Is it normal for my baby not to poo after switching to formula?

Day two, then three, then four

We asked this several times over several days, and the question kept getting more precise. Is it normal on day two with formula. What if she's on day three. What about day four. Do I wait until the end of day four or ring on day five.

We also asked, quite pointedly, what a five-day figure was even based on. Which was a fair challenge, and the honest answer is that these thresholds are rules of thumb rather than hard science.

We rang our baby's doctor. She told us that, during the move from breast milk to formula, five or six days without a poo could be okay for Ari as long as she was otherwise well.

That's her advice for our baby, and it's the version we followed. Which is rather the point — the number that matters is the one your own doctor gives you, not the one you find online.

What we'd say to anyone in the same spot: ring and ask what your limit is, before you're at it. Then you're waiting with a plan instead of waiting with a countdown.

Why it happens

Breast milk is very efficiently absorbed and leaves little behind. Formula leaves more, and it's digested differently, so poo becomes firmer, darker and usually less frequent.

During the change, her tummy is adjusting to both kinds of milk. Poo gaps can stretch before a new pattern settles. Ours was more complicated because Ari kept bringing different formulas back up. Just as she started getting used to one, we had to change it again. Her doctor eventually advised an anti-reflux formula. It was a stressful little loop: new milk, new tummy, new poo pattern, then start again.

That's a transition effect rather than constipation, and constipation is about what arrives rather than how long it took. Soft is fine, however many days it's been. Hard, dry or pellet-like is not.

What told us she was fine

She was weeing a lot. She was passing gas. Her belly was soft. She was eating very well.

All four of those together made waiting reasonable. Any one of them going the other way — particularly a firm or swollen tummy, or vomiting, or obvious pain — would have changed it.

She was also very fussy through it, which we assumed was the constipation and was probably just her age. Both things were happening at once, which is usually the case.