Post-Term and Late-Term Pregnancy: Risks, Follow-up and Action Plans

All pregnancies are different and require individualized monitoring, which becomes more frequent as the due date approaches. This follow-up is a means to prevent problems and guarantee maternal and fetal well-being.

Most deliveries occur naturally between 37 and 42 weeks. However, approximately 10 percent of patients pass their estimated delivery date, which has been associated with risks such as stillbirth.

"Prolonged pregnancy is when it is longer than 42 weeks. Over 41 weeks is considered late term," said Maria Helena Tur Torres, M.D., an OB-GYN based in Mallorca, Spain. Prolonged pregnancy is also known as post-term pregnancy.

The exact causes of late-term or prolonged pregnancy are not known, but according to Tur Torres, some risk factors include:

• First gestation
• Advanced maternal age
• Obesity
• Excessive weight gain during pregnancy

Monitoring post-term pregnancies

Health checkups are recommended to determine the gestational age. The mother can find out the exact age based on the date of the last menstrual period, a physical examination and a fetal ultrasound. Ideally, for the best accuracy, the estimated due date is calculated during the first few weeks of pregnancy.

With the gestational age clear, physicians can make decisions and inform the patient about the risks and benefits of all options if a late- or post-term pregnancy occurs—including labor induction or expectant management and monitored response.

"This is a personal and individual decision that needs to be made by a pregnant person and their doctor," said Allison K. Rodgers, M.D., who is board-certified in OB-GYN and reproductive endocrinology and infertility, and practices at Fertility Centers of Illinois in Chicago.

Fetal risks

A higher risk is observed as early as 41 weeks. These pregnancies are associated with increased perinatal morbidity and mortality, according to Tur Torres, due to factors such as decreased amniotic fluid, meconium aspiration syndrome and low Apgar scores at birth. The Apgar test evaluates a baby's health (heart rate, breathing, reflexes, etc.) immediately after birth.

Additionally, post-term fetuses can have complications due to body size and weight, with difficulty passing through the birth canal, prolonged labor and birth trauma. Fetal dysmaturity is another risk associated with malnutrition or weight loss resulting from problems with blood supply through the placenta.

Inducing labor or waiting?

Induction is often avoided to prevent risks to mother and baby associated with increased instrumental deliveries, hemorrhaging, severe tearing of the birth canal and infection. However, some of these risks, such as the weight of the baby, are linked to post-term pregnancy.

Besides fears about the risks, many women prefer to experience natural childbirth as a matter of life choice. This is why they choose a more expectant attitude to a greater extent. Nevertheless, keep in mind that when choosing to wait, between 41 and 42 weeks, fetal well-being monitoring is recommended every 48 to 72 hours, Tur Torres explained.

She said monitoring tests include:

• Cardiotocography recording
• Ultrasound
• Doppler flow studies
• Amniotic fluid testing
• Biophysical profile
• Fetal movement perception record

"Alteration in any of the tests will be signal for completion in the following 24 hours, so as not to harm the perinatal outcome," Tur Torres said.

In other words, close monitoring is essential to guarantee the health of the baby and the mother.

The protocols of the hospitals and a personal decision

Each case is unique, so medical evaluation at this stage of pregnancy is essential to have a clear idea of what steps to take.

"There are risks and benefits to all interventions, so understanding these to make the best decisions is important," Rodgers explained.

Protocols vary from hospital to hospital, meaning there is no international consensus on how to proceed with late-term or prolonged pregnancies. However, attending physicians must evaluate all options, and if they're considering induction or cesarean section, they will communicate this to the expectant mother.

More and more hospitals are recommending induction at 41 weeks if labor doesn't start naturally, Tur Torres said. She noted that recent scientific research suggests better results with these practices, without increasing the percentage of cesarean sections.

What does science say?

From week 41 onward, there is an increased risk of stillbirth, according to scientific evidence.

"In mothers who continued their pregnancy to 41 weeks, there was a 64 percent increase in the risk of stillbirth compared to those who delivered at 40 weeks, with one additional mother having a stillborn baby for every 1,449 women," stated a systematic review of more than 15 million pregnancies, published in 2019 in PLOS Medicine.

"It seems, therefore, that a policy of induction of labor at 41 weeks in post-term women could be beneficial with potential improvement in perinatal outcome and a reduction in maternal complications," according to an article published in 2012 in Facts, Views & Vision in ObGyn.

Even though induction has the potential to avoid perinatal complications, "both patients and clinicians alike are concerned about risks associated with induction of labor such as failure of induction and increases in cesarean section rates," the article stated.

For this reason, it is a challenge to predict which patient to induce, who will respond to induction and who will require a cesarean section.

In 2018, a study in Sweden was suspended for ethical reasons after the death of six babies. The study on post-term pregnancies had 2,760 women with an uncomplicated singleton pregnancy, of whom 1,379 women were assigned to an expectant management group and 1,381 to an induction group.

"The study was stopped early owing to a significantly higher rate of perinatal mortality in the expectant management group," the study authors wrote. "No perinatal deaths occurred in the induction group, but six occurred in the expectant management group."

After the study, hospitals in the region began to change their policies in these cases, offering to induce women before reaching 42 weeks. The researchers also recommended providing clear information to women about the associated risks.