27 ~ 32 weeks: Gestational (fetal) development (Weeks 25 ~ 30 weeks):

As the third trimester begins, the developing fetus experiences a marked growth period.  Fat storage increases, and a normal fetus grows anywhere from 15 to 17 inches in length, and 4 to 4.5 pounds in weight. At this point, the lungs are still maturing, although rhythmic breathing patterns begin to occur. Bones remain soft and flexible as the fetus builds up calcium, iron and phosphorus. At this time, the eyes first open for a glimpse of the fetus’ ever-dwindling environment.  The volume of amniotic fluid also decreases, to make room for the growing fetus.

33 ~ 36 weeks: Gestational (fetal) development (Weeks 31 ~ 34 weeks):

As the due-date approaches, the fetus grows to approximately 16 to 19 inches, roughly 5.75 to 6.75 pounds, and descends further into the mother’s pelvis, in a process known as “dropping” (also “lightening”). The fetus gains weight as rapidly as possible during these critical last weeks.  The fine, downy-like hair called lanugo falls away, and the body grows less red and wrinkly. The uterus itself presses against other internal organs, increasing the mother’s heartburn and gastrointestinal discomfort as well as the urge to urinate. The fetus will pack a good kick, although turning around in the womb lessens with maneuvering room.

At 36 weeks, growth will slow down.  This allows the fetus to store up energy in preparation for delivery.  The bones actually remain soft.  In fact, a newborn infant has about 300 bones, all of which will remain fairly soft and pliant.  It will take many years for these bones to grow longer and harder, while a few will eventually fuse together. A typical person’s bones develop until 25 years of age, at which time the number has dropped to 206 bones, after fusion is complete.

37 ~ 40 Weeks: Gestational (fetal) development (Weeks 35 ~ 38 weeks):

Development at 38 weeks is considered full-term, with the fetus at roughly 19 to 21 inches and anywhere from 6.75 to 10 pounds. Movement decreases, simply due to the cramped quarters in the mother’s uterus. Fingernails grow long, and the little hands develop a firm grip. This is a time when eye-pigmentation begins, although lighter colored eyes may darken over time. Both genders are born with small “breast buds.” The fetus receives a steady does of antibodies from the mother to help protect against disease.  Internal organs should be fully developed, with lungs continuing to mature right up until delivery. The mother may experience lower back and leg pain called “sciatica,” as well as pelvic and hip pain.  This is partly due to the mother’s joints loosening in preparation for childbirth, as well as the strain of carrying the baby’s weight in front.

To alleviate back pain, the mother can try different techniques, including observing good posture by keeping the spine in a straight line, alternately standing and sitting, rolling sideways when getting out of bed, excessive bending or lifting.  Also, applying heat pads to the sore back muscles may help.  If the discomfort becomes intolerable, it is best to check with the doctor before taking any medications.