- First Trimester- Human chorionic gonadotropin (hCG) increases until it reaches a maximum concentration near the end of the first 3 months of pregnancy and then decreases to a low level thereafter.
- Second Trimester- Progesterone continues to increase until it levels off near the end of pregnancy. Early in pregnancy, progesterone is produced by the corpus luteum in the ovary; by the second trimester, production shifts to the placenta.
- Third Trimester- Estrogen increases slowly throughout pregnancy but increases more rapidly as the end of pregnancy approaches. Early in pregnancy, estrogen is produced only in the ovary; by the second trimester, production shifts to the placenta.
Development of the Face:
- 28 days after fertilization. The face develops from five processes: frontonasal, two maxillary, and two mandibular
- 33 days after fertilization. Nasal placodes, areas of thickening, appear in the frontonasal process.
- 40 days after fertilization. Maxillary processes extend toward midline. The nasal placodes also move toward the midline and fuse with the maxillary processes to form the jaw and lip.
- 48 days after fertilization. Continued growth brings structures more toward the midline.
- 14 weeks after fertilization. Contributions of each process to the adult face.