Post-term pregnancy

Definition

• Prolonged pregnancy describes a pregnancy continuing beyond the estimated due date.
• Post-term pregnancy is defined as a pregnancy reaching 42 completed weeks (294 days) or the estimated due date plus 14 days.

Occurrence & epidemiology

Epidemiology

• Post-term pregnancy affects about 7% of all pregnancies; dating by early ultrasound reduced its frequency from 12% to 3% in one study.

Aetiopathogenesis

Aetiology and risk factors

• The most common cause of apparent post-term pregnancy is inaccurate dating; in true post-term pregnancy the cause usually remains unknown.
• Risk factors include primiparity, previous post-term pregnancy, a male fetus, obesity, hormonal factors and genetic predisposition.
• Rarely, placental sulphatase deficiency, fetal adrenal insufficiency or hypoplasia, or anencephaly is the cause.

Clinical features

Clinical features and complications

• The stillbirth rate rises from 39 weeks and increases sharply after 40 weeks; uteroplacental insufficiency, meconium aspiration and intrauterine infection are considered the causes.
• Post-term babies are more often macrosomic (2.5–10% versus 0.8–1% at term).
• Signs of postmaturity in the newborn are thin, wrinkled, peeling skin, a thin body, long hair and nails, oligohydramnios and frequent meconium passage.

Diagnosis

• The basis is accurate dating; first-trimester ultrasound is superior to mid-trimester ultrasound for this purpose.
• Fetal well-being is assessed with CTG, biophysical profile or modified profile combining CTG and amniotic fluid volume.

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Further reading (selection)

1. Facts, Views & Vision in ObGyn (2012): Postterm pregnancy (PubMed Central)

Cross-references