All about di­ag­nos­tic tests

Pregnancy Life & Style - - YOUR PREGNANCY -

If a preg­nancy is con­sid­ered high risk (where screen­ing re­sults show pos­si­ble ab­nor­mal­i­ties, the mother is over 35 or one par­ent has a fam­ily his­tory of ge­netic dis­or­der), you may con­sider chori­onic vil­lus sam­pling (CVS) and/or an am­nio­cen­te­sis.

Both tests de­tect Down syn­drome, chro­mo­so­mal ab­nor­mal­i­ties and cer­tain ge­netic dis­or­ders.

CVS is per­formed be­tween weeks 11 and 14, ei­ther vagi­nally, sim­i­lar to a Pap smear, or ab­dom­i­nally, where a nee­dle is passed into the pla­centa through the belly. A sam­ple of pla­cen­tal tis­sue is re­moved for anal­y­sis. The risk of mis­car­riage as­so­ci­ated with CVS is in­con­clu­sive but thought to be about one in 100.

An am­nio­cen­te­sis is car­ried out be­tween weeks 15 and 18. A nee­dle is passed into the stom­ach and am­ni­otic fluid is with­drawn.

The risk of mis­car­riage is less than one per cent.

A fairly new test, non-in­va­sive pre­na­tal test­ing (NIPT) can be help­ful for women at mod­er­ate to high risk for chro­mo­so­mal ab­nor­mal­i­ties. This in­volves iso­lat­ing foetal DNA frag­ments from a blood sam­ple.

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