What is it? Placenta previa is a rare pregnancy complication (occurring in less than one percent of pregnancies) that can be very serious if left undiagnosed. It occurs when a woman’s placenta forms in the lower portion of the uterus (instead of the top or side), close to, or covering, the cervix. “It’s a concern in pregnancy because the baby cannot be delivered through the placenta without risk of blood loss,” says Jane Calhoun, a registered midwife with Midwives Grey Bruce in Owen Sound, Ont. It is most commonly diagnosed by ultrasound. “If you choose to have the standard 18- to 20-week anatomical ultrasound, the radiologist will report on the location of the placenta,” she says.
What are the symptoms? Women may experience cramping and bright red vaginal bleeding, which can be heavy, coming and going over a number of days late in their second trimester or early in the third. (Any bleeding during your pregnancy should be reported to your doctor or midwife.)
Read more: All about the placenta and umbilical cord>
How will it affect your pregnancy? “As the baby grows and the uterus expands, the placenta will most likely move away from the opening of the cervix,” says Calhoun. “Most placenta previa will resolve by the third trimester.” An ultrasound will be scheduled to check.
What are they looking for? The ultrasound will determine the location of the placenta. “If the placenta is greater than 2 cm away from the opening of the cervix, your health-care provider can support you in having a vaginal birth, as long as there are no other contraindications,” says Calhoun. “If your placenta is less than 2 cm from the opening of your cervix, or still covering the opening of your cervix, she will recommend a planned Caesarean section ahead of your due date to ensure that you do not go into labour.” There is an increased risk of premature labour with placenta previa, but if a woman is diagnosed early, this concern is greatly minimized.
What should you do? Be sure that your health-care provider advises you of any special instructions (bed rest is sometimes recommended). Calhoun says it’s usually suggested that you abstain from sex, so you don’t stimulate vaginal bleeding.
A version of this article appeared in our Fall Pregnancy 2013 with the headline "Placenta previa," p. 36.
Keep up with your baby's development, get the latest parenting content and receive special offers from our partners