An overdue or post-dates pregnancy is one that lasts a week or more over the expected date of delivery. When your pregnancy goes past your due date, unless you have a high risk pregnancy, the usual practice is to wait up to 42 weeks to see if you will go into labor on your own.
Historically, a full-term pregnancy was defined as 40 weeks from the last normal menstrual period, and an overdue pregnancy was over 40 weeks. However, a 2013 joint opinion issued by the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) redefined the terms as follows:
- Full term = 39 weeks to 40 weeks plus six days
- Late-term (early overdue) = 41 to 41 weeks plus six days
- Post-term (late overdue) = 42 weeks and greater
By this definition, you are not considered overdue until you are at 41 weeks. This change was made to reduce the incidence of premature induction of labor.
Causes of Post-Dates Pregnancies
You are more likely to go past your due date if this is your first pregnancy, or if you previously had an overdue pregnancy. However, the true causes of overdue pregnancies are not known. Most pregnancies that appear to be overdue are a miscalculation of the due date, which is usually an estimation based on your last period.
If you are not sure of the date of your last period, your menstrual cycles are longer than the average 28 days, or they are irregular, then your due not may not be accurate. Getting an early ultrasound can give you a firmer due date and decrease your chance of being incorrectly labeled overdue.
Risks to Your Baby and You
According to the 2014 ACOG review of guidelines for management of overdue pregnancies, there are several risks, primarily to your baby and secondarily to you, when you go past your due date. The risks increase the longer you are overdue, especially after 42 weeks.
Risks to Your Baby
Post-term pregnancy presents several potential risks to your baby.
- Stillbirth: The risk of stillbirth increases after 41 weeks as a consequence of problems, such as an aging placenta and umbilical cord accidents.
- Aging placenta: A post-dates placenta begins to get smaller and show other signs of aging, especially after 42 weeks. This decreases supply of oxygen and nutrients to your baby.
- Umbilical cord accidents: The umbilical cord can wrap around your baby's neck or a limb, or get trapped between the baby and your uterus or cervix, cutting off his blood and oxygen supply. This increases the risk of stillbirth or neurologic problems after birth.
- Decreased amniotic fluid: Amniotic fluid production decreases as you get further past your due date. Decreased amniotic fluid (oligohydramnios), which is more common after 42 weeks, increases the risk of umbilical cord accidents and fetal and newborn death.
- Meconium aspiration: Your baby may pass stool into the amniotic fluid and inhale it into his lungs. The risk increases the further you go beyond your due date. This can lead to death or newborn lung infection.
- Dysmaturity: A dysmature baby is one who looks like he didn't get enough nourishment. He is long and lean and has long hair and fingers. This is especially seen after 42 weeks.
- Macrosomia: Your baby will continue to grow after term. A large baby has the risk that his shoulders can get stuck against your pubic bones during delivery (shoulder dystocia). The risk of clavicle or arm fracture and other injuries to your baby during delivery increase if his shoulders get stuck.
- Newborn seizures: Decreased oxygen supply can cause fetal brain injury leading to seizures after delivery and long term neurologic problems.
- Low APGAR scores: Low APGAR scores at five minutes after birth may include slow heartbeat and difficulty breathing.
Risks to You
You may also be at risk if your baby is overdue. Risks include:
- Increased risk of needing a forceps or vacuum vaginal delivery or a cesarean section
- Vaginal, cervical, and rectal tears because of a big baby or from use of forceps
- Increased chance of needing an episiotomy because of a big baby
- Hemorrhage after delivery
- Uterine and pelvic infections
- Risks of complications from a cesarean section
Observation of You and Your Baby
According to the Mayo Clinic, when you pass your due date, the usual procedure is to wait and see if you will go into spontaneous labor (expectant management). At your prenatal visits, your doctor or midwife will check to see if your cervix is getting thinner, shorter, and softer or dilating (getting favorable for delivery).
If you haven't delivered by 41 weeks your baby will be monitored. The ACOG review notes that there are no well-done studies to prove that standard fetal monitoring reduces the risks, but that they "may be indicated" at and after 41 weeks. Monitoring of your baby includes the following:
- Kick counts: Kick counts monitors your baby's kicks, rolls and other movements. A healthy baby is expected to move at least 10 times within two hours.
- Electronic fetal monitoring: This checks your baby's heartbeat and other factors and which include:
- Nonstress test (NST): Looks at how your baby's heartbeat responds when he moves spontaneously
- Contraction stress test (CST): :ooks at how your baby heartbeat responds to a stress, such as your contractions
- Biophysical profile (BPP): Looks at your baby's NST plus his breathing, movement, muscle tone, and the amount of amniotic fluid
Your doctor or midwife will initiate a delivery contingency plan once you pass your due date. The ACOG review of guidelines for management advises that:
- Between 41 and 42 weeks of pregnancy induction of labor "can be considered."
- Between 42 weeks and one day and 42 weeks and 6 days induction "is recommended."
The usual obstetrics practice is to plan for delivery by 42 weeks, and the following modes of delivery are possible:
- Spontaneous labor: During expectant management, you have a good chance of going into spontaneous labor. As long as you and your baby are doing well, it is OK to wait. Keeping active, including walking, may help to initiate your labor. Be wary of using herbal or other "natural" medicines to try to bring on labor.
- Induced labor: If you don't go into spontaneous labor by 41 weeks, your doctor or midwife may induce labor if your cervix is favourable, or schedule it to be done at 42 weeks if your cervix is not favorable. They may induce labor before 42 weeks for the following reasons:
- Your baby is becoming less active.
- An electronic fetal monitoring test shows signs of fetal distress or the amniotic fluid is low.
- You develop a new problem, such as high blood pressure or signs of preeclampsia.
- For convenience, such as delivering on a weekday with more personnel than on the weekend.
- Cesarean Section: You will need a cesarean section if your baby shows signs of distress, or if you develop a problem, and your cervix is not favorable for induction of labor. You will also have a C-section if you fail induction of labor, or if by 42 weeks, your cervix is not favorable for induction.
A 2012 Cochrane Database System Review looked at studies that compared induction of labor at 41 weeks compared to expectant management. They found that the risk of poor fetal and newborn death, meconium aspiration, and other outcomes is less if labor is induced at 41 weeks, rather than waiting longer for spontaneous labor.
If you go over your estimated due date, discuss any concerns with your obstetrics provider, as well as the plans for monitoring your baby and for delivery if you don't go into spontaneous labor. As long as your baby is not in distress and you have no complications, waiting a few days for spontaneous labor ensures that your baby is not born premature.