Placental Anomalies: Identification and Intervention

Introduction

There are a number of complications that are common during pregnancy. Most of these include maternal Infections which could be resolved with the prescription of non-teratogenic antibiotics for the stipulated duration and proper dosage. Nevertheless, there could be some other less common complications that require timely identification and intervention to prevent morbidity and mortality at the maternal and foetal levels. These include some placental anomalies – Abruptio placenta, placenta accreta and placenta previa.

Placenta Previa

This is a condition where the placenta is found to lie in the lower uterine segment. The incidence of developing placenta previa is 1 in 300 pregnancies. For localisation of the placenta, an Ultrasonography should be performed in the third trimester. If a major degree of placenta previa is detected, repeat the scan at 32weeks of gestation, whereas for minor degrees, repeat the scan at 36weeks. Trans-abdominal Ultrasonography is the investigation of choice to differentiate between placenta previa and Abruptio placenta. Also, it is important to be kept in mind that vaginal examination is contraindicated in a known case of placental Previa. It should be performed only after ruling out placenta previa.

Classification of Placenta previa

• Grade 1 – distance of the placenta lies is less than 2 cm from the internal os. Can be further classified into anterior and posterior types.
• Grade 2 – placenta lies at a distance of more than 2 cm from the internal os. This can also be further classified into the anterior and posterior types.
• Grade 3 – incomplete placenta previa.
• Grade 4 – complete placenta previa.

It is important to bear in mind that grade 1 and 2 are minor degrees, while grade 3 and 4 are major degrees of Placenta previa. Grade 2 posterior type is called the dangerous type because it is difficult to visualise on a USG. It is dangerous because there are more chances of placental compression if vaginal delivery is allowed which can lead to foetal hypoxia and foetal death. However, vaginal delivery can be tried for the other minor degrees of Placenta previa.

Symptoms

Bleeding in the third trimester which is painless, recurrent and occurs in the same pregnancy. Often, a  warning haemorrhage is present. The cause of bleeding can be attributed to the physiological phenomenon where in the later months of pregnancy the lower segment of the uterus dilates passively and the inelastic placental wall is sheared off. Therefore, bleeding is inevitable in this condition. It can be exaggerated by trauma, per vaginal examination and post-coital acts.

• Risk factors
• Previous history
• Caesarean section
• Placentomegaly
• Endometritis
• Curettage

Abruptio placenta

A condition where there is premature separation of a normally positioned placenta. Incidence is reported to be 1 in 200 pregnancies. PAGE classification is used to grade the types of placental abruption–

• Grade 0 – Retrospective diagnosis based on retroplacental clot.
• Grade 1 – abdominal pain, bleeding, normal foetal heart sounds.
• Grade 2 – abdominal pain, bleeding, foetal distress/foetal death.
• Grade 3 – abdominal pain, bleeding, foetal death ± Disseminated Intravascular Coagulation due to the release of thromboplastin.

Symptoms

Bleeding in the third trimester which is painful with passage of dark red blood, trauma or cause for bleeding not usually present. No warning sign and does not recur in the same pregnancy. Uterus is hard, tender and tensed on palpation due to release of thromboplastin. Types of bleeding in Abruptio placenta-

• Revealed variety – where there is evident bleeding.
• Concealed variety – blood collects behind the uterus and enters the myometrium to give it a dark purple colour, known as Couvelaire uterus. Since blood collects inside the uterus, height of the uterus is more than the period of gestation.
• Mixed variety – part of blood comes out and part of it stays inside the uterus. Components of both the types.

Risk factors

• Smoking
• Cocaine abuse
• Folic acid deficiency
• Thrombophilia
• Fibroids
• Polyhydramnios
• Premature rupture of membranes

Placenta accreta

This is a condition where the placenta is morbidly adherent to the uterus. Normally, a membrane called the Nitabuchs layer limits the penetration of blastocyst beyond the endometrium. The absence of this layer leads to no feedback and morbid adhesion of the placenta. Grades of placenta accreta are-

• In accreta, chorionic villi are superficially attached to the myometrium.
• In increta, the chorionic villi penetrate deep into the myometrium.
• In percreta, the chorionic villi cross the myometrium and attach to the serosal layer.

In all the conditions, there is absence of Nitabuchs layer and decidua basalis.

Risk factors

• Placenta previa
• History of caesarean section
• Uterine surgery/curettage

Perform antenatal trans-vaginal USG which is the investigation of choice. Early diagnosis is important because this causes significant post partum haemorrhage. Caesarean section is performed with hysterectomy to prevent further blood loss. However, if patient does not consent to hysterectomy, remove retained tissue by curettage, but keep in mind that excess curettage can lead to the development of intrauterine adhesions.

Diagnosis

• Placenta appears heterogeneous
• Intraplacental lakes are absent
• Sub-placental sonolucent area which marks the decidua basalis is absent

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