I am 20 weeks pregnant, and I lie on an exam chair in a semi-dark room at the Women’s Clinic, T-shirt pushed up to my bra. Sterile paper rustles under my back. I inhale, but my breath is not calming. I think of my friends who have recently been pregnant. They’ve all looked forward to this routine ultrasound with joyful anticipation: It’s the time when one can find out the gender of the baby and confirm the due date.

But for me, gender and due date seem frivolous. In my early twenties I spent two years working toward a master’s degree in genetic counseling, which means I learned everything that can go wrong with human chromosomes. I consider the list of fetal abnormalities the doctor could detect in the next 20 minutes: congenital heart defects, spinal cord issues, cleft palate, markers for Down syndrome, other genetic disorders.

On top of this, I’m 35, “advanced maternal age,” and this makes me feel like a glowing statistic. My chances of having a baby with Down syndrome are 1 in 385, and my chances of having a baby with any chromosome abnormality are 1 in 200: relatively low. But as much as I try to ignore it, I can’t help feeling like I am under the microscope.

As a student, I spent much of my time looking at others under a microscope. I remember one lab assignment involving a photo of chromosomes from a skin cell of a 16-week-old fetus, extracted from the amniotic fluid of a pregnant woman. My job was to clip out the chromosomes and arrange them into numbered pairs. After much scrutinizing, I noticed a tiny band missing on chromosome 15, the genetic defect seen in Prader-Willi syndrome. Although the baby would have a normal life span, she’d also have mild to moderate mental retardation and feeding problems in infancy that would turn into an obsession with food as a child. If I were her mother, how would I cope?

Questions like this intensified as I continued through my program, especially as I began observing and counseling real patients. Eventually I chose to close the door on a career that was a tangle of ethics and emotions.

Today, as the doctor rubs the wand on my lubed-up belly, I feel like I’ve reopened that door. I grip the edge of my exam chair and watch the doctor’s facial expressions as he measures the circumference of the head.

When he clicks on both ends of the femur to measure it, I almost scream, “What’s the length? Is it normal?” A short femur is one marker for Down syndrome.

Instead I croak, “Does everything look all right?”

“Just making notes,” he says.

His pager beeps, and he looks down. “Be right back,” he says.

When he returns, he glances at his notes. “Everything looks normal at this point,” he says. “But remember, ultrasound is a screening tool.” He quotes the statistics I already know.

As he stands to leave, he holds up a CD containing pictures of my baby. “Thanks,” I say. There will be no further testing for me—I decline the offer of an amnio or future ultrasounds. I walk out of the Women’s Clinic, the CD secure in my fingers, into an uncertain future.