Christian Aid are talking in far more general terms than medical issues in particular. Their apparent aim, though the waters are being thoroughly muddied, is to ask about the structural issues that affect WOMEN AND GIRLS on the basis of their SEX.
I applaud their aims, so I completed their survey, though commented about the gender/sex confusion on the FB link where I saw the survey.
Also commented within the survey where there was space.
And I selected the "other" option when given a list of genders to select from at the start of the survey.
I always tick "other" in similar situations, as I don't consider myself as having a gender. I'm a woman.
If we all did that, every time (I did it on the census too), I think it would be noted eventually.