Pregnancy calculators are there to help you know how long you have been pregnant. A pregnancy calculator will need to input the first day of your last menstrual period or LMF. Once you have done this the calculator will draw up the following information for you:
- When conception occurred
- The end of your first trimester
- The end of the second trimester
- The estimated due date.
Pregnancy calculators are not infallible- this is not because of the science behind these calculators or anything to do with the way they make their calculations, it is simply because births and babies can be very unpredictable. It is to begin with very difficult to know the exact date on conception, and even should you happened to know your calendar and dates on which you had intercourse, you might also know that a sperms cell can fertilize the ovum a few days after coitus (sexual intercourse) has occurred.
What are the assumptions of the pregnancy calculator?
The first assumption of a pregnancy calculator is that a pregnancy lasts 40 weeks. This is actually a very rough estimate and a normally pregnancy can actually last a week or two less or in unusual cases a week or two more. This is not to mention very premature births at 7 or 6 months. We can thus say that gestational age commencing from the first day of the last menstrual period is not an accurate science.
Calculating gestational age from the last menstrual period also assumes that conception took place two week after the LMP. Ovulation dates cannot be precisely known. A more scientific prenatal assessment of gestational age involves fetal biometric measurements are often employed to measure gestational age in ultrasonography. These also help determine fetal age and the estimated date of delivery (EDD). Pregnancy calculators can however, be used earlier and are provided online for free.
So how long does a pregnancy last?
Well months can be of two types:
- Calendar months – months as shown on the calendar (30 or 31 days)
- Lunar months – (28 days)
Most pregnancy calculations use lunar months rather than calendar months. A pregnancy will last 40 lunar months. In other words, every 28 days you have progressed by 1 month in your pregnancy. The total number of months for a normal pregnancy would thus be 10 lunar months. Hopefully, these elucidations will help you and your partners understand better how pregnancy calculators work.