A critical evaluation of tests used to assess gestational age.

The reliability of eight methods for estimating gestational age in the third trimester of pregnancy has been assessed in patients with fetuses of known maturity. Late ultrasound cephalometry, amniotic fluid creatinine estimations and lecithin/sphingomyelin ratio were found to be significantly more reliable than the other five methods. The mean of estimated gestational ages provided by the three techniques used in combination gave a significantly more accurate prediction of fetal age than any single test and allowed formation of a 'maturity profile'.