Germ cell numbers in human embryonic and fetal gonads during the first two trimesters of pregnancy: analysis of six published studies

Abstract

The number of germ cells in human embryonic and fetal ovaries in relation to age is currently based on volumetric estimations from one study including a total of 12 ovaries. Six recent publications present stereological estimations of the number of germ cells in ovaries and testes for the first two trimesters. Germ cell numbers from 103 human first and second trimester gonads aged 37-133 days post-conception (p.c.), obtained after legal termination of pregnancy, were collected from six independent studies that all used similar validated stereological methods for estimating germ cell numbers as well as somatic cell numbers. Statistically, the six studies estimated similar number of germ cells (P > 0.05) and no interaction between the studies and age was found (P > 0.05), indicating that the increase in cell numbers in relation to age was of comparable magnitude in each study. The number of germ cells increased from a mean of 7200 to 4,933,000 in fetal ovaries and from 3700 to 1,417,000 in fetal testes, from week 5 to week 19 p.c. A higher rate of increase was found for female germ cells as compared with males (P = 0.004). During the same period, the number of somatic cells increased from a mean of 158,000 to 1,017,000 in ovaries and from 154,000 to 2,035,000 in testes, respectively. CONCLUSIONS By the use of validated stereological methods, this study provides more accurate and improved information on human germ and somatic cell numbers in ovaries and testes during the first two trimesters of pregnancy.