Going overdue in pregnancy refers to when a pregnancy lasts longer than the typical 40 weeks (full term). While most pregnancies last around 40 weeks, it’s perfectly normal for some to last a little longer – up to 42 weeks. However, there are some factors that make certain women more likely than others to go past their due date. In this article, we’ll take a look at who is most at risk of going overdue, and why.
What is considered overdue?
A normal, full-term pregnancy lasts anywhere from 37-42 weeks. Going past 42 weeks is when a pregnancy is considered post-term or overdue. Here is a breakdown of the stages of pregnancy:
| Preterm | Before 37 weeks |
| Early term | 37-38 weeks |
| Full term | 39-40 weeks |
| Late term | 41 weeks |
| Postterm | After 42 weeks |
So any pregnancy that reaches 41 weeks and beyond is considered overdue. Most doctors will induce labor or perform a c-section for safety reasons if a pregnancy reaches 42 weeks with no signs of impending labor.
What percentage of pregnancies go overdue?
Going past your due date is actually quite common. Here are some key statistics on overdue pregnancies:
– About 10% of pregnancies last longer than 40 weeks.
– First-time moms are more likely to go overdue – around 50% go at least a week over their due date compared to under 10% of women who’ve had a baby before.
– The average first-time pregnancy lasts 41 weeks and 1 day. For women who’ve had a previous birth, the average is 40 weeks and 3 days.
So while most women will not go extremely overdue (like 42+ weeks), it is common to go a bit past 40 weeks, especially for first-time mothers. However, some women are at higher risk than others.
Risk factors for going overdue
What makes someone more prone to going overdue? Here are some of the top risk factors:
First pregnancy
As mentioned, first-time moms are much more likely to go past their due date than women who’ve been pregnant before. Some reasons why:
– The body is going through the process of labor for the first time and may take longer to get the process started.
– First time moms may not recognize early labor signs as well.
– There is some evidence the placenta ages faster in first pregnancies, which could contribute to going longer.
Advanced maternal age
Women over 35 are more likely to go past their due date than younger moms. Some studies have found:
– Women over 40 had 2x the risk of going overdue compared to women under 25.
– The risk continues going up the older the mother is.
Some reasons why age raises the risk include:
– Older women are more likely to have conditions like high blood pressure and diabetes which are associated with overdue pregnancies.
– Advanced age may cause placental aging or other changes that inhibit labor starting on its own.
High BMI
Women who have a BMI in the obese range have higher odds of going overdue. For example:
– Women with a BMI of 30-35 have a 15% higher risk of going past 40 weeks compared to women with normal BMIs.
– The risk increases to over 30% higher for women with BMIs above 35.
Excess fat tissue is thought to cause increased inflammation and insulin resistance, which may make it harder for labor to start naturally.
Previous overdue pregnancy
Unsurprisingly, women who went overdue with a previous pregnancy are more likely to have an overdue pregnancy again in the future. About 33% of women who had a prior postterm delivery will go overdue again.
If your body had difficulty initiating labor the first time around, it’s likely to follow a similar pattern.
Genetics
Research has identified some genetic factors that make women more prone to longer pregnancies and going past their due date. A few examples:
– Variants in genes related to collagen synthesis – collagen helps initiate labor.
– Gene variants affecting vitamin D receptors – vitamin D helps trigger labor.
– Mutations impacting placental formation and function.
So in some cases, genetics could simply predispose the body to longer pregnancies.
Carrying a boy
Male fetuses are associated with longer pregnancies compared to girls. Multiple studies have confirmed this link:
– On average, boy pregnancies last .5-1 days longer than girl pregnancies.
– Boys have higher rates of late term pregnancies (41+ weeks) and postterm deliveries.
– The odds of going postterm increase around 10-15% for women carrying a boy.
This may be related to hormonal differences that affect the initiation of labor. Boys tend to make moms’ bodies less responsive to the hormones that help trigger labor.
Complications associated with postterm pregnancy
While most women who go a little overdue will deliver safely, there are some potential complications to be aware of if pregnancies extend too long past the due date:
Stillbirth risk
The risk of stillbirth starts going up once pregnancies extend past 39 weeks. The risk increases steadily with each additional week past the due date:
| Weeks pregnant | Stillbirth rate (per 1,000 deliveries) |
| 37-38 | 1.5 |
| 39 | 1.9 |
| 40 | 2.9 |
| 41 | 3.5 |
| 42 | 4.6 |
| 43+ | 8.4 |
Going even just 1-2 weeks overdue increases the risk of stillbirth significantly. The placenta tends to age and deteriorate the longer a pregnancy lasts, which contributes to stillbirth odds going up.
Meconium aspiration
When babies pass their first bowel movement (meconium) while still in the uterus, they can inhale it which causes meconium aspiration syndrome. This risk increases substantially the longer a pregnancy goes past 40 weeks:
– At 40 weeks, the rate of meconium aspiration is around 5-8%
– By 42 weeks, the rate jumps to around 20%
Meconium aspiration can cause breathing problems, lung inflammation, and infection.
Abnormal fetal growth
The placenta’s function often starts to decline the longer a pregnancy lasts, which can restrict the fetus’ growth in utero.
– Rates of too small or too large babies go up with longer pregnancies.
– After 42 weeks, the rate of large babies is 39% higher.
Both very large and very small newborns face additional health risks.
Cesarean delivery
Overdue pregnancies raise the likelihood of needing interventions like induction or c-section.
– Women at 41 weeks have 2x higher odds of c-section compared to delivery at 39 weeks.
– By 42 weeks, the c-section rate is 40% higher than at 40 weeks.
Higher rates of fetal distress and failure to progress often lead to more unplanned cesareans as due dates come and go.
When to induce for postterm pregnancy
Due to increased risks after 41-42 weeks, most providers will recommend induction to prevent complications. Here are some general guidelines on when induction is recommended if pregnancies go past the due date:
– **41 weeks** – Induction may be offered, especially for first time moms. Lower threshold for induction in women with advanced age or obesity.
– **41 weeks, 3-4 days** – Induction strongly recommended if labor does not start spontaneously by this point.
– **42 weeks** – Induction is recommended for all women who reach 42 weeks with no signs of labor.
However, the timing of induction may be adjusted based on a variety of factors like the results of fetal monitoring tests (like biophysical profiles), fetal movement counting, and the mother’s health status.
Ways to help start labor if overdue
If you want to see if you can coax labor along naturally before opting for induction, there are some at-home methods commonly recommended:
– Walking/light exercise – Helps baby engage and stimulate hormones.
– Sex/nipple stimulation – Releases oxytocin to promote contractions.
– Dates – Contains chemicals that prime the uterus for labor.
– Evening primrose oil – Thought to soften the cervix.
– Spicy foods – Some foods may stimulate gut activity and promote prostaglandin release.
However, the effectiveness of these methods ranges widely. Studies show the only method proven to reliably help start labor is nipple stimulation. But most strategies are low risk, so they are reasonable to try before induction medications or procedures.
Conclusion
While going a little past your due date is common and often not concerning, extended pregnancies of 41+ weeks do carry higher risks. First-time mothers over 35 who are carrying boys have the highest chances of going overdue.
If you end up going past your due date, stay in close contact with your provider to monitor for any signs of fetal distress. Try some natural induction techniques if you want to encourage labor a bit longer. But be prepared for induction if you get close to 42 weeks without signs of labor starting on its own.
While going postterm can be frustrating and concerning, your provider will help guide the safest plan for delivery to avoid complications. With close monitoring and proactive management as needed, the chances of a healthy labor and delivery remain very high even if baby takes their time arriving.
