Dear Rekha , maybe you should check first with a gynecologist to check your hormones ,to see if there was some medical reason for your miscarriages . I would reply you here by some vedic advices and my own personal stand on sexuality as well, but its way too long , so i'll share a link to one article on a blog . After that article ,you will find a comment by "question" which was very educational ,and then reply by helitra (the admin and author there) . You can find Garbhadhana Samskara in some details , but i assure you that many prominent vaishnavas followed that rite , and yet their kids were not devotees at all , while some non vaishnavas have a great very spiritual children .
All what i am trying to say is ,that why shouldnt be bothered by detailes . This is kali yuga. I hope you and your husband will not forget to enjoy in your intimacy in the name of official approach to calculate for the baby. Be spontaneous .While God have a proper place in your lives ,he will take care of it all with time .