Vital signs: when twin bliss doesn’t measure up

Vital signs: when twin bliss doesn’t measure up
The gestational age is usually derived from the time elapsed since the last menstrual period (LMP). However, clinicians often rely on fetal biometry obtained in early pregnancy to achieve a better estimate of the true gestational age (GA) because menstrual cycles can display a great degree of variability both within and between patients, making a calendar-based GA unreliable. Of course, when the LMP-derived GA is reset based on fetal biometry, the assumption is that fetal growth has been normal up until then, and this is obviously not always the case.
Source: fertstert.org