There are lots of articles reporting that lower heartbeats are indicators of a pregnancy that is less likely to be viable.
This is the best article I found, showing the loss rate based on the heartbeat rate (beats per minute) between 4-6 weeks of “embryo age” (EA was defined as gestational age minus 14 days). In other words, 4-6 weeks of EA is 6-8 weeks “pregnant” (ie from LMP).
Embryo heartrate (bpm)
|
Total no. of cases
|
Overall ongoing pregnancies, n (%)
|
Pregnancy loss rate <=35 yrs
|
Pregnancy loss rate >35 yrs
|
60–110
|
41
|
11 (27%)
|
9 (50%)
|
21 (91%)
|
111–120
|
66
|
53 (80%)
|
2 (7%)
|
11 (29%)
|
121–130
|
137
|
112 (82%)
|
5 (7%)
|
20 (28%)
|
131–140
|
144
|
132 (92%)
|
3 (4%)
|
10 (14%)
|
141–150
|
123
|
112 (91%)
|
5 (7%)
|
6 (11%)
|
151–160
|
84
|
81 (96%)
|
0 (0%)
|
3 (7%)
|
>160
|
55
|
54 (98%)
|
0 (0%)
|
1 (3 %)
|
As can be seen, a faster heartrate is always better, and older moms were more likely to lose pregnancies even at higher heartrates. (The same percent of 35+ moms lost pregnancies at 151-160bpm as did the younger moms at 111-120bpm.)
It also shows the average heartrate for an ongoing pregnancy versus loss by week:
Embryo age (weeks)
|
Embryo heartrate (bpm) ongoing
pregnancy (n = 555)
|
Embryo heartrate (bpm), pregnancy
loss (n = 95)
|
4
[6 weeks pregnant] |
131
|
123
|
5
[7 weeks pregnant] |
143
|
118
|
6
[8 weeks pregnant] |
160
|
109
|
What’s interesting is that at embryo age 4 weeks (ie. 6 weeks pregnant), the difference in embryo heartrate between the ongoing pregnancies and losses is very small. By embryo age 6 weeks (ie. 8 weeks pregnant), there’s a noticeable difference.
Here’s another one showing the correlation between pregnancy loss and slow heartrate:
“The heart rate was classified as slow if it was fewer than 90 beats per minute prior to 6.3 weeks or fewer than 110 beats/min at 6.3–7.0 weeks, normal if it was 100 or more beats/min at less than 6.3 weeks or 120 or more beats/min at 6.3–7.0 weeks, or borderline if it was 90–99 beats/min prior to 6.3 weeks or 110–119 beats/min at 6.3–7.0 weeks…. The rates of first-trimester demise were 60.6% for pregnancies with slow heart rates at 6.0–7.0 weeks (188 of 310), 17.4% for those with borderline heart rates (103 of 593), and 9.1% for those with normal heart rates (186 of 2034).”
And another one:
“Below 6.2 weeks, prognosis improved as heart rate increased to 100 beats per minute, then plateaued for rates > or = 100 beats per minute. At 6.3-7.0 weeks, prognosis improved up to 120 beats per minute, then plateaued. Heart rate norms could not be established at 7.1-8.0 weeks because of the small number of embryonic or fetal deaths in this age group; however, all embryos with heart rates below 110 beats per minute at 7.1-8.0 weeks died. We conclude that the lower limit of normal is 100 beats per minute up to 6.2 weeks' gestation and 120 bpm at 6.3-7.0 weeks”
A slower heartrate is (unsurprisingly) correlated with chromosomal abnormalities:
This one has a super detailed chart showing gestation days, crown to rump length, embryonic heartrate, gestational sac diameter, and yolk sac diameter.
Tomorrow I will be 6 weeks 3 days in gestational age. That’s 45 days. Here are their numbers for 45 days:
Gestation days
|
CRL, mm
|
Embryonic HR, bpm
|
GSD, mm
|
YSD, mm
| ||||||||
50th
|
5th
|
95th
|
50th
|
5th
|
95th
|
50th
|
5th
|
95th
|
50th
|
5th
|
95th
| |
45
|
5.4
|
3.4
|
7.9
|
120
|
104
|
138
|
17.4
|
11.7
|
24.3
|
3.6
|
2.7
|
4.5
|
This is another super interesting article. (Not a medical journal article.) It shows what events are roughly occurring days after the last period, and ranges of HCG. Although there is no clear “science” behind these numbers, it made me feel better that at my last appointment there was no heartbeat seen at 5w3d and an HCG over 11,000. Of course by 6w3day (tomorrow) I better see a heartbeat.
Days from last period
|
Weeks from last period
|
Days from conception
|
Events
|
Mean hCG
|
Range hCG
|
26
|
3w+5d
|
12
|
25
|
0-50
| |
27
|
3w+6d
|
13
|
50
|
25-100
| |
28
|
4w+0d
|
14
|
75
|
50-100
| |
29
|
4w+1d
|
15
|
150
|
100-200
| |
30
|
4 2/7
|
16
|
300
|
200-400
| |
31
|
4 3/7
|
17
|
700
|
400-1,000
| |
32
|
4 4/7
|
18
|
1,710
|
1,050-2,800
| |
33
|
4 5/7
|
19
|
2,320
|
1,440-3,760
| |
34
|
4 6/7
|
20
|
3,100
|
1,940-4,980
| |
35
|
5
|
21
|
4,090
|
2,580-6,530
| |
36
|
5 1/7
|
22
|
5,340
|
3,400-8,450
| |
37
|
5 2/7
|
23
|
6,880
|
4,420-10,810
| |
38
|
5 3/7
|
24
|
yolk sac appears
|
8,770
|
5,680-13,660
|
39
|
5 4/7
|
25
|
yolk sac appears
|
11,040
|
7,220-17,050
|
40
|
5 5/7
|
26
|
yolk sac appears
|
13,730
|
9,050-21,040
|
41
|
5 6/7
|
27
|
yolk sac appears
|
15,300
|
10,140-23,340
|
42
|
6
|
28
|
heartbeat appears
|
16,870
|
11,230-25,640
|
43
|
6 1/7
|
29
|
heartbeat appears
|
20,480
|
13,750-30,880
|
44
|
6 2/7
|
30
|
heartbeat appears
|
24,560
|
16,650-36,750
|
45
|
6 3/7
|
31
|
embryo appears
|
29,110
|
19,910-43,220
|
46
|
6 4/7
|
32
|
embryo appears
|
34,100
|
25,530-50,210
|
47
|
6 5/7
|
33
|
embryo appears
|
39,460
|
27,470-57,640
|
48
|
6 6/7
|
34
|
embryo appears
|
45,120
|
31,700-65,380
|
49
|
7
|
35
|
50,970
|
36,130-73,280
| |
50
|
7 1/7
|
36
|
56,900
|
40,700-81,150
| |
51
|
7 2/7
|
37
|
62,760
|
45,300-88,790
| |
52
|
7 3/7
|
38
|
68,390
|
49,810-95,990
| |
53
|
7 4/7
|
39
|
73,640
|
54,120-102,540
| |
54
|
7 5/7
|
40
|
78,350
|
58,200-108,230
| |
55
|
7 6/7
|
41
|
82,370
|
61,640-112,870
| |
56
|
8
|
42
|
85,560
|
64,600-116,310
|
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