A healthy pregnancy hemoglobin by 28 weeks normally reduces, with good blood volume expansion, to between about 11.0 and 12.8 (preferably not lower than about 10.5).
Lower than around 10.0 may be associated with fatigue, postpartum hemorrhage and other resulting conditions.
Higher than about 13.0 rising in later 3rd trimester, can indicate a contracting blood volume and may be an earlier indication associated with preeclampsia (toxemia).
(These ranges may be slightly higher for those who live up in the mountains.)
Having balanced daily nutrition of easily-absorbed iron-rich foods and about 90 grams daily of good protein foods (add more for twins) by 3rd trimester along with sufficient high-quality calories, is part of a healthy pregnancy, birth and newborn. Also very important — make it tasty.