Reviewed by Medical Advisory Board
The placenta, also called the afterbirth, is the
organ that develops during pregnancy between the mother and the fetus. The
placenta has many blood vessels that allow oxygen and food to flow from the
mother to the fetus. A placenta that is too close to the cervix after 16
weeks is called low lying if the edge of the placenta or the enlarged vein
at the edge of the placenta (marginal sinus) is less than 2 centimeters away
from the opening of the cervix
A low lying placenta does not appear to affect the growth or development of the fetus. However, bleeding may occur from the blood vessels of the placenta during pregnancy or at the time of delivery.
Because of the increased risk for bleeding, you may be asked to avoid sexual intercourse
, exercise , and unnecessary travel.
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As a pregnancy progresses the placenta
tends to grow towards the upper uterus and most low-lying placentas will
have "moved away" from the cervix by the third trimester. A follow up
ultrasound is, therefore, recommended to be done at 32 weeks to
re-examine the location of the placenta. If the placenta is still less
than 2 centimeters away from the cervix at 32 weeks, then another exam
is recommended at 36 weeks,
Women who continue to have a
low-lying placenta at term may have a vaginal delivery, but have a
higher chance of an emergency cesarean section in particular if they
have a low marginal sinus . Hemorrhage after delivery is also more common
women with low lying placenta, whether or not the low lying placenta has
resolved.
By Mark Curran, MD
FACOG Updated 6/28/2022
REFERENCES
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6. Jansen C, de Mooij YM, Blomaard CM, Derks JB, van Leeuwen E, Limpens J, Schuit E, Mol BW, Pajkrt E. Vaginal delivery in women with a low-lying placenta: a systematic review and meta-analysis. BJOG. 2019 Aug;126(9):1118-1126. doi: 10.1111/1471-0528.15622. Epub 2019 Mar 10. PMID: 30663270.
7. Jain V, Bos H, Bujold E. Guideline No. 402: Diagnosis and Management of Placenta Previa. J Obstet Gynaecol Can. 2020 Jul;42(7):906-917.e1. doi: 10.1016/j.jogc.2019.07.019. PMID: 32591150.
8. Taga A, Sato Y, Sakae C, Satake Y, Emoto I, Maruyama S, Mise H, Kim T. Planned vaginal delivery versus planned cesarean delivery in cases of low-lying placenta. J Matern Fetal Neonatal Med. 2017 Mar;30(5):618-622. doi: 10.1080/14767058.2016.1181168. Epub 2016 May 16. PMID: 27180627.
9. DeBolt CA, Rosenberg HM, Pruzan A, Goldberger C, Kaplowitz E, Buckley A, Vieira L, Stone J, Bianco A. Patients with resolution of low-lying placenta and placenta previa remain at increased risk of postpartum hemorrhage. Ultrasound Obstet Gynecol. 2021 Nov 26. doi: 10.1002/uog.24825. Epub ahead of print. PMID: 34826174.
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