Hemoglobin and Pregnancy
Hemoglobin is the oxygen carrying component of red blood cells, and is a screening marker for problems, not a diagnostic tool. Your fingertip is pricked with a small lancet, a drop of blood taken and tested. All in all, it only takes a few minutes to know your hemoglobin status. It’s a valuable tool in any practice, but it isn’t the end all diagnostic for iron levels. Hemoglobin can also be checked in a blood draw lab test, included in the CBC, and those results can be more accurate than the quick finger prick.
During pregnancy, hemoglobin is a touchy subject. In some cases, it is the only tool used to monitor iron levels and risk of anemia, but as stated above, hemoglobin is simply a screening marker. One of the biggest changes to hemoglobin is a physiological decrease response to an increase in blood volume, which is normal in a healthy, well-nourished pregnancy. Falling hemoglobin levels and a well-growing baby coincide with each other, and they are an important factor in monitoring a healthy pregnancy.
Hemoglobin levels in pregnancy can be tested at any time, but generally are done at the first prenatal visit and then at the beginning of the third trimester, around 28 weeks. The first visit is a baseline value, normally done before 8 weeks of pregnancy, and shows what your hemoglobin is before your blood volume has expanded. Sometimes this first test can point to a lower than optimal beginning hemoglobin which can be corrected in most cases with diet and nutrition changes and supplements when needed.
In general, hemoglobin in the first trimester of pregnancy should be around 12-13g/dL, giving you enough room for a 2g fall by 28 weeks. At 28 weeks, Anne Frye says that the lower limit of normal is 10g/dL, but even then, hemoglobin is again just a screening marker.
During pregnancy, your hemoglobin will drop gradually as your blood volume increases, and you should see a 2g/dL drop by 28 weeks, IF you live in an area that is less than 5000 feet above sea level. Altitude matters in cases of hemoglobin levels! If you live between 5000 and 8000 feet, you may only see a drop of 1-1.5g/dL. If you are above 8000 feet, you may not see a drop at all. Your body has to compensate for the lower levels of oxygen in your area, and your hemoglobin will show that.
If your hemoglobin didn’t drop at all by 28 weeks and you live below 5000 feet, it’s a sign that your blood volume hasn’t expanded well, and can lead to problems with your baby’s growth and issues with blood loss and its effects after the birth.
Along this line, anemia is a marker of a problem, not a diagnosis, and hemoglobin alone is misleading as pregnancy advances. If your hemoglobin is low, or lower than where your provider would like, more tests are needed before any diagnosis is made.
LOW HEMOGLOBIN IS JUST A SCREENING MARKER.
If it’s low, the additional tests that may be run are serum iron, total iron binding capacity, transferrin saturation, and serum ferritin. In most cases, the serum ferritin may be the only additional test that is needed.
Ferritin is the major iron-storage protein, and the serum ferritin test is checking for available iron stores in bone marrow. This is more of an indicator of iron deficiency than hemoglobin. In normal menstruating women, the value should be 25-200ng/mL.
If your hemoglobin is low (again, below 10g/dL), serum ferritin should be the next test ordered to make sure your levels are within normal range. For most pregnant people, levels of ferritin below 30ng/mL confirms iron deficiency anemia. If this is run at the beginning of pregnancy, a hemoglobin level less than 11g/dL and serum ferritin level of less than 25ng/mL is the biggest sign that changes are necessary to increase both levels. In some cases, that can also point to other issues with iron and red blood cells, but that is more rare than simply being iron deficient.
Remember: Normal hemoglobin levels after 28 weeks of pregnancy are above 10g/dL, but it is simply a screening tool. More testing is needed, specifically a serum ferritin, which should be between 30-200ng/mL, showing that you are not anemic, your risk of bleeding during birth is not increased, and your hemoglobin level is not an issue.
RESOURCES:
Understanding Diagnostic Tests in Childbearing Year by Anne Frye, pages 258-298, Normal Hemodilution, Anemia, and Red Cell Disorders in Pregnancy.
Holistic Midwifery Vol 1 by Anne Frye, pages 195, 580, 828-832, 1007-1008.
https://www.uptodate.com/contents/maternal-adaptations-to-pregnancy-hematologic-changes/abstract/5" target="_blank">Hematological Changes
https://www.ncbi.nlm.nih.gov/pubmed/19935037" target="_blank">Pregnancy and Laboratory Studies