Clearly, the inaccuracies of history and physical examination may limit their usefulness in assessment of gestational age.
Methods that assess the time of ovulation or conception can accurately establish gestational age.
It is identified by transabdominal ultrasound as early as 5 weeks' gestation and may be seen as early as 4 weeks' gestation by transvaginal ultrasound.
The gestational sac is an echo-free space containing the fluid, embryo, and extraembryonic structures.
In another report, even among women with known LMP, neonatal age assessment differed markedly from that assigned by certain menstrual dates in 15%.
Bimanual examination in the first trimester may be accurate within ±2 weeks; however, fundal height measurement, which is more commonly used to assess gestational age, is only accurate within ±4 to 6 weeks.
Ultrasound assessment of gestational age is feasible in a majority of pregnancies and may be used to establish gestational age with greater accuracy than physical examination.
In the first trimester, gestational sac mean diameter and crown-rump length measurements have become the primary means of evaluating gestational age.
For example, antenatal test interpretation may be dependent on gestational age.
Specifically, the level of α-fetoprotein in both amniotic fluid and maternal serum is related to gestational age and when dates are inaccurate test results will be incorrect and misleading.