How to assess the nutritional status of pregnant woman?

The referenced paper puts forward 23 cm not 21 cm as the threshold for intervention. MUAC and weight are gross anthropometry. Micronutrient status is key in pregnancy for both the mother and the growing foetus and supplements are usually given. Important micronutrient deficiencies should be detected and corrected by supplementation either directly or by proxy (e.g. low dietary diversity). It is common to assume deficiency and supplement all pregnant women either with 'medicinal' preparations (e.g. FeFol tablets) and/or with mass fortification of staples such a bread flour. I hope this helps.