بسم الله الرحمن الرحيم
(Fatwa: 770/690/SN=7/1438)
If the below mentioned verse is written on some paper and tied with the stomach [of the pregnant woman], then in-shaAllah, the fetus shall remain safe. (Bahishti Zewar, vol. 9)
وَاصْبِرْ وَمَا صَبْرُكَ إِلاَّ بِاللّهِ وَلاَ تَحْزَنْ عَلَيْهِمْ وَلاَ تَكُ فِي ضَيْقٍ مِّمَّا يَمْكُرُونَ إِنَّ اللّهَ مَعَ الَّذِينَ اتَّقَواْ وَّالَّذِينَ هُم مُّحْسِنُونَ.
Also the woman should read the following dua after each fardh salah:
رَبِّ هَبْ لِي مِن لَّدُنْكَ ذُرِّيَّةً طَيِّبَةً إِنَّكَ سَمِيعُ الدُّعَاء [آل عمران : 38]
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband