Post-term Pregnancy Causes and Risks

Post-term pregnancy is defined as a pregnancy that lasts longer than 42 weeks; two weeks past the normal 40-week gestation period. Since a post-term pregnancy is linked with both fetal and maternal health complications, doctors usually do everything they can to ensure that an infant is delivered as close to the due date as possible, which in some cases means that labor is induced, which comes with its own set of complications.

Post-term Pregnancy Causes

In many cases, post-term pregnancy is a matter of miscalculating conception date. Yet, physicians should always perform an ultrasound during the first half of the pregnancy to ensure the highest accuracy. Although there is no 100% guarantee of an infant’s due date, an early ultrasound will give a better idea of the estimated due date. Other factor that may contribute to post-term pregnancy include:

  • Previous post-term pregnancies
  • Maternal obesity
  • Sulfatase deficiency in the placenta
  • Central nervous system abnormalities
  • Anencephaly

Post-term Pregnancy Risks

According to the American Academy of Family Physicians (AAFP), there are numerous dangerous health risks associated with post-term pregnancy, including:

Fetal Macrosomia

Fetal macrosomia is defined as an infant who is over 8 pounds, 13 ounces when born. This may cause childhood diabetes, obesity, and metabolic syndrome. Mothers are also as risk when delivering a large baby, including the uterine ruptures, genital tract lacerations, and excessive bleeding after delivery.

Placental Insufficiency

Placental insufficiency, also known as uteroplacental vascular insufficiency, occurs when the placenta fails to deliver adequate oxygen and nutrients to the infant. After 37 weeks of pregnancy, the placenta reaches its maximum size and its functions begin to reduce afterwards. The longer an infant goes without proper nutrition and oxygen, the more at risk they become for a host of health problems, including oxygen deprivation that can lead to cerebral palsy,  and learning disorders. Since the placental cord may compress in post-term pregnancies, there is a heightened risk of placental insufficiency. 

Meconium Aspiration

Meconium aspiration is marked by an infant breathing in amniotic fluid and meconium (newborn feces) shortly after birth. Infants who are born post-term are more likely to have a bowel movement while still in utero. Meconium aspiration is considered extremely dangerous and can lead to oxygen deprivation, lung inflammation, and lung infection. Although rare, it can also lead to persistent pulmonary hypertension of the newborn (PPHN) and permanent brain damage.

Mothers are also at risk for developing dangerous medical issues, including postpartum hemorrhaging, bacterial infections, perineum injuries, and increased chance of a cesarean section (C-Section) surgery.

Post-term Pregnancy Treatment

Treatment is imperative for post-term pregnancy and if done properly, may help prevent many of the aforementioned risks. Typical treatment options may include:

  •  Antenatal Fetal Monitoring: An infant may be monitored closely once the due date has passed in order to detect any signs of distress. AAFP doesn’t recommend antenatal fetal monitoring until the 42nd week pregnancy.
  • Contraction Stress Test: A contraction stress test will provide Oxycontin to the mother in an attempt to start contractions. The medicine is usually administered intravenously.
  • Biophysical Profile: A biophysical profile (BPP) is a test that will determine an infant’s overall physical score in regards to movement, breathing, fetal tone, and the volume of amniotic fluid.  
  • Labor Induction: It’s often difficult to determine the best time to induce labor, but if the results of the previously mentioned treatment options indicate fetal distress, physicians will normally induce labor. Labor induction can include a scheduled C-section or medication applied to the cervix that promotes contractions.

It’s important to note that labor induction comes with its own health risks, such as low fetal heart rate, excessive maternal bleeding, and umbilical cord problems. However, in most cases, labor induction greatly outweighs the risks associated with allowing the pregnancy to continue if the infant is in distress.