Embryonic heart rates: development in early first trimester and clinical evaluation.

One hundred and forty-three women in the early first trimester of gestation were examined 364 times using transvaginal sonography, and the development of embryonic heart rate was studied. In each case gestational age was revised retrospectively by either recorded basal body temperature or ultrasound crown-rump length dating between 9 and 10 weeks. Embryonic cardiac activity could be detected as early as 37 days of gestation. In 133 continuing pregnancies, embryonic heart rate rose from an average of 97.7 beats per min at 36-38 days to 174.7 beats per min at 60-62 days. A significant correlation was seen between gestational age and embryonic heart rate (p less than 0.001). The regression equation for heart rate was as follows: heart rate = 3.850 x gestational age (days) -54.64 (r = 0.908, n = 347), in short, embryonic heart rate continued to rise about 4 beats per min every day until 8 weeks of gestation. In this series, 10 pregnancies resulted in spontaneous abortion in the first trimester, and all of them showed relative bradycardia. Embryonic heart rate measurements in 8 of them were below the 95% prediction intervals for normal heart rate plotted against gestational age. This study suggests that embryonic heart rate measurement by ultrasound may be a new method for dating early first trimester, and that first trimester bradycardia may be associated with a poor prognosis for the pregnancy.     

First trimester embryonic/fetal heart rate in normal pregnant women

Objective: To establish reference ranges for first trimester embryonic/fetal heart rate in normal pregnant women. Materials and methods: This was a cross-sectional study. We performed ultrasonogram in 319 normal pregnant women, gestation age between 6⁺⁰ and 14⁺⁶ weeks and measured embryonic/fetal heart rates using M-mode. The embryonic/fetal heart rates were analyzed according to gestational ages (GA). Results: Data of 319 pregnancies were analyzed and the outcome revealed the mean of fetal heart rate according to gestational age. The mean embryonic heart rates during the 6th–7th week of gestation are lower when compared with the other gestational ages. At the 8th week of gestation, the embryonic heart rate is maximum. Then the embryonic/fetal heart rate gradually decreased to 161 beats/min at the 14th week of gestation. The regression equation for embryonic/fetal heart rate (beat/min) [y] according to GA (day) [x] was y = −53.124 + 6.1333x + (−0.0407)x ² (r ² = 0.525; P < 0.001). Conclusion: Embryonic/fetal heart rates during the 6⁺⁰ and 14⁺⁶ week of gestation are related to GA. Our reference ranges may be useful for further studies such as for prediction of adverse pregnancy outcome in threatened abortion.     

Predictive value of early embryonic cardiac activity for pregnancy outcome.

The biologic variation of the embryonic heart rate was investigated by transvaginal ultrasonography during the first trimester of normal (n = 141) and abnormal (n = 29) pregnancies, and the predictive value of a repeatedly diagnosed slow heart rate for pregnancy outcome was determined. The mean heart rate increased from 82 +/- 10.3 beats/min at 5 weeks' gestation to 156 +/- 9.6 beats/min at 9 weeks. A single observation of an abnormally slow heart rate did not necessarily predict subsequent embryonic death. However, a continued decline in embryonic heart activity, observed within a few days' interval, was always associated with a first-trimester abortion.     

Comparison of the accuracy of gestational age estimation from fetal heart rate and crown-rump length

Objective: To compare the accuracy of gestational age (GA) estimation predicted by fetal heart rate (FHR) versus crown-rump length (CRL) measurements in early pregnancies.Methods: A total of 145 infertile women with singleton intrauterine pregnancies conceived through in vitro fertilization underwent vaginal ultrasonographic examination in early stage of pregnancy. We performed 197 FHR and 398 CRL measurements. The relationship between GA (counted with the day of oocyte retrieval used as day 14) and the FHR or CRL was explored with regression analysis by means of least squares. Polynomials up to the third order were analyzed, and the coefficient of determination (R²) was calculated.Results: Fetal cardiac activity could be detected as early as 38 days, gradually increased to 188 beats per minute at 62 days of gestation. Regression analysis with GA as dependent variable resulted in R² values of 0.906, 0.907, and 0.908 for the first, second, and third order polynomials, respectively. The standard deviations around the regression line were 2.90, 2.81, and 2.84 days, respectively. The second order polynomial to describe GA (days) estimated by FHR (beats per min): GA = 3.02E-41FHR² + 1.60E-11FHR + 2.22E+1. On the other hand, the CRL was measured at 38 days to 62 days of gestation. Regression analysis resulted in R² values of 0.827, 0.839, and 0.841, respectively. The deviations were 4.11, 3.83, and 3.89 days, respectively. The second order polynomial to describe GA estimated by CRL (mm): GA = −2.10E-21CRL² + 1.49E+01CRL + 3.86E+1. There was no difference between the R² values and no difference between the standard deviations around the regression lines.Conclusion: Our results indicate no statistically significant difference in the accuracy of GA estimation predicted by FHR versus CRL measurements. But better mathematical fits were obtained when the data of FHR were used for GA estimation. These findings suggest that the FHR measurement may be a new method for early ultrasound dating. This study mentions for the first time the possibility of “FHR dating” with functional data.     

Estimation of gestational age with ultrasonographic measurement of the fetus in each trimester

The method of estimating gestational age (GA) was studied in each trimester. CRL, BPD and FFL were selected as the parameters of ultrasonic B-mode measurement, and each standard curve was recorded. The less erroneous range on each parameter was decided. The range of CRL was from 20 to 80mm, that of BPD from 20 to 70 mm and that of FFL from 20 to 55mm. Within these ranges, GA estimated by CRL showed 2.9 days difference on average compared to the GA determined by LMP, compared with BPD 4.6 days and with FFL 4.9 days. CRL was the most accurate, but that with BPD or FFL could be useful in the 2nd trimester. Since the difference in the growth of each fetus would become apparent in late stage, the ranges of GA for each measured value of BPD or FFL were determined in the 3rd trimester by the mean +/- 3/2 SD for GA determined by CRL. Since 67 to 100% of the studied cases were included in the ranges of GA, the estimation will be useful in the 3rd trimester. FFL is more useful than BPD in the 3rd trimester, and it is also utilized in cases where BPD measurement is not possible due to fetal head descent.     

First trimester dating by fetal heart rate assessment: a comparison with crown-rump length measurement

Objective: The purpose of this study was to determine whether fetal heart rate (FHR) can be used to date pregnancies in the early first trimester using the gold standard of crown-rump length (CRL) dating as a reference.

Methods: This single center study evaluated women undergoing obstetrical ultrasounds between 4.5 and 8.5 weeks. FHR and gestational age (GA) based on CRL were obtained. Linear regression analysis and a Bland–Altman plot were used to demonstrate the relationship between the two measurements. A further simplified version of the relationship between CRL and FHR that may be clinically useful was calculated.

Results: 176 patients were included in the study. The Pearson correlation coefficient was 0.95, indicating a strong correlation between the two dating methods. The Bland–Altman plot demonstrated agreement across GA tested. A simple arithmetic formula of GA(weeks)?=?FHR (beats per minute)/20 was calculated. 169/176 patients had <4 days discrepancy between FHR- and CRL-based dating using this formula.

Conclusion: We found that a simple formula based on FHR may accurately date early pregnancies. This method, if further validated, may represent an important tool for pregnancy dating.     

Early first-trimester crown-rump length measurements in male and female singleton fetuses in IVF pregnancies

Objectives: The generally higher birth-weight of male newborns compared to female newborns is attributed mainly to intrauterine exposure to testosterone. We aimed to determine if crown-rump length (CRL) differs between male and female fetuses early in the first trimester. Methods: A retrospective cohort study of 333 women with nondiabetic singleton IVF pregnancies attending a single university-affiliated tertiary medical center in 2000–2007 who underwent CRL measurement before 50 days of pregnancy (date of measurement minus oocyte retrieval date plus 14 days). Data on pregnancy outcome, including fetal sex, were collected by routine follow-up telephone interview and combined with the delivery data. Results: There were 169 female and 164 male fetuses according to the reported fetal sex at delivery. Most of the CRL measurements (68.7%) were performed at an actual gestational age of 43–45 days. On linear regression analysis, male fetal sex was a significant (p = 0.011) predictor of larger CRL: CRL (mm) = –23.851 + GA (days) × 0.621 + 0.334 × Sex (F = 1, M = 2), R² = 0.512, p <0.001. A general linear model, adjusted for gestational age (40–50 days), revealed that mean CRL was significantly higher in male than in female fetuses (4.58?±?0.09?mm, [95% CI: 4.3–4.7] vs 4.24?±?0.09?mm [4.0–4.4]; p < 0.001). Conclusions: Male fetuses are larger than female fetuses in the early first trimester. Given that gonadal differentiation has not yet occurred, still unidentified nonhormonal factors are apparently responsible for this difference.     

Spine length measurement in the first trimester of pregnancy

OBJECTIVES: The aim of the study was to evaluate spine length as an indicator of skeletal growth in the first trimester of pregnancy and to provide a nomogram of spine length at the end of the first trimester of pregnancy. METHODS: The study was carried out on 420 single pregnancies, at gestational ages ranging from 11 to 14 weeks, using high-resolution transabdominal echography. Biparietal diameter and crown-rump length (CRL) were measured to date the pregnancy. Using the same scanning plane used to measure CRL, the whole spine length in antero-dorsal position can be visualized as a double hyperechoic line from 10 weeks of gestation onwards. Spine length was measured three times by one observer and the mean of the three measurements was considered as definitive. Forty fetuses had multiple measurements for interobserver and intraobserver error analysis. RESULTS: Linear relationship between spine length, and gestational age, biparietal diameter and CRL were demonstrated. Spine length (millimetres) as a function of gestational age (days) was expressed by the regression equation: spine length = 1.09 x (gestational age in days) -60.56, with a determination coefficient of R(2) = 0.744. Spine length ranged from 21.5 mm at 11 weeks to 41.9 mm at 14 weeks. CONCLUSION: The data obtained showed that spine length increased progressively from the end of the first trimester to the beginning of the second. A high correlation between spine length, gestational age, biparietal diameter, and CRL was observed. Spine length measurement could therefore be considered a good indicator of fetal growth.     

An appropriate way to predict fetal gender at first trimester: anogenital distance

Background: Using anogenital distance to determine fetal sex is a new method. There is only one study in the literature. We predict that it will pass through the literature as a new method that can be used in determining fetal sex especially in first trimester.

Introduction: Determination of fetal gender before birth has been a matter of curiosity for both the family and the clinician. In the presence of gender-linked genetic disease, it becomes an obligation instead of an interest. The aim of this study was to determine the fetal gender accurately at first trimester with anogenital distance (AGD) and to investigate the correlations of nuchal translucency (NT), fetal heart rate (FHR), and crown-rump length (CRL) with AGD.

Materials and methods: In this prospective cross-sectional study, AGD measurement was performed in 111 patients with singleton pregnancy from 11 to 13 weeks and 6 days (CRL 45–84?mm). Measurements of AGD ≥4.8?mm were identified for males, and AGD <4.8?mm for females.

Results: Genders were demonstrated accurately for males as 76.7% and for females as 97.1%. The mean value of AGD was 3.6?mm for females and 5.1?mm for males. There were no relations between fetal gender and FHR and also NT.

Conclusions: Gender can be detected with great accuracy in gestations between 11 to 13 weeks and 6 days by using AGD. CRL and gestational week (GW) were determined as nonsignificant predictors of fetal gender by AGD measurement. In order to obtain more accurate results with AGD, consideration of further studies with larger series in different races is recommended.     

First-trimester examination of fetal nasal bone in the Chinese population

OBJECTIVES: Absence of the nasal bone in fetuses with trisomy 21 is a potential ultrasound marker for Down syndrome from the first trimester onwards. Racial differences in fetal nasal bone length have been reported. There was no reference range for the first-trimester fetal nasal bone length (NBL) in the Chinese population. METHODS: From January 2002 to February 2005, we investigated the reference range of NBL in 2169 singleton fetuses whose parents were Chinese with normal pregnancy outcome. Ultrasound measurements of NBL were performed on a midsagittal plane at 12-14 weeks' gestation. RESULTS: The nasal bone length measurement showed a significant increase with gestational age (GA) (p < 0.05). A linear relationship between nasal bone length and gestational age (NBL = -3.3462 x GA + 0.627, R(2) = 0.30, p < 0.001) as well as a linear relationship between nasal bone length and crown-rump length (CRL) (NBL = 0.3741 x CRL + 0.284, R(2) = 0.30, P < 0.001) was established. CONCLUSION: The measurement of nasal bone length was feasible in the first trimester. The reference range of NBL in normal Chinese fetuses in the first-trimester of pregnancy was established. This formed a basis for further study on the use of fetal nasal bone measurement in the screening for aneuploidy in the Chinese population.     

Is there a correlation between birth weights and first-trimester crown-rump length growth velocity?

Objective: To test the hypothesis that small- or large-for-gestational-age (SGA or LGA) newborns have anomalous crown-rump length (CRL) growth rates in the first trimester. Methods: Prospective observational study. Women in the first trimester presenting to the Early Pregnancy Unit, between November 2006 and December 2010, underwent transvaginal scan. Women with viable singleton pregnancies in the first trimester who had at least two CRL measurements > 5 mm, recorded at least 2 weeks apart, and also had birth weight data available were included in the final analysis. Birth weight percentiles were calculated and adjusted for gestational age and gender. SGA was equivalent to < 10th centile and LGA was equivalent to > 90th centile. Correlation analysis was performed between birthweight percentiles and first-trimester CRL growth-rate coefficients. In addition, we estimated early fetal growth rates (EFGR) by calculating the Δ CRL/Δ time (mm/day) to see if these differed according to the birth-weight percentiles. Results: A total of 107 women had complete data. The mean maternal characteristics were age 27.5 ± 6 years, weight 87 ± 29 kg and height 163 ± 8 cm. The mean birth weight and gestational age at delivery were 3405 g (SD = 597) and 269 days (SD = 13), respectively. The proportions of SGA and LGA were 7.5% and 18.7%, respectively. There were no significant correlations between birth-weight percentiles and any of the CRL growth rates. There were also no significant differences in the mean CRL velocities when comparing the SGA and LGA newborns birth weights. EFGR for SGA and LGA newborns were 1.34 mm/day (SD = 0.17) and 1.32 mm/day (SD = 0.24), respectively (p > 0.05). Conclusions: Newborns who are found to be SGA or LGA at delivery do not appear to have anomalous CRL growth patterns in the first trimester. The EFGR also did not correlate with birth-weight percentiles.     

Reference range for the fetal intracranial translucency measurement between 11 and 14 + 2 weeks of gestation in a Brazilian population

Objective: To establish a reference range for the fetal intracranial translucency (IT) measurement between 11 and 14?+?2 weeks in a Brazilian population.

Methods: A retrospective cross-sectional study was performed with 199 low-risk singleton pregnancies during the first trimester ultrasound exam. The IT (fourth ventricle width) measurement was performed in a mid-sagittal view of fetal profile defined by two echogenic borders – the dorsal part of the brain stem anteriorly and the choroid plexus of the fourth ventricle posteriorly. Polynomial regression was used to obtain the best fit using fetal IT measurements and crown-rump length (CRL). Percentiles 5th, 50th and 95th were determined for each gestational age.

Results: The mean of fetal IT ranged from 1.6 mm at CRL 45 to 2.0 mm at CRL 84 mm. A best fit curve was a first-degree polynomial regression: IT measurement?=?1.001?+?0.0124?×?CRL (R²=0.09).

Conclusion: Reference range for the fetal IT measurement between 11 and 14?+?2 weeks of gestation in a Brazilian population was established.     

Evolution of the amniotic sac and extracelomic space as seen by early ultrasound examination

OBJECTIVE: Amniotic sac and extracelomic space changes occurring from 5 to 14 weeks of pregnancy were observed with transvaginal ultrasound to gain new insights into their normal relationships during this time period. STUDY DESIGN: Ninety-seven women from 5 to 15 weeks' gestation were enrolled in the study. Gestational age was determined by measuring embryonic crown-rump length. The embryo, amniotic sac, and gestational sac areas were measured using the best-fitted computer-generated elliptical view. The embryonic heart rate was measured using the M-mode function of the ultrasound equipment. Associations were determined using the least-squares method and Pearson's correlation coefficient. RESULTS: Mean (range) gestational age calculated from CRL was 9.6 (5.3-14.6) weeks, embryonic heart rate 153 (100-188) beats per minute, embryonic surface 699.6 (5-2,199) mm(2), amniotic sac surface 1,383 (5-5,335) mm(2) and gestational sac surface was 1,517 (110-5,335) mm(2). Significant correlations between gestational sac surface, amniotic sac surface, embryonic surface, heart rate and gestational age were noted (p < 0.01). Changes in the amniotic sac surface correlated with embryonic surface but not with heart rate even when multiple regression analysis was attempted. CONCLUSION: These data describe the normal relationships between the embryonic, amniotic sac, extracelomic space, and gestational sac surface, suggesting that increases in embryonic surface area is a determining factor for early expansion of the amniotic sac at these gestational ages.     

Umbilical cord diameter at 11-14 weeks of gestation: relationship to nuchal translucency, ductus venous blood flow and chromosomal defects

OBJECTIVE: To compare the umbilical cord diameter (UCD) in euploid and aneuploid fetuses at 11-14 weeks of gestation. METHODS: In 299 fetuses at 11-14 weeks of gestation the UCD, the nuchal translucency and the a-wave of the ductus venosus were measured. Reference ranges for the UCD according to the gestational age and to the crown-rump-length (CRL) were obtained by measuring the UCD by outer-to-outer border of 244 singleton pregnancies with normal karyotype. The fetal karyotype was established by chorionic villus sampling, amniocentesis or in case of suspected chromosomal abnormalities in the newborn. Linear regression was used to determine the significance of the association between the UCD and CRL or gestational age. RESULTS: Two hundred and ninety-nine fetuses were examined. The median fetal CRL was 64.5 mm (range 45-84) and the median gestational age was 13 (range 11-14) weeks. In the chromosomally normal group the UCD significantly increased with the CRL (r=0.620; p<0.001) and the gestational age (r=0.555; p<0.001). The regression equation for the mean UCD (y) according to the gestational days (x) was: y=-0.604+0.051*x. The regression equation for the mean UCD (y) according to the CRL (x) was: y=1.962+0.029*x. There were no significant differences in the mean UCD in fetuses without and with chromosomal abnormalities. The proportion of fetuses with an UCD above the 95th centile for CRL was higher in aneuploid compared to euploid fetuses (5/14 vs. 13/285, p<0.005). In 5/14 (35.7%) fetuses with chromosomal defects the NT and the UCD were above the 95th centile, whereas none of the fetuses with normal karyotype showed this combination. The proportion of fetuses with increased UCD and abnormal DV blood flow was increased in the cases with chromosomal abnormalities (33.3 vs. 1.8%, p<0.005). CONCLUSION: Umbilical cord diameter at 11-14 weeks increases with fetal CRL. Fetuses with chromosomal abnormalities are more likely to have an UCD above the 95th centile. Therefore, sonographic evaluation of the umbilical cord during first trimester ultrasound might be of additional value in the assessment of fetuses at risk for aneuploidies.     

First trimester ultrasound estimation of gestational age in pregnancies conceived after in vitro fertilization

Objective

To evaluate BPD as an alternative to CRL for the estimation of gestation age in late first trimester pregnancies (between 9th and 13th gestational weeks), and to construct a first trimester reference chart of fetal BPD growth.

Study design

A prospective study that compared the gestational age estimated by BPD and CRL with the IVF gestational age in 167 first trimester pregnancies (127 singletons, 40 twins).

Results

Both BPD and CRL correlated well with the IVF gestational age (GA) from 9th to 13th gestation weeks. When comparing the difference of the GA (in days) estimated from the two respective ultrasound parameters versus the GA based on IVF (oocyte retrieval day +14 days), BPD estimations had a significantly lower mean difference than CRL (0.013 vs. 0.746; p < 0.01), as well as a lower standard deviation (2.414 vs. 3.008; p < 0.05). In addition, the 95% limits of agreement between the BPD estimated GA and IVF GA were also smaller than CRL estimated GA versus IVF GA (−4.719 to 4.745 vs. −5.149 to 6.641).

Conclusion

Biparietal diameter shares similar accuracy with crown rump length in late first trimester ultrasound estimation, with additional advantages of lower random measurement errors.     

Doppler study of the embryonic heart in normal pregnant women.

OBJECTIVE: To describe normal fetal cardiac and hemodynamic development in normal early first trimester pregnancies. MATERIALS AND METHODS: Eighty-eight women with singleton, uncomplicated pregnancies were prospectively studied with transvaginal ultrasound, pulsed and color Doppler. Heart diameter, heart rate, and inflow and outflow waveforms with valve signals were documented. The proportion of the cardiac cycle of isovolumetric relaxation time (IRT%) and isovolumetric contraction time (ICT%) as well as Tei index were calculated. RESULTS: Ninety-one percent of studies were successful. Heart diameter and the fetal heart rate showed a positive correlation with increasing gestational age: R = 0.80 (p < 0.000001), R = 0.76 (p < 0.000001), respectively. Mean heart diameter at 6 weeks was 1.28 +/- 0.26 mm and mean fetal heart rate was 117 +/- 6 bpm compared to 3.88 +/- 0.54 mm and 171 +/- 6 bpm at 10 weeks. The inflow waveform was monophasic (atrial contraction) in all cases from 6 to 9 weeks. Eight pregnancies (9%) miscarried between 6 and 12 weeks of gestation and the heart exams were characterized by increased IRT% compared with the survivors. In survivors, IRT% decreased between 7 and 8 weeks, from 32.9 +/- 10.7% to 20.8 +/- 5.7% (p < 0.0001). ICT% decreased from 18.6 +/- 4.4% of the cardiac cycle at 8 weeks to 12.6 +/- 4.4% at 9 weeks (p < 0.0008) (after heart development period). CONCLUSIONS: Doppler examination of the fetal cardiac function is possible after 5 weeks of gestation. After 8 weeks of gestation, the fetal heart is morphologically mature but has not yet achieved effective myocardial compliance. The embryonic human heart is dependent on the atrial contraction for ventricular filling throughout the period of cardiac development. Non-survivors manifest myocardial dysfunction.     

Three-vessel view of the fetal heart: in utero development of the great vessels

OBJECTIVES: The purpose of our study is to provide reference values for the great vessels obtained from images of the three-vessel view of the fetal heart, with an emphasis on the size discrepancy of the great vessels. METHODS: From February 2003 to May 2003, the main pulmonary artery (MPA), ascending aorta (AA), and SVC were measured in well-dated, nonanomalous fetuses scanned at 14-38 weeks of gestation. RESULTS: The size of each great vessel had a significant positive relationship with advance in gestation (P < 0.001); MPA (mm) = -2.76 + 0.34 x GA, ascending aorta (AA) (mm) = -1.73 + 0.26 x GA - 1.18E - 05 x GA(3), and SVC (mm) = 0.33 + 0.01 x GA(2) - 4.12E - 05 x GA(3). The AA/MPA ratio was significantly decreased with advance in gestation, while the SVC/AA ratio was significantly increased; AA/MPA ratio = -1.24 - 0.03 x GA + 3.88E - 04 x GA(2); P < 0.001, SVC/AA ratio = 0.63 - 5.43E - 03 x GA + 1.96E - 04 x GA(2); P < 0.001. CONCLUSION: On the three-vessel view of the fetal heart, the interpretation of the size discrepancy of the great vessels needs to be adjusted according to fetal growth.     

Yolk sac size and embryonic heart rate as prognostic factors of first trimester pregnancy outcome

OBJECTIVES: To investigate embryonic heart rate (EHR) and yolk sac diameter (YSD) during the first trimester and their role as prognostic markers of first trimester pregnancy outcome. STUDY DESIGN: Prospective cohort study involving 219 women conducted in the 4th Academic Department of Obstetrics and Gynaecology, Aristotle University of Thessaloniki, Greece. Gestational age (GA) was determined ultrasonographically based on gestational sac diameter and crown-rump length. EHR and YSD were evaluated during the first 12 weeks and subsequently compared between the pregnancies that continued beyond the first trimester and those that resulted in spontaneous abortion. Receiver-operating characteristic (ROC) curves were used for the evaluation of the prognostic value of the combination of gestational age with embryonic heart rate and yolk sac diameter. RESULTS: The EHR and YSD were significantly correlated to advancing gestational age (p<0.001) in pregnancies continuing beyond 12 weeks. Pregnancies that resulted in spontaneous abortion exhibited a statistically significant lower EHR (p<0.001), smaller YSD (p=0.001) or absent yolk sac. ROC curve analysis demonstrated the predictive value of the combination of GA with EHR (area under the ROC curve: 0.971, p<0.001) and GA with YSD (area under the ROC curve: 0.858, p<0.001) for first trimester pregnancy outcome. CONCLUSIONS: EHR and YSD progressively increase in healthy pregnancies during the first trimester. Embryonic bradycardia and absence of yolk sac or even a smaller yolk sac diameter than expected for any gestational age are predictors of poor pregnancy outcome during the first 12 weeks.