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The average human pregnancy is expected to last 40 weeks from the first day of the last menstrual period (LMP) to the estimated date of delivery (EDD); however, great variations can occur, with a significant impact on the mother and baby’s health.

Present definitions describe a full-term pregnancy as lasts between the start of the 39th week and the end of the 40th week (40 weeks 6 days) and births occurring in this timeframe are associated with the best outcomes for the mother and the baby.

While early term (births occurring between the start of the 37th week and the end of the 38th week) pregnancies and preterm (births occurring anytime before the 37th week) pregnancies bring with them problems for the still-developing baby, prolonged pregnancies (those extending beyond 42 weeks of gestation) have their own set of possible complications. Around 5-10% of all pregnancies globally are prolonged beyond 42 weeks and nearly 20% of all pregnant women require induction of labour - the majority of them being post-term pregnancies.

Most often, the cause of a wrongly labelled “post-term pregnancy” is an incorrect date of the last menstrual period and wrongly-calculated estimated date of delivery (EDD). Therefore, it is essential to date all pregnancies with an early pregnancy ultrasound, preferably in the first trimester. If the gestational age of the fetus by ultrasound is less or more than three weeks of that calculated by the LMP date recounted by the mother, the LMP date is considered incorrect. The crown-rump length (CRL) and head circumference (HC), measured in the first-trimester ultrasound, are used to date the pregnancy.

The use of first-trimester ultrasounds to date the pregnancy has reduced the incidence and complications of post-term pregnancies considerably. Although the causes of prolonged pregnancy are not fully understood, some factors increase the risk of post-term pregnancies.

  1. Signs and symptoms of post-term (or prolonged) pregnancy
  2. Causes of post-term (or prolonged) pregnancy
  3. Complications associated with post-term babies
  4. Management of post-term (or prolonged) pregnancy
  5. Prevention of post-term (or prolonged) pregnancy
Doctors for Post-term Pregnancy

The following features are usually present in a post-term pregnancy:

  • Mother, before delivery:
    • Pregnancy has extended 1 to  2 weeks beyond the estimated date of delivery 
    • Lack of labour pains or other signs of labour
    • Reduced fetal movement
    • Reduced uterus size that does not correspond with the expected weight for weeks of gestation due to reduced amniotic fluid or intrauterine growth retardation (IUGR)
    • Meconium-stained amniotic fluid (yellow to green) may be seen if the membranes have ruptured
  • Baby, after delivery:
    • The baby has lower than normal amounts of subcutaneous fat and a reduced mass of soft tissue
    • Babies can be low birth weight or macrosomic
    • The skin may be loose, flaky and dry
    • Fingernails and toenails may be longer than usual and stained yellow from meconium
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The most common cause is considered to be an incorrect LMP date. As a principle, the duration of gestation is calculated from the date of the first day of the last menstrual period. Provided that the length of the menstrual cycle is 28 days, with a regular frequency, the estimated date of delivery is 40 completed weeks from the first day of the last menstrual period. However, sometimes, patients may not recall the date correctly or have longer or irregular cycles, causing the estimated delivery date (EDD) to be wrongly calculated, resulting in a false “post-term pregnancy”.

Some other pre-existing factors have shown to be associated with cases of actual post-term pregnancies. These include, but may not be limited to:

  • Primiparity or first pregnancy
  • Prior post-term pregnancy
  • Male gender of the fetus
  • Genetic factors (studies have found a closer link with genetic factors inherited from the mother than the father)
  • Maternal obesity

The biggest cause of concern related to the correct calculation of the estimated date of delivery is undoubtedly to avoid delivering babies before term. This is because the changes and growth that take place in a developing fetus vary greatly from week to week. Even the difference of a few days can potentially impact the newborn baby’s health, require neonatal intensive care unit (NICU) admissions or even alter the course of their lives due to preventable complications. However, babies that have not been born by the 41st week (later-term pregnancy) or 42nd week (post-term pregnancy) have a unique set of complications plaguing them due to post maturity. Complications and risks to a postmature baby include the following:

  • Placental insufficiency and dysmaturity: The placenta is an organ that develops in the uterus during pregnancy to provide the developing baby with oxygen and nutrients through the mother’s blood. Toxic waste products are removed from the baby’s blood through the placenta as well. While placental insufficiency or breakdown and dysfunction of the placenta can occur in any week, normally the placenta begins to regress at 39 weeks when the pregnancy reaches term. Placental insufficiency leads to the fetus not receiving adequate nutrients or oxygen, resulting in a thin (due to soft tissue wasting), undernourished infant with depleted glycogen stores (low blood glucose levels) and decreased amniotic fluid volume.
  • Small for gestational age (SGA) babies: Depending on the week when placental insufficiency takes place, the growth and development of the baby may be retarded, resulting in a small, low birth weight baby despite a post-term delivery.
  • Intrauterine growth retardation: Similar to the previous complication, early onset of placental insufficiency can lead to the baby’s growth being retarded.
  • Macrosomic or large baby, weighing more than 4 kilograms at birth: As a result of continued development, the baby’s birth weight may be excessive. A large baby can cause the following problems in delivery:
    • Prolonged labour
    • Cephalo-pelvic disproportion, where the head of the baby may be too big for the outlet of the mother’s pelvis
    • Shoulder dystocia: One of the baby’s shoulders may become stuck at the mother’s pelvic opening. A sign (turtle sign) of this is the head of the baby recoiling back inward even after having fully emerged.
    • Birth injury resulting in cerebral palsy or damage to nerves of the arm
  • Perinatal asphyxia: The placental breakdown and dysfunction can cause oxygen deprivation of the fetus. Sometimes, due to the reduced amniotic fluid volume (oligohydramnios), the umbilical cord also gets compressed and further compromises the oxygen circulation of the baby.
  • Meconium aspiration syndrome: Meconium refers to the baby’s feces, which is passed normally within a day or two of birth. Sometimes, post-term and term babies may pass the meconium while still in the womb, causing the surrounding amniotic fluid to become stained yellow to green with it. Babies could inhale meconium during the birth and develop respiratory distress if it blocks their respiratory tract.
  • Neonatal hypoglycaemia: The lack of placental nutrients leads to the glycogen stores in the baby’s body to be used up for energy. This produces undernourished neonates with hypoglycaemia or low blood glucose levels.
  • Neonatal acidemia: Electrolyte imbalance can cause the pH of the newborn baby’s blood to be reduced or become acidic.
  • Low five-minute Apgar scores. Apgar score assesses five essential parameters of a newborn baby (skin colour, heart rate, activity, respiratory effort, tone of the body) and allots a score out of 10, to quickly decide whether the baby needs resuscitation.
  • Neonatal encephalopathy: It can be defined as disturbed neurologic function in the earliest days of life in an infant born at or beyond 35 weeks of gestation, manifested by a subnormal level of consciousness or seizures. The respiratory effort may also be weak.
  • Neonatal seizures: Newborn babies can experience seizures or fits due to the complications of neonatal encephalopathy or hypoglycaemia.

Maternal complications: Besides being harmful to the newborn, post-term pregnancies can cause complications to mothers as well. These problems include:

Although the timely induction of labour in prolonged pregnancies can improve outcomes, if done too soon when the uterus or cervix is not in a favourable state, obstetric complications can occur:

  • Need for a C-section 
  • Prolonged labour
  • Postpartum hemorrhage
  • Traumatic delivery

Current guidelines state that after a pregnancy reaches late-term (41 weeks and beyond), the option to undergo induction of labour (IOL) should be offered to patients. If the patients choose to decline the option to undergo induction of labour, their wishes are respected and intensive antepartum fetal monitoring is conducted starting at 42 weeks of pregnancy (post-term pregnancy).

  • Antepartum fetal monitoring: Post-term pregnancies that have not been induced for labour or delivered by 41 weeks should go through strict antepartum fetal surveillance. Tests used vary but the best method is to conduct twice a week modified biophysical profile test which includes two tests:
    • Non-stress test: Movement, heart rate and “reactivity” of heart rate to movement are measured for 20-30 minutes in babies. (Read more: Baby’s heartbeat during pregnancy)
    • Amniotic fluid index: Any indication of reduced fluid volume (oligohydramnios) or meconium staining should warrant an induction of labour (IOL) and delivery.
  • Expectant management: Expectant management of post-term pregnancies refers to the practice of allowing labour to set in naturally after 42 weeks, either upon patients request or due to unfavourable cervix or uterus for induction of labour (IOL).
  • Induction of labour: It is offered to prolonged pregnancy patients starting at 41 weeks, if the patient declines or the cervix or uterus are unfavourable then expectant management is carried out instead. A vaginal examination is conducted to assess the state of the cervix and membrane sweeping is done prior to starting induction. The following steps are followed while medically inducing labour:
    • A prostaglandin gel or suppository is placed in the vagina and after a few hours, the labour begins.
    • An intravenous drip of oxytocin is started to induce uterine contractions
    • Artificial rupture of membranes (ARM) is needed if the membranes are still intact. The obstetrician uses a special hook-like instrument to rupture the membranes. This is painless for the patient.
    • Labour, whether induced medically or occurring spontaneously, can be complicated in post-term pregnancies. If the practitioner cannot find reassurance that the fetus is tolerating labour and the fetal heart rate (FHR) is imperceptible, cesarean delivery is recommended.

Postmature infant: Babies born after 42 weeks of gestation suffer from a variety of complications. The urgent complications need to be addressed immediately by the pediatric team as soon as the baby is born. Some of the added measures, besides the routine management of newborn babies, that may be necessary for a post-term newborn baby include, but may not be limited to: 

  • Neonatal resuscitation is necessary for infants with a low APGAR score (less than 5)
  • Assisted ventilation, sometimes with sedation is needed in meconium aspiration syndrome (Read more: Ventilator)
  • Monitoring of blood glucose levels and correction
  • Therapeutic hypothermia (maintaining body temperature below normal) may help infants with moderate or severe encephalopathy at birth
  • Surfactant therapy: Surfactant is a naturally occurring chemical substance in human lungs that reduces the surface tension inside the alveoli (air-filled sacs in the lungs where oxygen and carbon dioxide exchange occurs). By 35 weeks of gestation, most babies normally develop surfactant in their lungs. Sometimes surfactant is used in babies for respiratory distress.
  • Extracorporeal membrane oxygenation (ECMO): Not very widely available, it is a means to provide prolonged respiratory and cardiac support to the baby by attaching a machine.
  • Inhaled nitric oxide or other pulmonary vasodilators: Persistent pulmonary hypertension, which can arise in postmature infants who suffered from meconium aspiration syndrome at birth, is tested with inhaled pulmonary vasodilators.
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The best outcomes arise with allowing pregnant patients to enter spontaneous labour after reaching term or 39 weeks of gestation. Even though definitive action may not always be possible between 40 and 42 weeks, some measures can help prevent the pregnancy from extending post-term (beyond 42 completed weeks). These include:

  • Membrane sweeping or stripping: If the patient’s cervix is dilated enough to allow a finger in, the obstetrician may digitally separate the fetal membrane of the baby from the cervical wall. This releases prostaglandins and stimulates uterus contractions, which can make way to labour.
  • Unprotected coitus: Prostaglandins, released during the sexual act, cause uterine contractions. Therefore, having sex can trigger labour in patients.
  • Acupuncture: Acupuncture has shown to trigger labour in some patients in later-term pregnancies. Due to the paucity of data, this claim cannot be substantiated fully.
Dr. Manisha Jain

Dr. Manisha Jain

Obstetrics & Gynaecology
10 Years of Experience

Dr Vijaylakshmi

Dr Vijaylakshmi

Obstetrics & Gynaecology
18 Years of Experience

Dr. Swati Rai

Dr. Swati Rai

Obstetrics & Gynaecology
10 Years of Experience

Dr. Bhagyalaxmi

Dr. Bhagyalaxmi

Obstetrics & Gynaecology
1 Years of Experience

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