1. What is the NHS Pregnancy Calculator?

The NHS Pregnancy Calculator estimates your current pregnancy week based on your last menstrual period (LMP) and provides week-by-week tracking according to NHS guidelines. It helps monitor fetal development and important milestones throughout pregnancy.

2. How Does the Calculator Work?

The calculator uses the standard pregnancy calculation formula:

Where:

• \( LMP \) — Last Menstrual Period (start date of last period)
• \( Current\ Date \) — Today's date or any specified date
• \( \lfloor \rfloor \) — Floor function (rounding down to nearest integer)

Explanation: Pregnancy is calculated from the first day of your last menstrual period, as this is typically easier to recall than conception date. The calculation divides the number of days since LMP by 7 to determine completed weeks.

3. Importance of Pregnancy Week Calculation

Details: Accurate pregnancy dating is crucial for monitoring fetal development, scheduling prenatal tests at appropriate times, determining due date, and identifying any potential complications. NHS guidelines emphasize regular week-by-week tracking for optimal prenatal care.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period and the current date (or any date you want to check). The calculator will determine how many weeks pregnant you are and provide your estimated due date (40 weeks from LMP).

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 conception date. Pregnancy is typically 40 weeks from LMP (38 weeks from conception).

Q2: What if I have irregular periods?
A: For irregular periods, an early ultrasound (dating scan) between 8-14 weeks provides the most accurate pregnancy dating and should be used instead of LMP-based calculations.

Q3: How accurate is the estimated due date?
A: Only about 5% of babies are born on their exact due date. Most births occur between 37-42 weeks. The due date is an estimate for planning purposes.

Q4: When should I contact my midwife or GP?
A: Contact healthcare providers as soon as you know you're pregnant to begin antenatal care. Early booking improves outcomes for both mother and baby.

Q5: What prenatal tests occur at specific weeks?
A: Different tests are scheduled throughout pregnancy: dating scan (8-14w), combined test (10-14w), anomaly scan (18-21w), and various screenings at specific gestational ages.