40 Weeks Pregnant

Baby’s Development

This is the week you’ve been counting down to — your due date week. Your baby is now about 51.2 centimeters long, roughly the size of a watermelon, and weighs around 3,400 grams (about 7.5 pounds) [1]. Your baby is fully developed and ready to meet the world. The vernix that protected your baby’s skin in the womb is mostly gone now, leaving the skin smooth and soft. Body fat makes up about 15 percent of your baby’s weight, and the brain and lungs are fully mature. Most babies are settled in the head-down (cephalic) position. On average, babies at this stage weigh about 7.5 pounds and measure 20 inches long, though there’s a wide range of normal — roughly 5.5 to 10 pounds and 18 to 22 inches. The survival rate at this point is over 99 percent [2].

Body Changes

Your uterus now measures about 40 centimeters in fundal height, and a total weight gain of 30 to 40 pounds by this point is typical. Your bump is large and has likely “dropped” as your baby settles lower into your pelvis. You may notice stretch marks, the linea nigra down your belly, melasma (the “pregnancy mask”), more visible veins, and varicose veins. Your breasts have likely grown two or more cup sizes, and some colostrum may be leaking as your body prepares to feed your baby. Swelling in your feet and ankles is common. Your cervix is likely effacing and may be dilating 1 to 4 centimeters [2].

Tips for Week 40

• Keep counting your baby’s kicks — aim for at least 10 movements within a 2-hour window each day. If you count fewer than 10, try eating a snack, drinking something cold, and lying on your left side before counting again. A second low count is a reason to call your provider.
• Ease your anxiety about being “overdue” — remember that the average first-time mom delivers at around 40 weeks and 5 days, so going past your due date is completely normal. Talk with your provider about the induction timeline so you know what to expect.
• Finalize your postpartum plan — line up who will be helping, plan meals ahead, arrange dog care, confirm your work leave, and prepare any siblings for the new arrival.
• Relieve pelvic pressure — practice Kegels, sleep on your side, try a support belt, and consider prenatal physical therapy if the pressure is significant.

Things To Do (Checklist)

• Continue kick counting (10 in 2 hrs daily)
• Address anxiety about being “overdue”
• Finalize postpartum plan
• Confirm hospital bag ready, route mapped
• Discuss induction timeline with OB (41 wk standard)

Frequently Asked Questions

Q: I’m at my due date. Is something wrong? A: No. Your due date is only an estimate — only about 5 percent of babies arrive on their actual due date. About half of first-time moms deliver by 40 weeks and 5 days, and about three-quarters by 41 weeks and 2 days. First babies are very often “late” [1].

Q: When will I be induced? A: The standard recommendation is to offer induction at 41 weeks, per ACOG. Some providers will offer it earlier, at 39 weeks, based on the ARRIVE trial. Talk this through with your provider. There are also medical reasons to induce sooner, such as preeclampsia, gestational diabetes, or growth restriction [1].

Q: How do I know if labor is real or false? A: True labor contractions are regular (following the 5-1-1 pattern), grow steadily more intense, don’t stop when you move or change positions, and may come with a bloody show or your water breaking. False labor contractions tend to be irregular, don’t increase in intensity, and often ease up when you move or rest [2].

Sources

1. ACOG — How Your Fetus Grows During Pregnancy
2. Mayo Clinic — 40 Weeks Pregnant
3. Expecting Better — Emily Oster (Chapters 15-16: Third Trimester and Labor)