After adjusting the monitor on my patient’s stomach so I could hear the baby’s heartbeat, I pulled up her chart to see her history.

“I see here it says you had your first child… [pause]… nine months ago?” I asked, not being able to hide the surprise from my voice.

“Yes, that’s right,” she said without hesitation. “I planned it that way. I wanted them to be really close in age.”

And close in age they were. According to my patient’s dates, she got pregnant again almost the moment she left the hospital. It was kind of impressive, actually.

As a labor and delivery nurse, I saw the same mothers coming back almost exactly nine months later more often than you would think.

So exactly how easy is it to get pregnant right after you have a baby? Let’s find out.

Breastfeeding, in theory, is supposed to prolong the return of the menstrual cycle, especially in the first six months postpartum. Some women choose to use this as a form of birth control called the lactational amenorrhea method (LAM), assuming that their cycle won’t return while they’re breastfeeding.

But exactly how long breastfeeding can delay the return of fertility varies. It depends how often and regularly a baby nurses, how long the baby will sleep for stretches at a time, and environmental factors, such as:

  • sleep disturbances
  • sickness
  • stress

Every person is different. For example, I didn’t get my period back until eight or nine months postpartum. But one of my friends who also exclusively breastfed got her period at only six weeks postpartum.

Although doctors have confirmed that the delay of the menstrual cycle with breastfeeding can be effective, it’s important to remember that relying on LAM for birth control is most effective if your baby is:

  • under 6 months old
  • exclusively breastfed: no bottles, pacifiers, or other food
  • nursing on demand
  • still nursing at night
  • nursing at least six times a day
  • nursing at least 60 minutes a day

Keep in mind that any fluctuation in the nursing routine, like if your baby sleeps through the night, can cause your cycle to return, too. To be safe, don’t rely on exclusive breastfeeding as effective birth control past nine weeks.

How soon you’ll get pregnant again depends if you’ll be breastfeeding or not.

Breastfeeding and the hormones that go along with milk production can suppress ovulation from returning.

If you’re not breastfeeding, ovulation usually doesn’t return until at least six weeks postpartum for most women. One review from 2011 found, on average, that ovulation returned for nonlactating women on day 74 postpartum. But the range of when ovulation occurred and if that ovulation was functional ovulation (meaning the woman could actually get pregnant with the ovulation) varied greatly.

A woman will ovulate before her period returns. Because of this, she might miss signs that she’s ovulating if she’s trying to avoid pregnancy. This is how some women can get pregnant without even having their periods back between pregnancies.

Ideally, mothers should wait at least 12 months between pregnancies, according to the U.S. Department of Health and Human Services.

Research has found that the risk for premature birth or your baby being born with a low birth weight increased for gaps shorter than 6 months, compared to those of 18 to 23 months. Intervals that are too short (under 18 months) and too long (over 60 months) have been associated with negative outcomes for both mom and baby.

In general, most women won’t start ovulating right away after having a baby, but the return of the menstrual cycle ranges widely for women.

Every woman’s personal cycle is different and factors like weight, stress, smoking, breastfeeding, diet, and contraceptive choices will affect the return of fertility.

If you’re planning on avoiding pregnancy, you’ll want to talk to your doctor about family planning options, especially if you’re breastfeeding and aren’t sure when your cycle will return.