Surah 13. Ar-Ra'd, Ayah 8

The term untha denotes any female being, whether human or animal. The "falling short" may refer either to a shortening of the usual period of gestation (e.g., to seven months in human beings) or to a falling short of the completion of pregnancy, i.e., a miscarriage; it is to be noted that the noun ghayd signifies "an abortive foetus" (Taj al-'Arus), i.e., in human beings, a foetus less than seven months old. The "increase", on the other hand, may mean either the completion of gestation or its being in excess of the average period (as, for instance, the occasional lengthening of human pregnancy from the usual period of about 280 days to 305 or, according to some medical authorities, even 307 days). In addition to this, God's knowledge of "what any female bears [in her womb]" obviously relates also to the sex of the unborn embryo as well as to the number of offspring involved in one pregnancy. - As the sequence shows, this reference to the mysteries of gestation, fully known only to God, is meant to bring out the idea that He who knows what is in the wombs knows also the innermost disposition of every human being and the direction in which that human being will develop.

Lit., "according to a measure" (bi-miqdar) - i.e., in accordance with the particular purpose for which it has been created, the exigencies of its existence and the role which it is destined to play within God's plan of creation.

 He knows whether the egg will be fertilized or not, whether the baby will be born before or after nine months, whether the pregnancy will end with delivery or miscarriage, and whether there will be one baby or more.

The female womb is just an example, a type, of extreme secrecy. Not even the female herself knows what is in the womb,-whether it is a male young or a female young, whether it is one or more, whether it is to be born short of the standard time or to exceed the standard time. But the most hidden and apparently unknowable things are clear to Allah's knowledge: there is no mere chance; all things are regulated by Allah in just measure and proportion. The general proposition comes in the last sentence: "every single thing is with Him in (due) proportion."