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A high hemoglobin level in the first half of pregnancy is one of the few early warning signs of preeclampsia in the second half of pregnancy.

Even doctors can sometimes miss life-changing health events. Elizabeth's pregnancy at the age of 46 took her by surprise.

A doctor with a busy practice, Elizabeth had assumed she was approaching menopause and didn't have to worry about contraception. Even when she missed her period, she thought it was probably just a sign of pending change of life.

But when she developed abdominal swelling a few months later, she took the time to take a pregnancy test just to check the possibility off the list, she understood why she had been feeling nauseous in the morning and craving strange food combinations. She was in her eighth week. And when her routine blood work came back normal except for high hemoglobin, she took that as a sign she wasn't anemic.

(Elizabeth isn't, by the way, an OB-GYN.)

Elizabeth and her husband decided to embrace the birth of their first child and were busy making the changes in their lives to provide a happy home for their new son. Then in the seventh month, a near-tragedy struck, Elizabeth developed preeclampsia. With expert medical care, she survived, but her child had to be delivered eight weeks early. Their brilliant child has been challenged by autism, but thanks to years of intervention he is an active and happy and "different but gifted" pre-teen today.

How Do You Define Eclampsia and Preeclampsia?

Preeclampsia is a condition that can develop during the last four months of pregnancy that is characterized by high blood pressure (hypertension) and protein in the urine (proteinuria). (It may be easier to understand the term if you think of it as "pre-eclampsia.") If it is not properly recognized and managed, it can progress to eclampsia, which involves the development of seizures in a woman with preeclampsia. They usually occur in the sixth or seventh month of pregnancy, although they can occur in early pregnancy or even, in the mother, after giving birth.

High blood pressure during pregnancy is dangerous because it interferes with the ability of the fetus to obtain oxygen and nutrients. It can result in low birth weight or premature delivery. If blood pressure gets extremely high, as is often the case with preeclampsia, the kidneys may quit working. Protein may leak into the urine. There can be changes in the makeup of the blood, so there are fewer platelets, which results in increased bleeding (including bleeding during pregnancy). 

About 5 percent of women get preeclampsia during pregnancy. It can occur in any pregnancy, but it's most likely if:

  • It is the woman's first pregnancy.
  • The mother developed eclampsia or preeclampsia in a prior pregnancy.
  • The mother is African-American.
  • The mother is under 20 or over 40.
  • The mother is significantly overweight.
  • The mother is carrying twins.
  • A mother or sister has had preeclampsia or eclampsia. [1]

Preeclampsia isn't hard to diagnose once it occurs. But there are relatively few early warning signals that preeclampsia is about to occur. One of them, researchers at the Islamic Azad University in Iran have discovered, is high hemoglobin protein levels in the first trimester of pregnancy [2].

What's High Hemoglobin?

Hemoglobin is the iron-rich, oxygen carrying protein found in red blood cells. Every complete blood count routinely measures hemoglobin. Hemoglobin isn't the same thing as hematocrit, the ratio of the total volume of red blood cells to the total volume of the blood. Red blood cells don't always contain the same amount of hemoglobin, so you can't rely on hematocrit as a measure of hemoglobin [3].

"High" is what your doctor's lab says is high. Different labs arrive at hemoglobin numbers through slightly different methods. Generally, in women, that is a value over 15.5 grams per deciliter (g/dl). If you are retaining fluid, or you are dehydrated, your number might be 0.5 to 1.0 grams per deciliter lower or higher the day of the test.

Why Is High Hemoglobin Important in Predicting Preeclampsia?

The reason some women's blood pressure during pregnancy goes high is that their bodies don't produce enough blood for both mother and fetus [4]. The hematocrit, the ratio of the volume of red blood cells to the total volume of blood, will increase as fluids go into the womb [5]. But it is "free" hemoglobin, that isn't bound to red blood cells that may be the real problem. Free hemoglobin forces blood vessels to constrict. The flow of blood is already restricted by the growth of the fetus. Constriction of blood vessels in contact with free hemoglobin makes blood pressure go even higher. [6]

Which high hemoglobin levels are dangerously high?

One study found that 42 percent of high-risk mothers (as defined above) who had hemoglobin levels above the "normal" hemoglobin level of 14.5 g/dl in their first trimester develop preeclampsia or eclampsia later in pregnancy, while only 7 percent of mothers with hemoglobin levels below 10.5 g/dl in the first trimester developed the condition later on [7]. The stage is set by hemoglobin levels during the first 12 weeks [8].

And the early warning signal is something your doctor tests for routinely. No additional, unusual, or expensive tests are needed to know whether your "high risk" of preeclampsia or preeclampsia is something closer to a certainty [9].

If you know you are prone to preeclampsia, then there are simple changes in prenatal nutrition, adding magnesium supplements [10], for example, that can help reduce the risk of your disease. These aren't a perfect solution, but at the very least they may spare you the sometimes-excruciating pain of having a high-potency IV drip of magnesium later on. You and your doctors will be on the lookout for the earliest symptoms of preeclampsia, and by treating earlier, you increase the probability of delivering a healthy, full-term baby who will grow into a healthy child.

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