Pregnancy normally lasts 40 weeks, but pregnancies that last from 38 to 42 weeks are considered within normal range. Pregnancy that lasts 43 weeks, or 3 weeks after the due date, is considered post term, or post dates. Six to 12 percent of all pregnancies are post term, according to Problem Based Clinical Cases published by the University of Alabama in June 2005, and 20 to 30 percent of these have fetal postmaturity syndrome (PMS), related to placental aging.
A post term baby with PMS may have dry, peeling skin, with cracking around the creases by the ankles, wrists and neck. Vernix, the white creamy material that normally protects an infant's skin from water immersion, is absent or scant. Nails and toenails may be long, extending past the tips of the fingers and toes. Postmature babies with PMS may lose fat in the last week or two of the pregnancy, and may have skin that’s loose; arms and legs may look thin due to the loss of subcutaneous fat. These babies have more scalp hair than most, and less fine body hair (lanugo), according to the University of Alabama.
As many as 70 to 80 percent of post term babies are macrosomic, weighing more than 4,000 grams, according to the University of Alabama, and can have problems with shoulder dystocia, where too large shoulders get stuck at the pelvic outlet, or with ossification of the skull and inability to mold to the birth canal. Postmature babies with PMS may stop gaining weight or even lose weight in the last week or two, as the placenta stops providing adequate nourishment, and so they may appear emaciated.
Post term babies with PMS often pass meconium, the first bowel movement, before birth. Meconium may stain the amniotic fluid and turn the baby’s skin a yellowish green. Since babies take “practice breaths” while still in the womb, some meconium may have been inhaled into the lungs before birth. Meconium aspiration may also occur if oxygen to the fetus is decreased at any time in labor. Meconium in the lungs can cause respiratory distress or infection at the time of delivery in postmature infants, according to an article written by Errol Norwitz, M.D. and published on uptodate.com.
Babies with PMS often have a wide eyed, alert look, according to the Merck Manual. This may be partly because of the loss of subcutaneous fat around the eyes. Post term babies with PMS are more likely to have low blood sugar after delivery. They may be jittery or lethargic.These babies may be prone to hypothermia, or low body temperature, because they don’t have enough fat cells to maintain their temperature.