My husband and I are grappling with a difficult decision. I’m 36 years old and have a 2.5 year old son. We’ve come to a point where we need to decide soon whether to have another child and we’re having a really hard time deciding. Are we one and done or do we want to escalate to the “next level of parenting”? I’m healthy, my pregnancy wasn’t terrible (but I didn’t like it) and we’re financially secure. But there are so many other aspects that go into this (do I want to give up the freedom I just regained, what type of lifestyle do we want as a family, will it affect our marriage, will I be withholding something from my son for selfish reasons, etc.). Not to mention the real stigma’s against only children and frankly their parents (“Oh, you don’t like being a mother, you don’t want to give your son a sibling?”). I’d love your perspective about how to approach such a big decision.

—Mom of 1 (For Now)

I think you’re doing a pretty good job approaching it, but let’s smooth it out a bit.

Frame the Question: At some level, your question is “Should we have another child now, or not?” As usual, the main issue is to fill in the “or not” with something concrete. I think what you are asking is “Should we have another child now or not have any more children?” (Which is a concrete question so, good). For others, the question may be more like “Should we have another child now, or have another child next year?” or “Should we have another child now or wait to re-evaluate next year?”

In this case, being concrete is important for thinking about what data you want to collect. If you are sure you want a second kid but wondering about the timing, the information you need is about if (and how fast) fertility falls and maybe something about the “optimal” kid spacing (see Cribsheet for the very limited incomplete data we have on that).

In your particular case, where you’re really asking about whether you want a second kid at all, one relevant piece of data is probably about the impacts of having siblings on kids.

Evaluate the “Data” : I put “data” in quotes here because while there are some piece of data, the right approach to this involves considerations well beyond academic studies.

The first and by far most important question is whether this is something you and your partner want. I’d urge you to be really concrete. Imagine the way your life will look over the next five or ten years with your son only, versus with another child. What will your finances look like? Your daily schedule? Your work life? Your partner’s work life? Vacations? Summers? And on and on. If you get pregnant right now, in 12 months you’ll have a 3.5 year old and a 3 month old. What will that look like, versus the 3.5 year old only? What about in 5 years, when you’ll either have just an 7.5 year old, or that plus a 4 year old? You don’t need to imagine 30 years down the road, but a little future imagination is a good idea.

Whether you feel you want another kid is also pretty important. Less easy to quantify in a schedule, but worth working through. Does your family feel “done”?

I will note, and I think you know this: what other people think shouldn’t matter. Even though it feels like it does!

There is also a data piece: is it bad for kids not to have siblings? You often hear the claim that only children are introverted or socially awkward or have some other issues. I investigated this when writing Cribsheet and, basically, there isn’t much evidence but what we haven’t doesn’t support that claim. One review article, which summarizes 140 studies of this, found some evidence of more “academic motivation” among only children, but no differences in personality traits like extroversion. Even this academic motivation fact may be more about birth order (firstborn children score higher on this regardless of siblings) than about being an only child.

(There is the flip of this idea, which is that children with more siblings get less attention and do less well in school. This is also not well supported in data).

In short: this particular piece of the data isn’t likely to push you strongly in one direction or the other. Leaving us back at the start, with your family preferences.

Final Decision: This is one where it can be pretty hard to make a final decision. I think sometimes people just kind of let the shot clock run out, so to speak, rather than deciding. But I would warrant you’d be happier — and have more mental space — if you made a formal decision. How to do this? Do some of the evidence gathering I suggest above, set a decision date, discuss and decide. You can always revisit, but it may be best to try to make the decision and live with it for a while before you do.