QuestionQUESTION: If on an ultrasound screen it shows 13weeks and 5days what does that mean you conceived 13weeks and 5days and i didnt tell them when my lmp was because i didnt member? so can you explain to me how to understand this ultrasound thing because i get alot of different answers some say that the ultrasound adds two weeks to dating so im confused so does the 13wks and 5days mean i count back 13weeks and 5days to find conception?
ANSWER: Hello Michelle,
In an early first trimester ultrasound, the CRL (crown-to-rump length) and gestational sac size are determined to date the pregnancy. It can be helpful to know/share the first day of your last period, but it is not mandatory. In the first weeks of pregnancy, fetuses grow at much the same rate as cells divide and multiply at very similar rates. It is only during the late first trimester/early second trimester when the placenta takes over to sustain the pregnancy that individual growth rates come into play determined by genetics, diet, maternal health, lifestyle, etc.
So, an early ultrasound will measure fetal markers such as those above and then yield dates based on those measurements to determine the fetal age, which is different from the gestational age. The gestational age is approximately two weeks more than fetal age and should roughly coincide with the first day of your last period. Conception typically occurs about 14 days before your next period is to begin, which is when the fetus would start to form and is why fetal age is 2 weeks less than gestational age.
Since pregnancy is measured by the gestational age (which includes approximately 2 weeks where you are not pregnant yet, as it's determined by adding two weeks to the fetal age which for most women with regular cycles will be in line with the first day of their last period), after your ultrasound, you will be told the gestational age or how many weeks pregnant you are. Subtracting two weeks will tell you approximately when the baby was conceived.
So, in your case, if you were told you were approximately 13 weeks, 5 days pregnant or that is what showed on the screen at the time of the ultrasound. Subtracting two weeks from this would give you the probable date of conception, or 11 weeks and 5 days before the ultrasound was performed.
Best,
Catherine Beier MS CBE
http://www.GivingBirthNaturally.com
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QUESTION: So what is a irregular period? my period comes around the end of the month every month does that make it regular? and another thing so what if my periods are irregular how is a pregnancy dated by ultrasound can you still figure out your lmp from an ultrasound if they are irregular or if it gives you and estimated due date can you figure out conception like that? and last how many weeks can an ultrasound be wrong by?
AnswerMichelle,
An irregular cycle is one that doesn't come at similar intervals every month. Women with regular cycles have them about the same length of time apart, such as every 28, 30, 33 days, etc. Women with irregular cycles may have 30 days between periods, then 46 days, 28 days the next month, then 50 days, 32 days, etc. Periods are irregular when they come without a predictable pattern from month to month.
So, it's not when in the month it comes, but rather how consistent the intervals between each period are that determines whether a woman's cycle is regular or not. From your description, it sounds as if your are regular.
To address the next part of your question, which I also addressed in the first question you sent, ultrasound looks at different fetal markers, including crown-to-rump length (CRL), diameter of the gestational sac, and in later ultrasounds, femur length, abdominal circumference and other such factors.
In an early first trimester ultrasound, the CRL (crown-to-rump length) and gestational sac size are determined to date the pregnancy, not the first day of your last period.
When these factors are measured, you're then told how many weeks/days pregnant you are, which should date back roughly to the first day of your last period if you have regular cycles as described above. If your cycles are not regular, then you would still be told how many weeks/days pregnant you are, but this would not necessarily coincide with the first day of your last period, rather it would be roughly two weeks before you conceived.
So, in either scenario, whether your cycle is regular or irregular, you can still calculate probable conception dates by subtracting two weeks from the dates given to you at the ultrasound.
Ultrasound accuracy varies throughout pregnancy. It is more accurate between 8-10 weeks when fetuses are growing at similar rates, with early transvaginal ultrasounds typically having a standard error of measure of +/- 1 day, and late term ultrasounds, those after 20 weeks, having a standard error of measure of up to +/- 2 weeks. Many factors can affect ultrasound accuracy later in pregnancy, such as the baby's position, activity level, maternal size, placental size and location. In any ultrasound, the quality of the equipment used and the skill of the ultrasound technician can also affect the validity of its results.
Best,
Catherine Beier MS CBE
http://www.GivingBirthNaturally.com
