(Reuters Health) - A year and a half after giving birth, one in four women report pain during vaginal intercourse - and odds for the problem are higher in women who had a cesarean section, according to a new study.

The researchers were surprised to find that almost all women experience pain the first time they have sex after childbirth, whether they resume sex in the first six weeks or wait several months, senior author Stephanie Brown told Reuters Health.

"This is not generally known, and certainly not what most women and their partners would be told to expect," said Brown, from the Healthy Mothers Healthy Families Research Group at Murdoch Childrens Research Institute in Melbourne, Australia,

Another surprise was that pain during intercourse was more likely after a C-section, she said.

Brown and her coauthors studied just over 1,200 women at six maternity hospitals in Melbourne.

Almost half had spontaneous vaginal deliveries, and most also required perineal stitches due to tearing or an episiotomy. About 11 percent gave birth vaginally with vacuum extraction or forceps, which usually caused some tearing.

Before pregnancy, about 27 percent reported having pain during sex. By three months postpartum, when nearly 95 percent of the women had resumed vaginal intercourse, more than 44 percent were still reporting pain during sex.

By a year and a half after childbirth almost 98 percent of women had resumed sex, and 24 percent reported pain.

"For most women, pain gradually resolves over the course of the first year, but for about one in four women pain persists or recurs," Brown said.

Women who delivered by emergency C-section or vacuum extraction were twice as likely to be having pain during sex at 18 months than women who had a spontaneous vaginal birth with no tearing, according to results in the British Journal of Obstetrics and Gynecology.

The odds were also higher, but less so, for women who had planned C-sections.

"Most people tend to assume that having a caesarean will protect the pelvic floor and therefore be associated with less problems after birth," but that doesn't appear to be the case, Brown said.

A caesarean is a significant operation and recovery be slow, said Dr. Hannah Woolhouse, also of Murdoch Childrens Research Institute, who was not an author of the new study. "Just because a woman doesn't have a vaginal birth, doesn't mean she won't experience ongoing pelvic and abdominal pain," Woolhouse told Reuters Health by email.

Fatigue, depression, younger age and having experienced pain with intercourse before giving birth were all associated with painful sex after childbirth, the authors found.

Talking to a trusted, empathic health professional can be helpful for some women, Brown said.

"When resuming a sexual relationship, taking things slowly and not feeling pressured to rush into it is important. Women taking part in our research say that knowing 'what's normal' and that what you are going through is not abnormal is also helpful," she said.

It's important to wait until the mother is physically and emotionally ready to resume sex, said Dr. Mohammad Reza Safarinejad, a private practice urologist in Tehran, Iran, who was not involved in the study.

"The intercourse should start with the positions she finds most comfortable," he told Reuters Health by email. "For example, side by side or spooning would be a good idea. This will put the least pressure on her abdomen, which is where the incision was done."

Vacuum extractions and emergency C-sections are by nature unpredictable. The potential sexual consequences are unlikely to affect decision making, but for a planned cesarean with no medical cause, the mother should be informed ahead of time before she makes that choice, said Dr. Eyal Sheiner, a maternity expert at Ben-Gurion University of the Negev in Beer-Sheva, Israel, who was not part of the new study.

The bigger issue the study raises is just how common pain during sex can be after delivery, Sheiner told Reuters Health by email.

"Part of the reason this may be surprising is that women tend not to talk about this issue after birth," Woolhouse said. "It remains a relatively taboo topic that can be difficult to discuss with both partners and health professionals."

SOURCE: British Journal of Obstetrics and Gynecology, online January 21, 2014.