This is a question you really have to search your soul about. I can only relate my experience, really that of my sister and friend. My sister married a man who was great but there was a history of mental illness in his family. She did not know the extent of the cousins with different diagnosises, including schizophrenia. Long story short, her son is severe aspergers, high functioning and severe adhd. Although he makes perfect grades in school, he makes terrible life choices, and is in and out of trouble. His early babyhood and childhood were miserable and heartbreaking.
She chose to not have any more children with her husband. I have a best friend that has almost the same issues with her son and she made the same decision. So many tears over the decision but both women knew they could not have another child like that again, as much as they love their sons.
My sister chose to have another baby with donated sperm from a sperm bank. She has another son who is night and day to her first one.
I know one other family where momma had a normal son and has a second son with terrible genetic problems. He is at home, on a vent, now about 7 yrs old. He can smile (that is all he can do) and when he does it lights his momma's life. But her first son does not have the happy childhood that he would have had if this tragedy had not hit their family. Momma stays at home but spends all of her time nursing the little brother because they can not afford a nurse and she does not want him to be in a nursing home. She is not going to be able to take care of him at home much longer. (I was the RN who took care of the second baby in our NICU when he was born and for several weeks afterward before we shipped him to one of the best and higher level NICU's in the country.)
I don't know what kind of markers you are talking about - I hope they are not this bad. It would have devastated me to only one child - would it you? If it were me, I would look into donated eggs or adoption. Sorry if this is not the answer you were looking for. This is such an emotional subject for me.