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Prenatal Form and Function – The Making of an Earth Suit


Unit 12:   11 to 12 Weeks

  Closer Look: 
  Applying the Science: 
Play Movie - Human fetus 11 to 12 weeks
Movie 12.1 - 11 to 12 Weeks
3 months, Fetus, Mouth, Tongue
Figure 12.1 - Open Mouth (Tongue Visible)
The Biology of Prenatal Development DVD
Copyright © 2006 EHD, Inc. All rights reserved.

baby sticking tongue out
What’s all over that tongue? Taste buds! Our taste buds appear twelve weeks after fertilization in plenty of time to explore a wide variety of tastes before and after birth.

Between 11 and 12 weeks, a second huge burst of growth occurs as weight increases by roughly 58 percent.1 12 weeks also marks the end of the first trimester of pregnancy.


The taste bud cells that appeared by 7 weeks have matured into discrete taste buds, but are still scattered throughout the mouth.2 By birth, the taste buds will be confined to the tongue and palate or roof of the mouth.3

Play Movie - Weight Gain
Movie 12.2 - Weight Gain
Play Movie - Taste Buds
Movie 12.3 - Taste Buds


Bowel movements begin as early as 12 weeks and continue until 18 weeks.4 The material first expelled from the fetal and newborn colon is called meconium (mĭ-kō'nē-ŭm).5 It is composed of digestive enzymes, proteins, and dead cells shed by the digestive tract.6

The bladder now contains cells organized in patterns and resembling smooth muscle.7

Baby Crawling
No diapers in the womb! From 12 to 18 weeks, the fetus expels waste directly into the amniotic fluid. (But remember, the umbilical cord is also removing waste.)
Play Movie - Bowel Movements 3 month fetus
Movie 12.4 - Bowel Movements

Father lifting baby in the air.
Arms and legs - already very active in the 12-week fetus – continue growing for a long time to come.

By 12 weeks, the arms have grown to approximate their final proportion relative to body size. As usual, leg development is slower than arm development and the legs still have not achieved their final proportion.8


The whole body surface, except the top of the head and the back, responds to light touch.9

Play Movie - Upper and Lower Limbs
Movie 12.5 - Upper and Lower Limbs
Play Movie - Response to Touch
Movie 12.6 - Response to Touch
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11 to 12

1 Brenner et al., 1976. 561.
2 Carmichael, 1970. 526; Miller, 1982. 169; Mistretta and Bradley, 1975. 80.
3 Lecanuet and Schaal, 1996. 3; Miller, 1982. 169; Mistretta and Bradley, 1975. 80.
4 Abramovich and Gray, 1982. 296; Ramón y Cajal and Martinez, 2003. 154-155.
5 Grand et al., 1976. 791; O'Rahilly and Müller, 2001. 257.
6 Grand et al., 1976. 806.
7 Konishi et al., 1984. 241.
8 Moore and Persaud, 2003. 105.
9 Carlson, 1994. 237; Lecanuet and Schaal, 1996. 2; Reinis and Goldman, 1980. 232.