Retained placenta affects 0.1% - 3.3% of women following delivery, and is a major factor in the cause of maternal death from post-partum haemorrhage (PPH) and puerperal sepsis [1] [2] . Developing countries contribute up to 90% to maternal mortality globally and about 25% of these deaths are due to haemorrhage during pregnancy, birth or post-partum period, of these, 15% - 20% is due to retained placenta [3] [4] . After uterine atony, retained placenta is the second major indication for blood transfusion in the third stage of labour with blood transfusion required in 10% of retained placenta group compared to 0.5% of the control group in a retrospective study conducted in Tanzania [5] .

Appropriate management of the third stage of labour can help to reduce complications associated with this stage of labour, including retained placenta. Retained placenta is a potentially preventable cause of primary post-partum haemorrhage. Although some factors that predispose a pregnant woman to retained placenta have been identified, there is no consensus on its significance and relative importance. For example, some authors have reported a significant increase in the incidence of retained placenta due to factors that include multiparity, augmentation of labour with oxytocin, uterine inertia/atony, uterine fibroids and home delivery [6] [7] . Others include pre-term labour/deliveries, prolonged labour, induction of labour, previous retained placenta, previous dilatation and curettage, and previous caesarean section [8] .

It would be relevant to investigate and identify independent risk factors for retained placenta before applying the risk approach for its prevention in any health facility. This will help to increase the sensitivity and specificity of the methods and selected risk factors in preventing retained placenta.

In the light of these facts, this study has reviewed the incidence, clinical presentation, risk factors, treatment and complications of retained placenta at our centre in order to proffer appropriate preventive measures to the menace.

The case record of patients with retained placenta, including those who had antenatal care at the our centre and all cases of retained placenta referred to our facility (the unbooked women from other healthcare facilities and those delivered at home, faith clinics and herbal homes) between 1^st January, 2011 and 31^st December, 2015 were retrieved and reviewed. A total of 11 of such case records were retrieved, and the needed information for analysis with respect to age, parity, risk factors, past and present obstetric and gynaecological characteristics, complications, conditions on admission and place of delivery prior to retained placenta were extracted. Also, 11 patients with similar demographic and Obstetric characteristics such as age and parity that were admitted and had normal deliveries after those with retained placenta, served as controls. All identified cases during the period were included in the study. The data were extracted from the case records by two of the authors (AAA and AMO) using standardized proforma designed for the purpose. The data so collected were analysed by Epi-Info software version 6 for statistical analysis. The variables were tested with Chi-square and Fisher’s exact test as appropriate. The level of significance was set at p-value of ≤0.05.

The 0.53% incidence of retained placenta in this study was within the reported incidence of 0.1% - 3.3% [1] [2] . The incidence was lower when compared with the previously reported incidence of 1.02% in Calabar but similar to incidence of 0.59% in Port Harcourt [9] [10] . Of women with retained placenta, 81.8% were not booked for antenatal care. This figure was similar to 81.2% unbooked women reported in Port Harcourt, Nigeria [10] . However, this was higher than 8.01% in the earlier study by Soltan and Khashoggi [11] .

Deliveries supervised by unskilled birth attendants or deliveries in inappropriately-staffed health centres are associated with a high incidence of poor management of third stage of labour especially with lack or poor implementation of active management of third stage of labour, leading to a high incidence of retained placenta in the unbooked women [9] .

The utilization of health services has fallen over the years as a result of many factors. These include illiteracy, unemployment, poverty and the charging of fees in most tertiary public health institutions. All these have contributed to the increased incidence of unbooked women with emergencies and the attendant obstetrical morbidity and mortality over the years [12] [13] .

This study identified non-booking for antenatal care, previous retained placenta, previous dilatation and curettage, previous myomectomy and unskilled birth attendants as factors associated with retained placenta. This is in agreement with the findings of other researchers [1] [2] [14] [15] . It is hypothesized that these factors cause injuries that lead to deficient or damaged endometrium predisposing the implanted ovum’s chorionic villi to penetrate into the uterine muscle. This penetration of the endometrium and the uterine muscle predisposes to placental retention. The severe form of this phenomenon is believed to be the cause of placenta accreta [16] .

Aversion to caesarean section by pregnant women in our environment causes a lot of high-risk women to deliver at inappropriate and under-equipped health facility with attendant complications including retained placenta [12] [17] . Increased abnormalities of placental implantations in grand multiparous women [18] and the notable association with uterine atony in this group of women, constitute factors leading to retained placenta [18] [19] . Each of the preterm delivery and low placental weight contributed a significant risk of retained placenta in this study.

Retained placenta was associated with primary post-partum haemorrhage in five (45.5%), this is comparable to a study done by Owolabi et al. (48.3%) in OAUTH, Ile-Ife [14] . One (9.1%) of the women was admitted in a state of shock and five (45.5%) of the women had blood transfusion.

Poor management of the third stage of labour, even in low-risk women, can lead to retained placenta. This may result from attempts to deliver the placenta when uterine contraction has not taken place, to separate the placenta from the decidua. Forceful traction on the umbilical cord may lead to snapping of the umbilical cord resulting in placental retention. The need for manual removal of placenta can be reduced by 20% by the use of intra-umbilical oxytocin (30 iu in 30 ml of saline) [20] . This could be further reduced by 49% with the use of Sulprostone, a potent stimulator of uterine smooth muscle contraction with high abortifacient ativity [21] .

Occasional entrapment of the placenta results from uterine and cervical constriction ring following delay in the delivery of the placenta after the injection of an oxytocic agent during the active management of the third stage of labour. This was noted in three (27.3%) of women in this study, which is comparable to the 24.4% findings in a study by Onwudiegwu and Makinde in OAUTH Ile-Ife [22] . However, a trapped placenta may respond to glyceryl trinitrate 500 microgram sublingually [23] .

This study has been able to identify some of the important risk factors, mode of presentation, management and complications of retained placenta among the women presented at Federal Teaching Hospital, Ido-Ekiti during the period under review (January 2011 to December 2015). Some of these risk factors include; non-booking for antenatal care during pregnancy, unemployment, previous history of retained placenta, previous history of dilatation & curettage and pregnancies that end up in preterm delivery or low placental weight.

Retained placenta remains an important cause of post-partum haemorrhage, maternal morbidity and a major factor in the cause of maternal mortality especially in Africa and other developing countries. There is a need for training and retaining of birth attendants at all levels in proper conduct of delivery and third stage of labour to prevent placental retentions and post-partum haemorrhage. Government should also improve the socio-economic conditions of the populace and provide free maternity services especially in rural communities where home deliveries abound to encourage early antenatal booking in centres with skilled health staff. The informal sector and the rural populace should be fully incorporated into the National health insurance scheme (NHIS). All these will improve the utilization of available delivery care services and reduce the number of unbooked emergencies. The generalization of the findings from this study is limited by the small sample size and being a retrospective and a single centre study, thus a larger, prospective and multi-centre study is desirable.