Fetal growth in early pregnancy was estimated by transvaginal ultrasonic measurement and serum hCG measurement in 13 women who became pregnant through in vitro fertilization and embryo transfer treatment. The first day of observation of a gestational sac (GS) or fetal heart movement (FHM) of over 120 beats/min confirmed the pregnancy. There were 6 or 7 days difference in GS or FHM confirmation within 20 or 30 days after insemination, although statistical deviations were very small (GS: 21.3 +/- 1.8, FHM: 29.5 +/- 1.8 days after insemination, mean +/- S.D.). Increases in crown-rump length (CRL) and serum hCG were used as indicators of fetal growth. There was a good correlation between CRL or serum hCG and days after insemination (CRL: r = 0.95, n = 55; hCG: r = 0.96, n = 77), and individual cases had almost the same velocity of CRL growth and serum hCG elevation as each regression line. This data suggests that each embryo has a different growth velocity from the fertilized oocyte until the first clinical confirmation of pregnancy.