Bismillaah-ir-Rahmaan-ir-Raheem.Assalaamu 'Alaykum wa Rahmatullaahi wa Barakaatuh.
Nobody can deny the fact that the behaviour of the mother affects the child she is carrying.
Doctors worldwide, urge mothers to look after themselves physically and emotionally so as not to cause any distress to the baby. Pregnant women are advised to maintain a healthy diet for the benefit of the unborn child. They are given calcium supplements in order to strengthen the baby's bones. It is observed, that women who lack calcium during pregnancy are prone to having children with bad teeth.
Similarly, the emotional condition of a pregnant woman also affects the child. Thus, women are exhorted to remain calm, composed, happy, free of stress and gloom. If the woman's physical and emotional condition can have an effect on the baby, why would it be farfetched to believe that the spiritual condition too, has a strong influence? Just as it is important for the mother-to-be to look after her health, it is equally important if not more, for her to remain clean spiritually. This will include refraining from ALL FORMS OF EVIL AND SIN.
Ofcourse, some sins have a stronger effect than others, just as carelessness in certain physical aspects is more dangerous than in others. Watching T.V, listening to music, viewing Haraam things, eating doubtful/haraam food, all of these immensely harm the spirutality of the unborn child, and continue to do so even while the mother is breastfeeding.
Accordingly, the pregnant mother should be punctual with Salaah and recitation of the Glorious Qur'aan.
A strong enough proof to this is we see that behind every pious child, is a lap of a pious mother. All the Prophets and saints had mothers with exceptional qualities. Women who take care to observe piety during their pregnancies, and also while breastfeeding, tend to produce children with exceptional qualities. And that is why we find that there have been children who knew large portions of the Qur'aan by heart even before they were weaned.
Shaykh Ashraf 'Ali Thanwi (rahmatullaai 'alayh) narrates, "If before the birth of the child, parents were to reform themselves and adopt piety, then there is no reason why the child born too, should not be pious. The actions of parents (especially mothers) during preganancy have a profound effect on the unborn child.
Shaykh also related, "There was a couple who made an agreement, 'Come, we shall perform tawbah and make a promise to refrain from all sins so that all our children are born pious.' Sometime thereafter she fell pregnant and a pious child was born to them. One day, this child stole some fruit from a shop and ate it.
The infuriated father asked his wife, 'Tell me the truth, where did this effect come from?' The mother replied, 'One day, whilst he was in my womb, I picked and ate fruit from the branch of our neighbour's tree, that is hanging in our garden.' Her husband replied, 'The effect of that act has surfaced today!'
And Allaah knows best.Wa Billaah-it-tawfiq Wassalaam
Taken from : http://www.muftisays.com