Introduction Several studies have shown association between lateral placenta on ultrasound and preeclampsia (PE).This meta-analysis aims to review majority of the articles published between 1990 and 2020 and analyze the data extracted from them to find whether such an association really exists. Objective To conduct a meta-analysis to determine the degree of the association of lateral placenta on ultrasound with preeclampsia.
Methods We searched electronic databases keeping filters for human studies and published in the English language, between the year 1990 and 2020. Studies were reviewed by reviewers and studies which were analytical in nature, having focused research question and where odds ratio could be derived were identified, and included in the metanalysis.
Result Out of 16 included studies, 15 studies showed positive association (OR > 1) out of which 13 were statistically significant and only one study showed negative association. Eight studies showed extremely significant statistical positive association. The meta-analysis points toward positive association with OR 3.48 and Mantel–Haenszel Chi square 325.82 with relatively narrow 95% confidence interval around OR as 3.03–3.99 which clearly indicates a positive association between laterally placed placenta and preeclampsia. The findings of the individual studies in terms of OR and 95% confidence interval were plotted as individual line for each study, one aggregate estimate with summary OR and its 95% confidence interval was plotted on the Forest Plot.
Conclusion The Forest plot revealed association between lateral placenta on ultrasound and preeclampsia (PE).Hence it can be concluded that there is an association between lateral placenta on ultrasound and preeclampsia.
Keywords : Lateral location of placenta · Lateral placenta on ultrasound · Pregnancy induced hypertension · Hypertensive disorders of pregnancy · Preeclampsia
Preeclampsia (PE) is the most common medical complication
affecting about 7–15% of all pregnancies and is
responsible for almost 25% of all the antenatal admissions
[1]. A systematic review on maternal mortality was conducted
worldwide by WHO and it was concluded that PE is
a leading cause of maternal mortality. Along with hemorrhage
and infection, hypertension forms the deadly triad that
contributes to morbidity and mortality during pregnancy and
childbirth [2]. In India 24% of all maternal deaths are due
to PE [3]. It has been observed that hypertensive disorders
have long-term complications and effect on the health of
women in the form of chronic hypertension and increase
in lifetime risk of cardiovascular diseases. PE is strongly
associated with stillbirth, fetal growth restriction, low birth
weight, spontaneous preterm delivery, respiratory distress
syndrome and NICU admissions [4]. Thus it is necessary to
protect mothers from hypertensive disorders by providing
good antenatal care, early diagnosis, timely intervention, and
having a high index of suspicion. In a developing country
like India it is necessary to identify and evaluate woman at
risk of developing PE with an accurate, sensitive, clinically
acceptable and affordable investigation.
For PE to occur the presence of placenta is needed [5].
The site on the uterine surface where the placenta implants
is an important factor determining the placental blood flow
[6]. Ultrasound (USG) has been the safest, easiest, readily
available and the most accurate diagnostic tool for determining
the placental location [7]. On USG when the placenta
is equally distributed between the right and left side of the
uterus irrespective of fundal, posterior or anterior position it
is classified as central placenta. It is classified as unilateral
right or left placenta, when more than 75% of the placenta
is situated on one side of the midline (Figs. 1, 2).
In a centrally located placenta the blood flow in the uteroplacental bed kept in equilibrium by equal contribution from both uterine arteries, whereas in a laterally located placenta the blood flow in the uteroplacental bed is primarily from one of the uterine arteries with minimal contribution from the other via a collateral circulation [8]. This collateral circulation is deficient in some patients which facilitates the development of PE, FGR or both [9]. Doppler studies reveal that in a laterally located placenta the uterine artery close to the placenta has resistance lower than the opposite one while in centrally located placenta both uterine arteries have same resistance [10–12].
Literature search revealed several studies on association of lateral placenta on USG and prediction of PE. A systematic review of literature was done on all studies on lateral placenta and occurrence of PE; data was extracted and prevalence of PE as well as its association with lateral placenta was analyzed. PRISMA guideline was used to frame the meta-analysis. Till date there has not been a study that collected and systematically analyzed the association between lateral placenta on USG and PE. Thus this study aims to systematically review the various studies on occurrence of PE in patients with lateral placenta and analyze the extracted data for prevalence and association of PE with placental laterality.
Sixteen observational analytical studies (cross sectional/case control studies) done at different geographical locations in India (1 study from Tehran, Iran) were filtered for processing for meta-analysis as per the inclusion criteria. All the studies were having sample size more than 100. Kadium et al. [14] studied maternal and fetal outcome in the form of severity and complications of PE like development of late onset PE, abruptio placenta, preterm labor, fetal growth restriction and intrauterine death in lateral placenta. This study also revealed deteriorating Doppler changes with lateral placenta on ultrasound. Kaur et al. [24] also studied Doppler changes in cases of lateral location of placenta and development of PE along with maternal and fetal outcome with similar results. Ambastha et al. [17] and Kakkar et al. [20] studied the maternal and fetal outcome in laterally located placenta in the form of severity of PE, fetal growth restriction, preterm premature rupture of membranes. Their results were consistent in showing all parameters to be worsening with lateral placenta. Fetal and maternal outcome according to placental location was also observed to be poor with lateral placenta in study by Keshavarz et al. [19], Sandhya et al. [7] and Kaku et al. [16] studied the severity of PE based on diastolic BP in laterally located placenta. They concluded more severe PE with significant rise in diastolic BP in laterally located placenta. The development of PE in lateral and central location of placenta was studied in all 16 studies. After plotting a 2 by 2 table the odds ratio was calculated in all the above studies with 95% confidence interval and statistical significance if any was noted in all the 16 studies. 13 out of 16 studies showed statistically significant positive association between laterally placed placenta and preeclampsia with Odd’s ratio ranging from 0.78 to 78.75. Two studies showing positive association were not statistically significant. Only one study showed negative association but was not statistically significant. An apparent aggregate positive association cannot be considered unless we do the statistical synthesis of these studies in terms of meta-analysis. The summary Odd’s Ratio of our meta-analysis is 3.48 with 95% confidence interval from 3.03 to 3.99 which clearly indicates that there is a strong positive association and relatively narrow 95% confidence interval suggests that this association is extremely statistically significant with Mantel–Haenszel Chi square value of 325.82. Forest plot also clearly indicates a strongly positive association between lateral location of placenta and PE.Declarations
Conflict of interest The authors declare that they have no conflict of interest.
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