In comparing a leech to the embryo at the transitory stage (alaqah) we find similarity between the two. (1)

Also, the embryo at this stage obtains nourishment from the blood of the mother, similar to the leech which feeds on the blood of others. (2)

The second meaning of the word alaqah is “suspended thing”... The suspension of the embryo, during the alaqah stage, in the womb of the mother. (3)

Suspension of an Embryo during the early stages in the womb of the mother.  (About 15 days old) The actual size of the embryo is about 0.6mm.
 

When comparing the appearance of an embryo at the mugdah stage with a piece of gum that has been chewed, we find similarity between the two.
 

“We created man from an extract of clay. Then We made him as a drop in a place of settlement, firmly fixed. Then We made the drop into an alaqah  (leech, suspended thing, blood clot), then We made the alaqah  into a mudghah (chewed, lump)”  (23:12-14)
 

We find that the external appearance of the embryo and its sacs during the transitory stage  (alaqah)  is similar to that of a blood clot. This is due to the presence of relatively large amounts of blood present in the embryo during this stage. (4) 

The blood in the embryo does not circulate until the end of the third week. (5)

Thus the embryo is like a clot of blood at this stage!

The embryo at the mudghah stage acquires the appearance of a chewed-like substance because of the somites at the back of the embryo that “somewhat resemble teeth marks in a chewed substance.” (6)
 

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*  Alaqah :  Bloodsucker (Pg.92),   Suspended  (Pg.745),   Clot (Pg.146).   Elias Modern Dictionary, E-A, 1992
** Mudghah : Chewed  (Pg.137)  Elias Modern Dictionary, E.A,  1992
(1) The developing Human, Moore and Persaud, 5th ed., Page:8
(2) Human Development as described in the Quran and Sunnah, Moore and others,  Page:36
(3) A  brief guide to understanding Islam with colorful illustrations, I. A. Ibrahim,  Page:6
(4) Human Development as described in the Quran , Moore and others,  Page:37-38
(5) The developing Human, Moore and Persaud, 5th ed., Page:65
(6) The developing Human, Moore and Persaud, 5th ed., Page:8

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 Joe Leigh Simpson, Professor of Obstetrics and  Gynecology at the North Western University in Chicago in the United States of America. As we know, these chromosomes contain all the characteristics which the new human being will have such as the color of the eyes, skin, hair,etc. Hence, many of the details in the human being’s make-up are determined in his chromosomes. These chromosomes begin to form during the early nutfah stage of embryonic development. In other words, the distinguishing features of the new human being are determined from the very beginning at the nutfah stage. Allah, the Most Exalted, the Most Glorified, has stated this fact in the Qur’aan.