UNSW Embryology

Cardiovascular System Development - Embryonic Heart Rate

© Dr Mark Hill (2011)

Acknowledgements

Introduction

Heart rate (beats / minute) is a measurement that can be made from early in development (when the heart first starts) through embryonic and fetal stages into labor and birth. It is a common clinical diagnostic tool, but data can be variable between countries and institutions.

Early ultrasonographic measurement of embryonic heart rate (EHR) shows a steady increase from Stage 9-10 (75 beats/minute) to Stage 18 (130 beats/minute) and on to Stage 20, following which a gradual decrease in EHR occurs (More? Embryonic Heart Rate). This increase correlates with heart development and a low EHR is used as an indicator of developmental failure and likely abortion. Late stethoscope measurements of fetal heart rate can monitor fetal stress and identifies the characteristic "lub-dub" heart valve sounds.

An article by Wisser and Dirschedl (1994) studied human ERH by serial ultrasound correlated heart development with the change in ERH, which increased to Stage 20 (22 mm crown rump length) then decreased. Wisser J, Dirschedl P Embryonic heart rate in dated human embryos. Early Hum Dev. 1994 May;37(2):107-15. (More? Embryonic Heart Rate)

Page Links: Introduction | Some Recent Findings | Embryonic Heart Rate | Low EHR | Fetal Heart Rate | Heart Sounds | Heart Rate and Embryo Sex | Heart Rate During Birth |References | Glossary

Some Recent Findings

The 2008 national institute of child health and human development report on fetal heart rate monitoring. Parer JT, Ikeda T, King TL. Obstet Gynecol. 2009 Jul;114(1):136-8. PMID: 19546770

"Standardization of fetal heart rate (FHR) interpretation and management guidelines has been elusive, and no system is currently widely accepted in the United States. The recently summarized 2008 Eunice Kennedy Shriver National Institute of Child Health and Human Development workshop proposed a three-tier system of interpretation of FHR patterns, but left management recommendations to the professional associations. The middle tier, called indeterminate Category II, which contains the variant FHR patterns seen most frequently, is vast and heterogeneous."

Smith JF Jr. Fetal health assessment using prenatal diagnostic techniques. Curr Opin Obstet Gynecol. 2008 Apr;20(2):152-6. Review.

"Fetal heart-rate monitoring remains the main form of fetal assessment for high-risk pregnancies. The additional assessments afforded by the analysis of ST and T-wave changes of the fetal electrocardiogram hold promise for improving the predictive value of fetal heart-rate assessments."

Mongiovì M, Pipitone S. Supraventricular tachycardia in fetus: how can we treat? Curr Pharm Des. 2008;14(8):736-42. Review.

"The normal fetal cardiac rhythm is characterized by a regular heart rate ranging between 100 and 160 -180 beats/min with a normal 1:1 atrioventricular electromechanical relationship during each cardiac cycle. Fetal tachycardia occurring in approximately 0.5% of all pregnancies and it is an important cause of fetal morbidity and mortality. ...Reliable diagnosis in utero of fetal arrhythmia is possible by ultrasound examination of the fetal heart. In fact pulsed wave Doppler guided by two-dimensional echocardiography provided important information on cardiac rhythm as it study the blood flow from different chambers."

Doubilet PM, Benson CB. Outcome of first-trimester pregnancies with slow embryonic heart rate at 6-7 weeks gestation and normal heart rate by 8 weeks at US. Radiology. 2005 Aug;236(2):643-6.

"Singleton pregnancies with an embryonic heart rate measured on a 6.0-7.0-week US scan were identified. 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."

Embryonic Heart Rate

In a later study by Coulam etal. (1996), normal successful human gestations were defined by EHR criteria at different early embryonic (34-56 days from last menstrual period) developmental stages (at the earliest stages when embryo length is difficult to measure gestational sac diameters are included). Coulam CB, Britten S, Soenksen DM. Early (34-56 days from last menstrual period) ultrasonographic measurements in normal pregnancies. Hum Reprod. 1996 Aug;11(8):1771-4.

• Stage 9-10  2 mm embryo (gestational sac diameter of 20 mm) EHR at least 75 beats / minute
• Stage 11-12  5 mm embryo (gestational sac diameter of 30 mm) EHR at least 100 beats / minute
• Stage 16  10 mm embryo EHR at least 120 beats / minute
• Stage 18  15 mm embryo EHR at least 130 beats / minute

(More about stages? Carnegie Stage table)

Low Embryonic Heart Rate

Low ERH is correlated with embryonic loss and is often used as a predictor for risk of spontaneous miscarriage, the majority of ERH research articles focus on this aspect as an indicator. "When a slow embryonic heart rate is detected at 6.0-7.0 weeks, the likelihood of subsequent first-trimester demise remains elevated (approximately 25%) even if the heart rate is normal at follow-up. In such pregnancies, at least one follow-up scan in late first trimester is warranted." Doubilet PM, Benson CB. Outcome of first-trimester pregnancies with slow embryonic heart rate at 6-7 weeks gestation and normal heart rate by 8 weeks at US. Radiology. 2005 Aug;236(2):643-6.

Deceleration

The following characteristics of decelerations comes from the 2008 National Institute of Child Health and Human Development Workshop Report on Electronic Fetal Monitoring: Update on Definitions, Interpretation, and Research Guidelines.

Late Deceleration

• Visually apparent usually symmetrical gradual decrease and return of the fetal heart rate (FHR) associated with a uterine contraction.
• A gradual FHR decrease is defined as from the onset to the FHR nadir of ≥30 seconds.
• The decrease in FHR is calculated from the onset to the nadir of the deceleration.
• The deceleration is delayed in timing, with the nadir of the deceleration occurring after the peak of the contraction.
• In most cases, the onset, nadir, and recovery of the deceleration occur after the beginning, peak, and ending of the contraction, respectively.
  

Early Deceleration

• Visually apparent, usually symmetrical, gradual decrease and return of the FHR associated with a uterine contraction.
• A gradual FHR decrease is defined as one from the onset to the FHR nadir of ≥30 seconds.
• The decrease in FHR is calculated from the onset to the nadir of the deceleration.
• The nadir of the deceleration occurs at the same time as the peak of the contraction.
• In most cases the onset, nadir, and recovery of the deceleration are coincident with the beginning, peak, and ending of the contraction, respectively.
  

Variable Deceleration

• Visually apparent abrupt decrease in FHR.
• An abrupt FHR decrease is defined as from the onset of the deceleration to the beginning of the FHR nadir of<30 seconds. The decrease in FHR is calculated from the onset to the nadir of the deceleration.
• The decrease in FHR is ≥15 beats per minute, lasting ≥15 seconds, and<2 minutes in duration.
• When variable decelerations are associated with uterine contractions, their onset, depth, and duration commonly vary with successive uterine contractions.

Fetal Heart Rate

Later in development, Fetal Heart Rate (FHR) can also be measured using ultrasound doppler techniques. Baseline fetal heart rate (FHR) ranges (normal limits) in many studies ranges from 120 to 160 beats/minute.

FHR decreases from 30-33 weeks to 34-35 weeks, and steadily falls from 36-37 weeks within the range from 130 to 140 beats / minute. An article by Park etal. (2001) found fetal heart rate (FHR) as 143 beats / minute at term (37-40 weeks), another study by Druzin et al. (1986) reported 132 beats / minute. FHR data is variable due to retrieval method, analysis of FHR parameters, different institutions, different countries, and collection under different conditions.

Human Fetal Heart Rate Changes

(Graph from: Park MI, Hwang JH, Cha KJ, Park YS, Koh SK. Computerized analysis of fetal heart rate parameters by gestational age. Int J Gynaecol Obstet. 2001 Aug;74(2):157-64.)

Heart Sounds

Embryonic heart sounds can be detected by Doppler during ultrasound examination. Fetal heart sounds can be detected by stethoscope.

The characteristic "lub-dup" sounds are associated with closing of heart valves.

The first sound (lub) occurs as atrioventricular valves close and signifies beginning of systole (contraction)

The second sound (dup) occurs when semilunar valves close at the beginning of ventricular diastole (relaxation)

Heart Rate and Embryo Sex

Embryonic heart rate has been suggested as an indicator of sex (male/female), scientific research to date does not support any correlation between EHR and the sex of the embryo/fetus.

"Baseline fetal heart rate was not significantly different between male and female fetuses." Druzin ML, Hutson JM, Edersheim TG. Relationship of baseline fetal heart rate to gestational age and fetal sex. Am J Obstet Gynecol. 1986 May;154(5):1102-3. | Glahn RP, et al. Evaluation of sex differences in embryonic heart rates. Poult Sci. 1987 Aug;66(8):1398-401. | DuBose TJ, et al. Fetal heart rate (FHR) is not an indicator of the baby's sex. J Ultrasound Med. 1988 Apr;7(4):237-8.

Heart Rate During Birth

Fetal heart rate is often monitored electronically during labor as a diagnostic and clinical management tool. At term, the normal, unmedicated fetus before labor has an average heart rate of 140 beats/minute. Preterm fetus (at 20 weeks gestational age) has a mean heart rate of 155 beats/minute.

Basal FHR

Normal 110-160 (beats/minute)

Tachycardia (Moderate) 161-180 (Marked) 181 or more

Bradycardia (Moderate) 100-119 (Marked 90) or less

Transitory FHR Changes

Variable 5-15 beats per minute amplitude

Accelerations Increased by 15 or more

Decelerations - Early Decreased by 10-40, Late Decreased by 5-60, Variable Decreased by 10-60, occasionally more

Tachycardia Causes: Fetal hypoxia, Maternal fever, amnionitis (inflammation of the amnion), Drugs, Maternal hyperthyroidism, Fetal anemia, Fetal heart failure and Fetal cardiac tachydysrhythmias

Bradycardia Causes: Fetal hypoxia, Fetal acidosis, Fetal cardiac bradydysrhythmias, Drugs, Hypothermia and Reflex

(data from NCBI Bookshelf hstat6.section.700#711)

References

Search Pubmed Now: heart[TITL]+rate[WORD]+development[WORD]

Reviews on Embryonic Heart Rate

• Choong S, Rombauts L, Ugoni A, Meagher S.    [See Related Articles] Ultrasound prediction of risk of spontaneous miscarriage in live embryos from assisted conceptions. Ultrasound Obstet Gynecol. 2003 Dec;22(6):571-7. Review.
• van Leeuwen I, Branch DW, Scott JR.    [See Related Articles] First-trimester ultrasonography findings in women with a history of recurrent pregnancy loss. Am J Obstet Gynecol. 1993 Jan;168(1 Pt 1):111-4. Review.

Articles on Embryonic Heart Rate

• Wisser J, et al.   [See Related Articles] Embryonic heart rate in dated human embryos. Early Hum Dev. 1994 May;37(2):107-15. PMID: 8088227; UI: 94374271.
• Using simultaneous B-mode and time-motion transvaginal ultrasonography we measured embryonic heart rate (EHR) in dated human embryos during the first trimester in a prospective study. In 160 pregnant women who had undergone assisted reproductive procedures, 139 singleton embryos and 46 embryos from 21 multiple pregnancies were studied between the 37th and 98th postmenstrual day. Because multiple measurements in one embryo at different ages were possible, a total of 348 measurements were taken. EHR in dated human embryos shows an increase up to 63 postmenstrual days or 22 mm greatest length. Thereafter a steady decrease of EHR was noted. Maximal EHR is reached when morphological development of the embryonic heart is completed. Furthermore, we examined 27 embryos with low EHR compared with greatest embryonic length. All of these ended in missed abortion within the embryonic period. According to our data the increase of EHR parallels the morphological development of the embryonic heart. Decline of EHR afterwards is interpreted as a functional adaption to muscular development of the heart.
• Coulam CB, Britten S, Soenksen DM.   [See Related Articles] Early (34-56 days from last menstrual period) ultrasonographic measurements in normal pregnancies. Hum Reprod. 1996 Aug;11(8):1771-4.
• Doubilet PM, Benson CB.   [See Related Articles] Outcome of first-trimester pregnancies with slow embryonic heart rate at 6-7 weeks gestation and normal heart rate by 8 weeks at US. Radiology. 2005 Aug;236(2):643-6.
• Park MI, Hwang JH, Cha KJ, Park YS, Koh SK.   [See Related Articles]Computerized analysis of fetal heart rate parameters by gestational age. Int J Gynaecol Obstet. 2001 Aug;74(2):157-64.
• Achiron R, et al.   [See Related Articles] Heart rate as a predictor of first-trimester spontaneous abortion after ultrasound-proven viability. Obstet Gynecol. 1991 Sep;78(3 Pt 1):330-4.
• Tezuka N, et al.   [See Related Articles] Development and sexual difference in embryonic heart rates in pregnancies resulting from in vitro fertilization. Gynecol Obstet Invest. 1998;46(4):217-9.
• Benson CB, et al.   [See Related Articles] Slow embryonic heart rate in early first trimester: indicator of poor pregnancy outcome. Radiology. 1994 Aug;192(2):343-4.
• Tezuka N, et al.   [See Related Articles] Embryonic heart rates: development in early first trimester and clinical evaluation. Gynecol Obstet Invest. 1991;32(4):210-2.
• Coulam CB, et al.   [See Related Articles] Early (34-56 days from last menstrual period) ultrasonographic measurements in normal pregnancies. Hum Reprod. 1996 Aug;11(8):1771-4.
• Howe RS, et al.   [See Related Articles] Embryonic heart rate in human pregnancy. J Ultrasound Med. 1991 Jul;10(7):367-71.
• Schats R, et al.   [See Related Articles] Embryonic heart activity: appearance and development in early human pregnancy. Br J Obstet Gynaecol. 1990 Nov;97(11):989-94.
• May DA, et al.   [See Related Articles] Embryonal heart rate as a predictor of pregnancy outcome: a prospective analysis. J Ultrasound Med. 1991 Oct;10(10):591-3.
• Druzin ML, Hutson JM, Edersheim TG.   [See Related Articles] Relationship of baseline fetal heart rate to gestational age and fetal sex. Am J Obstet Gynecol. 1986 May;154(5):1102-3.
• Stefos TI, et al.   [See Related Articles] Embryonic heart rate in early pregnancy. J Clin Ultrasound. 1998 Jan;26(1):33-6.
• van Leeuwen I, et al.   [See Related Articles] First-trimester ultrasonography findings in women with a history of recurrent pregnancy loss. Am J Obstet Gynecol. 1993 Jan;168(1 Pt 1):111-4.
• Goldstein SR.   [See Related Articles] Embryonic death in early pregnancy: a new look at the first trimester. Obstet Gynecol. 1994 Aug;84(2):294-7.
• Falco P, et al.   [See Related Articles] Sonography of pregnancies with first-trimester bleeding and a viable embryo: a study of prognostic indicators by logistic regression analysis. Ultrasound Obstet Gynecol. 1996 Mar;7(3):165-9.
• Mandarim-de-Lacerda CA, et al.   [See Related Articles] Quantitative study of the heart in human embryo at 17 mm C-R (stade 19). Anat Anz. 1989;169(4):261-5.
• Fujiwaki R, et al.   [See Related Articles] Intrauterine ultrasonographic assessments of embryonic development. Am J Obstet Gynecol. 1995 Dec;173(6):1770-4.
• Dickey RP, et al.   [See Related Articles] Computer analysis of the human embryo growth curve: differences between published ultrasound findings on living embryos in utero and data on fixed specimens. Anat Rec. 1993 Nov;237(3):400-7. PMID: 8291693; UI: 94121248.
• Glahn RP, et al.   [See Related Articles] Evaluation of sex differences in embryonic heart rates. Poult Sci. 1987 Aug;66(8):1398-401.
• Kaulfuss KH, et al.   [See Related Articles] [Real-time ultrasonic pregnancy diagnosis (B-mode) in sheep. 1. Frequent examinations during the first month of pregnancy]. Tierarztl Prax. 1996 Oct;24(5):443-52. German. PMID: 8999589; UI: 97079917.
• Sedmera D, et al.   [See Related Articles] Trabeculation in the embryonic heart. Bioessays. 1996 Jul;18(7):607.
• Nisikori K, et al.   [See Related Articles] Assessment of fetal growth and serum hCG titers after in vitro fertilization and embryo transfer. Int J Gynaecol Obstet. 1993 May;41(2):147-52.
• Skidmore FD.   [See Related Articles] An analysis of the age and size of 483 human embryos. Teratology. 1977 Feb;15(1):97-102.
• Dickey RP, et al.   [See Related Articles] The relationship of initial embryo crown--rump length to pregnancy outcome and abortus karyotype based on new growth curves for the 2-31 mm embryo. Hum Reprod. 1994 Feb;9(2):366-73.
• Grobstein C.   [See Related Articles] The early development of human embryos. J Med Philos. 1985 Aug;10(3):213-36.
• Ikegawa A.   [See Related Articles] Prediction of first-trimester miscarriage from embryonic bradycardia and embryonic growth delay. J Obstet Gynaecol. 1995 Dec;21(6):537-44.
• Sherer DM, et al.   [See Related Articles] Physiology of isolated long-term variability of the fetal heart rate. Am J Obstet Gynecol. 1993 Jul;169(1):113-5.
• Mitra AG, et al.   [See Related Articles] Transvaginal versus transabdominal Doppler auscultation of fetal heart activity: a comparative study. Am J Obstet Gynecol. 1996 Jul;175(1):41-4.
• Shiota K, et al.   [See Related Articles] High prevalence of defective human embryos at the early postimplantation period. Teratology. 1987 Jun;35(3):309-16.
• Blaas HG, et al.   [See Related Articles] Early development of the abdominal wall, stomach and heart from 7 to 12 weeks of gestation: a longitudinal ultrasound study. Ultrasound Obstet Gynecol. 1995 Oct;6(4):240-9. PMID: 8590186; UI: 96131968.
• Fadda G, et al.   [See Related Articles] Endovaginal ultrasound in patients at risk for repeated abortion. Clin Exp Obstet Gynecol. 1993;20(2):120-2. PMID: 8330433; UI: 93321392.
• Hall S, et al.   [See Related Articles] Fetal sex prediction: the heart of the matter. J Ky Med Assoc. 1993 Sep;91(9):409-10. No abstract available. PMID: 8228583; UI: 94045193.
• Coerdt W, et al.   [See Related Articles] [Pathologic embryo examinations of induced and spontaneous abortions in the 1st trimester of pregnancy]. Pathologe. 1994 Feb;15(1):32-9. German. PMID: 8153073; UI: 94203962.
• Bonilla-Musoles FM, et al.   [See Related Articles] Early detection of embryonic malformations by transvaginal and color Doppler sonography. J Ultrasound Med. 1994 May;13(5):347-55. PMID: 8015041; UI: 94285266.
• Sawin SW, et al.   [See Related Articles] Dating of pregnancy by trimesters: a review and reappraisal. Obstet Gynecol Surv. 1996 Apr;51(4):261-4. PMID: 8657403; UI: 96253888.
• Montenegro N, et al.   [See Related Articles] [Transvaginal endosonography and Doppler study in embryo-fetal hemodynamic assessment in the first pregnancy trimester]. Acta Med Port. 1993 Nov;6 Suppl 1:I3-8. Review. Portugese. PMID: 8285124; UI: 94113070.
• Goldstein SR.   [See Related Articles] Embryonic ultrasonographic measurements: crown-rump length revisited. Am J Obstet Gynecol. 1991 Sep;165(3):497-501. Review. PMID: 1892172; UI: 91368841.
• Rotsztejn D, et al.   [See Related Articles] Correlation between fetal heart rate, crown-rump length, and beta-human chorionic gonadotropin levels during the first trimester of well-timed conceptions resulting from infertility treatment. Fertil Steril. 1993 Jun;59(6):1169-73. PMID: 8495760; UI: 93265957.
• Ragavendra N, et al.   [See Related Articles] Transcervical sonography: an investigational technique for visualization of the embryo. Obstet Gynecol. 1993 Jan;81(1):155-8. PMID: 8416453; UI: 93101392.
• Mandarim-de-Lacerda CA, et al.   [See Related Articles] Sonographic quantitative analysis of the heart in the third trimester of gestation. Surg Radiol Anat. 1993;15(2):139-43.
• Gimovsky ML.   [See Related Articles] Electronic fetal heart rate monitoring. J Perinatol. 1994 May-Jun;14(3):173.
• Mandarim-de-Lacerda CA.   [See Related Articles] Cardiac growth in staged human embryos--stages from 15 to 23, post-somitic period. Anat Anz. 1991;173(1):60-4.
• Keller BB, et al.   [See Related Articles] In vivo assessment of embryonic cardiovascular dimensions and function in day-10.5 to -14.5 mouse embryos. Circ Res. 1996 Aug;79(2):247-55.
• Patrick J, et al.   [See Related Articles] The distribution of accelerations of the human fetal heart rate at 38 to 40 weeks' gestational age. Am J Obstet Gynecol. 1985 Jan 15;151(2):283-7.
• Burwinkel TH, et al.   [See Related Articles] Predicting pregnancy survival from a single first trimester vaginal ultrasonogram. J Ultrasound Med. 1993 Nov;12(11):665-8.
• Opsahl MS, et al.   [See Related Articles] First trimester sonographic characteristics of patients with recurrent spontaneous abortion. J Ultrasound Med. 1993 Sep;12(9):507-10.
• DuBose TJ, et al.   [See Related Articles] Fetal heart rate (FHR) is not an indicator of the baby's sex. J Ultrasound Med. 1988 Apr;7(4):237-8.
• Pearson JT, et al.   [See Related Articles] Developmental patterns of heart rate in altricial avian embryos and hatchlings. J Exp Biol. 1999;202(Pt 11):1545-1550.
• Smith KE, et al.   [See Related Articles] The profound impact of patient age on pregnancy outcome after early detection of fetal cardiac activity. Fertil Steril. 1996 Jan;65(1):35-40.
• Mandarim-de-Lacerda CA.   [See Related Articles] Morphometry of the human heart in the second and third trimesters of gestation. Early Hum Dev. 1993 Dec 31;35(3):173-82.
• Shepard TH, et al.   [See Related Articles] In vitro study of rat embryos. I. Effects of decreased oxygen on embryonic heart rate. Teratology. 1969 May;2(2):107-9.
• Gagnon R, et al.   [See Related Articles] External vibratory acoustic stimulation near term: fetal heart rate and heart rate variability responses. Am J Obstet Gynecol. 1987 Feb;156(2):323-7.
• Shiota K.   [See Related Articles] Maternal fertility, reproductive loss, and defective human embryos. J Epidemiol Community Health. 1989 Sep;43(3):261-7.
• Sada H, et al.   [See Related Articles] Developmental change in fast Na channel properties in embryonic chick ventricular heart cells. Can J Physiol Pharmacol. 1995 Oct;73(10):1475-84.
• Collins JH.   [See Related Articles] Fetal grasping of the umbilical cord with simultaneous fetal heart rate monitoring. Am J Obstet Gynecol. 1994 Jun;170(6):1836.

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