Calculating conception or the day you conceived is a common question for a variety of reasons. Some women are trying to determine when the baby is due so they can plan accordingly. Some women may be trying to determine their conception date because of a question related to paternity. Conception dates are based on the gestational age of the pregnancy which is calculated from the first day of your last menstrual period. The exact date of conception is hard to determine so most dates are generally calculated from the first day of the last menstrual period.
Calculating Conception Dates:
First Day of LMP: The first day of your last menstrual period is a good guide to calculate conception dates for moms-to-be who have a fairly regular period. This basically works by starting from the first day of the last menstrual period and going out 10 to 19 days which establishes the fertility window. Conception occurred some time during this period.
Sonogram: A sonogram can be used during the early part of pregnancy to help calculate conception dates. Songrams are fairly accurate in helping to determine conception dates, but they do become less accurate as the pregnancy progresses. Accuracy is enhanced when the first day of the last menstrual period is known along with an early sonogram.
In Vitro Fertilization: A mom-to-be who has become pregnant through in vitro fertilization or other assisted reproductive technologies will know when conception occurred.
Calculating Conception – Gestational Age Difficulties:
Last Menstrual Period: For women who have irregular menstrual periods or women who cannot remember the first day of their last menstrual period, it can be difficult to determine gestational age using this method. In these cases, an ultrasound exam is often required to determine gestational age.
Sperm Life: Sperm is expected to live for 24 hours, however it is possible to live for up to 2, 3 and even 5 days. So, sex may have occurred on one day and conception actually occurred 4 or 5 days later.
Baby’s Growth: In some cases it is difficult to determine the conception date because the baby is unusually large or small at the time a sonogram is performed.