Causes and Risk Factors for Post-Term Pregnancy
A pregnancy is considered post-term if it exceeds 42 weeks in duration. In fact, post-term deliveries are quite common among women; only a small fraction give birth precisely on their expected due date. While the majority of births occur between weeks 37 and 41, they typically happen within one week of the expected due date. It is important to note that the best indicators for estimating gestational age are through one of the following methods:
- Conducting an ultrasound examination between weeks 8 and 12 of the pregnancy.
- Knowing the exact date of the woman’s last menstrual period.
The most accurate way to determine gestational age is through an ultrasound performed during the first trimester, specifically between weeks 8 and 12. In some cases, a woman may not accurately remember the date of her last menstrual period, leading to a miscalculation of her pregnancy duration. This, in turn, can suggest a likelihood of post-term delivery. However, there are situations where the conception date is known precisely, such as in cases of in vitro fertilization (IVF). Notably, the main reasons for some pregnancies extending beyond the expected delivery date remain unclear. There are no significant causes linked to the activities or behaviors of the woman during pregnancy that lead to post-term outcomes. Nevertheless, several secondary reasons and risk factors may increase the chance of a post-term birth, including:
- Experiencing a first-time pregnancy.
- Becoming pregnant at an older age.
- A previous history of post-term delivery.
- A family history of post-term birth, for example, if the mother was also born post-term.
- Carrying a male fetus.
- Being overweight or obese.
- Having fair skin.
Actions Taken by Healthcare Providers for Post-Term Pregnancy
In general, if a pregnancy goes past the due date while the woman is healthy and does not wish to undergo labor induction, it is advisable for her to have regular check-ups and increased monitoring during the remaining weeks. Often, by the time a woman reaches 42 weeks, labor begins spontaneously. In this context, doctors may decide to induce labor if it is delayed for about a week. Labor induction refers to the process of stimulating uterine contractions before natural labor begins, with the goal of achieving a vaginal delivery. Alternatively, physicians might opt to wait a short period past the due date, hoping for natural labor onset, depending on the health of the fetus and the original due date. It is important to note that women planning to wait for labor commencement will likely undergo frequent monitoring—approximately twice a week—to assess fetal health. During this time, healthcare providers may request one or more of the following tests:
- Non-Stress Test (NST), which uses a device similar to that used during labor to monitor the fetal heart rate, movement, and check for signs of fetal distress.
- Ultrasound, to verify fetal growth and movement.
- Cervical examination to assess if the cervix is dilated adequately in preparation for labor.
- Measurement of amniotic fluid levels surrounding the fetus.
In cases where there are health concerns for the fetus or if the pregnancy exceeds two weeks beyond the due date, the doctor will likely determine that labor induction is necessary to promote vaginal delivery. This process can decrease the likelihood of requiring a cesarean section. There are various methods available for inducing labor, which may involve a single technique or a combination of more than one, including:
- Prostaglandins, which are medications that help soften and shorten the cervix to stimulate labor, available in vaginal gel or tablet form, often administered in doses every 6-8 hours.
- Artificial rupture of membranes (amniotomy), performed only if the cervix is open, where a small instrument is used to break the amniotic sac to encourage contractions.
- Oxytocin, a medication delivered intravenously to stimulate uterine contractions, with dose adjustments made as contractions begin and progress until delivery occurs; this method is only applicable following the rupture of the amniotic sac.
- Cervical balloon catheter insertion, where a small silicone tube is placed in the cervix to apply pressure and promote softening and shortening.
Recommendations for Preventing Post-Term Pregnancy
Understanding and determining the due date is the best approach to assess whether a pregnancy is truly post-term. As mentioned earlier, tracking the date of the last menstrual period, along with early pregnancy ultrasounds, allows the healthcare provider to ascertain the baby’s age based on size. It additionally helps check the placenta’s health through visible indicators. Importantly, there is insufficient evidence supporting the notion that consuming certain foods, such as spicy food, or engaging in specific exercises can accelerate or induce labor when a pregnancy is past the due date.
Video: Reasons for Post-Term Pregnancy
There can be instances when a pregnancy extends beyond the typical nine months. What could be the reasons for this?