1. What Is Pregnancy Calculated By LMP?

Pregnancy calculated by LMP (Last Menstrual Period) is the standard method for estimating gestational age and due date in obstetrics. It uses the first day of the woman's last menstrual period as the starting point for pregnancy dating.

2. How Does The Calculator Work?

The calculator uses the standard obstetric formula:

Where:

• \( LMP \) — First day of last menstrual period
• \( 280 days \) — Standard pregnancy duration (40 weeks)

Explanation: This method, known as Naegele's rule, assumes a 28-day menstrual cycle and ovulation occurring on day 14. The due date is calculated by adding 280 days (40 weeks) to the first day of the LMP.

3. Importance Of Pregnancy Dating

Details: Accurate pregnancy dating is crucial for monitoring fetal development, scheduling prenatal tests, determining appropriate timing for delivery, and identifying potential complications such as preterm or post-term pregnancy.

4. Using The Calculator

Tips: Enter the first day of your last menstrual period in the date field. The calculator will provide your estimated due date and current gestational age. Ensure the date entered is accurate for the most reliable results.

5. Frequently Asked Questions (FAQ)

Q1: Why is pregnancy calculated from LMP instead of conception?
A: LMP is used because most women can recall their last period date more accurately than their conception date, and it provides a standardized method for healthcare providers.

Q2: How accurate is the LMP method?
A: The LMP method is generally accurate within ±2 weeks. First-trimester ultrasound dating is more precise and may adjust the due date if there's significant discrepancy.

Q3: What if my menstrual cycles are irregular?
A: For women with irregular cycles, the LMP method may be less accurate. Ultrasound dating in the first trimester is recommended for more precise gestational age determination.

Q4: When should I confirm my due date with a healthcare provider?
A: It's recommended to schedule your first prenatal appointment within the first 8 weeks of pregnancy to confirm dating and begin proper prenatal care.

Q5: Can the due date change during pregnancy?
A: Yes, if early ultrasound measurements differ significantly from LMP-based dating (usually more than 5-7 days), healthcare providers may adjust the due date.