Calculateur de Date d'Accouchement – Quand votre bébé est-il attendu ?
Calculez votre date d'accouchement estimée à partir de vos dernières règles ou de la date de conception. Découvrez où vous en êtes dans votre grossesse.
Comment est calculée la date d'accouchement ?
La date prévue d'accouchement (DPA) est calculée selon la règle de Naegele : ajoutez 280 jours (40 semaines) au premier jour des dernières règles (DDR). Equivalently, you can add 7 days to the LMP date and subtract 3 months. This formula was developed by German obstetrician Franz Karl Naegele in the early 19th century and remains the standard clinical method today.
Exemple pratique : Si vos dernières règles ont commencé le 15 janvier, votre date prévue d'accouchement est le 15 janvier + 280 jours = le 22 octobre. Using the shortcut method: January 15 + 7 days = January 22, then subtract 3 months = October 22.
La période gestationnelle de 280 jours suppose un cycle menstruel de 28 jours avec une ovulation au jour 14. For cycles longer or shorter than 28 days, the calculation adjusts by adding or subtracting the difference from 14. A woman with a 35-day cycle (ovulation on day 21 rather than day 14) would have an EDD 7 days later than the standard calculation suggests.
According to the American College of Obstetricians and Gynecologists (ACOG), the most accurate method for establishing or confirming gestational age is a first-trimester ultrasound. ACOG recommends that if the ultrasound-based date differs from the LMP-based date by more than 5–7 days in the first trimester, the ultrasound date should be used as the official EDD.
Méthodes pour déterminer votre date d'accouchement
Several methods exist for calculating due dates, each with different accuracy levels. Understanding these methods helps you interpret your EDD with appropriate confidence:
| Méthode | Précision | Quand utilisée | Comment ça marche |
|---|---|---|---|
| DDR (Règle de Naegele) | ±2 weeks | Initial estimate at first prenatal visit | Adds 280 days to first day of last period |
| Échographie du 1er trimestre (6-13 semaines) | ±5–7 days | Référence ; méthode la plus précise | Measures crown-rump length (CRL) |
| Échographie du 2e trimestre (14-20 semaines) | ±10–14 days | Used if no first trimester scan available | Measures biparietal diameter, femur length |
| Échographie du 3e trimestre (28 semaines et plus) | ±3–4 weeks | Poor for dating; used for growth assessment | Fetal size varies too much for accurate dating |
| FIV/Date de conception connue | ±1–3 days | Plus précis quand la date de conception est certaine | Adds 266 days to conception date |
First trimester ultrasound is the most accurate dating method because fetal size variation is minimal in early pregnancy — at 8 weeks, nearly all embryos are virtually the same size regardless of genetics. By the third trimester, individual variation in fetal size makes ultrasound dating unreliable for establishing the due date.
Comprendre l'âge gestationnel et le calendrier de grossesse
L'âge gestationnel est compté à partir du premier jour des dernières règles — pas à partir de la conception. This means at the moment of conception (typically day 14 of a 28-day cycle), you're already considered 2 weeks pregnant. A "40-week pregnancy" therefore includes approximately 2 weeks before conception actually occurred.
The WHO and ACOG define pregnancy term categories as follows:
| Étape | Semaines depuis les DDR | Ce qui se passe |
|---|---|---|
| Fécondation | ~2 weeks | Egg meets sperm; LMP weeks 1–2 are pre-conception |
| Implantation | 3–4 weeks | Embryo implants in uterine lining; hCG production begins |
| Test de grossesse positif | 4–5 weeks | hCG levels detectable; ~35 weeks until due date |
| Battement cardiaque embryonnaire détecté | 6–8 weeks | Heartbeat visible on ultrasound |
| Fin du premier trimestre | 13 weeks | Miscarriage risk drops significantly (~80% occur before this) |
| Échographie morphologique | 18–22 weeks | Detailed organ and gender screening ultrasound |
| Seuil de viabilité | ~24 weeks | Survival outside the womb becomes possible with NICU care |
| Fin du deuxième trimestre | 27 weeks | Third trimester begins; rapid fetal growth phase |
| Début du terme | 37–38 weeks | Baby is nearly mature; elective delivery not recommended |
| Terme complet | 39–40 weeks | Optimal birth window; lowest complication rates |
| Terme tardif | 41 weeks | Increased monitoring recommended |
| Post-term | 42+ weeks | Induction usually recommended; increased fetal risk |
Only about 4–5% of babies are born on their exact due date. According to research published in the BMJ, the median gestational length for first-time mothers is approximately 283 days (40 weeks + 3 days), while subsequent pregnancies average about 280 days. About 80% of babies are born within 2 weeks of the estimated due date.
À quoi s'attendre à chaque trimestre
Understanding the three trimesters helps expectant mothers prepare physically and emotionally for each stage of pregnancy:
First Trimester (Weeks 1–12): All major organ systems develop during this critical period. The embryo grows from a single cell to approximately 6 cm in length. Common symptoms include morning sickness (affecting 70–80% of pregnancies, according to the CDC), extreme fatigue, breast tenderness, and frequent urination. The risk of miscarriage is highest during this trimester, with approximately 10–15% of known pregnancies ending in miscarriage, most before week 12.
Second Trimester (Weeks 13–27): Often called the "golden period" because nausea usually subsides and energy returns. Fetal movements (quickening) begin around weeks 16–20 — first-time mothers may not notice them until weeks 18–22. The anatomical ultrasound at 18–22 weeks screens for structural abnormalities and often reveals the baby's sex. The baby grows from about 7 cm to 36 cm and begins developing fingerprints, eyebrows, and the ability to hear sounds.
Third Trimester (Weeks 28–40): Rapid fetal growth dominates this phase. The baby gains approximately 250g per week and develops fat stores, mature lungs, and the ability to regulate body temperature. Common maternal symptoms include back pain, shortness of breath, Braxton-Hicks contractions, and difficulty sleeping. Prenatal visits increase to every 2 weeks at 28–36 weeks and weekly after 36 weeks. Group B streptococcus (GBS) screening occurs at 36–37 weeks.
Exercice pendant la grossesse : guide trimestre par trimestre
For active women and runners, knowing your due date allows thoughtful planning of modified training phases. The ACOG recommends that pregnant women with uncomplicated pregnancies engage in at least 150 minutes per week of moderate-intensity aerobic activity. Exercise during pregnancy reduces the risk of gestational diabetes by 25–30%, preeclampsia by 40%, and excessive weight gain.
| Trimester | Recommended Activities | Modifications Needed | Warning Signs to Stop |
|---|---|---|---|
| First (weeks 1–12) | Running, swimming, cycling, strength training | Reduce intensity if nausea/fatigue; stay hydrated | Vaginal bleeding, severe nausea, dizziness |
| Second (weeks 13–27) | Running (modified), swimming, prenatal yoga, walking | Avoid supine exercises after 20 weeks; modify impact as belly grows | Chest pain, headache, calf pain/swelling |
| Third (weeks 28–40) | Walking, swimming, stationary cycling, water running | Significantly reduce impact; focus on comfort | Contractions, fluid leaking, reduced fetal movement |
Running-specific guidance: Many recreational runners continue running into the second trimester with appropriate modifications (slower pace, shorter distances, well-supported sports bra). Most runners transition away from running between weeks 28–35 due to pelvic pressure, round ligament discomfort, or simply feeling too uncomfortable. Water running (aqua jogging) is an excellent alternative that maintains cardiovascular fitness without impact stress.
Postpartum return to running: The general guidance is to wait at least 6 weeks postpartum before beginning any running (12 weeks is more conservative). A 2019 consensus statement from UK physiotherapists recommends waiting at least 12 weeks before returning to high-impact exercise and completing a pelvic floor screening first. Factors affecting return include delivery type (vaginal vs. C-section), pelvic floor recovery, breastfeeding status, and sleep quality.
Mythes et réalités sur la date d'accouchement
Pregnancy is surrounded by myths and old wives' tales. Understanding the facts helps reduce anxiety and supports evidence-based decision-making:
- Myth: Your due date is precise and your baby should arrive that day. Reality: The EDD is an estimate representing the midpoint of a normal delivery window. Only 4–5% of babies arrive on their exact due date. Think of it as a "due month" rather than a "due date."
- Myth: Going past your due date means something is wrong. Reality: It's common and often normal for first-time mothers to deliver 7–10 days after their EDD. Post-term pregnancy (42 weeks or beyond) does carry increased risks and is typically managed with induction. According to the WHO, induction of labor at 41 weeks is associated with lower rates of perinatal death compared to expectant management.
- Myth: Fetal heart rate predicts gender. Reality: Fetal heart rate varies with gestational age (faster in early pregnancy, slowing slightly as the heart matures) and fetal activity. Studies have found no reliable relationship between fetal heart rate and sex.
- Myth: You can eat whatever you want because you're "eating for two." Reality: Caloric needs increase only modestly — by 0 extra calories in the first trimester, 340 kcal/day in the second, and 450 kcal/day in the third. That's roughly one extra healthy snack, not double portions.
- Myth: Spicy food, walking, or sex will induce labor. Reality: No food, exercise, or activity has been scientifically proven to reliably induce labor. While nipple stimulation has some evidence for promoting contractions in late pregnancy, most folk remedies lack scientific support.
Prenatal Care Schedule and Key Tests
Knowing your due date structures your entire prenatal care schedule. The CDC recommends that women receive regular prenatal care beginning in the first trimester. Here is a typical schedule of visits and screenings:
| Week | Visit/Test | Purpose |
|---|---|---|
| 6–8 | First prenatal appointment | Confirm pregnancy, blood work, establish EDD |
| 8–12 | Dating ultrasound | Confirm gestational age, detect multiples |
| 10–13 | First trimester screening (NIPT or NT scan) | Chromosomal abnormality risk assessment |
| 15–20 | Quad screen (optional) | Additional genetic screening |
| 18–22 | Anatomy ultrasound | Detailed fetal organ survey, sex determination |
| 24–28 | Glucose tolerance test | Screen for gestational diabetes |
| 28 | Rh antibody test, Tdap vaccine | Prevent Rh disease; protect newborn from pertussis |
| 36–37 | GBS screening | Group B streptococcus vaginal/rectal swab |
| 36–40 | Weekly visits | Monitor BP, fetal position, cervical changes |
Women with high-risk pregnancies (advanced maternal age, multiples, gestational diabetes, preeclampsia) will have more frequent monitoring and additional ultrasounds. Always follow your healthcare provider's individualized schedule.
When to Seek Medical Attention During Pregnancy
While this calculator provides an educational estimate of your due date, pregnancy requires professional medical care. Contact your healthcare provider immediately if you experience any of the following at any stage of pregnancy:
- Vaginal bleeding: Especially in the first trimester (may indicate miscarriage or ectopic pregnancy) or third trimester (may indicate placenta previa or abruption)
- Severe or persistent abdominal pain: One-sided pain in early pregnancy could indicate ectopic pregnancy — a medical emergency
- Sudden severe headache or vision changes: May indicate preeclampsia, particularly after 20 weeks
- Reduced fetal movement: After 28 weeks, fewer than 10 movements in 2 hours warrants immediate evaluation
- Fluid leaking from the vagina: May indicate premature rupture of membranes
- Fever above 100.4°F (38°C): Infection during pregnancy requires prompt treatment
- Signs of preterm labor: Regular contractions before 37 weeks, lower back pressure, pelvic pressure
This calculator is an educational tool for general guidance. It is not a medical device and does not replace professional prenatal care. The WHO recommends a minimum of 8 prenatal contacts for a positive pregnancy experience and improved maternal and neonatal outcomes.
Questions fréquemment posées
How is the due date calculated?
Using Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). Alternatively, take your LMP date, add 7 days, then subtract 3 months. For irregular cycles, a first trimester ultrasound provides the most accurate dating, typically within ±5–7 days.
How accurate is the due date calculation?
LMP-based calculation is accurate within ±2 weeks for women with regular 28-day cycles. First trimester ultrasound (6–13 weeks) is the most precise method, accurate within ±5–7 days. Only about 4–5% of babies are born on their exact due date, and 80% are born within 2 weeks of the EDD.
What if my periods are irregular?
For irregular cycles, LMP-based due date calculation is unreliable because the assumed ovulation on day 14 may be significantly off. First trimester ultrasound is the preferred dating method for women with irregular cycles. An 8–13 week ultrasound accurately establishes gestational age regardless of cycle regularity by measuring crown-rump length.
Can I run during pregnancy?
Yes, with modifications. ACOG recommends that pregnant women who were running before pregnancy can generally continue with appropriate modifications. Reduce intensity as pregnancy progresses, stay well hydrated, and stop if you experience pain, dizziness, vaginal bleeding, or contractions. Most runners transition to walking, swimming, or water running by 28–35 weeks due to discomfort.
When should I have my first prenatal appointment?
Schedule your first prenatal appointment as soon as you get a positive pregnancy test, ideally between weeks 6–8. This visit confirms the pregnancy, establishes your due date through examination or ultrasound, orders baseline blood work, and begins your prenatal care plan. Starting prenatal care early is associated with better outcomes for both mother and baby, according to the CDC.
What does "full term" mean?
ACOG defines full term as 39 weeks 0 days through 40 weeks 6 days. Early term is 37–38 weeks, late term is 41 weeks, and post-term is 42 weeks or later. Babies born at full term have the best health outcomes. Elective delivery before 39 weeks is discouraged unless medically indicated.
Is it normal to go past my due date?
Yes, especially for first-time mothers. About 50% of first pregnancies go past 40 weeks. Going to 41 weeks is common and usually not a concern, though your provider will increase monitoring. Post-term pregnancy (42+ weeks) does carry increased risks, and induction is typically recommended by 41–42 weeks.
Can my due date change?
Yes. ACOG recommends revising the due date if a first-trimester ultrasound differs from the LMP-based date by more than 5–7 days. In the second trimester, the threshold for revision is 10–14 days. Once established by early ultrasound, the due date generally should not be changed by later ultrasounds, as fetal size variation increases with gestational age.
Quelle est la différence entre l'âge gestationnel et l'âge fœtal ?
Gestational age is counted from the first day of the last menstrual period and includes approximately 2 weeks before conception. Fetal age (also called embryonic age or conceptional age) starts from the actual date of fertilization and is about 2 weeks less than gestational age. Medical professionals and this calculator use gestational age as the standard measurement.
How does a twin or multiple pregnancy affect the due date?
The due date calculation is the same (40 weeks from LMP), but twins rarely go to full term. The average delivery for twins is 36–37 weeks, and for triplets about 32–33 weeks. Most OB-GYNs plan delivery of twins between 37–38 weeks due to increased risks of complications after that point. Twin pregnancies require more frequent monitoring and ultrasounds throughout gestation.
"Accurate determination of gestational age is fundamental to obstetric care and is important in a variety of situations. Methods for estimating the due date include last menstrual period, ultrasonography, and assisted reproductive technology. The best estimate is based on first-trimester ultrasonography."
"WHO recommends a minimum of eight contacts with the health system during pregnancy to reduce perinatal mortality and improve women's experience of care. Positive pregnancy experiences include effective clinical practices, relevant and timely information, and psychosocial and emotional support."