That was what the doctor told me during my first ultrasound appointment at 12 weeks gestation. The little creature growing inside me was apparently measuring smaller than the average size of a baby at that point, and was closer to the size of a fetus 12 days younger.

My first reaction was, of course, instant panic. Too small? What was that supposed to mean? Is the baby not growing? Is it going to be premature? How many different panic-inducing scenarios can I think of before my brain explodes from worry?

Well, I’m pleased to say that after discussing the problem with my doctor, being told that your baby is “too small” isn’t necessarily the major problem it might seem at first. There are apparently a bunch of reasons for a baby to appear too small in an ultrasound. And most of them present no danger to the fetus at all.

The simplest, and most common, explanation is that the estimated date of conception is off by a little bit. Because they estimate the date based on the mother’s last menstrual period, there could be some slight variation in the gestational age if she tends to have irregular cycles. Implantation can also be slightly later than the estimated week after conception, and this can account for a few days of variation between the estimated gestational age and what they see on ultrasound. To determine if this is the case, the doctor will usually look for other potential problems, such as issues with the umbilical cord or any problems in the mom’s blood sample that indicate the baby might not be getting enough nutrients. If no such problems exist, the most common scenario at that point is for the doctor to presume the dates are off and to adjust the due date to match the ultrasound.

In rare cases, if a problem is found, the doctor will likely make sure the mother is taking prenatal vitamins and might suggest sleeping positions that provide more bloodflow to the uterus, such as lying on the left side. In some cases, bedrest may be recommended to reduce the mother’s body being overtaxed. This is extremely rare, however.

More commonly, the doc will do a follow-up ultrasound a few weeks or a month later. If the baby is still measuring according to the new due date, everyone will presume it was a dating error and move on. The only problem then is telling everyone “Oops, I’m due a week later now!”

In my case, this turned out to be the solution. My doctor moved my date one week ahead, putting my baby in the “a–little-small-but- completely-in-normal-range” category. I’m ok with that, actually. I wasn’t too keen on the idea of a Christmas baby, so post-New Years due date suits me just fine.