Evidence That Really Matters

Sex—can you get it right?

BMJ 2002; 325 doi: https://doi.org/10.1136/bmj.325.7378.1446 (Published 21 December 2002) Cite this as: BMJ 2002;325:1446
  1. Jonathan E C Round, specialist registrar (jround{at}doctors.org.uk),
  2. Maesha Deheragoda, senior house officer
  1. Neonatal Intensive Care Unit, Guy's Hospital, London SE1 9RT
  1. Correspondence to: J E C Round

    Neonatologists often get the sex of their patients wrong. A review of the literature on identifying sex from facial appearances yielded one small study from Nashville, Tennessee.1 The low level of success (60%) found by the study suggests either that sex specific characteristics are inconsistent or that adults do not notice them. We wondered whether newborn babies' sex could be determined from their facial characteristics; whether particular facial characteristics, such as delicacy, were associated with the attribution of sex; and whether adults' degree of contact with neonates increased accuracy. The study was approved by the research and ethics committee at Guy's Hospital.

    Participants, methods, and results

    Thirty babies born at term were enrolled consecutively on the postnatal ward at Guy's Hospital. Unwell babies and babies who were not fully Afro-Caribbean or white were excluded. The babies were wrapped, with the face left exposed, and photographed. Eight photographs of Afro-Caribbean babies and 16 of white babies were randomly selected from the 30, with equal numbers of boys and girls in each sample. The photographs were shown to 53 adults, who were also asked to complete a questionnaire on the babies' characteristics. Of these observers, 21 were men. Twelve were paediatricians, 14 were paediatric or neonatal nurses, and 27 were not health workers. Forty were parents. The observers guessed the sex of each baby from the photographs and then rated, on scales from 1 to 3, the babies' hairiness, delicateness of features, coarseness of features, and chubbiness.

    We used Student's t test to compare the results for each observer and baby. This showed that the observations were independent. Among all the adults, the mean number of babies whose sex was correctly identified was 13.3 (95% confidence interval 12.7 to 13.9), or 55% of babies, a significantly better proportion than expected by chance (P<0.001). The nurses correctly identified 14.3 (13.3 to 15.3) babies, or 59%, and thus were more successful than the paediatricians (12.1 (10.9 to 13.3); P<0.02). Non-health workers identified 13.3 babies correctly (12.6 to 14.0; not significant). There was no significant difference between the scores of women (13.6 (12.9 to 14.3)) and men (12.8 (11.9 to 13.7)) or between those of parents (13.4 (12.8 to 14.0)) and non-parents (12.9 (11.6 to 14.2)).

    Overall, observers thought that 58% of the babies were boys. Babies thought to be girls were rated hairier (figure). Observers' identification of sex did not correlate with their ratings of chubbiness or coarseness or delicateness of features or with the babies' gestation or birth weight. There was no relation between the babies' actual sex and any of the variables, though the results do suggest a trend towards girls being hairier than boys (hairiness rating 2.1 (1.8 to 2.4) v 1.9 (1.6 to 2.2)).


    Relation between proportion of 53 observers who identified baby in photo (n=24) as female, and hairiness rating of baby

    Afro-Caribbean babies were more often identified by the observers as girls and were rated as hairier than white babies, but differences were not significant. Only 15% of observers correctly guessed the sex of one white girl—this baby had the sixth lowest hairiness rating but was similar in all other characteristics to the other babies. More than four fifths of observers (83%) correctly guessed the sex of one white boy, the least hairy baby. He weighed much less than the mean and had a higher than average delicateness rating.


    The proportion of babies whose sex was correctly identified by the observers, on the basis of facial characteristics, was higher than that expected by chance. Distinguishing features that are present in newborns' faces allow adults to identify the babies' sex, but these cues are subtle and easily missed or inconsistent. Accuracy increases with exposure to newborns, as seen with the nurses in our study. Perhaps people who have more contact with babies are more able to see differences between babies. Preconceptions relating to hairiness may influence people's assumption of neonates' sex. Our sample size did not allow us to determine whether girls really are hairier than boys. It could be concluded that the major clue to a baby's sex is its hairiness; perhaps experienced observers subconsciously take note of hairiness and so are better at identifying sex. Overall, the observers in our study could identify the babies' sex from their faces—but why couldn't the paediatricians get it right?


    We thank the participants and staff at Guy's Hospital, especially Grenville Fox, Judy Rissik, and Richard Morris for support, inspiration, and advice.

    Contributors: JECR managed the study. Both authors collected and analysed the data and wrote the paper.


    • Funding None.

    • Competing interests None declared.


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