Placenta previa is a complication of pregnancy where the placenta is partially or fully covering the opening of the uterus. It is the most common cause of painless bleeding in pregnancy and can have varied outcomes in pregnancy and mode of delivery depending on its severity.
There are 4 grades of placenta previa:
- Grade 1 (minor) Placenta is low-lying but does not cover the internal opening
- Grade 2 (marginal) Placental edge is reaching the internal opening
- Grade 3 (partial) Lower placental edge partially covering the internal opening
- Grade 4 (complete) Placenta is completely covering the internal opening
Sometimes Grade 1 or 2 placenta previa can resolve during pregnancy as your uterus expands and moves. This is because the site where your placenta attaches usually stretches upwards as the pregnancy progresses.
The position of your placenta will be checked at your 18-22 week ultrasound. If your placenta is low-lying at this scan, you will be offered additional ultrasound scanning throughout your pregnancy to monitor its position.
What does placenta previa mean for your pregnancy?
If you have placenta previa, your baby may need to be monitored frequently during your pregnancy. This may mean more regular scans, blood tests and cardiotocography (CTG) monitoring. This is when your baby’s heartrate is recorded on a continuous trace for short periods of time to assess wellbeing.
If you experience light bleeding during your pregnancy due to placenta previa you may need to be admitted to hospital for intermittent monitoring or in some circumstances, admitted for monitoring until your delivery.
If you have heavy bleeding in your pregnancy you may need to have an emergency caesarean (even prematurely) as a lifesaving procedure.
What does placenta previa mean for your delivery?
If you have Grade 3 or 4 placenta previa after 32 weeks gestation, you will be advised to have an elective caesarean section when it comes to the right time. This is because the placenta is blocking your baby’s safe passage through the vaginal canal and vaginal birth carries significant risk of bleeding or fetal demise.
Timing of your caesarean will be impacted by several variables such as baby growth and wellbeing, your wellbeing, bleeding in pregnancy and its frequency/severity.
Placenta previa is associated with serious risk of complication and monitoring/awareness should not be disregarded. Serious complications can include:
- Haemorrhage (significant blood loss)
- Emergency Caesarean
- Premature delivery
- Negative infant outcomes
- Hysterectomy (removal of the uterus)
What causes placenta previa?
There are no recognised causes for placenta previa, however there are several risk factors that may increase your chances of having placenta previa:
- Twin pregnancy
- Advanced maternal age
- History of Caesarean section
- Breech presentation
- Unicornuate or Bicornuate uterus
If diagnosed, there is nothing you can do to resolve placenta previa on your own. It is important to receive routine antenatal care and scheduled ultrasound scanning to check the location of your placenta and its movement in your pregnancy.
Written by Keryn Thompson RM & IBCLC (L-301766)
Alouini, S., Megier, P., Fauconnier, A., Huchon, C., Fievet, A., Ramos, A., Megier, C., & Valéry, A. (2019). Diagnosis and management of placenta previa and low placental implantation. The Journal of Maternal-Fetal & Neonatal Medicine, 33(19), 3221–3226. https://doi.org/10.1080/14767058.2019.1570118
Baumfeld, Y., Herskovitz, R., Niv, Z. B., Mastrolia, S. A., & Weintraub, A. Y. (2017). Placenta associated pregnancy complications in pregnancies complicated with placenta previa. Taiwanese Journal of Obstetrics and Gynecology, 56(3), 331–335. https://doi.org/10.1016/j.tjog.2017.04.012
Eschbach, S., Burgers, M., Rengerink, K., Pampus, M., Goes, B., Mol, B., Graaf, I., Pajkrt, E., & Ruiter, L. (2016). Predictors for Emergency Cesarean Delivery in Women with Placenta Previa. American Journal of Perinatology, 33(14), 1407–1414. https://doi.org/10.1055/s-0036-1584148
Fan, D., Xia, Q., Liu, L., Wu, S., Tian, G., Wang, W., Wu, S., Guo, X., & Liu, Z. (2017). The Incidence of Postpartum Hemorrhage in Pregnant Women with Placenta Previa: A Systematic Review and Meta-Analysis. PLOS ONE, 12(1), Article e0170194. https://doi.org/10.1371/journal.pone.0170194
Gibbins, K. J., Einerson, B. D., Varner, M. W., & Silver, R. M. (2017). Placenta previa and maternal hemorrhagic morbidity. The Journal of Maternal-Fetal & Neonatal Medicine, 31(4), 494–499. https://doi.org/10.1080/14767058.2017.1289163
Grönvall, M., Stefanovic, V., Paavonen, J., Loukovaara, M., & Tikkanen, M. (2019). Major or minor placenta previa: Does it make a difference? Placenta, 85, 9–14. https://doi.org/10.1016/j.placenta.2019.08.080
Jenabi, E., Salimi, Z., Bashirian, S., Khazaei, S., & Ayubi, E. (2022). The risk factors associated with placenta previa: An umbrella review. Placenta, 117, 21–27. https://doi.org/10.1016/j.placenta.2021.10.009
Jing, L., Wei, G., Mengfan, S., & Yanyan, H. (2018). Effect of site of placentation on pregnancy outcomes in patients with placenta previa. PLOS ONE, 13(7), Article e0200252. https://doi.org/10.1371/journal.pone.0200252
Jung, E. J., Cho, H. J., Byun, J. M., Jeong, D. H., Lee, K. B., Sung, M. S., Kim, K. T., & Kim, Y. N. (2018). Placental pathologic changes and perinatal outcomes in placenta previa. Placenta, 63, 15–20. https://doi.org/10.1016/j.placenta.2017.12.016
King, L. J., Dhanya Mackeen, A., Nordberg, C., & Paglia, M. J. (2020). Maternal risk factors associated with persistent placenta previa. Placenta, 99, 189–192. https://doi.org/10.1016/j.placenta.2020.08.004
Shobeiri, F., & Jenabi, E. (2017). Smoking and placenta previa: a meta-analysis. The Journal of Maternal-Fetal & Neonatal Medicine, 30(24), 2985–2990. https://doi.org/10.1080/14767058.2016.127140
Silver, R. M. (2015). Abnormal Placentation. Obstetrics & Gynecology, 126(3), 654–668. https://doi.org/10.1097/aog.0000000000001005
Takeda, S., Takeda, J., & Makino, S. (2020). Cesarean Section for Placenta Previa and Placenta Previa Accreta Spectrum. The Surgery Journal, 06(S 02), S110—S121. https://doi.org/10.1055/s-0039-3402036
Wasim, T., Bushra, N., Riaz, S., & Iqbal, H. I. (2020). Fetomaternal outcome in patients with placenta previa. Pakistan Journal of Medical Sciences, 36(5). https://doi.org/10.12669/pjms.36.5.1647