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Maternal Serum Screening

Down Syndrome, Trisomy 18 and Neural Tube Defects



March 2011

Beyond Hot Topic is an opportunity for viewers to submit questions to the Hot Topic presenter. The opportunity to submit questions for this topic is now closed.

The following questions were submitted by viewers and answered by the presenter, Alicia Algeciras-Schimnich, PhD, Assistant Professor of Laboratory Medicine and Pathology and Director of the Automated Immunoassay Laboratory in the Division of Clinical Biochemistry & Immunology at Mayo Clinic. Questions are presented as submitted (unedited).

  1. I wonder why in vitro fertilization (IVF) is one of the reasons the test would have to be weighted differently. What effect does this have compared to ethnic, diabetes, etc.? How does IVF affect the prenatal screening tests?

    In IVF pregnancies, estriol and PAPP-A values are on average lower and hCG is higher. If not taken into account by adjusting these values, the positive rate will be elevated. Another important factor is whether or not a donor egg was used. If a donor egg is used, the donor’s date of birth or age needs to be supplied to ensure accurate risk assessment. 

  2. What are the ages of women with high-risk pregnancies?

    With regard to maternal age, each woman has her own perception as to what she feels is a high risk. The risk for Down syndrome does increase with age as shown in table below. The age related risk is incorporated with risk factors derived from the ultrasound and biochemical markers. It should also be noted that the detection rate and positive rate increase with age.

    Age at expected
    date of delivery (years)
    Risk at term
    15
    1/1516
    16
    1/1512
    17
    1/1508
    18
    1/1502
    19
    1/1494 
    20
    1/1484
    21
    1/1470
    22
    1/1452
    23
    1/1430
    24
    1/1400
    25
    1/1362
    26
    1/1315
    27
    1/1255
    28
    1/1182
    29
    1/1095
    30
    1/994
    31
    1/881
    32
    1/759 
    33
    1/634
    34
    1/513
    35
    1/403
    36
    1/308 
    37
    1/231
    38
    1/172
    39
    1/129
    40
    1/98
    41
    1/76
    42
    1/61
    43
    1/50
    44
    1/43
    45
    1/38 
    46
    1/34
    47
    1/31
    48
    1/29
    49
    1/28
    50
    1/27
    51
    1/26
    52
    1/25
    53
    1/25
    54
    1/25
    55
    1/24

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