The embryo attaches itself to the mother to feed, just like a leech attaches itself to a host to feed.
The embryo also looks like a leech:
The embryo looks like a leech but these pictures are magnified by microscope; nobody knew this 1400 years ago. However this was portrayed in the Quran.
١٤ ثُمَّ خَلَقْنَا النُّطْفَةَ عَلَقَةً فَخَلَقْنَا الْعَلَقَةَ مُضْغَةً فَخَلَقْنَا الْمُضْغَةَ عِظَامًا فَكَسَوْنَا الْعِظَامَ لَحْمًا ثُمَّ أَنْشَأْنَاهُ خَلْقًا آخَرَ ۚ فَتَبَارَكَ اللَّهُ أَحْسَنُ الْخَالِقِينَ
"Alaqa عَلَقَةً" means leech. It turned-out that the embryo looks like a leach. Then later it develops into a "Mudgha مُضْغَةً" meaning something chewed. It turned-out that at week 6 the vertebra of the embryo looks likes something chewed.
Today we know that the vertebra of the embryo looks like something chewed. No mistakes in the Quran.
How could an illiterate man who lived 1400 years ago have known how an embryo looks like?
The Quran (Koran, the book of Islam) contains scientific knowledge that could not have been known 1400 years ago. It ranges from basic arithmetics to the most advanced topics in astrophysics. You are invited to go through those miracles and judge for yourself.