Due dates are tricky because it's hard to pinpoint the exact age of a fetus. Reasons for this include irregular periods since due dates are calculated based on a perfect day cycle , 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:. Even so, the reality is that 80 percent of babies arrive between 38 and 42 weeks of pregnancy, so your due date window is much bigger than you might think. Only about 1 out of every 10 babies is officially overdue, which means that the baby is born after 42 weeks of pregnancy. Recent research has shown that delivery after 40 weeks may come with certain risks , and OB-GYNs have responded.
Warshak, M. At the week mark, your doctor or midwife will become more vigilant about monitoring the overdue baby. Ross, M. Methods that your physician can use to monitor your post-term baby's condition are:. After 39 or 40 weeks, it's sometimes best to deliver sooner rather than later: Studies have shown that newborn admissions to the neonatal intensive care unit NICU increase slightly when a pregnancy lasts 40 to 42 weeks.
And stillbirth, though still rare, becomes a concern: At 40 weeks, the risk is 2 to 3 per 1, babies; at 42 weeks, it's 4 to 7 per 1, If labor hasn't started spontaneously, you'll probably be induced at 41 weeks—at the latest.
Translation: You won't end up having a Cesarean section. Whether or not you'll be induced depends on your own health, the status of your cervix, and the baby's well-being as determined by a non-invasive procedure called fetal non-stress testing. The conditions inside your uterus past due date may also stress the baby during labor and vaginal delivery. As a result, Warshak says, "Even if your cervix is at 8 centimeters and labor is progressing, we'll do a C-section if the overdue baby is not tolerating labor well.
We also try natural methods and refer women for acupuncture, reflexology, or reiki. At 40 to 41 weeks, if your cervix is dilated at least 2 centimeters, the midwives in Hasman's practice perform what's called a "cervical sweep," using a finger to separate the cervix from the amniotic sac. This can sometimes kick-start labor. An ongoing concern has been whether induction, as opposed to what's known as expectant management waiting for labor to start spontaneously while monitoring the mother's and baby's well-being , might lead to a higher risk for emergency Cesarean section , and studies have been conflicting.
But a new Danish study of more than , women found that inducing labor from week 39 to week 41 is not connected with higher C-section rates compared with waiting for labor to begin spontaneously or inducing labor later.
Backaches, heartburn, hemorrhoids—at 40 weeks all you want to do is hold your baby in your arms. However, during the second and third trimesters babies grow at different speeds, so this ability to accurately estimate age based on baby size diminishes. When a labor extends beyond 41 weeks late term and beyond 42 weeks post term there are increased risks of certain health problems. Some of the most common risks associated with a post term baby are:.
If your due date has come and gone, you can rest assured that you will continue to receive medical care. Your doctor may suggest some extra monitoring and medical tests to make sure that your baby is healthy.
Many doctors will begin to recommend this around 40 or 41 weeks. In making a determination to recommend induction, your doctor will take into account things like your age and health history, the health of the pregnancy, and the birthing wishes of the parents-to-be. If your doctor or midwife would like to induce you, there are many things you can do to help nudge your little one along that range from more natural methods to medical procedures.
Some methods of induction with varying effectiveness include:. You should have a discussion with your provider about which methods make sense in your particular situation. Most babies are born within a few weeks of their due date.
If you find yourself nearing the end of your estimated due date window with no signs of labor, there may be actions you can take to help nudge your baby into the world. Before doing so, you should always consult with your doctor or midwife. They can discuss the benefits and risks of your specific health situation and offer guidance on the safest ways to help your little one arrive in your arms. While it can be hard to wait, there are benefits to allowing your baby plenty of time to develop before entering the world.
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The State of Victoria and the Department of Health shall not bear any liability for reliance by any user on the materials contained on this website. Skip to main content. Healthy pregnancy. Home Healthy pregnancy. Baby due date. Actions for this page Listen Print. Summary Read the full fact sheet.
On this page. Length of gestation Determining baby due date Pregnancy ultrasound Premature babies Overdue babies Where to get help Things to remember. Some clues to the length of gestation include: Ultrasound examination especially when performed between six and 12 weeks Size of uterus on vaginal or abdominal examination The time fetal movements are first felt an approximate guide only.
The general procedure for a pregnancy ultrasound includes: The woman lies on a table. The transducer is moved across the abdomen. The sound waves bounce off internal structures including the baby and are transmitted back to the transducer.
There was no additional risk of newborn death when giving birth between 38 and 41 weeks, but the risk of newborn death did increase beyond 41 weeks. Other factors that do not necessarily cause stillbirth but may increase the risk of stillbirth, in general, include:. Of course, parents can still experience the stillbirth of a child even when none of these risk factors are present.
To read more about theories of unexplained stillbirth, read this article here. However, up until recently, there was no research on this topic. In , researchers published the first study looking at biological markers of aging in placentas. In this study, researchers in Australia collected placentas from 34 people who gave birth between weeks of pregnancy, 28 people who gave birth between weeks, and 4 people who experienced stillbirths between 32 and 41 weeks Maiti et al.
Five or more tissue samples were removed from each placenta, and the samples were analyzed using a variety of biochemical tests. Overall, the analysis of the placentas from the week pregnancies and from the stillbirths showed increased signs of aging, with decreased ability to transport nutrients to the baby and waste products away from the baby, compared to the placentas from the earlier term births.
The rate of placental aging varied in different pregnancies, and the authors stated that not all of the week placentas showed signs of aging.
We reached out to the authors to find out more, and they told us that one-third of the week placentas showed increased signs of aging compared to the week placentas. This means that two-thirds of the week placentas did not show signs of aging. You can watch a minute video describing the findings of this emerging research here.
I would also like to thank my expert reviewers for an earlier version of this article—Shannon J. Join others who also want to help bring evidence-based care to their local community. Rebecca Dekker Don't miss an episode! Don't miss an episode!
Subscribe to our podcast: iTunes Stitcher On today's podcast, we're going to talk with Ihotu Ali, MPH, who is writing about research on the effects of racism on pregnancy and birth outcomes. Rebecca Dekker. PhD, RN. Get our one-page handout on Inducing for Due Dates to use in your informed decision making!
Early term babies are born between 37 weeks 0 days and 38 weeks 6 days Full term babies are born between 39 weeks 0 days and 40 weeks 6 days. Late term babies are born between 41 weeks 0 days and 41 weeks 6 days Post term babies are born at 42 weeks and 0 days or later. How do you figure out your estimated due date? What is the most accurate way to tell how far along you are? Why is LMP less accurate than using ultrasound? LMP is less accurate because it can have these problems: People can have irregular menstrual cycles, or cycles that are not 28 days People may be uncertain about the date of their LMP Many people do not ovulate on the 14 th day of their cycle The embryo may take longer to implant in the uterus for some people Research indicates that some people are more likely to recall a date that includes the number 5, or even numbers, so they may inaccurately recall that the first day of their LMP has one of these numbers in it.
What is the best time to have an ultrasound to determine gestational age? Should a due date be changed based on a third trimester ultrasound? How long is a normal pregnancy? Is it really 40 weeks? Why is this method wrong? So how can we deal with this problem?
There have been two studies that measured the average length of pregnancy using survival analysis: Study finds that estimated due date is 3 to 5 days AFTER 40 weeks In a very important study published in , Smith looked at the length of pregnancy in 1, healthy women whose estimated due dates, as calculated by the first day of the last menstrual period, were perfect matches with estimated due dates from their first trimester ultrasound Smith, a.
Study finds that estimated due date should be closer to 40 weeks and 5 days In , Jukic et al. So what was the average length of a pregnancy in this study? Are there some things that can make your pregnancy longer? Other factors that may make your pregnancy more likely to go longer include: Higher body mass index before you get pregnant Halloran et al. In , Caughey et al. The participants in this sample all gave birth at Kaiser Permanente hospitals in northern California. The overall use of interventions Cesareans and inductions in this sample was not listed.
The participants in this study were mostly well-educated. The rate of inductions was not listed. This was the same time period and same hospital as his study, but this time the researchers only looked at low-risk people who had health insurance. The overall Cesarean rate was The authors also took whether or not people had inductions into account when they calculated the risks of going past your due date Caughey et al. Risks for mothers: The risk of chorioamnionitis infection of the membranes was lowest at 37 weeks 0.
However, these numbers are much higher than are typically seen, and are partially related to the high use of vacuum and forceps in this study. What about the risk of stillbirth? There are two very important things for you to understand when learning about stillbirth rates.
First, there is a difference between absolute risk and relative risk. Absolute risk is the actual risk of something happening to you. Relative risk is the risk of something happening to you in comparison to somebody else. How do you measure stillbirth rates? Actual stillbirth rates vs. So what is the risk of stillbirth as you go past your due date?
What factors can increase the risk of stillbirth? Also, small for gestational age babies are often growth restricted at the week ultrasound. So, the gestational age for these babies is often under-estimated. This means that babies who are small for gestational age may be more post-term than we realize they are—increasing their risk while also leaving us unaware of their true gestational age Morken et al.
The traditional way of calculating the estimated due date 40 weeks after the last menstrual period is not evidence-based. This is more accurate than using the last menstrual period because it no longer assumes a Day 14 ovulation. An ultrasound before 20 weeks is usually more accurate than using the last menstrual period, and the accuracy of an ultrasound is highest if it is done between 11 and 14 weeks.
Changes to the estimated due date in late pregnancy should only be made in rare circumstances. Some individuals, such as first-time mothers, are at higher risk for experiencing stillbirth in late pregnancy than other individuals. Committee opinion no. Obstet Gynecol , American College of Obstetricians and Gynecologists , Reaffirmed Committee Opinion No.
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