Abnormally invasive placenta---Can we predict and do better?

Clinical Pearls:

• Previous cesarean section or uterine surgery is the single most important predisposing factors for Abnormally Invasive placenta.
• One cesarean section increases the risk of AIP seven fold in subsequent pregnancy.
• History of post-partum hemorrhage is also a risk factor for AIP and increases the risk 6 fold in current pregnancy.
• In 70% of cases, the diagnosis of AIP was missed during antenatal period.
• Increasing clinician awareness for incidence of AIP in the high risk patients leads to increased diagnosis in antenatal period.
• Avoiding unnecessary cesarean section is the only way to decrease the incidence of AIP.  

Lowering the Cesarean section rate in the population is the only most effective way in reducing the incidence of Abnormally invasive placenta(AIP) is the conclusion of a large, population based cohort study from the Nordic countries.

The Nordic Obstetric Surveillance Study (NOSS) required obstetricians’ collaboration in reporting AIP, uterine rupture, excessive blood loss and peripartum hysterectomy from 2009-2012. Due to paucity of cases at a single hospital the data was pooled and validated by National Health Registries. 

The data was analyzed and identified 205 cases of AIP amounting to an incidence of 3.4 per 10,000 deliveries.

The study was published in the current issue of British Journal of Obstetrics and Gynecology(BJOG).[1]

The study goal was to gauge the prevalence, risk prediction, predisposing factors, antenatal suspicion, maternal morbidity and birth complications in cases of AIP.

The study confirmed the association between AIP and previous cesarean section or any other previous uterine surgeries like endometrial ablation, and in vitro fertilization. The risk of AIP in subsequent pregnancy is seven fold with one prior Cesarean section to 56-fold after three or more CS.

Placenta previa was the single most important risk factor identified in nearly half of the pregnancies.

 In addition, patient who had postpartum hemorrhage in previous pregnancy have 6 times the risk of AIP in current pregnancy as compared to patients who did not have PPH.

An antenatal diagnosis of AIP can strikingly reduce the complication rate but in nearly two-third of patients (70%) of patients the diagnosis was missed. Of these, 39% had prior CS and 33% had placenta praevia.

Increased awareness about the risk factors among clinicians can raise the index of suspicion and led to more and more patients being diagnosed in prenatal period. Clinicians performing Ultrasound(USG) should have high index of suspicion in high risk women with previous uterine surgery or a placenta over uterine scar. These women should be offered additional sonography.

Nordic countries have lower rates of AIP than US, perhaps due to lower rate of cesarean section and high order cesarean births or better obstetrics facilities. 

But, the only sure way to decrease the incidence of AIP is to avoid unnecessary cesarean delivery, especially the first cesarean section.

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[1] Thurn L, Lindqvist PG, Jakobsson M, Colmorn LB, Klungsoyr K, Bjarnadóttir RI, Tapper AM, Børdahl PE, Gottvall K, Petersen KB, Krebs L, Gissler M, Langhoff-Roos J, Källen K. Abnormally invasive placenta—prevalence, risk factors and antenatal suspicion: results from a large population-based pregnancy cohort study in the Nordic countries. BJOG 2015; DOI: 10.1111/1471-0528.13547.