Background: Threatened miscarriage is a common complication in the first trimester of pregnancy and is often associated with anxiety regarding pregnancy outcome.
Objective: We undertook a systematic review to explore the effects of threatened miscarriage in the first trimester on maternal and perinatal outcomes.
Search strategy: An electronic literature search using MEDLINE and EMBASE, and bibliographies of retrieved primary articles. No language restrictions were applied.
Selection criteria: All studies analysing outcomes of first-trimester bleeding where viability was confirmed on ultrasound or the pregnancy continued beyond viability.
Data collection and analysis: Two review authors independently selected studies and extracted data on study characteristics, quality and accuracy. Meta-analysis was performed using Review Manager software.
Main outcome measures: The outcome was broadly categorised into maternal and perinatal outcomes. The chief maternal outcomes included pre-eclampsia/eclampsia or pregnancy-induced hypertension, antepartum haemorrhage, preterm prelabour rupture of membranes (PPROM) and mode of delivery. The perinatal outcomes evaluated were preterm delivery, low birthweight, intrauterine growth restriction, perinatal mortality, indicators of perinatal morbidity (Apgar scores and neonatal unit admission) and presence of congenital anomalies.
Main results: Fourteen studies met the inclusion criteria. Women with threatened miscarriage had a significantly higher incidence of antepartum haemorrhage due to placenta praevia [odds ratio (OR) 1.62, 95% CI 1.19, 2.22] or antepartum haemorrhage of unknown origin (OR 2.47, 95% CI 1.52, 4.02) when compared with those without first-trimester bleeding. They were more likely to experience PPROM (OR 1.78, 95% CI 1.28, 2.48), preterm delivery (OR 2.05, 95% CI 1.76, 2.4) and to have babies with intrauterine growth restriction (OR 1.54, 95% CI 1.18, 2.00). First-trimester bleeding was associated with significantly higher rates of perinatal mortality (OR 2.15, 95% CI 1.41, 3.27) and low-birthweight babies (OR 1.83, 95% CI 1.48, 2.28).
Authors' conclusions: Threatened miscarriage in the first trimester is associated with increased incidence of adverse maternal and perinatal outcome.