Is Heparin 7500 Injection Required To Avoid Miscarriage?

Hi Mam, My wife is 7weeks pregnant.Last time she had miscarriage(heartbeat was not come for baby after 8 weeks).Now she is taking Heparin 7500 injection twice a day and doctor ask her to continue this injection for another 20 weeks so my question is is it really required for her or there is any other alter native that i opt for and any side effect will appear after taking this injection.