Objective To establish preliminarily the reference range of embryonic/fetal heart rate（EHR）during early pregnancy

and to explore its rules.MethodsThe EHR and clinical data of pregnant women and embryos from January2016 to January 2018 in our hospital were collected.Embryonic/crown-rump length（CRL）and the heartbeat was detected by ultrasound.EHR was measured by M mode ultrasound or pulse Doppler.ResultsWhen CRL was 2～3 mm or gestational age（GA）was 40～41 d

the EHR was（117.31±11.64）beat/min.EHR increased with the GA/CRL gradually increasing

and at the63～69 d of the GA or CRL was 23～30 mm

the EHR reached the peak of（172.69±9.27）beat/min.After that

the EHR gradually decreased and tend to be stable with the increase of GA or CRL.The regression equation was established based on the changes of EHR in each period:EHR=-223.751 + 11.746 GA-0.086 GA

2

（R

2

=0.772

R=0.877

P

<

0.001）

EHR=101.83 + 5.108 CRL-0.084 CRL

2

（R

2

=0.765

R=0.875

P

<

0.001）.ConclusionBased on the GA and CRL

the reference range of EHR for the 5 th

50 th and 95 th percentiles in the early pregnancy period is initially established

which can provide a reference for abortion risk prediction in clinic.