On average, pregnancy lasts 280 days (40 weeks) from the first day of the last menstrual period. In most pregnancies that go a little beyond, up to 41 to 42 weeks, no problems develop. However, beyond that time, problems may develop because the placenta often cannot continue to deliver adequate nutrients to the fetus. This condition is called postmaturity Postterm Newborns A postterm newborn is a baby delivered after 42 weeks of gestation. Near the end of a term pregnancy, the function of the placenta decreases, providing fewer nutrients and less oxygen to the... read more .
Postterm pregnancies increase the risk of problems such as
Difficult labor due to shoulder dystocia Shoulder Dystocia Position refers to whether the fetus is facing rearward (toward the woman’s back—that is, face down when the woman lies on her back) or forward (face up). It’s important to check the baby’s... read more (the fetus's shoulder lodges against the woman's pubic bone, and the baby is caught in the birth canal)
The need for cesarean delivery Cesarean Delivery Cesarean delivery is surgical delivery of a baby by incision through a woman’s abdomen and uterus. In the United States, up to 30% of deliveries are cesarean. Doctors use a cesarean delivery... read more
or operative vaginal delivery Operative Vaginal Delivery Operative vaginal delivery is delivery using a vacuum extractor or forceps. A vacuum extractor consists of a small cup made of a rubberlike material that is connected to a vacuum. It is inserted... read more (with forceps or a vacuum extractor)Abnormal growth of the fetus (for example, an abnormally large fetus Large-for-Gestational-Age (LGA) Newborns A newborn who weighs more than 90% of newborns of the same gestational age at birth (above the 90th percentile) is considered large for gestational age. Newborns may be large because the parents... read more or abnormally small fetus Small-for-Gestational-Age (SGA) Newborns A newborn who weighs less than 90% of newborns of the same gestational age at birth (below the 10th percentile) is considered small for gestational age. Newborns may be small because their parents... read more )
Problems with blood flow to the fetus, depriving the fetus or newborn of oxygen
Passage of meconium (the fetus’s first stool) before delivery
A newborn who needs care in a neonatal intensive care unit
Death of the fetus or newborn
Tears in the area between the opening of the vagina and anus (perineum)
Excessive bleeding at delivery (postpartum hemorrhage Excessive Uterine Bleeding at Delivery Excessive bleeding from the uterus refers to loss of more than 2 pints of blood or symptoms of significant blood loss that occur within 24 hours of delivery. After the baby is delivered, excessive... read more )
Meconium can sometimes be inhaled before or during delivery, causing the baby to have difficulty breathing shortly after birth. This disorder is called meconium aspiration syndrome Meconium Aspiration Syndrome Meconium aspiration syndrome is trouble breathing (respiratory distress) in a newborn who has breathed (aspirated) a dark green, sterile fecal material called meconium into the lungs before... read more .
A postmature fetus may have dry, peeling skin, overgrown nails, a large amount of scalp hair, deep creases on the palms and soles, little body fat, and skin that is stained green or yellow by meconium.
To diagnose a postterm pregnancy, doctors must accurately determine the due date Due date Pregnancy begins when an egg is fertilized by a sperm. For about 9 months, a pregnant woman’s body provides a protective, nourishing environment in which the fertilized egg can develop into... read more . If women have regular menstrual cycles, doctors can calculate the due date based on when their last menstrual period was. But the most accurate way to date a pregnancy is ultrasonography, especially if done during the first 12 weeks of pregnancy.
Typically, tests are started at 41 weeks to evaluate the fetus’s movement and heart rate and the amount of amniotic fluid (the fluid around the fetus), which decreases markedly in postterm pregnancies. Doctors use ultrasonography Ultrasonography Ultrasonography uses high-frequency sound (ultrasound) waves to produce images of internal organs and other tissues. A device called a transducer converts electrical current into sound waves... read more 
and may use electronic fetal heart monitoring Fetal monitoring Labor is a series of rhythmic, progressive contractions of the uterus that gradually move the fetus through the lower part of the uterus (cervix) and birth canal (vagina) to the outside world... read more to monitor the fetus's status.
Labor is started (induced Induction of Labor Induction of labor is the artificial starting of labor. Usually, labor is induced by giving the woman oxytocin, a drug that makes the uterus contract more frequently and more forcefully. The... read more ) if the fetus is having problems or amniotic fluid has decreased too much. Even if there are no obvious problems, doctors consider inducing labor at 41 weeks. Typically after 42 weeks, labor is induced.
Sometimes cesarean delivery Cesarean Delivery Cesarean delivery is surgical delivery of a baby by incision through a woman’s abdomen and uterus. In the United States, up to 30% of deliveries are cesarean. Doctors use a cesarean delivery... read more is required.
