Praise be to Allah.
Using the coil is permissible subject to two conditions:
The first condition is that it should not cause harm to the woman.
We would like to remind women that a woman should not do things to prevent pregnancy, because this goes against the aims of sharee‘ah. It is better for her to remain as Allah created her, bearing lots of children, because having lots of children serves a great purpose and does not harm a person in his provision, in raising them or in health.
Hence it is prescribed in Islam for a man to marry a woman who is loving and fertile, i.e., she should be one of the women who are known to have many children, so that the Prophet (peace and blessings of Allah be upon him) may feel proud of the great numbers of his ummah, and the numbers of Muslims may be increased thereby.