Question 1

Can my due date change later in my pregnancy?

Accepted Answer

While your doctor may adjust your due date based on a first-trimester ultrasound, it is strictly against medical best practices to change a due date during the second or third trimester. As a fetus grows, its size becomes influenced by genetics (e.g., tall parents have longer babies) rather than just age. If an ultrasound at 30 weeks shows the baby measuring three weeks large, the due date does not change; instead, the doctor uses the original due date to determine that the baby is simply large for its gestational age. The earliest established date, whether by LMP or first-trimester ultrasound, remains the permanent anchor for the duration of the pregnancy.

Question 2

Why am I considered two weeks pregnant on the day I conceive?

Accepted Answer

Gestational age is calculated from the first day of your Last Menstrual Period (LMP), not from the moment of conception. Because ovulation and conception typically occur two weeks after the start of a menstrual cycle, those first two weeks of your cycle are mathematically included in the total 40-week pregnancy timeline. Medical professionals use this standard because the LMP is a visible, definitive event, whereas the exact moment of fertilization is invisible and impossible to prove without IVF. Therefore, the 40-week countdown begins before the egg is even released.

Question 3

What if I have irregular periods and don't know my LMP?

Accepted Answer

If you have conditions like PCOS, highly irregular cycles, or simply cannot remember your LMP, standard calculators using Naegele's Rule will provide highly inaccurate results. In these situations, your healthcare provider will rely entirely on an early dating ultrasound. By measuring the physical length of the embryo (Crown-Rump Length) during the first trimester, the ultrasound machine's software can calculate your exact gestational age with a margin of error of only 3 to 5 days, completely bypassing the need for menstrual history.

Question 4

Is it normal to give birth after my calculated due date?

Accepted Answer

Yes, it is exceedingly normal and common to deliver after your due date, particularly for first-time mothers. The due date marks the end of 40 weeks, but a pregnancy is not considered "late term" until 41 weeks, and not "postterm" until 42 weeks. Studies show that the average spontaneous labor for a first-time mother naturally begins at roughly 40 weeks and 5 days. You are well within the normal biological window if you deliver anywhere up to 14 days after your calculated EDD, provided medical monitoring shows the placenta and amniotic fluid remain healthy.

Question 5

How does IVF change the way my due date is calculated?

Accepted Answer

In Vitro Fertilization (IVF) provides the most mathematically precise due date possible because the exact age of the embryo is known. Instead of guessing the date of ovulation, calculators use the exact date the embryo was transferred into the uterus and subtract the number of days the embryo developed in the laboratory (usually 3 or 5 days). Because there is zero guesswork regarding when fertilization occurred, an IVF due date is considered biologically absolute and is virtually never overridden by subsequent ultrasound measurements.

Question 6

What happens if my due date calculator and my ultrasound give different dates?

Accepted Answer

If there is a discrepancy between your LMP-calculated due date and your first-trimester ultrasound date, your doctor will follow strict guidelines established by the American College of Obstetricians and Gynecologists (ACOG). If the ultrasound is performed before 9 weeks and the dates differ by more than 5 days, the ultrasound date becomes your official due date. If the ultrasound is performed between 9 and 13 weeks, the dates must differ by more than 7 days to justify a change. If the difference is smaller than these thresholds, the original LMP calculator date is kept to maintain consistency.

Pregnancy Due Date Calculator

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