Your Mileage May Vary is an advice column offering you a unique framework for thinking through your moral dilemmas. It’s based on value pluralism — the idea that each of us has multiple values that are equally valid but that often conflict with each other. To submit a question, fill out this anonymous form. Here’s this week’s question from a reader, condensed and edited for clarity:

My partner and I did IVF recently and luckily we ended up with several embryos. One of those will be implanted in me so I hopefully get pregnant. But which one?

My fertility clinic is encouraging me to do PGT-A testing, which would screen for things like Down syndrome and would also let me see the sex of each embryo so I could potentially choose whichever I want. (And to be honest, I really want a girl!) I’m also hearing about these new companies that can test embryos for all kinds of things — like how smart the kid might be, how tall they’ll get, and whether they’ll have a lower chance of getting breast cancer, diabetes, mental illness, stuff like that.

I don’t know how to feel about any of this. On the one hand, it feels weirdly eugenics-y to do so much tinkering with embryos, and I can’t help feeling a little pressured into overmedicalizing everything with these expensive tests. But then again, if I could do something to make my baby healthier and happier, don’t I kind of have to do everything in my power? What does a parent owe their child?

Dear Expecting,

This is such an exciting — and also confusing — time. You’re about to have your first kid, and that comes with all sorts of fears and insecurities and hopes and dreams. You want to do the right thing — no, the best thing! — for your child. It’s a beautiful impulse. Unfortunately, it makes it easy for companies to prey on you.

So let me walk you through what these companies can and can’t really provide. After we talk about the science, we can talk about the ethics.

The simpler test you mentioned, PGT-A, has been around since the 1990s. It can indeed screen for conditions like Down syndrome and let you see the sex of each embryo. Mind you, that doesn’t predict what gender your child will ultimately end up identifying with — more on that soon.

The newer testing you mentioned is called polygenic testing. The conditions it screens for are complex ones, influenced by thousands of genes. We’re talking about everything from breast cancer to depression. Some companies even offer screenings not for disease prevention, but for genetic enhancement — so you can select for a taller kid or a kid with higher IQ.

Polygenic testing companies claim to predict each embryo’s risk for each condition, and the potential reduction of risk you’ll get if you choose one embryo over another. As the statistical geneticist Sasha Gusev explains, it’s very, very easy to be misled by this claim. If the company claims to lower absolute risk of Type 2 diabetes by 12 percent, you might think this means, “The chance of my kid ever developing diabetes just went down by 12 percent — great!” But really what it means is that, all else equal, a kid who would’ve developed diabetes is likely now at the high end of pre-diabetes instead, or just develops diabetes a few years later. The same holds true for other conditions, like breast cancer. Sure, if your kid is going to develop diabetes or breast cancer, you’d rather they........

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