OB Gestational Age Calculator

Gestational Age Calculation:

\[ \text{Gestational Age (weeks)} = \frac{\text{Current Date} - \text{Last Menstrual Period (LMP)}}{7} \]

Gestational Age:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Gestational Age?

Gestational age is the common term used during pregnancy to describe how far along the pregnancy is. It is measured in weeks from the first day of the woman's last menstrual period (LMP) to the current date.

2. How Does the Calculator Work?

The calculator uses the standard obstetric formula:

\[ \text{Gestational Age (weeks)} = \frac{\text{Current Date} - \text{Last Menstrual Period (LMP)}}{7} \]

Where:

Current Date — Today's date or any date you want to calculate for
LMP — First day of the last menstrual period
7 — Number of days in a week

Explanation: This calculation assumes a regular 28-day menstrual cycle with ovulation occurring on day 14. For women with irregular cycles, ultrasound dating may be more accurate.

3. Importance of Gestational Age Calculation

Details: Accurate gestational age determination is crucial for proper prenatal care, timing of tests and interventions, monitoring fetal growth, and determining the due date (estimated date of delivery).

4. Using the Calculator

Tips: Enter the first day of the last menstrual period and the current date (defaults to today). The calculator will determine how many weeks pregnant this corresponds to.

5. Frequently Asked Questions (FAQ)

Q1: What if I don't know my LMP?
A: If LMP is unknown or cycles are irregular, an ultrasound measurement in early pregnancy (first trimester) provides the most accurate dating.

Q2: How accurate is LMP dating?
A: LMP dating is accurate to ±5 days if the woman has regular cycles and is certain of her dates. Ultrasound is more accurate if done early.

Q3: What's the difference between gestational age and fetal age?
A: Gestational age counts from LMP (about 2 weeks before conception), while fetal age counts from conception. Gestational age is always about 2 weeks more than fetal age.

Q4: How is this different from Naegele's rule?
A: Naegele's rule estimates the due date (LMP + 1 year - 3 months + 7 days), while this calculator gives current gestational age in weeks.

Q5: What if my cycle isn't 28 days?
A: For cycles longer or shorter than 28 days, adjustments can be made, but ultrasound dating is more reliable in these cases.