Late Term and Postterm Pregnancy

Pregnancy extending beyond the expected term delivery window. It is classified as late term (between 41 weeks 0 days and 41 weeks 6 days of gestation) or postterm (42 weeks 0 days of gestation or beyond).

The clinical importance lies in the recognised, progressive increase in specific perinatal risks beyond this point, including stillbirth, meconium aspiration and macrosomia-related delivery complications.

Structured, proactive surveillance and, where appropriate, induction of labour are established, evidence-based approaches to mitigating these gestational age-related risks.

Pathophysiology and associated risks

• The cause in an individual case frequently remains unclear. Recognised contributing factors include inaccurate gestational age dating (underscoring the importance of accurate, early ultrasound dating) and a family history of prolonged pregnancy.
• In a small proportion of cases, specific fetal conditions affect the mechanisms that trigger normal labour onset.
• Placental function is generally adequate in the great majority of pregnancies at and beyond term. Reserve capacity is recognised to decline gradually as gestation advances well beyond term, contributing to the progressive increase in stillbirth risk with advancing postterm gestation.
• Continued fetal growth beyond term increases the risk of macrosomia and its intrapartum complications, including shoulder dystocia.
• Oligohydramnios (reduced amniotic fluid volume) becomes more likely as pregnancy extends well beyond term. It is relevant to both fetal wellbeing assessment and labour management.

• The specific clinical presentation of late term or postterm pregnancy is defined entirely by gestational age itself, with careful, accurate confirmation of gestational age (ideally established through early, first-trimester ultrasound dating) representing an essential, foundational element of accurate classification and appropriate subsequent management.
• Meconium-stained liquor occurs with increased frequency as gestation extends beyond term, reflecting maturation of the fetal gastrointestinal tract and its neural control, with this finding carrying relevance to intrapartum management and neonatal resuscitation preparation.
• Macrosomia, and its associated intrapartum implications, together with the potential for reduced amniotic fluid volume as pregnancy extends significantly beyond term, represent important, relevant clinical considerations directly informing the structured surveillance and management approach.

• Accurate confirmation of gestational age is the essential, foundational requirement. It is ideally established by early, first-trimester ultrasound dating (crown-rump length measurement).
• Accurate dating is critical to correctly classifying a pregnancy as late term or postterm and to timing any recommended intervention.
• Structured antenatal surveillance for pregnancies extending into the late term period supports assessment of fetal wellbeing during this period of progressively increasing risk. It incorporates regular fetal heart rate monitoring (cardiotocography) and assessment of amniotic fluid volume.
• The frequency and components of surveillance follow established local or national protocol guidance.

• Induction of labour is generally recommended once pregnancy reaches the late term period (typically offered from 41 weeks). It is well established, evidence-based standard practice in contemporary obstetric care.
• Clinical trials show a reduction in perinatal mortality with induction compared with continued expectant management awaiting spontaneous labour onset, without any increase in caesarean delivery rate.
• Discuss with the woman the relative risks and benefits of induction compared with continued expectant management with enhanced surveillance. Respect her autonomy and informed preference where she wishes to decline or delay recommended induction.
• Provide enhanced fetal surveillance during any period of continued expectant management. Shared, patient-centred decision-making is an essential component of care.
• Where labour is induced, standard induction protocols are followed, with careful, ongoing intrapartum monitoring given the associated risks of meconium-stained liquor and macrosomia.
• Neonatal assessment is an important component of intrapartum and immediate postnatal management for pregnancies delivered late term or postterm. Where meconium-stained liquor or other relevant risk factors are present, prepare for potential neonatal resuscitation.
• Communicate clearly the evidence base supporting the recommended induction timing. Discuss respectfully and individually, accommodating the woman's own values and preferences where these differ from standard recommendations.