Testing for diabetes, genetic abnormalities during pregnancy

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Brian Bell, M.D.

Pregnancy involves special medical considerations, as two individuals are involved. Diseases affecting the mother may or may not affect her unborn child and vice-versa. For this reason, certain conditions are screened for to avoid potentially serious consequences.

One of the most common diseases complicating pregnancy is diabetes. During pregnancy, a hormone is produced that increases resistance to insulin, which can cause elevated blood sugars. When combined with other risk factors, such as obesity, family history, age (over 35), excessive weight gain during pregnancy, polycystic ovarian syndrome and a sedentary lifestyle, diabetes can develop.

This is called gestational diabetes. Left untreated, it increases the risk for stillbirth, excessive growth of the baby, leading to difficult births, and obesity and diabetes in the child later in life.

To prevent these complications, it is important to identify those mothers who develop gestational diabetes as it generally has no symptoms. This is usually done between 24 and 28 weeks gestation by having the mother drink a glucose solution and checking her blood sugar an hour later. Additional testing may be necessary to establish a diagnosis if the result is abnormal.

Another condition that doesnít have symptoms or cause any problems for the mother is having a blood type that is Rh negative. The Rh factor is a protein that is present on the surface of red blood cells in Rh-positive individuals.

If an Rh negative individual is exposed to the Rh factor, the bodyís immune system acts as if itís a foreign invader. It attempts to neutralize Rh positive cells by creating antibodies against them.

This can happen during pregnancy as the babyís red blood cells cross the placenta into the motherís circulation. If the baby is Rh positive and mother is Rh negative, antibodies develop that can have a devastating effect on the pregnancy. Administering a blocking agent called RhoGam around 28 weeks gestation prevents this situation. For this reason, the motherís blood type is tested early in pregnancy.

There are many tests undertaken that cannot properly be called screening tests as there is no effective treatment for abnormal results. Nonetheless they are often worth reviewing.

Ultrasound has revolutionized the practice of obstetrics. Most pregnancies will have a least two. The first comes early in the pregnancy to confirm viability and gestational age. The second is performed between 16 and 20 weeks to assess the developing babyís organ systems and growth.

This is not a perfect test and small abnormalities may be missed, but if found the information can help guide decision-making regarding timing and location of delivery.

Finally, there are tests that look for genetic abnormalities. The most commonly done is a blood test between 15 and 21 weeks gestation called a quad screen, because it measures four pregnancy-associated hormones. This can help determine the babyís risk for Down syndrome.

There also is testing available based on the fact that fetal DNA can be found in the motherís bloodstream. This is quite accurate, but expensive. Many genetic defects can be found by this method, but as with the quad screen, an abnormal test requires removing fluid surrounding the baby to obtain skin cells for a chromosomal analysis to know with certainty.

Most of these tests are routinely done, but some are optional. As with any testing, discussing options with your obstetrics provider is the best course of action.

Brian Bell, M.D. is Lincoln Countyís only board-certified OB/GYN and serves as chief of staff at Cabinet Peaks Medical Center.

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