The likelihood of two chromosomal abnormalities occurring in a biochemical pregnancy is not necessarily high.
The chances of having a biochemical pregnancy are already high, and are significantly higher than the chances of having a normal pregnancy. There are many women who have not had a blood test for HCG, or who think that their period has been delayed for a few days, or has not been delayed significantly, and do not know that there has been an embryo implantation, or that there has been an increase in blood HCG.
Generally, there is no need to check for chromosomal problems if there are only two biochemical pregnancies, but if a woman has infertility, or has a history of adverse pregnancies, including spontaneous abortions or embryonic arrest, or fetal malformations, then it is necessary to consider the possibility of chromosomal abnormalities, and chromosomal testing can be done to see if there are any abnormalities.