Review article
Maternal clinical predictors of preterm birth in twin pregnancies: A systematic review involving 2,930,958 twin pregnancies

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Abstract

In twin pregnancies, which are at high risk of preterm birth, it is not known if maternal clinical characteristics pose additional risks.

We undertook a systematic review to assess the risk of both spontaneous and iatrogenic early (<34 weeks) or late preterm birth (<37 weeks) in twin pregnancies based on maternal clinical predictors. We searched the electronic databases from January 1990 to November 2017 without language restrictions. We included studies on women with monochorionic or dichorionic twin pregnancies that evaluated clinical predictors and preterm births. We reported our findings as odds ratio (OR) with 95% confidence intervals (CI) and pooled the estimates using random-effects meta-analysis for various predictor thresholds.

From 12, 473 citations, we included 59 studies (2,930,958 pregnancies). The risks of early preterm birth in twin pregnancies were significantly increased in women with a previous history of preterm birth (OR 2.67, 95% CI 2.16–3.29, I2 = 0%), teenagers (OR 1.81, 95% CI 1.68–1.95, I2 = 0%), BMI > 35 (OR 1.63, 95% CI 1.30–2.05, I2 = 52%), nulliparous (OR 1.51, 95% CI 1.38–1.65, I2 = 73%), non-white vs. white (OR 1.31, 95% CI 1.20–1.43, I2 = 0%), black vs. non-black (OR 1.38, 95% CI 1.07–1.77, I2 = 98%), diabetes (OR 1.73, 95% CI 1.29–2.33, I2 = 0%) and smokers (OR 1.30, 95% CI 1.23–1.37, I2 = 0%). The odds of late preterm birth were also increased in women with history of preterm birth (OR 3.08, 95% CI 2.10–4.51, I2 = 73%), teenagers (OR 1.36, 95% CI 1.18–1.57, I2 = 57%), BMI > 35 (OR 1.18, 95% CI 1.02–1.35, I2 = 46%), nulliparous (OR 1.41, 95% CI 1.23–1.62, I2 = 68%), diabetes (OR 1.44, 95% CI 1.05–1.98, I2 = 55%) and hypertension (OR 1.49, CI 1.20–1.86, I2 = 52%).

The additional risks posed by maternal clinical characteristics for early and late preterm birth should be taken into account while counseling and managing women with twin pregnancies.

Introduction

Preterm birth is the leading cause of perinatal morbidity and mortality in developed countries, accounting for two-thirds of deaths in infants without congenital anomalies [1]. The perinatal mortality rate in twins is three times higher than that of singleton pregnancies, much of which is driven by prematurity [2]. Over the last 30 years, the increased incidence of twin pregnancies has contributed to a further increase in the rates of preterm birth [3]. Half of all twins are born before 37 weeks gestation with about one fifth delivering before 34 weeks [4]. Preterm born twins often need significant support in the short and long-term, from complications including neurodevelopmental problems [5].

The etiology of preterm birth in twin pregnancies is likely multifactorial and different from singletons. In addition to the number of fetuses, the added risks from other factors are essential in identifying twin pregnancies at high risk of preterm birth to determine the place, frequency of monitoring, initiation of preventative treatment and timely administration of antenatal corticosteroids. This is particularly relevant for countries with limited tertiary neonatal care, where high-risk twin pregnancies can benefit from appropriate counselling, early referral and in utero transfer.

The first antenatal visit offers an ideal opportunity to determine the risk of preterm birth in women based on their clinical characteristics. Although numerous studies and prediction models have been developed to predict the risk of preterm birth in singletons, limited data exists for twin pregnancies. Existing individual studies vary in the risk estimates that are imprecise, as they are often limited by small sample sizes to make robust conclusions. No systematic reviews exist. We undertook a systematic review to assess the risk of early and late preterm birth in twin pregnancies for various maternal characteristics.

Section snippets

Methods

We undertook our review using a prospective protocol and complied with reporting guidelines [6,7]. The PROSPERO ID of this systematic review’s protocol is CRD42015026465.

Results

From 12,473 citations, we included 59 studies (2,930,958 pregnancies). Detailed study selection process is shown in Fig. 1.

Summary of the main findings

This systematic review has provided precise quantitative estimates of the association between maternal clinical predictors and preterm delivery in twin pregnancies. In addition to the underlying risk of prematurity due to being pregnant with twins, being young (age < 20 years), obese (BMI > 35 kg/m2), nulliparous or multiparous with a previous history of preterm delivery is associated with an increased risk of both early and late preterm birth. For early preterm birth where iatrogenic preterm

Conclusion

The results of this review highlight the importance of maternal clinical predictors in identifying twin pregnancies at high risk of preterm birth based on obstetric history alone. Although maternal clinical predictors are not entirely predictive of preterm birth in a twin pregnancy, information on obstetric history is available to the clinician at booking and does not rely on the availability of expensive resources. The risk estimates on maternal clinical predictors can be used in the

Role of the funding source

There was no funding source for this study.

Conflict of interest

None of the authors has a conflict of interest.

Acknowledgements

We would like to thank Jenny Franklin for assisting with the literature search and Dr Chalitha Dimuth for assistance in obtaining articles.

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