Published online before print July 1, 2005, 10.1148/radiol.2362040880
(Radiology 2005;236:643-646.)
© RSNA, 2005
Outcome of First-Trimester Pregnancies with Slow Embryonic Heart Rate at 6–7 Weeks Gestation and Normal Heart Rate by 8 Weeks at US1
Peter M. Doubilet, MD, PhD and
Carol B. Benson, MD
1 From the Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, 75 Francis St, Boston, MA 02115. Received May 18, 2004; revision requested August 3; revision received August 24; accepted October 1.
Address correspondence to P.M.D. (e-mail: Pdoubilet{at}Partners.org).
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ABSTRACT
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PURPOSE: To determine retrospectively the outcome of pregnancies in which the embryo has a slow heart rate at 6.0–7.0 weeks gestation and a normal heart rate at follow-up ultrasonography (US) by 8.0 weeks gestation.
MATERIALS AND METHODS: Institutional review board approval was granted; informed consent was not required. The study was Health Insurance Portability and Accountability Act compliant. 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. Pregnancies were excluded from the analysis if they were lost to follow-up before the end of first trimester. The Fisher exact test was used for all statistical comparisons.
RESULTS: 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). There were 59 pregnancies with a slow heart rate at 6.0–7.0 weeks and a normal heart rate at follow-up US by 8.0 weeks; 15 (25.4%) resulted in first-trimester demise. This rate of demise was significantly higher than that of 7.2% (28 of 390) in pregnancies with a normal heart rate at 6.0–7.0 weeks and a normal heart rate by 8.0 weeks (P <.001, Fisher exact test). Pregnancies with a borderline heart rate early in pregnancy followed by a normal heart rate had a demise rate of 7.6% (nine of 118), which is similar to those with normal heart rates early in pregnancy followed by normal heart rates at follow-up (P = .84).
CONCLUSION: 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.
© RSNA, 2005
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INTRODUCTION
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The embryonic heartbeat can usually be identified at prenatal ultrasonography (US) by 6 weeks gestation, and the heart rate can be measured via M mode. Several studies have demonstrated that a slow embryonic heart rate early in pregnancy, 6.0–7.0 weeks gestation, is associated with a high rate of subsequent fetal demise by the end of the first trimester (1–9). In a previous study, we have demonstrated that a heart rate below 80 beats per minute at 6.0–6.2 weeks gestation or below 100 beats per minute at 6.3–7.0 weeks is associated with a very high rate of first-trimester demise, a heart rate of 80–89 beats per minute at 6.0–6.2 weeks or 100–109 beats per minute at 6.3–7.0 weeks is associated with a moderately high rate of demise, and a heart rate of 90–99 beats per minute at 6.0–6.2 weeks or 110–119 beats per minute at 6.3–7.0 weeks is associated with a mildly elevated rate of demise. All of these demise rates were found to be significantly higher than the first-trimester demise rate when the heart rate is 100 or more beats per minute at 6.0–6.2 weeks or 120 or more beats per minute at 6.3–7.0 weeks (6).
When there is a demise of pregnancy following a slow embryonic heart rate early in pregnancy, the demise often occurs within 1 week after the slow heart rate is first detected and almost always occurs by the end of the first trimester (9). Thus, when a slow heart rate is seen at 6.0–7.0 weeks, a follow-up US performed approximately 1 week later will often reveal that cardiac activity has ceased. If the embryonic heart is still beating on the follow-up US scan, the heart rate may still be slow or it may be normal.
We questioned whether a follow-up normal heart rate after a slow embryonic heart rate early in pregnancy means that the embryo is no longer at elevated risk for demise by the end of the first trimester. Thus, the purpose of our study was to determine retrospectively the outcome of pregnancies in which the embryo has a slow heart rate at 6.0–7.0 weeks gestation and a normal heart rate on a follow-up scan obtained by 8.0 weeks gestation.
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MATERIALS AND METHODS
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Data Collection
Our study was based on a retrospective review of patient data. Our institutional review board approved the review of medical records and publication of the results for this study; informed consent was not required. Our study was Health Insurance Portability and Accountability Act compliant. From the database of obstetric US examinations performed at our institution, one of the authors (P.M.D.) identified all pregnancies with a 6.0–7.0 week US scan obtained between January 1998 and October 2003 in which the embryonic heart rate was recorded. During that period, it was our standard protocol to measure and record embryonic or fetal heart rate via M mode on first-trimester scans. The heart rate was classified as slow if it was fewer than 90 beats per minute prior to 6.3 weeks gestation or fewer than 110 beats per minute at 6.3–7.0 weeks, normal if it was 100 or more beats per minute prior to 6.3 weeks or 120 or more beats per minute at 6.3–7.0 weeks, or borderline if it was 90–99 beats per minute prior to 6.3 weeks or 110–119 beats per minute at 6.3–7.0 weeks.
Study and Control Groups
Pregnancies were divided into two study groups and one control group on the basis of the embryonic heart rate early in pregnancy (ie, 6.0–7.0-week scan). The slow study group comprised all pregnancies in which the embryonic heart rate early in pregnancy was slow, and the borderline study group comprised those in which the heart rate was borderline. The normal study group, which comprised pregnancies in which the embryonic heart rate early in pregnancy was normal, served as the control group.
We then identified a subset of each of these groups in which a follow-up US performed prior to 8.0 weeks gestation demonstrated a live embryo with a normal heart rate. The three subsets were slow then normal, borderline then normal, and normal then normal.
Follow-up
Follow-up information was obtained by both authors (P.M.D., C.B.B.) from the database of US scans, as well as from the hospital's electronic medical records. The first-trimester outcome was recorded as "demise" if by 13.0 weeks a US scan demonstrated that cardiac activity was no longer present or a pathologic examination identified products of conception in tissue spontaneously passed from the mother; it was recorded as "alive" if after 13.0 weeks a US scan or notes from an office visit documented that the patient was still pregnant or if hospital records documented that a baby was delivered. Pregnancies were excluded from our analysis if the pregnancy was electively terminated during the first trimester or if it was lost to follow-up before the end of the first trimester.
Data Analysis
We compared first-trimester pregnancy outcome in each of the slow and borderline study groups with the outcome in the normal study group. We also compared the outcome in the slow-then-normal group with that of the entire slow study group. In addition, we compared outcomes in the slow-then-normal group and borderline-then-normal group with that in the normal-then-normal group. We then stratified the pregnancies according to gestational age at initial US (6.0–6.2 and 6.3–7.0 weeks) and repeated the aforementioned analyses.
Statistical Analysis
Statistical analyses were conducted by one author (P.M.D.) using Systat software (version 9; SPSS, Chicago, Ill). All comparisons involved 2 x 2 contingency tables for comparing the two groups with respect to the binary outcome (demise vs alive), and the Fisher exact test was used for the analyses. Results were considered statistically significant for P values of less than .05.
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RESULTS
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First-Trimester Outcome in Relation to Embryonic Heart Rate at 6.0–7.0 Weeks
There were 4556 pregnancies in which a heart rate was recorded on a 6.0–7.0-week US scan. First-trimester outcome was known for 2937 (64.5%) of the pregnancies and was unknown for the remaining 1619 (35.5%). Among the 2937 pregnancies with known outcome, 310 were in the slow group, 593 were in the borderline group, and 2034 were in the normal group. In the slow study group, 188 (60.6%) embryos had died by the end of the first trimester (Table 1). The rate of demise was especially high (77.9%) for embryos with very slow heart rates (<80 beats per minute prior to 6.3 weeks or <100 beats per minute at 6.3–7.0 weeks). In the borderline study group, the demise rate was 17.4% (103 of 593). All of these rates of demise were significantly higher (P < .001, Fisher exact test) than the rate of 9.1% (186 of 2034) in the normal group. The findings were similar when the data were stratified according to gestational age at initial US (Table 1). These results, which demonstrate a relationship between slow heart rate at 6.0–7.0 weeks and poor first-trimester outcome, corroborate the results of prior studies.
First-Trimester Outcome for Embryos with Slow Heart Rate at 6.0–7.0 Weeks and Normal Heart Rate at Follow-up US by 8.0 Weeks
There were 567 pregnancies that met all of the following criteria: heart rate measured on a 6.0–7.0-week US scan, follow-up scan obtained by 8.0 weeks demonstrating a normal heart rate (
120 beats per minute), and known first-trimester outcome. Of these, 59 pregnancies were in the slow-then-normal group, 118 were in the borderline-then-normal group, and 390 were in the normal-then-normal group. Among pregnancies in the slow-then-normal group, 15 (25.4%) resulted in fetal demise by the end of the first trimester (Table 2). This rate of demise was lower than that of 60.6% found in the entire slow study group (P < .001, Fisher exact test). It was, however, significantly higher than the demise rate of 7.2% in the normal-then-normal group (P < .001, Fisher exact test). Pregnancies in the borderline-then-normal group, on the other hand, had a demise rate (7.6%) that did not differ significantly from that in the normal-then-normal group.
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TABLE 2. First-Trimester Demise Based on Embryonic Heart Rate at 6.0–7.0 Weeks Gestation in Pregnancies with Normal Heart Rate at Follow-up US by 8.0 Weeks Gestation
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Stratification according to Gestational Age and Heart Rate on 6.0–7.0-week US Scan
We also analyzed our data by stratifying pregnancies according to gestational age at initial US scan (into subgroups of 6.0–6.2 weeks and 6.3–7.0 weeks) and dividing slow heart rates into very slow and moderately slow subgroups (Table 2). When the data were analyzed in any of these ways, the results were similar to those described earlier. In particular, when the heart rate early in pregnancy was slow and then was normal on a follow-up scan obtained by 8.0 weeks, the incidence of subsequent first-trimester demise was significantly elevated (approximately 25%), whether the initial slow rate was seen at 6.0–6.2 or at 6.3–7.0 weeks and whether it was very slow or moderately slow (P < .05 for all these comparisons, Fisher exact test). When a borderline heart rate was seen at either 6.0–6.2 or 6.3–7.0 weeks, a normal heart rate on follow-up scan eliminated the elevated risk of subsequent demise.
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DISCUSSION
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Several studies have documented that a slow embryonic heart rate at 6.0–7.0 weeks gestation is associated with a high rate of first-trimester pregnancy demise, and that demise often occurs soon after the slow heartbeat is detected (1–9). If demise does occur, it is advantageous to make the diagnosis quickly to avoid the occurrence of vaginal bleeding at an inconvenient time and place and to minimize the period of concern and uncertainty for the parents. For these reasons, a follow-up US is advisable approximately 1 week after detection of a slow early-embryonic heartbeat.
If the follow-up US scan demonstrates no live embryo or fetus, the diagnosis of pregnancy demise is established. If the follow-up US scan demonstrates continued slow cardiac activity, further scans are warranted. If, however, the follow-up US scan demonstrates a normal heart rate, the appropriate course of action is less clear, as investigators in previous studies have not examined, to our knowledge, whether a follow-up normal heart rate negates the elevated risk of a prior slow rate. Our study provides information to answer this question. If a 6.0–7.0 week scan demonstrates a slow heartbeat, which indicates a high risk of subsequent demise, a normal heart rate on a follow-up scan obtained by 8.0 weeks lowers the risk somewhat but not entirely. Specifically, in our study the risk of first-trimester pregnancy demise was 60.6% following a slow heart rate at 6.0–7.0 weeks, and this risk decreased to 25.4% if the heart rate was normal on a follow-up scan obtained by 8.0 weeks. This latter risk, however, was over three times as high as the risk in the control group of pregnancies with a normal heart rate at 6.0–7.0 weeks and a normal rate on a follow-up scan obtained by 8.0 weeks. The incidence of pregnancy demise was elevated regardless of the timing of the initial scan (6.0–6.2 or 6.3–7.0 weeks) or the severity of the slow heart rate (moderately or very slow).
Pregnancies with a borderline slow heart rate at early pregnancy had a worse outcome than those with normal heart rates at early pregnancy. A normal follow-up heart rate after a borderline slow rate, however, was fully reassuring in that it indicated that the risk of subsequent demise in the first trimester was no longer elevated.
A limitation of our study is that 35.5% of pregnancies (1619 of 4556) for which scanning was performed at 6.0–7.0 weeks at our institution could not be included because no follow-up information was available. Such a limitation is unavoidable in a retrospective study of this type and is unlikely to have substantially affected our conclusions since the main reasons for loss to follow-up–decision to seek pregnancy care at another facility or to electively terminate the pregnancy–were unrelated to spontaneous pregnancy demise.
In summary, when a slow embryonic heart rate is detected on a 6.0–7.0 week US scan, the likelihood of subsequent first-trimester pregnancy demise remains elevated (approximately 25%) even if the heart rate is normal on a follow-up scan obtained by 8.0 weeks. In such pregnancies, we believe that at least one follow-up scan in the late first trimester is warranted.
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FOOTNOTES
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Authors stated no financial relationship to disclose.
Author contributions: Guarantors of integrity of entire study, P.M.D., C.B.B.; study concepts and design, P.M.D., C.B.B.; literature research, P.M.D.; clinical studies, P.M.D., C.B.B. data acquisition and analysis/interpretation, P.M.D., C.B.B.; statistical analysis, P.M.D.; manuscript preparation, definition of intellectual content, editing, revision/review, and final version approval, P.M.D., C.B.B.
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References
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- Laboda LA, Estroff JA, Benacerraf BR. First trimester bradycardia: a sign of impending fetal loss. J Ultrasound Med 1989; 8:561–563.[Abstract]
- May DA, Sturdevant NV. Embryonal heart rate as a predictor of pregnancy outcome: a prospective analysis. J Ultrasound Med 1991; 10:591–593.[Abstract]
- Tezuka N, Sato S, Kansugi H, Hiroi M. Embryonic heart rates: development in early first trimester and clinical evaluation. Gynecol Obstet Invest 1991; 32:210–212.[Medline]
- Burwinkel TH, Emerson DS, Buster JE, Felker RE, Altieri LA, Carson SA. Predicting pregnancy survival from a single first trimester vaginal ultrasonogram. J Ultrasound Med 1993; 12:665–668.[Abstract]
- Benson CB, Doubilet PM. Slow embryonic heart rate in early first trimester: indicator of poor pregnancy outcome. Radiology 1994; 192:343–344.[Abstract/Free Full Text]
- Doubilet PM, Benson CB. Embryonic heart rate in the early first trimester: what rate is normal? J Ultrasound Med 1995; 14:431–434.[Abstract]
- Falco P, Milano V, Pilu G, et al. Sonography of pregnancies with first-trimester bleeding and a viable embryo: a study of prognostic indicators by logistic regression analysis. Ultrasound Obstet Gynecol 1996; 7:165–169.[CrossRef][Medline]
- Stefos TI, Lolis DE, Sotiriadis AJ, Ziakis GV. Embryonic heart rate in early pregnancy. J Clin Ultrasound 1998; 26:33–36.[CrossRef][Medline]
- 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.[Abstract]
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ABSTRACT
INTRODUCTION
