04.01.2014

Pregnancy after 35 down syndrome

In 2007, the medical guidelines changed from only offering women 35 years old and older prenatal testing for Down syndrome to offering it to all expectant mothers. Another reason for offering prenatal testing to all expectant mothers was the assertion that most children with Down syndrome are born to women under the age of 35. The age of the mother is the only factor that has been shown to increase the risk of having a baby with Down syndrome. Until recently, medical studies in which ultrasound evaluation of fetal anatomy has been used to identify fetuses with Down syndrome have focused on individual features of Down syndrome. At the present time Genetic Ultrasound is an accepted methodology that can be used to determine the risk for Down syndrome. The reduction in risk depends upon how accurate the Genetic Ultrasound detects Down syndrome. This graph illustrates the change in risk for Down syndrome after a normal Genetic Ultrasound.
For women between 35 and 40 years of age the risk of pregnancy complications is higher for Triple Marker testing than it is for Genetic Ultrasound, with a lower yield for detecting this condition.
The percentage of pregnancies in women aged 35 years or older has tripled since 1975 and currently about 14% of births in the United States are to women aged 35 and older. Resta’s article indicate that he is correct in stating that the increasing number of pregnancies occurring in women who are 35 years of age and older has recently resulted in that cohort accounting for slightly more than half the number of Down syndrome fetuses conceived in the United States. This, then, means that there is an even higher percentage of older mothers being pregnant and, ergo, even more cases of Down syndrome are due to pregnancies of women over the age of 35. DeVore, a more comprehensive study was published in 2000 in the journal of Ultrasound in Obstetrics and Gynecology in which 80 fetuses with Down syndrome and 2,000 controls were examined. Using a B-Mode ultrasound, without examining the fetal heart, detected 60 of fetuses with Down syndrome.


Using B-Mode ultrasound and evaluating the four-chamber view of the heart for disproportion, 75% of fetuses with Down syndrome were detected. Using B-Mode ultrasound plus color Doppler ultrasound to examine the fetal heart in greater detail identified 91% of fetuses with Down syndrome. Genetic Ultrasound, when practiced by physicians with special training in this area, is a useful tool to adjust the risk for Down syndrome.
With the inception of maternal serum screening using the Triple Marker test and more recently the QUAD test, approximately 25% of women 35 years of age and older will be identified to be at high risk for Down syndrome.
For example, if B-Mode and color Doppler are used, the detection rate of Down syndrome is 91%, as described above. Therefore, not only is the detection rate for Down syndrome higher using Genetic Ultrasound, the amniocentesis rate is lower (14%) than for Triple Marker testing (13% to 36%).
From this graph it is apparent that the detection rate for Down syndrome is higher for Genetic Ultasound than Triple Marker screening for maternal ages 35 to 43. However, because younger women are more likely to have babies than older women, 80% of babies with Down syndrome are born to women younger than 35 years of age. The net result is that since about the year 2000, women aged 35 and older have accounted for slightly more than 50% of pregnancies with Down syndrome. Contrary to the CDC statement, women under the age of 35 account for a minority of Down syndrome pregnancies, and have since the start of this century. While these studies have been helpful, they did not demonstrate a detection rate for Down syndrome which was greater than maternal Triple Marker serum screening. Therefore, if a woman 35 years of age or older is informed that she has an increased risk for Down syndrome following maternal serum screening, then her final risk can be reduced if the Genetic Ultrasound is normal.
They found that if all women who tested negative underwent Genetic Ultrasound, the detection rate for Down syndrome would increase to 98%, and was a safe alternative to universal amniocentesis.


So, the earlier and just-as-accurate prenatal test justified offering prenatal testing for Down syndrome to all expectant mothers. In addition, no studies focused on examination of the fetal heart, the most frequent birth defect in infants with Down syndrome.
The purpose of the study was to determine whether color Doppler ultrasound evaluation of the cardiovascular system could be used to improve the detection rate for Down syndrome as well as other chromosomal abnormalities. The following graph illustrates the reduction in risk for Down syndrome based an abnormal risk following maternal serum screening. The results of the study found that examination of the fetus with real-time ultrasound identified 30% of fetuses with Down syndrome, a number which was consistent with prior studies in which multiple organ systems were examined.
However, the detection rate for Down syndrome using Genetic Sonography is 91%, irrespective of maternal age. In addition, the detection rate of all abnormal chromosomes, of which Down syndrome is the most common, increased from 36% to 75%. Therefore, Genetic Ultrasound is more advantageous for detecting Down syndrome than maternal serum Triple Marker screening for women between ages 35 and 40. If the patients who were obese in which ultrasound examination was inadequate were removed from the analysis, the detection rate for Down syndrome increased from 87% to 93%.



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