Children are wonderful, priceless joys—but they’re also expensive, time-consuming and a drag on marital satisfaction.  Conflicted?

The pressures to have more than one come from all sides. There’s the notion that only-children are sad. Or maybe you want a girl now that you have a boy. Or Grandma might be hinting that she expects more grandkids. And a recent survey by the Pew Research Center found that 1 in 3 parents with more than 2 kids say that in retrospect, 2 is the perfect family size.

So how do you choose? In his book, Creating Your Perfect Family Size, family therapist Dr. Alan Singer uses anecdotal evidence, research findings and a series of self-test questionnaires to help moms and dads make the choice that works for them.

Katie Quirk spoke to Dr. Singer about the advice he offers in his book.

What questions can a couple ask themselves to help them decide about family size?

I think it’s a waste of time for couples to talk about what’s the ideal number of children in a family. If you really want to have children, have one child and then stop and think and talk and see. Ask yourself, do you like the experience, is your marriage still strong, or did you put your marriage on the back burner. How about family finances? It’s important to decide each child, one at a time. After you have one and you’re thinking about a second, ask yourself is now the best time to have a second child.

Let's assume I have 1 child and I’m unsure about number 2. When’s the best time to start thinking about a second child?

The earliest is when child number one is 1 year old, because the minimum space between births should be 2 years. This comes straight from the New England Journal of Medicine, based on the recovery of a mother’s body, which has to be the first priority. They say not less than 2, and no more than 5 years between births. It also makes sense, in terms of the gaps between children and them getting along together.

What would be the main reason not to have a second child?

The main reason to stop, or to wait, would be for the strength of your marriage. It’s my strong belief - based on what I’ve learned professionally, personally, and through my research and the research of others - that the most important and most delicate relationship in a family is that between the parents. Those parents and their nurturing of their relationship takes first priority. Having another child, a sibling, comes second.

And a good reason to go ahead and have another child?

Ask yourself, do you like parenting and are you good at it - because those two are not the same. If you love the child that you have and desperately want to have another child, that’s the right reason. It shouldn’t be because society dictates, or because you came from a family of two children and you want to emulate your childhood experience. And it shouldn’t be for gender. If you have one child and it’s a boy, and you’ve always dreamed of a daughter, don’t think, well, I always wanted a daughter, so I’m going to go take another shot on the hopes that I’ll have that daughter. The best reason to have another child is you love the child you have, you love parenting and you want to have another child regardless of gender, because that’s not something you can’t control.

Some couples worry about having an only child – what do you tell them?

To absolutely NOT worry. Only children are not lonely, they are typical, happy children. Don’t force yourself to have another child because of the stigma of the only child; that’s external pressure instead of internal desire. The reason to have another child should not come from the pressure of people who don’t mind their own business and say, ‘You’re going to give little Susie a brother or sister, aren’t you?’ like being an only child is some kind of disease or affliction. Only children are wonderful children. And you can spoil five children just like you can spoil one if you don’t have good parenting skills.