From Robin Elise Weiss, LCCE,
Your Guide to Pregnancy & Childbirth.
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Full-term pregnancies range from thirty-eight to forty-two weeks. But what if your pregnancy continues beyond forty-two weeks? It's not unheard of--in fact according to the American College of Obstetricians and Gynecologists, 10 percent of all pregnancies go past forty-two weeks. But why is the process longer for some?

Why do women deliver past their due dates?

Some pregnancies are post-term. But as it turns out, others 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. 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 difficult to accurately predict a due date.

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:

• Non-stress Tests (NST)
• Biophysical Profile (BPP) [li0 Other testing as indicated

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.