for 1 hour), water breaking, or bloody show.
- ● Stay close to home, keep your hospital bag in the car, and ensure your support person is on standby.
- ● Cervical softening, effacement, and dilation may be well advanced — your provider monitors this at weekly visits and discusses your options if labor does not begin spontaneously.
- ● Extreme nesting may continue — balance productive preparation with intentional rest, as labor demands significant energy.
- ● Emotional intensity often peaks at 40 weeks: impatience, anxiety, excitement, and physical discomfort combine as you wait for the moment of birth.
Week 40 Checklist
- ☐ Review the signs of labor and know exactly when to go to the hospital: regular contractions following the 5-1-1 rule, water breaking, or bloody show.
- ☐ Contact your healthcare provider immediately if you notice significantly decreased fetal movement or no movement for 2 hours.
- ☐ Discuss your provider's post-dates policy — most will offer induction between 41–42 weeks if labor has not begun spontaneously.
- ☐ Rest as much as possible and stay nourished — labor requires significant energy and adequate hydration.
- ☐ Confirm your postpartum support logistics: home help for the first week, meal arrangements, and your pediatrician appointment within 3–5 days of discharge.
- ☐ Know when to call your doctor immediately: heavy bleeding, severe headache with vision changes, no fetal movement, or signs of infection (fever with rupture of membranes).
Frequently Asked Questions
What should I expect at 40 weeks pregnant?
At 40 weeks pregnant, you have reached your due date. Your baby is about the size of a Watermelon (51.2 cm) and is fully ready for birth. Labor can begin at any time. Common experiences include intense pelvic pressure, cervical changes, nesting, emotional intensity, and early signs of labor. Only about 5% of babies arrive on their exact due date — going past 40 weeks is common and normal. Always consult your healthcare provider for personalized guidance.
How big is my baby at 40 weeks?
At week 40, your baby is approximately 51.2 cm in length and weighs around 3462g — roughly the size of a Watermelon. These measurements are averages based on WHO fetal growth charts; individual babies vary naturally in size.
What happens if I don't go into labor by my due date?
Only about 5% of babies are born on their exact due date. Going past 40 weeks (up to 42 weeks) is medically common and often low-risk for healthy pregnancies. Your provider will typically recommend increased monitoring (non-stress tests, biophysical profiles) starting at 40–41 weeks, and will discuss induction of labor between 41–42 weeks. The risks of continuing pregnancy beyond 42 weeks include increased placental aging, meconium-stained fluid, and a rising risk of stillbirth.
What is a non-stress test (NST) and why might I need one at 40 weeks?
A non-stress test (NST) monitors your baby's heart rate over 20–40 minutes using external fetal monitors strapped to your abdomen. A reactive NST shows the heart rate accelerating with movement, which is reassuring. NSTs are often ordered at 40+ weeks to assess fetal well-being when pregnancy continues past the due date. They may be performed 1–2 times per week, sometimes alongside a biophysical profile (ultrasound assessing amniotic fluid, movement, and tone).
How can I manage the emotional stress of waiting past my due date?
Waiting past your due date is one of the most emotionally challenging parts of pregnancy. Strategies that help include staying off social media if birth announcements trigger anxiety, planning small enjoyable activities each day, staying connected with a supportive partner or friend, and practicing mindfulness or relaxation techniques. Remember that due dates are estimates with a natural variation of 2 weeks. Focus on monitoring your baby's movement and attending your monitoring appointments — your team is watching closely.
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.