Risk of preterm birth for placenta previa or low-lying placenta and possible preventive interventions: A systematic review and meta-analysis.

Objective: To investigate the risk of preterm birth in women with a placenta previa or a low-lying placenta for different cut-offs of gestational age and to evaluate preventive interventions. Search and methods: MEDLINE, EMBASE, CENTRAL, Web of Science, WHO-ICTRP and clinicaltrials.gov were searched until December 2021. Randomized controlled trials, cohort studies and case-control studies assessing preterm birth in women with placenta previa or low-lying placenta with a placental edge within 2 cm of the internal os in the second or third trimester were eligible for inclusion. Pooled proportions and odds ratios for the risk of preterm birth before 37, 34, 32 and 28 weeks of gestation were calculated. Additionally, the results of the evaluation of preventive interventions for preterm birth in these women are described. Results: In total, 34 studies were included, 24 reporting on preterm birth and 9 on preventive interventions. The pooled proportions were 46% (95% CI [39 - 53%]), 17% (95% CI [11 - 25%]), 10% (95% CI [7 - 13%]) and 2% (95% CI [1 - 3%]), regarding preterm birth <37, <34, <32 and <28 weeks in women with placenta previa. For low-lying placentas the risk of preterm birth was 30% (95% CI [19 - 43%]) and 1% (95% CI [0 - 6%]) before 37 and 34 weeks, respectively. Women with a placenta previa were more likely to have a preterm birth compared to women with a low-lying placenta or women without a placenta previa for all gestational ages. The studies about preventive interventions all showed potential prolongation of pregnancy with the use of intramuscular progesterone, intramuscular progesterone + cerclage or pessary. Conclusions: Both women with a placenta previa and a low-lying placenta have an increased risk of preterm birth. This increased risk is consistent across all severities of preterm birth between 28-37 weeks of gestation. Women with placenta previa have a higher risk of preterm birth than women with a low-lying placenta have. Cervical cerclage, pessary and intramuscular progesterone all might have benefit for both women with placenta previa and low-lying placenta, but data in this population are lacking and inconsistent, so that solid conclusions about their effectiveness cannot be drawn. Systematic review registration: PROSPERO https://www.crd.york.ac.uk/prospero/, identifier CRD42019123675.

Tocolysis with nifedipine versus atosiban and perinatal outcome: an individual participant data meta-analysis.

BACKGROUND: Worldwide, nifedipine and atosiban are the two most commonly used tocolytic agents for the treatment of threatened preterm birth. The aim of this study was to evaluate the effectiveness of nifedipine and atosiban in an individual participant data meta-analysis (IPDMA). METHODS: We investigated the occurrence of adverse neonatal outcomes in women with threatened preterm birth by performing an IPDMA, and sought to identify possible subgroups in which one treatment may be preferred. We searched PubMed, Embase, and Cochrane for trials comparing nifedipine and atosiban for treatment of threatened preterm birth between 240/7 and 340/7 weeks' gestational age. Primary outcome was a composite of perinatal mortality and neonatal morbidities including respiratory distress syndrome, intraventricular haemorrhage, periventricular leucomalacia, necrotising enterocolitis, and sepsis. Secondary outcomes included NICU admission, prolongation of pregnancy and GA at delivery. For studies that did not have the original databases available, metadata was used. This led to a two-stage meta-analysis that combined individual participant data with aggregate metadata. RESULTS: We detected four studies (N = 791 women), of which two provided individual participant data (N = 650 women). The composite neonatal outcome occurred in 58/364 (16%) after nifedipine versus 69/359 (19%) after atosiban (OR 0.76, 95%CI 0.47-1.23). Perinatal death occurred in 14/392 (3.6%) after nifedipine versus 7/380 (1.8%) after atosiban (OR 2.0, 95%CI 0.80-5.1). Nifedipine results in longer prolongation of pregnancy, with a 18 days to delivery compared with 10 days for atosiban (HR 0.83 (96% CI 0.69-0.99)). NICU admission occurred less often after nifedipine (46%) than after atosiban (59%), (OR 0.32, 95%CI 0.14-0.75). The sensitivity analysis revealed no difference in prolongation of pregnancy for 48 hours (OR 1.0, 95% CI 0.73-1.4) or 7 days (OR 1.3, 95% CI 0.85-5.8) between nifedipine and atosiban. There was a non-significant higher neonatal mortality in the nifedipine-exposed group (OR 1.4, 95% CI 0.60-3.4). CONCLUSIONS: In this IPDMA, we found no differences in composite outcome between nifedipine and atosiban in the treatment of threatened preterm birth. However, the non-significant higher mortality after administering nifedipine warrants further investigation of the use of nifedipine as a tocolytic drug. STUDY REGISTRATION: We conducted this study according to a prospectively prepared protocol, registered with PROSPERO (the International Prospective Register of Systematic Reviews) under CRD42016024244.

Which second trimester placenta previa remains a placenta previa in the third trimester: A prospective cohort study.

OBJECTIVE: The far majority of women with a placenta previa in the second trimester will no longer have a placenta that overlies the internal os in the third trimester. Women with a placenta previa in the third trimester are at risk for complication such as preterm birth and blood loss. Four counselling purposes we aim to identify which women with a second trimester placenta previa have a low-risk and a high-risk for persistence of the placenta previa. STUDY DESIGN: A prospective cohort study of women with a placenta previa in the second trimester between 2014 and 2019. The odds for having a placenta previa in the third trimester were calculated for different baseline characteristics. Multilevel likelihood ratios for ranges of the placenta overlying the internal os in the second trimester and the corresponding ROC curve were calculated to identify the optimal cut-off values. RESULTS: We included 313 women with a placenta previa in the second trimester. The placenta was more frequently located on the posterior wall (62 %) than on the anterior wall (38 %). At evaluation in the third trimester, 37 women (14 %) still had a placenta previa. Women with a larger distance of the placenta overlying the internal os, women having a previous cesarean delivery and women after a conception with assisted reproductive technique had a significant higher risk of placenta previa persistence (p-values <0.001). Women with a placenta overlying less than 14 mm can be considered as low-risk, indicated by a likelihood ratio of 0. Women with a placenta with more than 55 mm overlap can be considered as high-risk, indicated a the likelihood ratio of ∞. CONCLUSION: The majority of the second trimester placenta previa will no longer overly the internal os in the third trimester. Placenta previa persistence is associated with the distance overlying the internal os, a previous cesarean delivery and assisted reproductive techniques. In the second trimester, women can be identified as low-risk and high-risk for persistence of placenta previa. This can be used for risk stratification, counselling and individualized care for women with a second trimester placenta previa.

Development of placental abnormalities in location and anatomy.

Low-lying placentas, placenta previa and abnormally invasive placentas are the most frequently occurring placental abnormalities in location and anatomy. These conditions can have serious consequences for mother and fetus mainly due to excessive blood loss before, during or after delivery. The incidence of such abnormalities is increasing, but treatment options and preventive strategies are limited. Therefore, it is crucial to understand the etiology of placental abnormalities in location and anatomy. Placental formation already starts at implantation and therefore disorders during implantation may cause these abnormalities. Understanding of the normal placental structure and development is essential to comprehend the etiology of placental abnormalities in location and anatomy, to diagnose the affected women and to guide future research for treatment and preventive strategies. We reviewed the literature on the structure and development of the normal placenta and the placental development resulting in low-lying placentas, placenta previa and abnormally invasive placentas.

Final outcome of a second trimester low-positioned placenta: A systematic review and meta-analysis.

Low-positioned placentas which are located in the lower uterine segment (LUS), either a low-lying placenta or a placenta previa, are associated with increased obstetric risks. However, most second trimester low-positioned placentas resolve during pregnancy and have a higher position in the third trimester, without posing any risks. We performed a systematic review and meta-analysis to evaluate the proportion of second trimester low-positioned placentas that have a position towards the fundus in the third trimester. Our aim was to find a cut-off value that included all women in whom the placenta will remain low in the third trimester, thus who are at increased risk of obstetric complications. Subsequently, we assessed whether an anterior or posterior placental location influenced this proportion. We searched MEDLINE and EMBASE and clinicaltrials.gov up to April 2019 for studies on the sonographic follow-up of second trimester low-positioned placentas, with a distance between the placenta and the internal os of the cervix of 20 mm or less at a gestational age of above 15 week and a follow up after 28 weeks. Studies were scored on methodological quality using the Newcastle-Ottowa Scale (NOS). A meta-analysis was conducted to summarize the proportion of second trimester low-positioned placentas with a position towards the fundus in the third trimester. We calculated the proportion at different cut-off values of the distance from the placental edge to the internal os of the cervix (0 mm, 10 mm and 20 mm). Also, anteriorly and posteriorly located placentas and women with and without a prior cesarean delivery were compared. We included 11 eligible studies which reported on 3586 women with a low-positioned placenta in the second trimester. Proportions of placentas with a position towards the fundus in the third trimester ranged between 0.63 and 1.0. Pooled proportions were 0.90 (95% CI 0.87-0.93) for IOD <10 mm and 0.80 (95% CI 0.74-0.85) for IOD < 0 mm. Due to heterogeneity between studies, the subgroup of <20 mm could not be pooled. Overall, anteriorly located placentas more often had a position towards the fundus in the third trimester, but studies did report conflicting results. Prior cesarean section had no influence except for an IOD of <0 mm, in which women without a prior cesarean delivery more often had a placenta towards the fundus. The majority of second trimester low-positioned placentas will be located towards the fundus at the time of follow-up. However, we could not determine a cut-off value for anterior and posterior placentas that included all women at high risk. The cut-off value, placental side and prior cesarean section should be assessed in a large prospective observational study.

Determination of threshold value for follow-up of isolated antenatal hydronephrosis detected in the second trimester.

INTRODUCTION: Isolated antenatal hydronephrosis (ANH), defined as a dilation of the renal pelvis (≥5 mm), is one of the most common abnormalities detected on prenatal ultrasound. However, established cut-off values for postnatal follow-up differ between countries and are based on little evidence. The current protocol in the Netherlands for follow-up might be too conservative. OBJECTIVE: To assess the applicability of a higher threshold for follow-up of isolated antenatal hydronephrosis (ANH) than the current practice, without the risk of missing significant postnatal urinary tract obstruction. STUDY DESIGN: Retrospective case series on all fetuses with isolated ANH (anteroposterior pelvic diameter (APPD) ≥5 mm) at the second trimester anomaly scan, and diagnosed between 2000 and 2009, in relationship to renal outcome. RESULTS: A total of 279 infants with second trimester isolated ANH were included. In 201/279 (72%) fetuses, ANH had normalized (APPD <10 mm) before the third trimester scans. Hydronephrosis persisted postnatally in a minority of 56/279 (20.1%). Postnatal assessment showed signs of obstruction in 41/279 (14.7%) infants, duplicated collecting system or vesicoureteral reflux (VUR). Surgery was performed in 18/279 (6.5%) infants. A non-functioning kidney was shown in 6/279 (2.2%) infants with ANH. Mild ANH (APPD <7 mm) during the second trimester (172/279 (61.6%)) never resulted in surgery for renal anomalies or non-functioning kidney. Infants with an APPD ≥10 mm in the second trimester were far more likely to develop renal anomalies or undergo surgery compared with infants with an APPD 7-10 mm. The number of non-functioning kidneys was too low to be conclusive. CONCLUSIONS: Follow-up ultrasounds for isolated ANH ≥7 mm instead of ≥5 mm at the second trimester scan would have saved 62% of third trimester scans, without missing any infant with a non-functioning kidney, significant obstruction or symptomatic VUR. In view of the results, it is reasonable that referral for follow-up of second trimester ANH is not strictly indicated in cases with an APPD <7 mm.

Prognostic models in obstetrics: available, but far from applicable.

Health care provision is increasingly focused on the prediction of patients' individual risk for developing a particular health outcome in planning further tests and treatments. There has been a steady increase in the development and publication of prognostic models for various maternal and fetal outcomes in obstetrics. We undertook a systematic review to give an overview of the current status of available prognostic models in obstetrics in the context of their potential advantages and the process of developing and validating models. Important aspects to consider when assessing a prognostic model are discussed and recommendations on how to proceed on this within the obstetric domain are given. We searched MEDLINE (up to July 2012) for articles developing prognostic models in obstetrics. We identified 177 papers that reported the development of 263 prognostic models for 40 different outcomes. The most frequently predicted outcomes were preeclampsia (n = 69), preterm delivery (n = 63), mode of delivery (n = 22), gestational hypertension (n = 11), and small-for-gestational-age infants (n = 10). The performance of newer models was generally not better than that of older models predicting the same outcome. The most important measures of predictive accuracy (ie, a model's discrimination and calibration) were often (82.9%, 218/263) not both assessed. Very few developed models were validated in data other than the development data (8.7%, 23/263). Only two-thirds of the papers (62.4%, 164/263) presented the model such that validation in other populations was possible, and the clinical applicability was discussed in only 11.0% (29/263). The impact of developed models on clinical practice was unknown. We identified a large number of prognostic models in obstetrics, but there is relatively little evidence about their performance, impact, and usefulness in clinical practice so that at this point, clinical implementation cannot be recommended. New efforts should be directed toward evaluating the performance and impact of the existing models.

Preventing Preterm Birth with Progesterone in Women with a Short Cervical Length from a Low-Risk Population: A Multicenter Double-Blind Placebo-Controlled Randomized Trial.

OBJECTIVE: The objective of this study was to evaluate the effectiveness of vaginal progesterone in reducing adverse neonatal outcome due to preterm birth (PTB) in low-risk pregnant women with a short cervical length (CL). STUDY DESIGN: Women with a singleton pregnancy without a history of PTB underwent CL measurement at 18 to 22 weeks. Women with a CL ≤ 30 mm received vaginal progesterone or placebo. Primary outcome was adverse neonatal outcome, defined as a composite of respiratory distress syndrome, bronchopulmonary dysplasia, intracerebral hemorrhage > grade II, necrotizing enterocolitis > stage 1, proven sepsis, or death before discharge. Secondary outcomes included time to delivery, PTB before 32, 34, and 37 weeks of gestation. Analysis was by intention to treat. RESULTS: Between 2009 and 2013, 20,234 women were screened. A CL of 30 mm or less was seen in 375 women (1.8%). In 151 women, a CL ≤ 30 mm was confirmed with a second measurement and 80 of these women agreed to participate in the trial. We randomly allocated 41 women to progesterone and 39 to placebo. Adverse neonatal outcomes occurred in two (5.0%) women in the progesterone and in four (11%) women in the control group (relative risk [RR], 0.47; 95% confidence interval [CI], 0.09-2.4). The use of progesterone resulted in a nonsignificant reduction of PTB < 32 weeks (2.0 vs. 8.0%; RR, 0.33; 95% CI, 0.04-3.0) and < 34 weeks (7.0 vs. 10%; RR, 0.73; 95% CI, 0.18-3.1) but not on PTB < 37 weeks (15 vs. 13%; RR, 1.2; 95% CI, 0.39-3.5). CONCLUSION: In women with a short cervix, who are otherwise low risk, we could not show a significant benefit of progesterone in reducing adverse neonatal outcome and PTB.

Differentially expressed genes in the pre-eclamptic placenta: a systematic review and meta-analysis.

OBJECTIVE: To systematically review the literature on human gene expression data of placental tissue in pre-eclampsia and to characterize a meta-signature of differentially expressed genes in order to identify novel putative diagnostic markers. DATA SOURCES: Medline through 11 February 2011 using MeSH terms and keywords related to placenta, gene expression and gene expression arrays; GEO database using the term "placent*"; and reference lists of eligible primary studies, without constraints. METHODS: From 1068 studies retrieved from the search, we included original publications that had performed gene expression array analyses of placental tissue in the third trimester and that reported on differentially expressed genes in pre-eclampsia versus normotensive controls. Two reviewers independently identified eligible studies, extracted descriptive and gene expression data and assessed study quality. Using a vote-counting method based on a comparative meta-profiling algorithm, we determined a meta-signature that characterizes the significant intersection of differentially expressed genes from the collection of independent gene signatures. RESULTS: We identified 33 eligible gene expression array studies of placental tissue in the 3(rd) trimester comprising 30 datasets on mRNA expression and 4 datasets on microRNA expression. The pre-eclamptic placental meta-signature consisted of 40 annotated gene transcripts and 17 microRNAs. At least half of the mRNA transcripts encode a protein that is secreted from the cell and could potentially serve as a biomarker. CONCLUSIONS: In addition to well-known and validated genes, we identified 14 transcripts not reported previously in relation to pre-eclampsia of which the majority is also expressed in the 1(st) trimester placenta, and three encode a secreted protein.

Preventing preterm birth with progesterone: costs and effects of screening low risk women with a singleton pregnancy for short cervical length, the Triple P study.

BACKGROUND: Women with a short cervical length in mid-trimester pregnancy have a higher risk of preterm birth and therefore a higher rate of neonatal mortality and morbidity. Progesterone can potentially decrease the number of preterm births and lower neonatal mortality and morbidity. Previous studies showed good results of progesterone in women with either a history of preterm birth or a short cervix. However, it is unknown whether screening for a short cervix and subsequent treatment in mid trimester pregnancy is effective in low risk women. METHODS/DESIGN: We plan a combined screen and treat study among women with a singleton pregnancy without a previous preterm birth. In these women, we will measure cervical length at the standard anomaly scan performed between 18 and 22 weeks. Women with cervical length ≤ 30 mm at two independent measurements will be randomly allocated to receive either vaginal progesterone tablets or placebo between 22 and 34 weeks. The primary outcome of this trial is adverse neonatal condition, defined as a composite outcome of neonatal mortality and severe morbidity. Secondary outcomes are time to delivery, preterm birth rate before 32, 34 and 37 weeks, days of admission in neonatal intensive care unit, maternal morbidity, maternal admission days for preterm labour and costs. We will assess growth, physical condition and neurodevelopmental outcome of the children at two years of age. DISCUSSION: This study will provide evidence for the usefulness and cost-effectiveness of screening for short cervical length at the 18-22 weeks and subsequent progesterone treatment among low risk women. TRIAL REGISTRATION: Netherlands Trial Register (NTR): NTR207.