Pregnency , fetus heartbeat low 93 bpm.

Dear sir/mam My wife is pregnent through IVF which embryo transfered on 24th may initially there was low HCG and latter it comes normal and .At 5 week 3 days of LMP as per doctor calculation Yolk sac seen but No fetal pole seen.Doctor told us less chance of heartbeat .Latter USG done on 6week 5 days and fortunately fetal pole seen and CRL measures 6.1 mm and fetal heartbeat recorded 93 bpm. Doctor again told us that heartbeat found but it's feeble(low) and recorded 93 bpm. He was expecting 120 or above .He told to scan after 7 days . I want to ask is it any complication ,would it9 be a viable pregnancy .How much chance of to increase heartbeat rate .What percentage of pregnancies increased after such situation .Is their any medicine or treatment for that . Thanking you.