「第三隻眼」

小寶寶的成長由一顆受精卵開始，越變越多顆成為像桑椹般的囊胚，然後變化成像三明治般多層的胚胎，最後再慢慢成型為胎兒。整個過程像西遊記裡孫悟空的七十二變般神奇，卻是每個人類自然的發育過程。孫悟空的千變萬化雖然讓他與二郎神大戰三百回合難分難解，只是最後還是逃不過二郎神的第三隻眼，原形畢露。超音波 就像是婦產科醫師的第三隻眼，將孕期中胎兒與子宮環境的變化，清楚的反映出來。

在懷孕的前幾週，當胎苞還只是0.5公分大小的時候，超音波即可掃瞄出小寶寶的存在；當懷孕三個月時超音波便能觀察到寶寶初為人形的樣子，也能開始做一些測量如唐氏症頸部透明帶的篩檢。 懷孕中期，高層次超音波主要是做器官系統形體上的篩檢，小至0.2 公分的心室中隔缺陷都有可能被找出來。在第三孕期時，超音波會做生產風險的評估或再找出一些寶寶先天性異常的型態。

雖然說超音波不是萬能的，還是有許多疾病與問題無法以超音波發現，如新陳代謝疾病，但對婦產科醫師來說已是不可或缺的工具。

A baby’s journey in life starts with a single fertilised egg, which multiplies to become like a mulberry called morula. Then it becomes a 3-layered structure that will eventually develop different organ systems. The whole process involves innumerable steps of morphological changes. The ability of the embryo to undertake these changes reminds me of the monkey king from the classic Chinese novel “Journey to the West”, who is able to morph into infinite number of objects. However, the rebel monkey king was captured by the Jade Emperor’s nephew because he has a 3rd eye that sees through each the monkey king’s tricks. I think prenatal ultrasound is like the third eye because it sees clearly the many changes an embryo undergoes as it grows.

During the first trimester, an implanted embryo as small as 0.5cm in size may be “seen” by a modern ultrasound. And by 3 months, the risk of Down Syndrome can be calculated based on the measurements done on the already-humanoid embryo. A more sophisticated ultrasound (level II) May be utilised during the second trimester to detect birth defects. For example, a hole as small as 0.2cm may be detected in the heart. During the third trimester, the ultrasound is usually used for obstetrics risk evaluation and/or further screening of any birth defects.

Ultrasound does not detect all prenatal defects because some conditions simply cannot be “seen” on ultrasound, such as inborn error of metabolism. However, the use of ultrasound is an essential tool for all obstetricians.