Embryo Depth During the First Trimester

Abstract

To provide data regarding embryo depth during the extremely radiosensitive gestational stages of organogenesis and early fetal period for use in embryo dosimetry. Ultrasound examination was performed in 73 pregnant women at gestational age 5 to 13 weeks and in a control group of 75 nonpregnant women. Embryo skull and abdominal depth from the maternal skin surface were determined in the anteroposterior direction. Uterus depth was measured in the control group. Measurements were taken before and after voiding. Gestational age and maternal age, height, and weight were noted. Body mass index (BMI) was estimated for every woman from the formula BMI = W/H2. The mean embryo pre- and postvoid skull depth was 8.3 and 5.7 cm and the mean abdominal depth was 8.4 and 5.8 cm, respectively. The mean pre- and postvoid uterus depth was 9.5 and 4.7 cm. Mean abdominal depth and mean skull depth values were significantly different than mean uterus depth for full as well as for empty bladder. Embryo skull depth and abdominal depth were found to be significantly correlated with maternal BMI. Skull and abdominal dimensions were found to be significantly correlated with gestational age. During the first trimester, embryo depth ranges from 4 to 10 cm, depending on the individual, the status of the bladder, and the maternal BMI. For an accurate determination of embryo depth, ultrasound measurement should be performed.