Calculating Your Due Date
Pregnancy is dated from the first day of your last menstrual period (LMP), making a full-term pregnancy 40 weeks — even though conception occurs around week 2. Only about 5% of babies are born on their exact due date; most arrive within a 2-week window around it.
Naegele's Rule
The standard method: LMP + 280 days = Due Date
- Assumes a 28-day cycle with ovulation on day 14
- If your cycles are longer (e.g., 35 days), your due date may be about a week later than this formula suggests
- First-trimester ultrasound dating is more accurate and may adjust your due date
Key Pregnancy Milestones
- Week 6-8: First ultrasound, heartbeat visible. Most accurate time for dating
- Week 10-13: NIPT (non-invasive prenatal testing) available for chromosomal screening
- Week 12: End of first trimester, miscarriage risk drops significantly
- Week 18-22: Anatomy scan — detailed check of baby's development. Gender can be determined
- Week 24: Viability milestone — survival outside the womb becomes possible with NICU care
- Week 28: Glucose screening for gestational diabetes
- Week 37: Considered "early term." Full term is 39-40 weeks
Understanding Trimesters
- First trimester (weeks 1-12): All major organs begin forming. Common symptoms include nausea, fatigue, and breast tenderness. Highest miscarriage risk (80% of miscarriages occur in this trimester)
- Second trimester (weeks 13-26): Often called the "honeymoon period" as nausea fades. Baby movement (quickening) first felt around weeks 16-20. Energy typically returns
- Third trimester (weeks 27-40): Rapid growth — the baby doubles or triples in weight. Common symptoms include back pain, heartburn, and difficulty sleeping. Baby moves into head-down position for delivery
Full Term vs Premature vs Late
- Preterm: Before 37 weeks — may need NICU care
- Early term: 37-38 weeks — healthy but benefits from more time
- Full term: 39-40 weeks — ideal delivery window
- Late term: 41 weeks
- Post term: 42+ weeks — most providers recommend induction by 41-42 weeks