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National Geographic Society This program is distributed in the U.S. and Canada by National Geographic and EHD. [learn more]

Multilingual Illustrated DVD [Tutorial]

The Biology of Prenatal Development



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Explore the fascinating imagery and facts presented in The Biology of Prenatal Development at your own pace. Each clip from the program is accompanied by its corresponding written script. Select Play Movie to watch any clip. Select See Snapshots to view high resolution images. See the program script and subtitles in 88 languages by using the Choose Language drop-down menu and clicking Refresh. Subtitles are displayed in your chosen language and may be turned on and off by clicking the button found in the lower right corner of the movie player. A "full screen" option is also available by clicking the button.


 
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Chapter 40   3 to 4 Months (12 to 16 Weeks): Taste Buds, Jaw Motion, Rooting Reflex, Quickening

Between 11 and 12 weeks, fetal weight increases nearly 60%.

Twelve weeks marks the end of the first third, or trimester, of pregnancy.

Distinct taste buds now cover the inside of the mouth.
By birth, taste buds will remain only on the tongue and roof of the mouth.

Bowel movements begin as early as 12 weeks and continue for about 6 weeks.

The material first expelled from the fetal and newborn colon is called meconium. It is composed of digestive enzymes, proteins, and dead cells shed by the digestive tract.

By 12 weeks, upper limb length has nearly reached its final proportion to body size. The lower limbs take longer to attain their ultimate proportions.

With the exception of the back and the top of the head, the body of the entire fetus now responds to light touch.

Sex-dependent developmental differences appear for the first time. For instance, female fetuses exhibit jaw movement more frequently than males.

In contrast to the withdrawal response seen earlier, stimulation near the mouth now evokes a turning toward the stimulus and an opening of the mouth. This response is called the "rooting reflex" and it persists after birth, helping the newborn find his or her mother's nipple during breastfeeding.

The face continues to mature as fat deposits begin to fill out the cheeks and tooth development begins.

By 15 weeks, blood-forming stem cells arrive and multiply in the bone marrow. Most blood cell formation will occur here.

Although movement begins in the 6-week embryo, a pregnant woman first senses fetal movement between 14 and 18 weeks. Traditionally, this event has been called quickening.


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