Full-term pregnancies typically last from 39 to 41 weeks, but it is also not uncommon for a baby to come slightly before or after that timeframe. In fact, studies show that fewer than 5% of women deliver on their due date and only 70% give birth within 10 days of their due date. Additionally, most doctors do not consider a baby to be “late” until at least 41 weeks, and some wait until 42 weeks before they intervene.
Delayed Deliveries
Doctors often refer to babies born past 40 weeks as “late-term” or “post-term,” depending on how far past the full-term date range your pregnancy goes. Babies born in certain timeframes of pregnancy are categorized in the following ways:
“Early term” is from 37 weeks, 0 days to 38 weeks, 6 days “Full-term” is from 39 weeks, 0 days to 40 weeks, 6 days “Late-term” is from 41 weeks, 0 days to 41 weeks, 6 days “Post-term” is from 42 weeks, 0 days or more
According to the American College of Obstetricians and Gynecologists, 10% of all pregnancies go past forty-two weeks. However, some pregnancies categorized as “post-term” are actually the result of the incorrect assignment of a due date. Due dates and the exact age of the fetus can be tricky to pinpoint because of many factors. Sometimes, this is because the woman’s last period date is off or she had irregular periods. Ultrasound and other tests can only put the date in the ballpark.
Why Due Dates Fluctuate
Reasons for inexact due dates include irregular periods, miscalculated or inaccurate menstrual history, 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 mother usually feels the first movements between 16 and 20 weeks) Fetal heartbeat (in normal pregnancies, the doctor can detect it between 18 and 20 weeks with a stethoscope and around 6 weeks using a vaginal ultrasound) 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 even more difficult to accurately predict a due date. In general, a family history of long pregnancies (your own, your mother’s and sisters’ pregnancy histories, and your male partner’s family history) is the most important predictor of longer pregnancy duration.
Possible Interventions
Depending on your specific pregnancy, your doctor will determine if and when any interventions are needed to speed things along. In most routine pregnancies, your doctor will recommend letting nature take its course until you pass the due date by a week or so. After 41 weeks of gestation, your doctor or midwife may have you do additional testing to ensure that you and your baby are healthy. This may include:
Biophysical profile (BPP) Non-stress tests (NST) Other tests as indicated
Based on the results of these tests, you will either go home and wait for labor to begin on its own, or you will discuss alternatives like induction or cesarean section. Induction is usually only indicated for medical conditions of the mother or baby that make staying pregnant riskier than waiting for labor to begin on its own.
Increased Risk of Complications
Studies have shown that there may be a greater risk of complications for both mother and baby associated with going post-term (42 weeks or more), including the following:
Cesarean section Higher neonatal intensive care unit admission rates Infections and/or high blood pressure in the mother Low amniotic fluid volume Thicker meconium and/or ingestion of meconium by the baby Use of forceps or vacuum assistance to extract the baby once in labor Vaginal tears in the mother due to a larger baby
Your doctor or midwife is the best resource on how these risks may or may not impact your pregnancy or be applicable to your situation. Consult with them about any concerns you may have about going past your due date.
A Word From Verywell
It can be stressful when your due date comes and goes without your baby’s arrival. Rest assured that, in most cases, a longer pregnancy is perfectly healthy—and your baby will certainly come in the days ahead. Sometimes, interventions will be needed to get labor going, but this is routine and safe as well. The key is patience. Listen to your body and aim to enjoy your last few days before childbirth and the adventure of motherhood begins.
