出産予定日計算機
最終月経日（LMP）から出産予定日、現在の妊娠週数、妊娠段階、重要な検診日程を計算します。
Enter the first day of your last menstrual period
💡 This calculator is for reference only. Consult your healthcare provider for accurate due date and pregnancy information. Calculations are based on Naegele's Rule.
📖 使い方
- Enter the first day of your last menstrual period
- View your due date, current pregnancy week, and trimester info
- Check key milestones for upcoming appointments
- Use reverse calculation to estimate conception date
✨ 主な機能
- ✓Due date calculation based on Naegele's Rule
- ✓Current pregnancy week and days display
- ✓Trimester information (1st/2nd/3rd)
- ✓Key milestones (12-week screening, 20-week anatomy scan, etc.)
- ✓Reverse calculation for conception date and fertile window
📐 計算式
Due Date = Last Menstrual Period + 280 days (40 weeks)
Conception ≈ Last Menstrual Period + 14 days💡 計算原理
- •Naegele's Rule calculates the due date by adding 280 days (40 weeks) to the last menstrual period (LMP).
- •Actual conception occurs around ovulation, typically about 14 days after LMP.
- •Pregnancy lasts about 38 weeks (266 days), but counting from LMP makes it 40 weeks.
- •1st Trimester (1-12 weeks): Major organ formation, morning sickness period
- •2nd Trimester (13-26 weeks): Stable period, feeling baby movements, gender determination
- •3rd Trimester (27-40 weeks): Baby growth completion, birth preparation
- •From 37 weeks, pregnancy is considered full-term and delivery is normal.
❓ よくある質問
Q. How accurate is the due date?
A. The due date is an estimate. Most births occur within 2 weeks of the due date. Only about 5% of babies are born exactly on their due date.
Q. What if I don't know my last menstrual period?
A. An ultrasound can measure the baby's size to estimate pregnancy weeks and due date. Consult your healthcare provider for accurate assessment.
Q. What is a trimester?
A. Pregnancy is divided into three trimesters: 1st (1-12 weeks), 2nd (13-26 weeks), and 3rd (27-40 weeks). Each period has different fetal development and maternal symptoms.
Q. When is full term?
A. Pregnancy is considered full-term at 37 weeks. Birth before 37 weeks is preterm, and after 42 weeks is post-term.
Q. Is the conception date the same as intercourse date?
A. Not necessarily. Sperm can survive up to 5 days in the female body, so the intercourse date and actual conception date may differ. Conception occurs around ovulation.
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