Sonogram dating and birthdate


However, unless there is a great difference between what is seen on an ultrasound and what was reported as LMP, doctors still use LMP to establish a due date.For example, if in the first trimester the ultrasound estimate falls within one week of the LMP estimate, we still use LMP to determine due date and length of pregnancy.



In addition, although a woman is most likely to become pregnant if she has sex on the day of ovulation conception may also occur from live sperm still in her reproductive tract on the day of ovulation if she had sex for up to five days before ovulation [26,27]. The average time between menstrual periods is about 28 days, and ovulation occurs about 14 days before the next period begins.So when we say a woman’s estimated gestational age is six weeks’ LMP, we mean she conceived about four weeks ago, around the time of ovulation.Some women will deliver on their due date, others before, and others after.