Editor who approved publication: To determine the probability of correctly diagnosing fetal sex during the first trimester by ultrasound according to crown—rump length CRL and previous ultrasound experience.
A cohort study was performed from March to April The 2, first trimester pregnancy ultrasounds were examined.
Eight sonographers, according to previous ultrasound experience, were divided into two groups: For fetal sex estimation, the method of a sagittal section and the relation between the angle formed by the genital tubercle and spinal column was used. In 1, cases, fetal sex was diagnosed, with a success rate of The rate of success in male fetuses was significantly higher than in female fetuses In the senior sonographers group, the rate of overall success was Both CRL and fetal sex influence the rate of success; however, the experience of a sonographer has not proven to be an influential factor.
These results could be explained because the technique for diagnosing sex during the first trimester is very simple to learn.
At the beginning of the 5th week of pregnancy, a pair of swelling or cloacal folds form on both sides of the cloacal membrane, which joins in front of the membrane to form a thickening in the midline called the genital tubercle primordium penis or clitoris.
During the 9th week, they begin to differentiate, but the similar appearance of the external genitalia in embryos of both sexes may persist until the 9th week of development. Various methodologies have been reported to describe the fetal sex during the first trimester. In female fetuses, however, only two echogenic lines corresponding to the clitoris are identified. This technique has an accuracy of This method achieved an overall accuracy of Patients and methods A cohort study was performed with prospective follow-up of pregnant women attending the Prenatal Diagnosis Unit to perform an ultrasound study for obtaining combined first trimester screening during the period from March to April Oral informed consent was obtained from all patients.
Each pregnant woman was evaluated by one of eight sonographers who applied the correct algorithm to determine fetal sex. Inclusion criteria for patients were singleton pregnancy, a viable fetus without congenital anomalies, and CRL between 45 and 80 mm.
The exclusion criteria included patient refusal to continue the study, attended birth at another hospital and the diagnosis of fetal death, congenital anomaly, or inability to confirm fetal sex at birth. An initial assessment of the type of gestation, vitality, embryo morphology, and possibility to describe the fetal sex without telling the patient was performed. The assessment of fetal sex and CRL by ultrasound was performed according to the following guidelines: It is very important that the fetus is visualized in the neutral position, otherwise the angle may be overestimated or underestimated and the result may be misleading.
Figure 1 Male sex: Figure 2 Female sex: Inset shows full ultrasound scan. The outcome variable was described by ultrasound fetal sex.
A second outcome variable is secondary to obtaining rightness or wrongness true or false as matching or not sex described by first trimester ultrasound and sex at birth. The collection of variables was performed in two stages, recruitment coinciding with the ultrasound examination during the first trimester and post-delivery. Perinatal data were obtained for eight obstetricians blinded to the results of the variables display during the first trimester ultrasound. Records of newborns were created to collect perinatal data.
All data were collected in coded form and were entered into a database designed for this purpose. The statistical package used was SPSS To describe the characteristics of the pregnant women included in the study, predictor and outcome variables were evaluated descriptively.
Qualitative variables are detailed as a percentage. To check the fit to normal of each of the variables analyzed in this study, the Kolmogorov—Smirnov test was used. Chi-square and logistic regression according to variable types using bivariate and multivariate analysis were used. Results Between March and April , 2, first trimester pregnancy ultrasounds were examined.
A total of patients who aborted after the first trimester ultrasound or the patients who gave birth at another hospital were not included in the sample The average age of pregnant women was Mean days to delivery adjusted CRL was — days. In cases The outcome was confirmed at delivery without encountering any case of ambiguous genitalia. In 1, cases Analyzing the rate of success in the diagnosis of fetal sex, it was found that fetuses were significantly higher in males than in females Figure 3 Success rate according to fetal sex algorithm.
Analyzing the association between the rate of success in the diagnosis of fetal sex and the CRL, it was noted that in male fetuses compared with female fetuses, the rate of success is higher for short CRL.
Figure 4 Global success rate according to CRL and divided by sex. The average rate of success in the fetal sex diagnosis for all cases was The total number of cases was 2. However, in the senior sonographers group, the rate of overall success was Finally, Table 1 describes the results of univariate and multivariate analysis of independent variables and its relation to the success rate in the diagnosis of fetal sex.
Consistently, both the CRL with an odds ratio of 1. Table 1 Results of univariate and multivariate analysis of independent variables and its relation to the success rate in the diagnosis of fetal sex Abbreviations: Discussion Factors that have been analyzed are the experience of the sonographer and fetal CRL determining the accuracy of the estimation of fetal sex using the method of a sagittal section and the relation between the angle formed by the genital tubercle and spinal column.
Whitlow et al combined fetal sex identification in a sagittal and transverse plane with an accuracy that increases with increasing gestational age. This rate was significantly associated with the CRL, and it increases in male fetuses.
The rate of success was higher in male fetuses than in female ones, Adiego Burgos et al also had similar results with a success rate in male fetuses of Finally, in the multivariate analysis, these data are consistent and the experience of the sonographer does not influence the probability of success.
There have been no previous studies on whether learning technique or the experience of the sonographer influences the rate of success of fetal sex determination. Our results show with the largest sample studied to date that 1-week training is enough to make a correct diagnosis, thanks to the good visualization of equipment, the simplicity of viewing genital tubercles and usually the fetus being placed on the back. Of the three variables that have been analyzed, it was found that CRL and fetal sex do influence the rate of success; however, the experience of the sonographer has not been shown to be an influential factor.
Therefore, knowing the methodology, with a short learning curve and ultrasound equipment available today, we have a simple and practical tool to establish fetal sex during the first trimester with great reliability. Acknowledgment The authors are grateful for editorial assistance. Disclosure The authors report no conflicts of interest in this work.