FIRST TRIMESTER PREGNANCY LOSS

- HEART RATE

Fetal heart activity is the earliest proof of a viable pregnancy and it has been documented in utero by TVS as early as 36 days' menstrual age, approximately at the time when the heart tube starts to beat (4).

Cardiac activity should be evident when the embryo is over 2 mm (18), however:

· in 5-10% of embryos between 2 and 4 mm it cannot be demonstrated, although the corresponding pregnancies will have a normal outcome (19,20).

· from 5 to 9 weeks of gestation there is a rapid increase in the mean heart rate from 110 to 175 beats per minutes (bpm).

· the heart rate then gradually decreases to around 160-170 bpm.

Fetal heart rate and pregnancy outcome

Study	Year	Study type	Entry criteria	n	Outcome
1	1989	P	Low-risk population	65	FHR < 85 bpm = 100 miscarriage rate
2	1990	P	CRL < 12 mm	398	Absence of FHA with CRL > 5 mm diagnostic of miscarriage
3	1990	P	IVF population	?	Later FHA detected = higher risk of miscarriage
4	1991	P	Low-risk population	143	8/10 miscarriages FHR < 5th centile for gestation
5	1991	P	4.5-7.3 weeks' gestation	50	6/11 miscarriages FHR < 85 bpm
6	1991	P / XS	Low-risk population	603	Miscarriage group: FHR < 5th centile (sensitivity 65%, FNR 35%). Normal outcome group: FHR < 5th centile (specificity 98%, FPR 2%)
7	1994	P	FHR < 90 bpm < 8 weeks	40	100% miscarriage rate if FHR < 70 bpm. 80% miscarriage rate if FHR < 90 bpm
8	1995	P	6-8 weeks	1185	Higher FHR = better outcome
9	1996	P	5-8 weeks	361	20-30 mm sac should contain 2-5 mm embryo with FHR 75-100 bpm
10	1997	P	Subfertile population	116	Lower FHR = higher risk of miscarriage
11	1998	P	6-8 weeks	2164	100% miscarriage rate if FHR < 85 bpm, linear increase in FHR with gestation
12	1999	P	< 7 weeks	531	38% miscarriage rate, 90% normal long-term outcome, increased aneuploidy
13	2000	P	< 7 weeks	2817	Increased FHR - no relation to outcome
14	2003	P	Threatened miscarriage	87	No difference in outcome (three miscarriages)
15	2004	P / XS	Threatened miscarriage; live embryo	240	FHR < 120 bpm = Increased risk miscarriage (sensitivity 54%, specificity 94%, PPV 72%, NPV 89%)
bpm, beats per minute; CRL, crown-rump length; FHA, fetal heart activity; FHR, fetal heart rate; FNR, false-negative rate; FPR, false-positive rate; IVF, in-vitro fertilization; NPV, negative predictive value; PPV positive predictive value. P, Prosepective study; XS – transverse study.
From: E. Jauniaux, J. Johns, G. J. Burton. The role of ultrasound imaging in diagnosing and investigating early pregnancy failure. Ultrasound Obstet Gynecol 2005;25:613-624

1. Presence of a heart beat and rate.
• All embryos >5mm should demonstrate cardiac activity.
• Visualization of a fetal heartbeat does not ensure fetal viability, however, the abortion rate decreases markedly for living embryos (0.5% demise rate for living embryos between 6 and 10mm). (1,2).

Estimates of pregnancy failure rates
Embryo + heartbeat	Clinical Findings
	Bleeding	No Bleeding
<6 weeks 7-9 weeks 9-11 weeks	33% 10% 4%	16% 5% 1-2%
Heart Rate	Embryonic Demise
40-69 bpm	100%
70-79 bpm	91%
80-90 bpm	79%
Overall < 90 bpm	86%

2. Bradycardia.
• Poor prognosticator of pregnancy.
• Heart rate of <90 beats per minute in embryos <8 weeks is associated with an 80% rate of embryonic demise (1).
• Normal embryos start life with heart rates of <85 beats per minute (2).

	Fetal Bradycardia – 6 wks GA 75 beats / min
	Fetal Bradycardia – 6 wks 3 days GA 77 beats / min
	Marked fetal bradycardia – 6 wks 4 days GA 49 beats / min

1. Feta Tachycardia.

Fetal Tachycardia – 7 wks 2 days GA 189 beats / min

2. Fetal arrhythmia in the first trimester.

Note irregular heart rate on M-mode scan	Rates of 88 and 123 beats / min

Bradycardia (6.5 wks GA)

REFERENCES

1. Laboda LA, Estroff JA, Benacerraf BR. First trimester bradycardia. A sign of impeding fetal loss. J Ultrasound Med 1989; 8: 561-563.
2. Brown DL, Emerson DS, Felker RE, Cartier MS, Smith WC. Diagnosis of early embryonic demise by endovaginal sonography. J Ultrasound Med 1990; 9: 631-636
3. Schats R, Jansen CA, Wladimiroff JW. Embryonic heart activity: appearance and development in early human pregnancy. Br J Obstet Gynaecol 1990; 97: 989-994
4. Tezuka N, Sato S, Kanasugi H, Hiroi M. Embryonic heart rates: development in early first trimester and clinical evaluation. Gynecol Obstet Invest 1991; 32: 210-212
5. May DA, Sturtevant NV. Embryonal heart rate as a predictor of pregnancy outcome: a prospective analysis. J Ultrasound Med 1991; 10: 591-593
6. Achiron R, Tadmor O, Mashiach S. Heart rate as a predictor of first-trimester spontaneous abortion after ultrasound proven viability. Obstet Gynecol 1991; 78: 330-334
7. Benson CB, Doubilet PM. Slow embryonic heart rate in early first trimester: indicator of poor pregnancy outcome. Radiology 1994; 192: 343-344
8. Doubilet PM, Benson CB. Embryonic heart rate in the early first trimester: what rate is normal? J Ultrasound Med 1995; 14: 431-434
9. Coulam CB, Britten S, Soenksen DM. Early (34-56 days from last menstrual period) ultrasonographic measurements in normal pregnancies. Hum Reprod 1996; 11: 1771-1774.
10. Qasim SM, Sachdev R, Trias A, Senkowski K, Kemmann E. The predictive value of first-trimester embryonic heart rates in infertility patients. Obstet Gynecol 1997; 89: 934-936.
11. Stefos TI, Lolis DE, Sotiriadis AJ, Ziakas GV. Embryonic heart rate in early pregnancy. J Clin Ultrasound 1998; 26: 33-36.
12. Doubilet PM, Benson CB, Chow JS. Long-term prognosis of pregnancies complicated by slow embryonic heart rates in the early first trimester. J Ultrasound Med 1999; 18: 537-541.
13. Doubilet PM, Benson CB, Chow JS. Outcome of pregnancies with rapid embryonic heart rates in the early first trimester. Am J Roentgenol 2000; 175: 67-69.
14. Tannirandorn Y, Sangsawang S, Manotaya S, Uerpairojkit B, Samritpradit P, Charoenvidhya D. Fetal loss in threatened abortion after embryonic/fetal heart activity. Int J Gynaecol Obstet 2003; 81: 263-266
15. Coulam CB, Britten S, Soenksen DM. Early (34-56 days from last menstrual period) ultrasonographic measurements in normal pregnancies. Hum Reprod 1996; 11: 1771-1774.
16. Benson CB, Doubilet PM. Slow embryonic heart rate in early first trimester: Indicator of poor pregnancy outcome. Radiology 1994,192:343-344.
17. Goldstein SR. Embryonic death in early pregnancy: A new look at the first trimester. Obstet Gynecol 1994,84:294-297.
18. Levi CS, Lyons EA, Zheng XH, Lindsay DJ, Holt SC. Endovaginal US: demonstration of cardiac activity in embryos of less than 5.0 mm in crown-rump length. Radiology 1990; 176: 71-74.
19. Goldstein SR. Significance of cardiac activity on endovaginal ultrasound in very early embryos. Obstet Gynecol 1992; 80: 670-672
20. Brown DL, Emerson DS, Felker RE, Cartier MS, Smith WC. Diagnosis of early embryonic demise by endovaginal sonography. J Ultrasound Med 1990; 9: 631-636.