Unfortunately, though, not all placentas attach in the right spot. If a placenta attaches either too low in the uterus or right over the cervix, it can create a potentially dangerous situation called placenta previa. "Placenta previa usually presents with painless vaginal bleeding after the 12th week, when the placenta is fully developed, and it's caused by the wrong placement of the placenta over the cervix," says Marra Francis, M.D., an ob-gyn in Woodlands, Texas, and an author of the Mommy MD Guides. "Before 20 weeks, placenta previa can be seen in as many as 1 out of 3 pregnancies. In approximately 1 out of 200 pregnancies, the placenta previa continues into the third trimester, making labor dangerous. Placenta previa is very dangerous if the previa is complete--meaning completely covering the cervix or if the large blood vessels cross over. Bleeding from either of these can result in large volumes of blood loss in the mother very quickly."
Here's what all moms-to-be really need to know:
Unfortunately, there's nothing you can do to prevent it. "Women don't have any control over where the placenta attaches on the uterus," says Siobhan Kubesh, a certified midwife with OB-GYN North in Austin.
Some things may put you more at risk of developing placenta previa. "Depending on age of the mother, depending on how many previous pregnancies she's had, placenta previa may be more likely," says Titi Otunla, a certified nurse midwife at Texas Children's Pavilion for Women in Houston.
There are few symptoms associated with this complication. "Placenta previa usually presents with painless vaginal bleeding, especially after the 12th week," Dr. Francis says. "If that happens, typically an ultrasound is done to check the placenta's placement." But it's also important to note that you could bleed without having placenta previa.
For most moms-to-be, placenta placement becomes a non-issue as the pregnancy progresses. "The majority of placenta previa will resolve on its own," Dr. Francis says. "As the uterus grows, it pulls up the placenta, and the positioning becomes normal by 20 weeks. But after 20 weeks, if a placenta previa is still present, typically women will have ultrasounds every 2 to 4 weeks to monitor the previa, as some will still resolve later."
If your placenta doesn't move to a safer spot in your uterus, placenta previa will affect the way your baby comes into the world. "For the small percentage of women where placenta previa isn't resolved, they [have to] have pelvic rest, which means no sex and that nothing goes into the vagina--not even digital exams to see how things are going," Dr. Francis says. That's to prevent damage to the placenta that could lead to hemorrhaging and put both you and your baby at risk.
As you can imagine, placenta previa also makes vaginal birth a riskier proposition. "You don't want a woman with placenta previa to go into labor, because if the uterus starts to contract, there could be very brisk bleeding that puts both the mom and the baby at risk," Dr. Francis says. "These babies are typically delivered early by C-section, as they cannot deliver vaginally." But if it means a happy, healthy baby (and it almost always does!)--and a happy, healthy you, it's worth it!