Placental implantation abnormalities as the risk factors of prematurity, cesarean section and poor perinatal outcome

• Devyatova E.A.

Abstract

Preterm birth (PB) forms perinatal, newborns' and maternal morbidity and mortality. Frequency of PB reaches 18% in general population. Placenta previa, marginal or low-lying placenta, placenta accreta, vasa previa, velamentous umbilical cord insertion is the most often placental implantation abnormalities (PIA). PIA is on the second place among the indications for preterm Cesarean section (CC). The gestational age at the moment of CC depends on severity of complications (volume of hemorrhage, uterine contractions, rupture of membranes). Stillbirth is the poorest result of many obstetric complications. Previous CC can be independent risk factor of «unexplained» stillbirth and PB for future pregnancies. PB can be the result of anamnestic risk factors and complicated pregnancy and can be complicated with stillbirth in connection with presence of PIA and other obstetric disorders. Individual assessment of risk of PB should include anamnestic features and complications of pregnancy. Prophylaxis of PB should be performed considering this information.

Aims: 1) to evaluate the role of PIA and CC as risk factors of poor perinatal outcome; 2) to evaluate advantages of routine PIA diagnostics; 3) to evaluate modern ways of prophylaxis of PB.

Results. Placenta previa is associated with fivefold growth of prematurity, high risk of intensive neonatal care unit necessity, perinatal/neonatal mortality in comparison to patients without placenta previa. In the cases of placenta accreta and vasa previa the frequency of PB is higher than in cases of placenta previa. PIA risk factors are associated with in vitro fertilization and CC in modern obstetric practice. Odd ratio (OR) for placenta previa depends on the number of previous CC and rises exponentially from 4.5 for the 1^st tt, to 7.4 for the 2^nd, 6.5 and 44.9 for the 3^rd and ≥4^th СС. In the cases of placenta previa the risk of invasive placentation also depends on the number of CC: from 4.5-5 (without previous CC) to 3-24, 11-47, 40 and to 61-67% after the 1^st, 2^nd, 3^rd and ≥4^th previous CC. Significant risk factor of placenta accreta is the implantation of pregnancy in the notch of the scar after previous CC.

Useful parameters of transvaginal sonography for assessment of risk of hemorrhage and preterm CC are: cervical length ≤25 mm, distance between internal os and placental edge ≤20 mm; thickness of placental margin ≤10 mm. If the distance between internal os and placental edge is ≤10 mm, the risk of hemorrhage is much higher than, if the distance is 11-20 mm (ОR=11.5; 95% confident interval (CI) 1.6-76.7), the frequency of preterm CC is higher (73-91 vs. 24-40%). Shortened cervix ≤25 mm in combination with low-lying placenta is associated with high frequency of hemorrhage (75 vs. 31%; p=0.02), hemotransfusion necessity (25 vs. 3%; p=0.02), low birth weight (62 vs. 17%; p=0.02), high necessity of neonatal intensive care unit (50 vs. 17%; p=0.04). Vasa previa and velamentous umbilical cord insertion is associated with high risk of placental abruption, CC, prematurity, low birth weight, low Apgar scores, necessity of neonatal intensive care unit, perinatal mortality. In presence of PIA the OR of perinatal mortality is from 5.4 to 8.0. CC during the 1^st pregnancy is the independent risk factor of «unexplained» stillbirth during future pregnancies. OR grows to 1.4 (95% CI 1.10-1.77; p=0.006) from 34 weeks of gestation and more, the time interval between pregnancies, the outcome of previous pregnancy and the time for CC do not affect these relations.

Progesterone administration for PB prophylaxis in patients with chronic endometritis and recurrent pregnancy loss is the most perspective way nowadays. Low OR for the present pregnancy loss is registered in the cohort of the women who were treated with progesterone получавших прогестерон versus the cases of placebo administration or without any treatment (OR=0.39; 95% CI 0.21-0.72).

Conclusion. Previous CC and PIA are the most important risk factors of PB and poor perinatal outcome. Growing frequency of PIA is associated with growth of during past decades. The decision of the time of hospitalization and delivery are determined with the symptoms of PIA (hemorrhage, preterm rupture of membranes, etc.). Effective consulting can offer the patient full information about the risks and the profit of CC and should be aimed at decrease of CC. this practical approach can affect the patient's opinion about the choice of vaginal delivery and avoid elective CC PIA diagnostics should be based at the evaluation of risk factors, with routine application of transvaginal sonography during the 2^nd trimester of pregnancy. In absence of PIA symptoms other risk factors should also be considered (the history of previous PB, cervical cerclage, other obstetric complications of previous pregnancy). Differential approach to patients with PIA based on ultrasound monitoring is helpful in planning of the time of the delivery and can also shorten the period of obstetric care unit for asymptomatic pregnancies with PIA.

To decrease the risk of PB progesterone should be applied in the cases of chronic endometritis and miscarriage during preconception period and during early pregnancy. Prophylaxis of obstetric complications and correction of obstetric disorders should also be confirmed.

Keywords:pregnancy, caesarean section, preterm delivery, stillbirth, bleeding, hemorrhage, imaging, marginal or low-lying placenta, placenta previa, placenta accreta, transvaginal ultrasound, vasa previa, velamentous umbilical cord insertion, tocolysis, progesterone

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