Why Second Pregnancies Are Often Unplanned

A new study found that 30 percent of women who have a baby became pregnant again within 18 months. While most women are happy with the result, their body can suffer.

Why Second Pregnancies Are Often Unplanned Anna Omelchenko/Shutterstock

Christine Burns remembers exactly what prompted her to take the pregnancy test that told her she was going to have a third baby. She was watching television one evening when a beach resort commercial inexplicably made her cry. "I remember telling my husband I was going to take a pregnancy test, and he highly doubted it would be positive," she says. After all, Burns had a 5-month-old baby she was nursing, she hadn't gotten her period since his birth and she certainly wasn't trying to conceive. "I was pretty confident that the combination of being 37 years old and exclusively breastfeeding would be sufficient contraception," she recalls. "Clearly, I was wrong." When she saw two purple lines on the stick, her head started spinning.

Although Burns is now thrilled beyond measure with her family, it took her time to come to terms with the surprising news. And believe it or not, her story is a common one.

According to a new study released by The Centers for Disease Control and Prevention, 30 percent of women who had a child became pregnant again within 18 months.

Having babies back to back like this has ramifications beyond exhaustion. A mom who conceives again quickly is more likely to develop anemia and preeclampsia during pregnancy, and her baby is more likely to be born premature, at a low birth weight and is slightly more likely to die during infancy. "It generally takes your body 18 months to restore everything that you need for another pregnancy," says Keith Eddelman, M.D., director of obstetrics at Mount Sinai Hospital in New York City.

For women who have had C-sections, waiting at least that long is especially beneficial. "It is very important for that uterine incision to heal before the uterus starts to stretch again with another baby," says Stephanie Teal, M.D., an OB-GYN at the University of Colorado Hospital in Aurora. Uterine rupture happens in less than 1 percent of all pregnancies, but it puts Baby's life at risk.

Why this is happening

So how exactly are so many women, especially those who meticulously planned the arrival of their first babe, finding themselves unexpectedly expecting again? One major reason: Most new moms are sexually active. A 2013 study reported that 41 percent of mothers have intercourse within six weeks of giving birth, and 78 percent have sex within 12 weeks. Yet many don't use contraception, either because they don't think they can get pregnant so quickly or because they haven't been counseled about it by their doctors.

Other women use birth control but not properly: The progestin-only "mini-pill," which is frequently prescribed to breastfeeding mothers, must be taken within a three-hour window each day to be effective—a requirement that can feel next to impossible when you're lucky if you even remember to shower.

"The first two years after delivery are especially hectic for moms," says Teal. "This means that the time period when it is most important to delay the next pregnancy is the time when it is least convenient to be worrying about birth control."

And it's not just mamas who miss a dose that wind up with an unplanned bump. Even when the mini-pill is used properly, it's still not as effective as the regular version (which isn't recommended for nursing moms). Only 1 woman out of 1000 will get pregnant during the first year of taking the regular pill perfectly, five times as many will get pregnant taking the mini-pill correctly.

Surprisingly, women who have had trouble conceiving in the past are especially at risk for an unplanned pregnancy. A 2013 study reported that 61 percent of subsequent pregnancies to women who had previously used assisted reproductive technologies were unplanned.

"I think those couples feel like it took so much effort the last time that they don't have to worry about getting pregnant again," Eddelman says. Although no one knows exactly why, "once these couples get pregnant, it's sort of like 'priming the system', and conceiving the next time can happen much more easily."

Science says: Nursing isn't birth control

Then there are many women, like Burns, who associate breastfeeding with built-in contraception. The reality is far from black and white. After you've accomplished the marathon that was L&D, your body has to transform all over again. Among other things, you have to shed your old uterine lining and begin to produce breast milk. If you don't nurse, your body quickly realizes that it's off the feeding hook and starts to pour its resources into the possibility of creating another human. Shockingly, a non-breastfeeding mother can become pregnant within four weeks of a previous birth.

For nursing moms, the situation is more complicated. Breastfeeding does suppress the hormone that releases your eggs. Research suggests that a woman who exclusively breastfeeds her infant—meaning that she doesn't supplement with formula or solid food—and who hasn't gotten her period since the birth has only a 2 percent chance of getting pregnant in the first six months of her baby's life. Those are better odds than you get with a condom.

"But the kicker is that once a mom gets her period back, or starts supplementing with a little rice cereal or lets the baby sleep eight hours through the night without getting up to nurse, breastfeeding is no longer a reliable birth control method," Teal says. Plus, you can ovulate even before you get your first period back. "I see so many patients who are absolutely shocked when they have a positive pregnancy test with a 6- or 8-month-old at home," Teal says.

Reasons to plan ahead

Besides the immediate risks of anemia, low birth weight or simply not giving your baby the nutrients he needs in the womb, "pregnancy depletes important nutrients like folate, which may not be sufficiently replenished when there isn't adequate time between pregnancies," says Aparna Sridhar, M.D., an OB-GYN at the David Geffen School of Medicine at UCLA and a contributor to Bedsider.org—there are more long-reaching reasons for mothers to wait at least 18 months before getting pregnant again. One 2013 study conducted by researchers at Columbia University and other institutions found that babies born to women who got pregnant within 11 months of a prior birth had nearly twice the odds of having a child who developed autism.

That said, some of the association between back-to-back pregnancies and health problems could stem from other causes: Women who conceive quickly and frequently may be making other lifestyle choices that increase health risks, experts say.

Still, for some women having kids close in age—intentionally or not—is nothing short of amazing. "My children caught up to each other quickly and have a special bond with their closest siblings," says Lura Baker, who has two sets of two children born a year apart. But to minimize potential health risks, you may want to take a break before conceiving your next child. It's never too early to think about how you'd like your family to grow and talk to your doctor about making those dreams come true.

Related: Post-Baby Birth Control: Options for Postpartum Sex