Only about 4 to 5% of babies arrive on their exact due date, so the real question isn’t whether your baby will be “on time” but where in a wide window of normal your delivery will fall. In the United States, 39 weeks is the single most common gestational age at birth, and roughly 76% of all births happen before the 40-week mark. Understanding which signals your body gives, what your medical history suggests, and which clinical tests actually have predictive power can help you get a realistic sense of your timeline.
What “Early” and “Late” Actually Mean
The American College of Obstetricians and Gynecologists breaks the final stretch of pregnancy into specific categories. Early term runs from 37 weeks 0 days through 38 weeks 6 days. Full term covers 39 weeks 0 days through 40 weeks 6 days. Late term is 41 weeks 0 days through 41 weeks 6 days. Post-term begins at 42 weeks 0 days and beyond. These categories matter because a baby born at 37 weeks faces different health considerations than one born at 39 or 41 weeks, even though all three fall within a broadly “normal” range.
Risk Factors That Push Toward a Late Delivery
Certain factors make it more likely you’ll still be pregnant past 41 or even 42 weeks. The strongest predictor is having already had a post-term pregnancy. If this is your first baby, you’re statistically more likely to go past your due date than someone who has given birth before. Being over 30 and having a higher BMI also increase the odds.
Genetics play a surprisingly large role. A woman who was herself born post-term has a 49% increased risk of delivering past 42 weeks. If the baby’s father was born post-term, the risk rises by about 23%. So if your mother says “you were two weeks late,” that’s worth paying attention to.
Risk Factors That Point to an Earlier Arrival
Preterm birth (before 37 weeks) has its own set of risk factors: a history of previous preterm delivery, carrying multiples, a short cervix found on ultrasound, infections, smoking, high blood pressure, and chronic stress. Having had a prior preterm birth is the single most powerful predictor that it could happen again. Short intervals between pregnancies (less than 18 months) also raise the risk.
Physical Signs Your Body Gives You
Your body drops several hints that labor is getting closer, though none of them come with a precise countdown.
Baby dropping (lightening). When the baby settles lower into your pelvis, you may notice it’s easier to breathe but harder to walk. First-time mothers typically notice this about two weeks before delivery. Women who’ve had previous babies may not feel it until labor is already underway, or the baby may settle lower earlier in pregnancy without it meaning much about timing.
Mucus plug and bloody show. Losing your mucus plug, sometimes accompanied by a pink or blood-streaked discharge called “bloody show,” signals that your cervix is starting to change. For some people, labor starts within hours. For others, it’s still days away. On its own, losing the mucus plug doesn’t tell you to grab your hospital bag right this minute, but it does mean things are moving in the right direction.
Cervical changes. At prenatal visits near the end of pregnancy, your provider may check five features of your cervix: how dilated it is, how thin (effaced) it’s become, where it sits (forward or back), how soft it feels, and how low the baby’s head is in your pelvis. These five factors make up the Bishop score. A score above 8 suggests your body is primed for labor soon. A low score doesn’t mean labor is weeks away, but it does suggest your body hasn’t started the final preparation yet.
Real Contractions vs. Practice Contractions
Braxton Hicks contractions can fool you into thinking labor is starting when it isn’t. The differences are consistent enough to be useful. Practice contractions are irregular, don’t get closer together over time, and tend to be felt only in the front of your abdomen or in one spot. They often stop if you change positions, take a walk, or lie down. If you can sleep through them, they’re almost certainly Braxton Hicks.
True labor contractions follow a pattern: they come at regular intervals, get progressively closer together and stronger, and don’t let up when you move around. The pain typically starts in the middle of your back and wraps around toward the front. If timing them shows a clear trend of increasing frequency and intensity over an hour or two, that’s the real thing.
Clinical Tests That Help Predict Timing
Cervical Length on Ultrasound
If your provider is concerned about preterm birth, they may measure your cervix using a transvaginal ultrasound. A cervix measuring 25 millimeters or shorter before 24 weeks is the standard threshold that triggers preventive action, such as progesterone treatment or a cervical cerclage. At that cutoff, the rate of delivery before 35 weeks is about 18%. If the cervix is even shorter, 15 millimeters or less, the risk of delivering before 35 weeks jumps to around 50%. A cervix that measures well above 25 millimeters is reassuring.
Fetal Fibronectin Test
This swab test checks for a protein that acts like a biological glue between the amniotic sac and the uterine lining. It’s typically used between 22 and 34 weeks when a woman has symptoms of preterm labor. The test is far better at telling you labor is NOT imminent than confirming it is. A negative result carries about a 99% chance you won’t deliver in the next seven days. A positive result is much less definitive: at the standard cutoff, only about 16% of women with a positive test deliver within a week. So a negative result can offer real peace of mind, while a positive result mainly means closer monitoring.
First Pregnancy vs. Subsequent Pregnancies
Conventional wisdom holds that first babies come late and second babies come early. The reality is more nuanced. A detailed study that tracked pregnancies from ovulation to delivery found no statistically significant difference in gestation length based on whether it was a first or later pregnancy. What is well established is that first-time mothers tend to have longer labors once contractions start, which may contribute to the perception that “everything takes longer” with a first baby. The biggest predictor of your timing isn’t whether this is baby number one or three. It’s your own prior birth history and your individual biology.
What Your Due Date Actually Tells You
A due date is the midpoint of a probability curve, not a deadline. The natural variation in healthy pregnancies spans about five weeks, from 37 to 42 weeks. Even with perfect dating from an early ultrasound, your delivery could fall anywhere in that window and be completely normal. In the U.S., medical practices have shifted toward more births at 39 weeks through scheduled inductions and cesarean sections, which is why the national peak has moved from 40 weeks to 39. In countries with lower intervention rates, like the Netherlands, the peak stays closer to 40 weeks.
The most honest answer to “will my baby come early or late?” is that no single sign or test gives you a reliable date. But you can narrow the window. A long cervix, a negative fibronectin test, no prior preterm births, and the absence of risk factors all point toward making it to full term. A family history of going past the due date, a first pregnancy, and a low Bishop score near your due date suggest you may be waiting a bit longer. And if contractions start coming in a regular, intensifying pattern that wraps from your back to your front and doesn’t quit when you move, that’s your body giving you the most reliable signal of all.