Post-term pregnancy is when the gestation has extended 2 weeks beyond the expected date of delivery (>42 weeks gestation).
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Epidemiology
The reported prevalence is 7% of pregnancies 3.
Risk factors
Some risk factors have been identified such as:
Maternal factors:
primiparity
obesity
history of prior post-term pregnancy: the risk increases from 27% with one prior prolonged pregnancy to 39% with two prior prolonged pregnancies
hormonal factors
genetic predisposition: the risk is higher for women whose mothers had prolonged pregnancies
Fetal-placental factors:
anencephaly: decreases production of 16α-hydroxydehydroepiandrosterone beta-sulfate (a precursor of estriol)
fetal adrenal hypoplasia: decreases the production of estriol precursors
placental sulfatase deficiency: prevents placenta conversion of sulfated estrogen precursors 3
Pathology
The etiology of post-term pregnancy is still unknown.
Research has shown that the synthesis of corticotrophin-releasing hormone (CRH) by the placenta is increased in late pregnancy and peaks at the time of labor, and this fact is related to the length of gestation. However, the exponential rise of CRH production is slower in women who deliver post-term.
Radiographic features
Obstetric ultrasound commonly shows:
oligohydramnios (82%) 4
macrosomia
placenta grade 2 or 3
Treatment and prognosis
elective induction of labor
expectant management
antenatal testing
Complications
Fetal complications:
-
fetal macrosomia: which in turn can cause added complications such as
dismaturity syndrome
higher rate of meconium aspiration
neonatal acidemia
higher rate of neonatal encephalopathy 3
increased risk of placental insufficiency
duplicates the rate of stillbirth and early neonatal death
Maternal complications:
increased risk of severe perineal injury
increased risk of endometritis 3
Differential diagnosis
inaccurate dating
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