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Discover your baby’s gender from the start !

The nub theory

1 - What is the nub theory ?

According to the scientific nub theory, it is possible to predict your baby’s gender as early as 12 weeks pregnant based on your first trimester ultrasound. The nub is your child's indeterminate sexual organ, which will transform into a penis or a clitoris during the second trimester of pregnancy.
Genital nub example on a fetal ultrasound
Introduced in 1999, the nub theory consists of analyzing the angle between your child's nub and its spine. If the nub forms a 30 degree angle or more in relation to the spine, it is likely a male fetus. If it is pointing straight out, under 30 degrees, or down, it is likely a female fetus.
The nub theory applied to a girl nub
The nub theory applied to a boy nub
This method has an average reliability of more than 90% for ultrasounds performed i) after 12 weeks of pregnancy (14 weeks after the last menstruations) ; ii) for fetuses whose cranio-caudal length is greater than 60mm, and iii) when the ultrasound image reveals the entire nub. However, the method is significantly less reliable if the ultrasound is performed before 12 weeks of pregnancy or if the nub is not clearly visible. An expertise in scan reading is necessary to deduce your baby’s gender from your scan because pictures can be misleading as you can see below !

2- The limits of the nub theory

As explained, the nub theory is reliable only if we can see the baby from the side and if the nub is fully visible. However, babies are not robots: they move a lot in utero and very often the nub happens to be totally or partially hidden. The analysis can then be very difficult or even misleading, as shown by the cases presented below.
Partial view of a boy's genital nub
Partial view of a girl's genital nub
Sometimes the analysis is difficult to the point that one baby shown in two positions may present a very different looking nub: on the first picture below the expert’s eye sees a boy whereas on the second picture it looks like a girl ! Same baby, two nubs ! Likewise, two babies, girl and boy, can have a nub of the same appearance ! See the examples below which are great classics of cases that are very difficult to identify.
Limits of the nub thoery: different-looking nubs for the same baby girl
Limits of the nub thoery: same-looking nubs but different genders
What’s more, sometimes the nub cannot be seen at all or its appearance is of no particular gender, as shown in the photos below.
Limits of the nub thoery: unclear examples of baby nubs
Finally, before 12 weeks of pregnancy and especially for fetuses smaller than 60mm, a flat nub indicating a girl is not reliable as the nub can rise and finally show a boy!

3- BABYGRAM's solution to identify your baby’s gender

All in all, the scientific nub theory is reliable under certain conditions but those conditions are not always met to predict with sufficient confidence the gender of the baby during the first trimester. Indeed, if the ultrasound is performed before 12 weeks of pregnancy (14 weeks of amenorrhea), if the baby does not show its profile with a clear nub or if the nub does not have a very determined appearance, even the eye of an expert will not be enough to identify with enough confidence the gender of the baby. For these reasons, BABYGRAM has developed a unique image recognition software based on the latest artificial intelligence techniques to give you a prediction regardless of the ultrasound image of the baby and the visibility of the genital nub ! Our technology is based on a database of more than 10,000 ultrasound images for which we know the gender and term of pregnancy: the algorithm compares your image to the images of our database to identify the gender hidden behind your image ! Finally, to make a prediction, we follow a three-step methodology : i) first of all, your ultrasound is analyzed by our intelligent image recognition software which gives a first result by comparing your ultrasound to thousands of others ; ii) then your ultrasound is also analyzed by a gender expert based on the nub theory when conditions are met for this theory to be reliable iii) finally, the two results are then combined, a gender and a crossed probability of reliability is deduced from these analyzes.
When you order an analysis from BABYGRAM you are sure to get a reliable result or a full refund ! Indeed, we reveal to you the probable gender of your baby only if the reliability of the analysis is greater than 70% which is almost always the case because our 3-step method has a 85% reliability on average and in some cases we can even provide a prediction with a 99% reliability ! If no gender can be deduced from your pictures with enough certainty, we fully refund the cost of the analysis.
Find out more about our method HERE or order your ultrasound analysis now on THIS PAGE.

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At BABYGRAM, we work in a scientific and documented way, here is the state of scientific research on the genital bud for the most curious:

1. Callen PW. Ultrasonography in Obstetrics and Gynecology. 5th ed. Philadelphia: Saunders Elsevier; 2008. [Google Scholar]
2. Eze CU, Ezugwu FO, Agbo JA. Sonographic determination of fetal gender in the second and third trimesters in a private hospital in Enugu, Southeast Nigeria. Radiography 2010; 16: 292–96. [Google Scholar]
3. Whitlow BJ, Lazanakis MS, Economides DL. The sonographic identification of fetal gender from 11 to 14 weeks of gestation. Ultrasound in Obstetrics and Gynaecology 1999; 13: 301–4. [PubMed] [Google Scholar]
4. Efrat Z, Perri T, Ramati E, Tugendreich D, Meizner I. Fetal gender assignment by first trimester ultrasound. Ultrasound Obstet Gynaecol 2006; 27: 619–21. [PubMed] [Google Scholar]
5. Youssef A, Arcangeli T, Radico D, Contro E, Guasina F, Bellissi F, Maroni E, Morselli‐Labate AM, Farina A, Pilu G, Pelusi G, Ghi T. Accuracy of fetal gender determinationin the first trimester using three‐dimensional ultrasound. Ultrasound Obstet Gynecol 2011; 37: 557–61. [PubMed] [Google Scholar]
6. Hsiao CH, Wang HC, Hsieh CF, Hsu JJ. Fetal gender screening by ultrasound at 11 to 13+6weeks. Acta Obstetrica et Gynecologica 2008; 87: 8–13. [PubMed] [Google Scholar]
7. Chelli D, Methni A, Dimassi K, Boudaya F, Sfar E, Zouaoui B, Chelli H, Chennoufi MB. Fetal sex assignment by first trimester ultrasound: a Tunisian experience. Prenatal Diagnosis 2009; 29: 1145–48. [PubMed] [Google Scholar]
8. Mazza V, Di Monte I, Pati M, Contu G, Ottolenghi C, Forabosco A, Volpe A. Sonographic biometrical range of external genitalia differentiation in the first trimester of pregnancy: Analysis of 2593 cases. Prenat Diag 2004; 24: 677–84. [PubMed] [Google Scholar]
9. Podobnik MP, Podgajski M, Podobnik P, Brlecic I. First‐trimester determination of fetal gender by ultrasound. Ultrasound in Obstetrics and Gynecology 2003; 22: (suppl. 1); 84. [Google Scholar]
10. Mazza V, Falcinelli C, Paganelli S, Contu G, Mantuano SM, Battafarano SD, Forabosco A, Volpe A. Sonographic early gender assignment: a longitudinal study in pregnancies after invitro fertilisation. Ultrasound Obstet Gynaecol 2001; 17: 513–16. [PubMed] [Google Scholar]
11. Efrat Z, Akinfenwa OO, Nicolaides KH. First‐trimester determination of fetal gender by ultrasound. Ultrasound Obstet Gynaecol 1999; 13: 305–7. [PubMed] [Google Scholar]
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