At 11 Weeks Pregnant Can You Tell the Gender

Introduction

Development of a non-invasive method for accurate prenatal diagnosing of fetal condition has been a long-standing goal. A number of previous studies using ultrasound to detect fetal gender in the early second and third trimesters have been previously reported 1-3. A method of first trimester screening using ultrasound to measure the difference in angle of the genital tubercle to a horizontal line through the lumbosacral skin surface to determine fetal gender was reported with high accuracy rates 4. Another reported improving rates of gender identification between 11 and 14 weeks using a combination of transverse and sagittal views at the first trimester screening in 1999 5.

Prenatal screening of foetuses for Down's syndrome during the second trimester has become part of routine prenatal care in Taiwan since 1993. This screening method uses 2-marker maternal serum screening of AFP + β-hCG, and is undertaken in most Taiwanese maternity hospitals with the detection rate for Down's syndrome around 59.5–62.5% 6. First-trimester Down's syndrome screening was introduced into Taiwan in 2002, and continues to be practised. A number of Obstetricians in Taiwan have now been certified to perform such 11–13⁺⁶ weeks scanning by the Fetal Medicine Foundation (FMF). The first trimester combined test includes ultrasound scanning and nuchal translucency amongst other tests. During this scan, the fetal genital tubercle can usually be identified, and in Taiwan most expectant woman undergoing such testing request information regarding fetal gender.

The aim of this study was to determine the accuracy rate of fetal gender assessment by ultrasound at 11–13⁺⁶ weeks gestation, a test that can be combined with screening for abnormalities during the first trimester 7, 8.

Material and methods

A prospective observational study was performed upon 496 mothers featuring singleton pregnancies during their first trimester ultrasound screening. These patients were attending the fetal maternal unit for an assessment of risk of fetal chromosomal abnormalities using maternal age, fetal nuchal translucency, and maternal biochemistry of free-hCG and pregnant associated plasma protein-A. Testing was undertaken using the FMF OSCAR (One-Stop Clinic for Assessment Risk) technique. The attending obstetrician was a certified sonographer for first-trimester screening registered with the FMF of England. Ultrasound examination was performed by means of transabdominal scanning (5.0 MHz GE Voluson 730 Pro, Milwaukee, US) and was performed between 11 and 13⁺⁶ weeks of gestation. The total scanning time was no more than 25 min, and included measurement of nuchal translucency, present or absent nasal-bone, and assessment of certain features of fetal anatomy. Gestational age was calculated from crown-rump length and adjusted with menstrual or ovulation dating. Both transverse and midsagittal plane sections were undertaken with the fetus in a horizontal to the probe and supine position for screening of the fetal genital tubercle, in order to identify the gender of the fetus. Under sonography, the male genitalia in the midsagittal planes revealed a rather prominent fetal genital tubercle, the mid-line echogenic line being observed at the base of the scrotum under the tip of the developing fetal penis (Figure 1), and in the transverse plane, the dome-shape of the scrotum was identified at the base with a rather prominent fetal-penile tip structure detectable (Figure 2). Fetal female genitalia were typically assessed in a midsagittal-plane view, and are characterised by the absence of any prominent genital tubercle (Figure 3), the transverse view was performed parallel to the fetal vulvae, to reveal the labia majora and minora (Figure 4). The subsequent definitive gender assessment at birth for this study was obtained from the karyotyping reports and/or the hospital birth records for the delivered neonates. The scanning gender-accuracy rate for total fetuses assessed and for the 2 genders, was calculated as the proportion (percentage) of correctly identified fetal genders with respect to the total number of cases where a determination of gender was made. In addition, the relative accuracy of gender determination for each of 3 gestational age groups at 11, 12 and 13 weeks was calculated in the same way. The accuracy rates for the different gestational ages were compared using Fisher's exact test. Statistical analysis was performed using the SAS software for Windows, version 9.0. A p value <0.05 was considered to represent statistically significant difference between tested data sets.

Male, 12 weeks gestational age, mid-sagittal planes view of a section of the fetal genital tubercle by ultrasound.

Male, 12 weeks gestational age, transverse view of a section of the fetal genital tubercle by ultrasound.

Female, 12 weeks gestational age, mid-sagittal planes view of a section of the fetal genital tubercle by ultrasound.

Female, 12 weeks gestational age, transverse view of a section of the fetal genital tubercle by ultrasound.

Results

Over the course of this study, 496 patients requested fetal gender information at the time of routine first trimester screening for aneuploides. For those patients for whom it was possible to determine gender (441 out of 496), the fetal gender scan achieved an overall success rate of 91.8% in correctly identifying fetal gender.

It was noted, however, that accurate identification of fetal gender using ultrasonography improved significantly with increasing gestational age over the period from 11 to 13⁺⁶ weeks in utero (p<0.001, Table I). At 11 weeks' gestational age (crown-rump length 'CRL' between 45 and 57 mm) the accuracy of gender identification was only 71.9% of those cases where a determination was made, at 12 weeks (CRL 57–67 mm) the accuracy was 92%, and at 13 weeks (CRL 67–84 mm) the accuracy rose to 98.3%.

Table I. The identified accuracy rate of 11–13⁺⁶ weeks scans.

GA	CRL (mm)	Median GA (weeks)	Cases	Gender not identified	Correct identified number	Accuracy rate (%)	Total identified accuracy rate	Overall correct (% of total fetuses)	p-Value
11	45–56	11.71	96	39/96 (40.63%)	Male: 22/30; female: 19/27	73.30; 70.3	41/57 (71.93%)	41/96 (42.71)	*
12	57–67	12.50	224	12/224 (5.35%)	Male: 100/108; female: 95/104	92.6; 91.3	195/212 (91.98%)	195/224 (87.05%)	0.001
13	67–84	13.29	176	4/176 (2.27%)	Male: 87/88; female: 82/84	98.9; 97.6	169/172 (98.26%)	169/176 (96.02%)	<0.001†
Total			496	55/496 (11.09%)	Male: 209/226; female: 196/215	92.5; 91.2	405/441 (91.84%)	405/496 (81.65%)

• *Reference group.
• †Compared with GA12, the p-value was 0.004.

Further, the percentage of cases where no gender determination was possible fell with gestational age from 40.6% of foetuses at 11 weeks, to 5.4% at 12 weeks, to only 2.3% at 13 weeks.

Taking into account both the fetuses where no gender determination was possible and those where a determination was made, the overall correct fetal gender determination accuracy was 42.71%, 87.05%, and 96.02% for the 3 different gestational age groupings, respectively (Figure 5).

Effect of increasing gestational age upon ability to carry out gender determination and accuracy of determination.

The fetal gender accuracy rate for male fetuses was slightly greater than for female fetuses (92.5 versus 91.2%), but such difference did not prove to be statistically significant (p = 0.614).

Discussion

External fetal genitalia originate in the region of the primitive streak in the third week of development, subsequently migrating around the cloaca membrane to form a pair of slightly elevated folds, which then unite to form the genital tubercle. The genital tubercle then subdivides into the urethral folds anteriorly, and the anal folds posteriorly. At around the sixth week of development, another pair of elevations, the genital swellings become visible on each side of the urethral folds. For the male, these swellings subsequently form the scrotum, and for the female, the labia majora. Such development for males is caused by the influence of androgens secreted by the fetal testes, and is typically characterised by rapid elongation of the genital tubercle – the phallus. At about the twelfth gestational week, the 2 urethral folds close over the urethral plate, thus forming the penile urethra. The external genitalia of the female develops under the influence of the estrogens produced by the placenta, the genital tubercle elongating only slightly to form the clitoris, the urethral folds later developing into the labia minora, and the genital swellings enlarge greatly forming the labia majora 9.

The mid-sagittal view of the fetal genital area at 11–13⁺⁶ gestational weeks using ultrasound scanning typically reveals the presence of a prominent tip of the fetal genital tubercle for males, but the absence of such a feature for females (Figures 1 and 3). In the transverse plane, the genital swellings at around this time form a double line-shaped scrotum with a prominent tip of the penis for the male fetus (Figure 2) and, correspondingly, 3 or 4 parallel lines for the labia for the female fetus (Figure 4).

In 1999, Efrat and Whitlow produced papers on first trimester scanning for gender 4, 5. Whitlow used a combination of transverse and sagittal views, whereas Efrat adopted a midsagittal plane to measure the angle of the genital tubercle to a horizontal line through the lumbosacral skin surface. Results from both these studies, and also the results from our study revealed that fetal gender prediction identification accuracy at 11 weeks' gestational age was, respectively 78% (35/45), 70.3% (26/37), and 71.9% (41/57), where a gender determination was made, however, the 3 corresponding figures for correct gender identification of the fetuses, including those cases where no gender determination was made was, respectively, only 46% (34/76), 65% (26/40) and 42.7% (41/96). The results of the studies of Whitlow, Efrat and ourselves suggest that the success rate for correctly identifying fetal gender where a gender determination was made significantly increases with gestational age at 12 weeks and above, ranging from, respectively, 86% (123/143), 92.8% (77/83), and 92.0% (195/212) at 12 weeks to, respectively, 87% (123/142), 87.8% (43/49), and 98.3% (169/172) at 13 weeks. It would appear that there is a significant improvement in the probability of a correct identification of fetal gender after CRL exceeds 57 mm, i.e at around 12 weeks gestational age by means of ultrasound scanning.

It has often been reported that a number of different factors can affect the correct identification of fetal gender in utero during the first trimester. First, the relative skill of the operator: appropriate training for the sonographer as regards first trimester screening techniques will likely result in a greater level of accuracy in correctly identifying fetal gender. Second, the resolution of the specific transducer used for the ultrasound scan: the transvaginal transducer is superior to the transabdominal alternative, but, in our experience, most women feel much more comfortable with a transabdominal approach than with a transvaginal approach. Third, certain prevailing maternal conditions may impact upon correct fetal determination: e.g. bowel gas-induced shadowing of the fetus or maternal obesity. Fourth, fetus posture: fetal legs being crossed, umbilical cord between the fetus' legs, fetal hyperactivity, and an unfavourable fetal position may all impede accurate gender determination by ultrasound scanning 5.

In a number of western countries, fetal gender diagnosis is not the patient's main concern for routine scans 10. The clinical value of the determination of fetal gender by ultrasound scanning when deciding whether to perform prenatal invasive testing for pregnancies at risk of sex-linked genetic abnormalities is quite apparent because invasive testing would be necessary only for pregnancies featuring male fetuses. It is, thus, possible to avoid the inevitable small risk of miscarriage associated with invasive testing for those fetuses determined to be female 5.

In respect of the social implications of antenatal gender identification, practise has shown that the majority of Taiwanese women favour being informed of fetal gender during ultrasonography. For Chinese people, it has been our experience that most soon-to-be parents desire to know their fetus' gender as soon as possible despite the difficulties and risk of misidentification at an early stage. Chorionic villus sampling for fetal karyotyping was introduced into Taiwan in 1985, and has been typically performed from the seventh week of gestation as a result of patient requests to be made aware of fetal karyotype and gender as early as possible. However, following the report by Hsieh et al. in 1995 that, in Taiwan, the procedure was associated with an increased risk of miscarriage and fetal limb-reduction defects 11, most women in Taiwan have been unwilling to undergo chorionic villus sampling in the first trimester.

Other methods of identifying fetal gender, such as the detection of fetal cells or fetal DNA in maternal blood, have been previously used for prenatal gender diagnosis 12, 13, and cell-free fetal DNA has also been utilised for fetal gender determination 14. The long-term presence of circulating fetal cells and cell-free fetal DNA in maternal blood following delivery or even subsequent to abortions either featuring embryo formation or not, however, has been previously reported 15, 16. Therefore, the use of fetal DNA in maternal blood for fetal gender determination still reveals some limitations as regards accuracy of prediction.

The non-invasive first trimester ultrasound scan described above not only improves the aneuploidy-screening detection rate, but can also offer fetal-gender information for pregnant women. This study has demonstrated that the 11–13⁺⁶ weeks' ultrasound scan achieved an accuracy rate of 91.8% in correctly determining fetal gender in utero for those cases where a determination of gender was made. This would appear to be a rather noteworthy ultrasound technique-associated performance for fetal gender identification within the first trimester of pregnancy. However, the relative gestational age of the fetus did introduce a significant impact upon the relative accuracy of such fetal gender determination, with accuracy of 94.85% for those fetuses at 12 weeks gestational age and over, but only 71.9% at 11 weeks. Any attempted diagnosis of gender by this technique at less than 12 weeks should be accompanied by a warning of the significant risk of misidentification.

References

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At 11 Weeks Pregnant Can You Tell the Gender

Source: https://obgyn.onlinelibrary.wiley.com/doi/10.1080/00016340701571905

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