Confession: Even sounding out the words “baby” and “number” and “two” in one breath right now scares me a little. No. A lot.

But a recent study published in the journal Obstetrics and Gynecology found that as many as one-third of babies that follow are conceived within 18 months of a previous birth. The chances are higher if a woman is between the ages of 15 to 19 or older than 30, or if she was married when the previous child was conceived. And in many cases, the subsequent pregnancy is intended.

From a health perspective, a pregnancy interval of 18 months or less is considered short, and in some cases, can be risky. Short intervals between pregnancies increase the chances of preeclampsia, premature births, and a lower birth weight for the baby.

Women should no longer need a doctor’s prescription to get birth control pills, according to a new opinion statement released Tuesday by one of the largest physician-based women’s health care organizations.