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Home   3rd Trimester   40 Weeks Pregnant

You’re 40 Weeks Pregnant!

Developments in Baby:

Still Growing

Your baby tips the scales at an average of 7 to 8 pounds (3.2 to 3.6 kilograms) and is a very long 18 to 20.5 inches (45.7 to 52 centimeters) from head to toe. It is common for babies to be smaller or larger than this estimate, but rest assured that your little one will still be within the realm of normal. For the remainder of her stay in the womb, Baby will continue to shed the vernix and lanugo that was originally covering the skin, and you may still see traces of them at birth. Fat will continue to accumulate, but Baby is chubby enough to regulate her temperature with the aid of any adorable newborn outfits you may have purchased.1 Baby’s hair and fingernails are still growing,1 and while many babies are born with a full head of hair, it is completely normal for some to be bald. Most of the newborn hair is lost within the first three weeks of life and replaced simultaneously with proper hair.

Outstanding Organs

Internal organs are ready and awaiting her first breath of oxygen. The lungs are fully mature, and as Baby produces large quantities of cortisol, the lungs pump out plenty of surfactant to create a smooth transition from amniotic fluid to air. Her heart is beating anywhere from 120 to 160 beats per minute. When she inhales her first oxygenated breath, dramatic changes will occur within the heart and circulatory system.  The digestive system is another major player at birth. It is ready for its first taste of liquid food. In fact, the system has already been hard at work as Baby has ingested dead skin cells and remnants of the lanugo, which have combined with secretions from the bowel, liver, and gall bladder to create a green, sticky substance called meconium. Meconium will be passed within the first few days of life, but if your baby becomes distressed or frightened before delivery, she may have a bowel movement into the amniotic fluid. If meconium is visible in the amniotic fluid after the waters have broken, it may signify that she is experiencing stress and may need to be closely monitored.

After Delivery

Once your body has initiated labor, it will spur on some changes within Baby. Baby will experience a surge in hormones, which may help maintain blood pressure and blood sugar levels after birth. It might also have something to do with communicating to your uterus that the time has come. The increased hormones can cause swelling in the genitals, breasts, and his nipples may even leak a white substance. Circulation will also change as each contraction decreases blood flow to the placenta. Baby is ready to tolerate short periods of decreased circulation as your uterus prepares to push Baby through the birth canal. Her skull is just as tolerant as his circulatory system, able to be molded as she is squeezed through a tight tunnel. Baby’s head may appear misshapen after birth (conehead-like),2 but it will correct within the first few days. Baby may also appear blue, purplish, or pale yellow and covered in a variety of substances including vernix, maternal blood, lanugo, and possibly bits of meconium. He may experience skin discolorations, spots and dry patches which will usually fade over time.

Developments in Mother:

Happy Due Date

Your due date is here! Don’t expect to have baby on the actual day since only 5 percent of babies will arrive on their predicted delivery date. The due date is simply an estimate based on your last menstrual cycle, and many women ovulate early or late within their cycles.3 Needless to say, Baby will come when she’s good and ready. If you remain pregnant for the next day or so, your practitioner may suggest a biophysical profile (BPP) in order to ensure that Baby is safe and sound within your womb. The BPP will include an ultrasound to observe your baby’s overall movements such as the ability to flex fingers, hands, and limbs. The ultrasound will be used to monitor breathing movements as well as muscle tone. The practitioner will also look at the level of amniotic fluid. If for some reason he/she feels that it is not an acceptable level, you will be induced as soon as possible.3 If everything checks out, then you will not be induced unless you have not naturally reached labor sometime between 41st and 42nd weeks.2

Final Demands

With the due date coming (and going), you are probably feeling more impatient than ever to meet your baby. The growing discomfort of your ever-expanding abdomen may also be getting to you. Believe it or not, your lungs are struggling to absorb 20% more oxygen than usual, leaving you a bit out of breath (again). The final phase of pregnancy is very demanding on you. Many women feel uncomfortable throughout the last months. The weight of the baby, pressure on your spine, and the battle for space in your midsection can make your back and legs ache. Hold strong. You are so close to the end.  Perhaps the increasing discomfort is your body’s way of strengthening your desire for delivery and quelling the fear of delivery that you may have experienced in the second trimester.1

Decisions, Decisions

If you are a procrastinator, the time has come to make all final preparations. Be sure that the car seat is installed, bassinet made up, hospital bag packed and by the door.  It’s also a good time to fill the car with gas and charge your cell phone.1 There will be plenty of joyous calls to make when your little one enters the world. You will also want to review any breathing techniques that you may have learned. False labor contractions, being stronger than merely Braxton Hicks, are a great time to practice your relaxation and breathing strategies. Review your birth plan with your partner because once you are in full labor, it will be up to that person to enforce the birth plan. Nevertheless, be flexible because some labors do not go according to plan. As you’ve probably imagined, labor is very painful, thus decide whether or not you will use pain relief. Keep in mind that even if you have decided to go all natural, you can change your mind at any time.

Some women choose to invest in a waterproof mattress cover in the event that their water ruptures in bed. It’s not a bad idea when you consider that many other wet substances may hit the bed once Baby’s home.

Week 40 Basics:

5% of babies are born on the actual due date
Biophysical profile may be performed by your practitioner
Increased impatience and discomfort are normal
Finish making final preparations
Review your birth plan with your partner

7-8 lbs. (3.2-3.6 kilos), 18-20.5 in. (45.7-52 cm)
Fat percentage, hair, and fingernails are still growing
Lungs, circulatory system, and digestive tract are ready to perform
Meconium is being produced for the first several diapers
Hormone levels will change as labor begins
Appearance (possibly a misshapen head, skin discoloration, and swollen genitals) will change within the first few days of birth


1. Roney C.  The Baby Bump: 100s of Secrets to Surviving Those 9 Long Months.  San Francisco, CA: Chronicle Books; 2010

2. Murkoff H, Mazel S.  What to Expect When You’re Expecting.  4th ed.  New York, NY: Workman Publishing Company, Inc.; 2008

3. Murray LJ, ed.  Pregnancy: From Preconception to Birth.  New York, NY: DK Publishing; 2010


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