However, ultrasound determination of the date of ovulation has the same imprecision as does the ultrasound estimate of the gestational age and, therefore, a precise date of conception cannot usually be determined as with in vitro fertilization.
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].
To compare gestational age (GA) estimates in early pregnancy, determined by last menstrual period (LMP), human chorionic gonadotropin (h CG) concentration, ultrasound crown–rump length (Hadlock formula), and ovulation day (luteinizing hormone surge plus 1 day).
Female volunteers seeking to conceive (at 5 US sites) collected daily early-morning urine for up to 3 menstrual cycles. Conception cycle urine was quantitatively assessed for luteinizing hormone and h CG.
Summary statistics for GA using each reference method were determined (n = 131).
When people discuss how far along in pregnancy someone is, they tend to do so in general terms: “She’s in the first trimester” or “She’s four months along.” However, many people have only a vague idea of what those phrases really mean.
Also, when providers all use the same LMP date, we are using one system that provides a standard convention.
Dating Scans A scan can date the time of conception if you are uncertain of when your baby was conceived.
However, the timing of the actual delivery is not so predictable.
Some women will deliver on their due date, others before, and others after.