getBiologicalSex().md

Get the biological sex (gender). If the BiologicalSex read permission is missing or the user has denied it then the value will be unknown. The possible values are:

Value	HKBiologicalSex
unknown	HKBiologicalSexNotSet
male	HKBiologicalSexMale
female	HKBiologicalSexFemale
other	HKBiologicalSexOther

AppleHealthKit.getBiologicalSex(null, (err: Object, results: Object) => {
    if (this._handleHealthkitError(err, 'getBiologicalSex')) {
      return;
    }
    console.log(results)
});

{
   value: 'female',
}