User:Alastair Haines/Human sexual differentiation
| Fetal age (weeks) |
Crown-rump length (mm) |
Sex differentiating events |
| 0 | blastocyst | Inactivation of one X chromosome |
| 4 | 2-3 | Development of wolffian ducts |
| 5 | 7 | Migration of primordial germ cells in the undifferentiated gonad |
| 6 | 10-15 | Development of müllerian ducts |
| 7 | 13-20 | Differentiation of seminiferous tubules |
| 8 | 30 | Regression of müllerian ducts in male fetus |
| 8 | 32-35 | Appearance of Leydig cells. First synthesis of testosterone |
| 9 | 43 | Total regression of müllerian ducts. Loss of sensitivity of müllerian ducts in the female fetus |
| 9 | 43 | First meiotic prophase in oogonia |
| 10 | 43-45 | Beginning of masculinization of external genitalia |
| 10 | 50 | Beginning of regression of wolffian ducts in the female fetus |
| 12 | 70 | Fetal testis is in the internal inguinal ring |
| 12-14 | 70-90 | Male penile urethra is completed |
| 14 | 90 | Appearance of first spermatogonia |
| 16 | 100 | Appearance of first ovarian follicles |
| 17 | 120 | Numerous Leydig cells. Peak of testosterone secretion |
| 20 | 150 | Regression of Leydig cells. Diminished testosterone secretion |
| 24 | 200 | First multilayered ovarian follicles. Canalisation of the vagina |
| 28 | 230 | Cessation of oogonia multiplication |
| 28 | 230 | Descent of testis |
- Reference: PC Sizonenko in Pediatric Endocrinology, edited by J. Bertrand, R. Rappaport, and PC Sizonenko, (Baltimore: Williams & Wilkins, 1993), pp. 88-99.