Post-Term Pregnancy

Definition - What does Post-Term Pregnancy mean?

Post-term pregnancy is a pregnancy that extends beyond the normal 42 weeks (294 days) of pregnancy, or when the pregnancy is 14 days past the due date. It is usually calculated from the first day of the last menstrual period (LMP). The baby born post-term may be alive (called live birth) or dead (known as stillbirth). Post-term pregnancies constitute about 7-10% of all deliveries.

The other names for a post-term pregnancy are prolonged pregnancy and postdate.

FertilitySmarts explains Post-Term Pregnancy

A normal pregnancy (also known as a "term pregnancy") lasts for about 37 to 42 weeks. In women with regular menstrual periods, the estimated delivery date (due date) is typically calculated based on the LMP and pelvic examination by measuring the size of the uterus.

However, this may not be the ideal approach for every case as it overestimates the pregnancy age and consequently leads to a false estimation of post-term pregnancy. In fact, the most common cause of prolonged pregnancy is inaccurate dating of the pregnancy rather than true post dates. Most of the doctors, therefore, suggest the use of ultrasound in early pregnancy to accurately identify how far along a woman is in her pregnancy so as to avoid any miscalculations in dates.

With that said, when post-term pregnancy truly exists, the cause is usually not clear, but the pregnancy is much more likely to be prolonged if:

  • previous pregnancies went beyond 42 weeks
  • a woman is giving birth for the first time
  • a woman is carrying a male baby
  • a woman is obese (the slowed metabolism alters the hormones involved in kick-starting labor)
  • a woman has imbalanced hormonal levels
  • a woman has a twin sister who has had a previous post-term birth

True post-term pregnancies pose risks for both the mother and baby. Post-term babies can grow huge (≥4.5 kg) depending on the interval they have been inside the mother's uterus. This causes vaginal trauma during vaginal delivery of a large baby. In addition, longer labors and operative delivery, such as forceps or vacuum-assisted birth may also contribute to vaginal and child trauma. The rate of cesarean section is thus twice as more likely in these pregnancies so as to avoid trauma to the mother or the baby. Mothers are also at increased risk for infection and wound complications, and postpartum (after-birth) bleeding.

There are also risks for the baby in a post-term pregnancy before, during, and even after delivery, such as:

  • Stillbirth (death or loss of a baby before or during delivery)
  • Death of the newborn baby (as the placenta may stop supplying nutrients, oxygen, and blood flow to the baby after the 42 weeks, eventually resulting in death)
  • Birth injury due to the large size of the baby
  • Meconium aspiration, in which a baby breathes in the fluid containing the first, dark green stool into the lungs, causing difficulty breathing that demands emergency measures to save a baby's life.
  • Low blood sugars because the baby doesn't have enough sugar stores
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