What is meant by a low lying placenta?

What are the different grades of placenta praevia?

 

What is meant by a low lying placenta?

(26th January 2025)

When the developing conceptus reaches the uterus towards the end of the first week of development after fertilisation, it generally implants in the endometrium lining the posterior wall of the body of the uterus. If implantation occurs lower in the uterus, close to the cervix, problems may arise later in pregnancy. Although the baby can develop normally, the placenta may end up bridging across the cervix, and this can result in haemorrhage later in pregnancy and put the lives of the baby and mother at risk.

The condition of a low-lying placenta is called placenta praevia, and occurs in approximately 0.5% of pregnancies. If the mother has delivered many babies already (ie: she is grandmultiparous), the risk of placenta praevia for her can be as high as 2%. Other risk factors include multiple pregnancy (twins, triplets etc.), age (risk increases for older mothers), scarring of the uterus after a Caesarean section, and smoking. It is interesting that a substantial proportion of the cases of placenta praevia detected by ultrasound scanning during pregnancy manage to resolve themselves by the time the baby is delivered – the lower part of the uterus grows and the placental site appears to rise up the uterine wall, away from the cervix.

Reference

Sweet, B.R. (Editor), and Tiran, D. (2024) Mayes’ Midwifery: a textbook for midwives (12th edition). London: Baillière Tindall (pp 522-523).

Our thanks to Mary Rossiter, Senior Lecturer (Midwifery), University of Plymouth for help with this answer.

 

What are the different grades of placenta praevia?

7th December 2025

It is conventional to describe 4 grades of placenta praevia:

Type 1:

the placenta is mainly in the upper segment of the uterus but encroaches on the lower segment

Type 2:

the placenta extends to, but does not cover, the internal opening into the cervical canal

Type 3:

the placenta covers the internal os of the cervical canal during the later stages of pregnancy but does not cover it completely as the cervix dilates during labour

Type 4:

the placenta completely covers the internal os of the cervical canal

This information is derived from:

Sweet, B.R. (Editor) and Tiran, D. (2024) Mayes’ midwifery: a textbook for midwives (12th edition). London: Baillière Tindall (pp 522-523).