Pregnancy Going Past Your Due Date—What Now?

The Risks and Monitoring Methods Available When You Go Past Your Due Date

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Full-term pregnancies range from thirty-eight to forty weeks. But what actually happens if your pregnancy is past your due date, continuing beyond the forty weeks time frame and date that your doctor gave you?

Why Women May Deliver Past Their Due Dates

Typically, doctors refer to babies born past 40 weeks as "late term" or "post term" depending on how far past the full term date range your baby falls into.

Babies born in certain time frames of pregnancy are categorized in the following ways:

  • “Early term” is 37 weeks, 0 days to 38 weeks, 6 days
  • “Full term”  is 39 weeks, 0 days to 40 weeks, 6 days
  • “Late term” is 41 weeks, 0 days to 41 weeks, 6 days
  • “Post term” is 42 weeks, 0 days or more

Some pregnancies are actually post term, in fact according to the American College of Obstetricians and Gynecologists, 10 percent of all pregnancies go past forty-two weeks. But as it turns out, other pregnancies categorized as "post term" are actually the result of the incorrect assignment of a due date. Due dates are tricky because it's hard to pinpoint the exact age of a fetus and so most doctors can only offer their best estimates. 

Reasons for this include irregular periods, sketchy or inaccurate menstrual history presented to the obstetrician, and mistaking spotting during very early pregnancy for a period.

Doctors usually use several methods together to make their best estimate of a due date, including:

  • Calculation based on your last ovulation (the most reliable method)
  • Calculation based on the first day of your last menstrual period
  • Clinical examination of the uterus for size
  • Your first detection of fetal movement (the fetus usually makes its first movements between 16 and 20 weeks)
  • Fetal heartbeat (in normal pregnancies, the doctor can detect it between 18 and 20 weeks)
  • Ultrasound which during early pregnancy can estimate fetal age within 7 to 10 days (it's not as effective later in the pregnancy)

Unfortunately, if you have irregular cycles it could prove even more difficult to accurately predict a due date. In general, family history of long pregnancies (your own, your mother and sisters’ pregnancy histories, and your male partner’s family history) is the most important predictor of a longer pregnancy duration.

What Happens After 40 Weeks Has Passed?

It is not that uncommon for mothers to experience pregnancies longer than the allocated "full term" duration. 

After 41 weeks gestation, your doctor or midwife may have you do additional testing to ensure that you and your baby are healthy. This may include:

Based on the results from these tests you will either go home and wait for labor to begin on its own or you will discuss alternatives like induction.

Induction is only indicated for medical conditions of the mother or baby that make staying pregnant more risky than waiting for labor to begin on its own.

Common Risks of Going Past Your Due Date

Recent studies have shown that there may be some risk of complications associated with going post term (42 weeks or more), including:

  • Possible infections and/or high blood pressure in the mother
  • Cesareans
  • Increased use of forceps or vacuum assistance to extract the baby once in labor
  • Vaginal tears in the mother due to large babies
  • Low fluid
  • Possible risk of thicker meconium
  • An increase in neonatal intensive care unit admission rates

Sources:

Spong, C. Y. (2013). Defining “term” pregnancy: recommendations from the Defining “Term” Pregnancy Workgroup. JAMA 309(23): 2445-2446.

Caughey, A. B. and T. J. Musci (2004). Complications of term pregnancies beyond 37 weeks of gestation. Obstet Gynecol 103(1): 57-62. 

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