What are the dangers of going past your due date?

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As if 40 weeks of pregnancy wasn't long enough, many women don't deliver until after their due date. Some don't even go into labor for another a week or two! But is this normal, and is it safe for your baby? When will a caregiver intervene if nature doesn't take its course? Obstetrician/Gynecologist David Barrere discusses post-date pregnancies.

Your question
What are the dangers of going past your due date? - Monica in Nome, Alaska

The expert answers
The definition (based on World Health Organization [WHO] and International Federation of Gynecology and Obstetrics [FIGO] guidelines) of a post-term or prolonged pregnancy is a gestational age of 42 weeks or more (greater than 294 days) from the first day of the last menstrual period (LMP). As many as 14 percent of all pregnancies will proceed beyond 42 weeks of gestation, while 4 percent continue beyond 43 completed weeks. When pregnancy exceeds 42 weeks gestation, the perinatal mortality rate (stillbirths plus early neonatal deaths) increases to 4 to 7 per 1,000, which is double the rate seen for deliveries at 40 weeks gestation. As more time passes, more calcium is deposited within the placenta (calcification), which can markedly affect its function. This may be one explanation for the increased mortality rates that are seen in post-term pregnancies.

On average, post-term infants are larger than term infants. Approximately 2.5 to 10% of fetuses delivered after 42 weeks gestation exceed 4500 grams as compared to 0.8 to 1% of infants delivered at 40 weeks. These larger infants are at more risk for mechanical problems of labor such as prolonged labor, cephalopelvic disproportion requiring c-section, and shoulder dystocia.

Post-date pregnancies are associated with an increased risk for umbilical cord compression, fetal distress, meconium aspiration, as well as newborn complications, such as hypoglycemia and seizures. Because of the associated morbidity and mortality, The American College of Obstetricians and Gynecologists (ACOG) currently recommends induction of labor for post-term, low risk pregnancies sometime during the 43rd week of gestation.

If an induction is not planned and pregnancy continues post-term, then fetal surveillance is mandated. No set regimen is required, but may include any combination of non-stress testing(NST), biophysical profiles (BPP) or modified biophysical profiles (amniotic fluid volume plus NST). It is generally agreed that fetal surveillance in the high risk or post-term pregnancy is associated with a decreased perinatal mortality rate.