What carrier screening is

Carrier screening is a blood or saliva test that assesses whether you carry a gene for certain inherited conditions. Most of these conditions are recessive, which means it takes two copies of the gene (one from each biological parent) to pass it down to a child. If you carry a single copy, you're a carrier, and you almost certainly have no symptoms. 

Being a carrier for a condition is far more common than it sounds, and most carriers have no idea, because there's nothing to feel.

Why carrier screening tests both you and your partner

On its own, one carrier result isn't a problem. It starts to matter if you and a partner happen to carry a gene for the same condition, which is uncommon. That's the whole reason the test looks at the two of you together instead of reading either result by itself. 

When you and your partner are both carriers for the same condition, each pregnancy carries a one-in-four chance of passing on the condition. Getting screened lets you know in advance that there’s a chance of it happening.

What if you and your partner are both carriers for the same condition?

First things first: it’s uncommon to both be carriers for the same condition, and it’s why it’s helpful to know early if it applies to you. If you and a partner carry the same gene, the next step is typically genetic counseling. In a genetic counseling session, where you’ll speak to an expert about your family history, what your results mean, what your risk of passing on an inheritable condition is, and what to consider as you move forward.

There are options for people who are both carriers for a condition and who want to be parents: testing embryos through IVF, using a donor, testing during the pregnancy, or going ahead fully informed. Screening opens those choices rather than closing them.

Should everyone go through carrier screening?

Carrier screening is offered to everyone, not just people with an inheritable condition. ACOG recommends that anyone considering pregnancy be offered screening to check for conditions like cystic fibrosis and spinal muscular atrophy, regardless of background, because carriers show up in every group. It's also completely optional, and plenty of people decline it. Family history can add context, but it isn't the gatekeeper it once was.

In the end it's a small test with a narrow job: telling you, before pregnancy, whether you and a partner carry the same recessive gene. For most, the answer is uneventful, and for the few where it isn't, it's something they get to know earlier rather than later.